CLS5520

announcement

2009-11-30T07:29:00.000-08:00

zoonotic viruses will not be covered in this module.

GI viruses

2009-11-30T07:28:00.001-08:00

GI Viruses
Associated with gastroenteritis
Rotaviruses
Adenoviruses 40 41
Caliciviruses
Norwalk like viruses or SRSV (Small Round Structured Viruses)
Astroviruses
SRV (Small Round Viruses)
Coronaviruses
Toroviruses
Found in the gut, not normally associated with gastroenteritis
Polio
Coxsackie A
Coxsackie B
Echo
Enteroviruses 68-71
Hepatitis A
Hepatitis E
Adenoviruses 1-39
Reoviruses
Found in the gut as opportunistic infection
CMV
HSV
VZV
HIV

Gastrointestinal Viruses
Gastrointestinal Viruses
Infants:
Rotavirus A; Adenovirus 40,41; Coxsackie A24 virus
Infants, children, and adults
Norwalk virus; Calicivirus
Astrovirus; Rotavirus B; Reovirus.
Human Rotavirus
Important Characteristics
70 nm round, double shelled, enclosing a genome of segments of double stranded RNA.

Groups of Rotaviruses
Group A subtypes 1, 2, 3, 4 (main human pathogens)(Further 7 subtypes) also infect animals (monkey, calf, mouse)
Group B Infects pigs and ratsFound to cause extensive outbreaks in China in past decade
Group C Infects Pigs (Occasionally Man)
Group D Infects birds
Group E Infects pigs

Pathogenesis
Essentially an ingestion disease (faecal-oral route)
Incubation is short : 1 to 3 days
Illness: Sudden onset watery diarrhoea, with or without vomiting. May last up to 6 days (or longer if immunocompromised). The disease is self limiting.
Complications: Dehydration may result, this can be severe and life threatening in young children.
Pathogenesis
Group A: Main pathogen of infantile diarrhea
Group B : Cause epidemic adult diarrhea
Group C: Cause human or animal sporadic diarrhea

Immunity:sIgA
Lab. Diagnosis
IEM,
Cell culture,
PAGE of RNA segments,
PCR
Latex agglutination
ELISA
Treatment
Treatment of dehydration by oral and/or intravenous fluids and electrolytes
Prevention
Non specific factors: improved hygiene, education, clean waterSpecific - Breast feeding helps to provide passive immunity in the newborn (from maternal antibodies), Vaccination is still experimental.
Enteric Adenoviruses
Naked DNA viruses, 75 nm in diameter.
Fastidious enteric adenovirus types 40 and 41 are associated with gastroenteritis.
Associated with cases of endemic gastroenteritis, usually in young children and neonates. Can cause occasional outbreaks.
Possibly the second most common viral cause of gastroenteritis (7-15% of all endemic cases).
Similar disease to rotaviruses
Most people have antibodies against enteric adenoviruses by the age of three.
Diagnosed by electron microscopy or by the detection of adenovirus antigens in faeces by ELISA or other assays.
Astroviruses
Surface morphology, 28 nm in diameter.
Associated with cases of endemic gastroenteritis, usually in young children and neonates. Can cause occasional outbreaks.
Responsible for up to 10% of cases of gastroenteritis.
Similar disease to rota and adenoviruses.
Most people have antibodies by the age of three.
Diagnosed by electron microscopy only, often very difficult because of small size.
Caliciviruses
Small RNA viruses, characteristic surface morphology consisting of hollows. particles 35 nm in diameter.
Associated mainly with epidemic outbreaks of gastroenteritis, although occasionally responsible for endemic cases.
Like Norwalk type viruses, vomiting is the prominent feature of disease.
Majority of children have antibodies against caliciviruses by the age of three.
Diagnosed by electron microscopy only, often difficult to diagnose because of small size.
Norovirus-Norwalk-like Viruses
Small RNA viruses, with ragged surface, 35 nm in diameter, now classified as caliciviruses.
Always associated with epidemic outbreaks of gastroenteritis, adults more commonly affected than children.
Associated with consumption of shellfish and other contaminated foods. Aerosol spread possible as well as faecal-oral spread.
Also named "winter vomiting disease", with vomiting being the prominent symptom, diarrhoea usually mild.
Antibodies acquired later in life, in the US, only 50% of adults are seropositive by the age of 50.
Diagnosis is made by electron microscopy and by PCR.
Other Possible Diarrheal Viruses
Coronaviruses
RNA viruses with a crown-like appearance
Not convincing associated with gastroenteritis at present

Small Round Viruses
Small virus-like particles with a smooth surface, 22-28nm in diameter
May possibly be parvoviruses, enteroviruses, or cubic bacteriophages
Occasionally seen in the faeces of endemic or epidemic cases of gastroenteritis

Gastrointestinal Viruses

Respiratory Viruses

2009-11-30T07:27:00.000-08:00

Respiratory Viruses
Viruses Associated with Respiratory Infections
Influenza Virus
RNA virus, genome consists of 8 segments
enveloped virus, with haemagglutinin and neuraminidase spikes
3 types: A, B, and C
Type A undergoes antigenic shift and drift.
Type B undergoes antigenic drift only and type C is relatively stable
Influenza A Virus

Undergoes antigenic shifts and antigenic drifts with the haemagglutinin and neuraminidase proteins.
Antigenic shifts of the haemagglutinin results in pandemics. Antigenic drifts in the H and N proteins result in epidemics.

Usually causes a mild febrile illness.

Death may result from complications such as viral/bacterial pneumonia.
Epidemiology
Pandemics - influenza A pandemics arise when a virus with a new haemagglutinin subtype emerges as a result of antigenic shift. As a result, the population has no immunity against the new strain. Antigenic shifts had occurred 3 times in the 20th century.

Epidemics - epidemics of influenza A and B arise through more minor antigenic drifts as a result of mutation.
Past Antigenic Shifts
1918 H1N1“Spanish Influenza” 20-40 million deaths

1957 H2N2“Asian Flu” 1-2 million deaths

1968 H3N2“Hong Kong Flu” 700,000 deaths

1977 H1N1Re-emergence No pandemic

At least 15 HA subtypes and 9 NA subtypes occur in nature. Up until 1997, only viruses of H1, H2, and H3 are known to infect and cause disease in humans.

Avian Influenza
H5N1
An outbreak of Avian Influenza H5N1 occurred in Hong Kong in 1997 where 18 persons were infected of which 6 died.
The source of the virus was probably from infected chickens and the outbreak was eventually controlled by a mass slaughter of chickens in the territory.
All strains of the infecting virus were totally avian in origin and there was no evidence of reassortment.
However, the strains involved were highly virulent for their natural avian hosts.

H9N2
Several cases of human infection with avian H9N2 virus occurred in Hong Kong and Southern China in 1999.
The disease was mild and all patients made a complete recovery
Again, there was no evidence of reassortment
Theories Behind Antigenic Shift
1. Reassortment of the H and N genes between human and avian influenza viruses through a third host. There is good evidence that this occurred in the 1957 H2N2 and the 1968 H3N2 pandemics.
2. Recycling of pre-existing strains – this probably occurred in 1977 when H1N1 re-surfaced.
3. Gradual adaptation of avian influenza viruses to human transmission. There is some evidence that this occurred in the 1918 H1N1 pandemic.
Reassortment
Laboratory Diagnosis
Detection of Antigen - a rapid diagnosis can be made by the detection of influenza antigen from nasopharyngeal aspirates and throat washings by IFT and ELISA

Virus Isolation - virus may be readily isolated from nasopharyngeal aspirates and throat swabs.

Serology - a retrospective diagnosis may be made by serology. CFT most widely used. HAI and EIA may be used to give a type-specific diagnosis

Management
Amantidine is effective against influenza A if given early in the illness. However, resistance to amantidine emerges rapidly
Rimantidine is similar to amantidine but fewer neurological side effects.
Ribavirin is thought to be effective against both influenza A and B.
Neuraminidase inhibitors are becoming available. They are highly effective and have fewer side effects than amantidine. Moreover, resistance to these agents emerge slowly
Prevention
Inactivated split/subunit vaccines are available against influenza A and B.
The vaccine is normally trivalent, consisting of one A H3N2 strain, one A H1N1 strain, and one B strain.
The strains used are reviewed by the WHO each year.
The vaccine should be given to debilitated and elderly individuals who are at risk of severe influenza infection.
Amantidine can be used as an prophylaxis for those who are allergic to the vaccine or during the period before the vaccine takes effect.
Parainfluenza Virus
ssRNA virus
enveloped, pleomorphic morphology
5 serotypes: 1, 2, 3, 4a and 4b
No common group antigen
Closely related to Mumps virus
Clinical Manifestations
Croup (laryngotraheobroncitis) - most common manifestation of parainfluenza virus infection. However other viruses may induce croup e.g. influenza and RSV.
Other conditions that may be caused by parainfluenza viruses include Bronchiolitis, Pneumonia, Flu-like tracheobronchitis, and Corza-like illnesses.
Laboratory Diagnosis
Detection of Antigen - a rapid diagnosis can be made by the detection of parainfluenza antigen from nasopharyngeal aspirates and throat washings.

Virus Isolation - virus may be readily isolated from nasopharyngeal aspirates and throat swabs.

Serology - a retrospective diagnosis may be made by serology. CFT most widely used.
Management
No specific antiviral chemotherapy available.
Severe cases of croup should be admitted to hospital and placed in oxygen tents.
No vaccine is available.
Respiratory Syncytial Virus (RSV)
ssRNA eveloped virus.
belong to the genus Pneumovirus of the Paramyxovirus family.
Considerable strain variation exists, may be classified into subgroups A and B by monoclonal sera.
Both subgroups circulate in the community at any one time.
Causes a sizable epidemic each year.
Clinical Manifestations
Most common cause of severe lower respiratory tract disease in infants, responsible for 50-90% of Bronchiolitis and 5-40% of Bronchopneumonia
Other manifestations include croup (10% of all cases).
In older children and adults, the symptoms are much milder: it may cause a corza-like illness or bronchitis.
Infants at Risk of Severe Infection
1. Infants with congenital heart disease - infants who were hospitalized within the first few days of life with congenital disease are particularly at risk.
2. Infants with underlying pulmonary disease - infants with underlying pulmonary disease, especially bronchopulmonary dysplasia, are at risk of developing prolonged infection with RSV.
3. Immunocompromized infants - children who are immunosuppressed or have a congenital immunodeficiency disease may develop lower respiratory tract disease at any age.
Laboratory Diagnosis
Detection of Antigen - a rapid diagnosis can be made by the detection of RSV antigen from nasopharyngeal aspirates. A rapid diagnosis is important because of the availability of therapy

Virus Isolation - virus may be readily isolated from nasopharyngeal aspirates. However, this will take several days.

Serology - a retrospective diagnosis may be made by serology. CFT most widely used.
Treatment and Prevention
Aerosolized ribavirin can be used for infants with severe infection, and for those at risk of severe disease.

There is no vaccine available.

RSV immunoglobulin can be used to protect infants at risk of severe RSV disease.
Adenovirus
ds DNA virus
non-enveloped
At least 47 serotypes are known
classified into 6 subgenera: A to F

Clinical Syndromes
1. Pharyngitis 1, 2, 3, 5, 72. Pharyngoconjunctival fever 3, 7 3. Acute respiratory disease of recruits 4, 7, 14, 21 4. Pneumonia 1, 2, 3, 7 5. Follicular conjunctivitis 3, 4, 116. Epidemic keratoconjunctivitis 8, 19, 37 7. Pertussis-like syndrome 5 8. Acute haemorrhaghic cystitis 11, 21 9. Acute infantile gastroenteritis 40, 41 10. Intussusception 1, 2, 5
11. Severe disease in AIDS and other immunocompromized patients 5, 34, 35
12. Meningitis 3, 7
Laboratory Diagnosis
Detection of Antigen - a rapid diagnosis can be made by the detection of adenovirus antigen from nasopharyngeal aspirates and throat washings.

Virus Isolation - virus may be readily isolated from nasopharyngeal aspirates, throat swabs, and faeces.

Serology - a retrospective diagnosis may be made by serology. CFT most widely used.
Treatment and Prevention
There is no specific antiviral therapy.

A vaccine is available against Adult Respiratory Distress Syndrome. It consists live adenovirus 4, 7, and 21 in enterically coated capsules. It is given to new recruits into various arm forces around the world.
Common Cold Viruses
Common colds account for one-third to one-half of all acute respiratory infections in humans.

Rhinoviruses are responsible for 30-50% of common colds, coronaviruses 10-30%.

The rest are due to adenoviruses, enteroviruses, RSV, influenza, and parainfluenza viruses, which may cause symptoms indistinguishable to those of rhinoviruses and coronaviruses.
Other respiratory viruses
Rhinovirus
the most important virus that cause common cold)
Ⅲ.Other respiratory viruses
2. Coronaviridae:
HUMAN METAPNEUMOVIRUS
This virus (Pneumovirinae subfamily, Paramyxoviridae family) is closely related to RSV and was first recognized as a pathogen in the Netherlands in 2001.
Its role in upper and lower respiratory tract infections is now being recognized world-wide and it may cause 5% of respiratory illness in children. There is often co-infection with RSV.
Metapneumovirus is ubiquitous and, by the age of five, most people are seropositive and have thus been infected by the virus. Many infections are asymptomatic but the virus can cause both upper and lower respiratory tract infections with symptoms of a cold, otitis media, pneumonia or bronchitis. There can also be pneumonia in marrow recipients that can possibly be fatal.
There are distinct epidemics in the winter months. There are two main HMPV types (A and B), each with 2 subtypes (A1, A2; B1, B2) and allfour of these circulate in the population with the dominant strain varying.Metapneumovirus can be detected by PCR but there is no commercial available testing.

Hepatitis A-E

2009-11-30T05:23:00.000-08:00

Hepatitis A-E Viruses
An Overview

Close personal contact(e.g., household contact, sex contact, child day care centers)
Contaminated food, water(e.g., infected food handlers, raw shellfish)
Blood exposure (rare)(e.g., injecting drug use, transfusion)

Laboratory Diagnosis
Acute infection is diagnosed by the detection of HAV-IgM in serum by EIA.
Past Infection i.e. immunity is determined by the detection of HAV-IgG by EIA.

Many cases occur in community-wide outbreaks
no risk factor identified for most cases
highest attack rates in 5-14 year olds
children serve as reservoir of infection
Persons at increased risk of infection
travelers
homosexual men
injecting drug users

Pre-exposure
Travelers to intermediate and high HAV-endemic regions
Post-exposure (within 14 days)
Routine
household and other intimate contacts
Selected situations
institutions (e.g., day care centers)
common source exposure (e.g., food prepared by infected food handler)

Spectrum of Chronic Hepatitis B Diseases
Chronic persistent Hepatitis-Asymptomatic
Chronic persistent Hepatitis – Symptomatic excerbations of hepatitis.
Cirrhosis of Liver
Hepatocellular Carcinoma

High (>8%): 45% of global population
lifetime risk of infection >60%
early childhood infections common
Intermediate (2%-7%): 43% of global population
lifetime risk of infection 20%-60%
infections occur in all age groups
Low (<2%): 12% of global population
lifetime risk of infection <20%
most infections occur in adult risk groups

A battery of serological tests are used for the diagnosis of acute and chronic hepatitis B infection.
HBsAg - used as a general marker of infection.
HBsAb - used to document recovery and/or immunity to HBV infection.
anti-HBc IgM - marker of acute infection.
anti-HBcIgG - past or chronic infection.
HBeAg - indicates active replication of virus and therefore infectiveness.
Anti-Hbe - virus no longer replicating. However, the patient can still be positive for HBsAg which is made by integrated HBV.
HBV-DNA - indicates active replication of virus, more accurate than HBeAg especially in cases of escape mutants. Used mainly for monitoring response to therapy.
Treatment
Interferon - for HBeAg (+) carriers with chronic active hepatitis. Response rate is 30 to 40%.
Lamivudine - a nucleoside analogue reverse transcriptase inhibitor. Well tolerated, most patients will respond favorably. However, tendency to relapse on cessation of treatment. Another problem is the rapid emergence of drug resistance.
Successful response to treatment will result in the disappearance of HBsAg, HBV-DNA, and seroconversion to HBeAg.

Prevention
Vaccination - highly effective recombinant vaccines are now available. Vaccine can be given to those who are at increased risk of HBV infection such as health care workers. It is also given routinely to neonates as universal vaccination in many countries.
Hepatitis B Immunoglobulin - HBIG may be used to protect persons who are exposed to hepatitis B. It is particular efficacious within 48 hours of the incident. It may also be given to neonates who are at increased risk of contracting hepatitis B i.e. whose mothers are HBsAg and HBeAg positive.
Other measures - screening of blood donors, blood and body fluid precautions.

the diagnosis of acute and chronic hepatitis B infection:
HBsAg - used as a general marker of infection
anti-HBc IgM - marker of acute infection
anti-HBcIgG - past or chronic infection
HBeAg - indicates active replication of virus and therefore infectiveness.
Anti-HBe - virus no longer replicating. However, the patient can still be positive for HBsAg which is made by integrated HBV.
HBV-DNA -indicates active replication of the virus, more accurate than HBeAg especially in cases of escape mutants. Used mainly for monitoring response to therapy.

Chronic Hepatitis C Infection
The spectrum of chronic hepatitis C infection is essentially the same as chronic hepatitis B infection.

All the manifestations of chronic hepatitis B infection may be seen, albeit with a lower frequency i.e. chronic persistent hepatitis, chronic active hepatitis, cirrhosis, and hepatocellular carcinoma.

Laboratory Diagnosis
HCV antibody - generally used to diagnose hepatitis C infection. Not useful in the acute phase as it takes at least 4 weeks after infection before antibody appears.
HCV-RNA - various techniques are available e.g. PCR and branched DNA. May be used to diagnose HCV infection in the acute phase. However, its main use is in monitoring the response to antiviral therapy.
HCV-antigen - an EIA for HCV antigen is available. It is used in the same capacity as HCV-RNA tests but is much easier to carry out.
Treatment
Interferon - may be considered for patients with chronic active hepatitis. The response rate is around 50% but 50% of responders will relapse upon withdrawal of treatment.
Ribavirin - there is less experience with ribavirin than interferon. However, recent studies suggest that a combination of interferon and ribavirin is more effective than interferon alone.

Acute infection is diagnosed by the detection of HAV-IgM in serum by EIA.
Past Infection, i.e., immunity, is diagnosed by the detection of HAV-IgG by EIA.

HIV

2009-11-29T20:11:00.000-08:00

•HIV

•The History of HIV

•Early 1980’s, U.S.

–Physicians in New York and California made the first observations of a new infectious disease of homosexual men.

–Sudden appearance of rare skin cancer called Kaposi’s sarcoma

–Atypical pneumonia caused by Pneumocystis carinii

–CMV infections

–Candiasis

–Other observed opportunistic infections

•Gay-Related Immune Deficiency (GRID)

•All observed individuals suffered from immune suppression

•1981 named the syndrome GRID

•1982 disease renamed Acquired Immune Deficiency Syndrome (AIDS)

•1983—2304 AIDS deaths

•1985 Rock Hudson announced he had AIDS and died

•

•The Discovery of HIV

•2 research teams

–Robert Gallo’s group, NCI, NIH, U.S.

–Luc Montagnier’s team, Pasteur Institute, France

•Upon investigation, Montagnier’s team was the first to isolate HIV

•HIV-1 vs. HIV-2

•HIV-1 isolated by Gallo and Montagnier’s teams were designated HIV-1.

•Montagnier isolated another strain, that is rare in the U.S. but is endemic to Western Africa.

–HIV-2

•HIV-2 is significantly less infectious and progresses more slowly to AIDS than HIV-1

•The Origin of HIV-1 and the AIDS Pandemic

•House Cat theory

•The Hunter theory (or crossing the species barrier theory)

•The contaminated poliovirus vaccines theory

•The colonization theory (or Heart of Darkness theory)

•The conspiracy theory

•The Hunter Theory
(Most Commonly Accepted Theory)

•HIV is a viral zoonosis.

–A virus related to HIV-1, called SIVcpz that infects chimpanzees (native to Cameroon) crossed the species barrier

–Naturally infected chimps were killed for food (bushmeat) and eaten; their blood entered cuts or wounds on the hunter.

•Subsequently, SIVcpz adapted to become HIV-1

•Geographic Distribution of Chimpanzees and Mangabeys

•Where Did HIV-2 Originate?

•HIV-2 entered the human population as a zoonosis (like HIV-1).

•Sooty mangabeys are native to Guinea Bissau, Gabon and Cameroon and naturally carry SIVSM.

•SIVSM from sooty mangabeys (an Old World Monkey) likely evolved into HIV-2 when humans were hunting sooty mangabeys for food and through contaminated blood transfusions and mass vaccination efforts.

•10% of the general population in Guinea Bissau is HIV-2 sero-positive.

•

•The AIDS Pandemic
Patient Zero vs. the Earliest AIDS Cases

•Who was patient zero?

•Randy Shilts book, And the Band Played On proposed that a homosexual French-Canadian flight attendant who died of AIDS in 1984 was patient zero.

•HIV had been found in blood samples and frozen tissues older than the 1980’s.

•

•HIV Transmission

•HIV is present in blood, semen, vaginal fluids, breast milk, saliva (low levels) and tears (low levels).

•Most common ways HIV is transmitted are:

–Anal and vaginal intercourse

–Sharing of contaminated needles (IV drug users)

–Blood transfusions (using infected blood or blood products)

–Accidental needlestick injuries

–Congenital AIDS

–Sharing HIV-contaminated tattoo needles, razors, acupuncture needles, ear-piercing implements

•Can Kissing and Oral Sex Transmit HIV?

•Social kissing is not high-risk behavior

•Open-mouthed (French) kissing increases risk.

•The risk increases if the infected person has canker sores or lesions in his/her mouth.

•Oral sex poses similar risks.

–HIV infected T lymphocytes from semen may enter abrasions or lesions in the mouth.

•Ways HIV is NOT Transmitted
The Fragility of HIV in the Environment

•Soap and water easily disrupts HIV.

•HIV is highly susceptible to drying out.

•Contact with sweat, saliva or tears has never shown to result in transmission.

•Handshaking and hugging has not resulted in transmission.

•Mosquitoes or other insects cannot transmit HIV.

•Prevention of HIV

•Abstinence

•Barrier methods (condoms)

•Microbiocides

•Preexposure prophylaxis (PREP) reduces risk

•Postexposure prophylaxis (PEP) reduces risk

•AIDS in Africa

•Africa, the world’s largest continent, has been hit harder by HIV/AIDS than any other region of the world.

•Each day in Africa:

–660 people die of AIDS

–8800 people are infected with the HIV virus

–1400 newborns are infected with HIV virus during birth or through breastfeeding

•At least 12 million children have lost 1 or more parents to AIDS

•Average Estimates of Adults and Children Living with HIV at the end of 2005

•16.5 General Epidemiology
HIV/AIDS in the United States Today

•HIV cases and deaths among adults and adolescents diagnosed with AIDS 1985-2005

•Prevalence Rates for Adults and Adolescents Living with HIV infection (not AIDS) in 2005

•Proportion of HIV/AIDS Cases Among Adults and Adolescents by Sex and Transmission Category in 2005

•A Risky Workplace? AIDS in the Adult Film Industry

•Over 200 pornographic film production companies in Los Angeles County, California.

•At least 1200 workers engage in work-related sexual contract.

•Workers participate in voluntary programs that screen for HIV and other STDs.

–At least 62 male and 6 female porn film performers died of AIDS from 1985-2002.

•HIV/AIDS in U.S. Correctional Facilities

•Activities in prisons that pose a risk for HIV transmission:

–Homosexual activity

–Intravenous drug use

–Tattooing and body piercing

–Sharing of toothbrushes and shaving equipment

–Incidents of violence

•Known HIV Cases in State Correctional Facilities

•AIDS and Seniors

•11-17% of people living with HIV in the U.S. are 50+ years old

•Between 1990 and 2001 cases in seniors quintupled in the U.S.

•24-30% of men and women ages 60-74 report they are sexually active

•Erectile dysfunction drugs such as Viagra, Cialis and Levitra which may be used by older adults has been shown to be associated with higher risk of STDs, especially HIV transmission

•

•Barriers to HIV Diagnosis in Seniors

•The symptoms of chronic illnesses in older adults resembles those of AIDS:

–Night sweats and hot flashes

–Weight loss or fatigue

–Respiratory problems

–Skin rashes

–Flulike symptoms or diarrhea

–Chronic pain or numbness

–Early signs of dementia

•Clinical Symptoms

•3 Phases of HIV-1 Infection

–Primary HIV-1 infection

–The chronic asymptomatic phase of infection

–AIDS

•Primary HIV-1 Infection

•Period after infection but before the development of detectable antibodies against HIV-1.

•

•The Chronic Asymptomatic Phase

•Neither signs nor symptoms of the disease present

•This phase typically lasts an average of 10 years

–Typical progressors

–Rapid progressors

–Slow progressors

–Long term progressors

•Graphs Demonstrating the
Different Types of Progressors

•AIDS

•Without anti-retroviral therapy, the patient will die within 2 to 3 years.

•As T-lymphocyte counts decrease below 50 cells/µl, the number of opportunistic infections increases.

•AIDS patients also suffer from malignancies such as nonHodgkin’s lymphoma.

•Wasting syndrome also common (a loss of more than 10% of body weight due to fever or diarrhea for more than 30 days).

•AIDS patients managed with antimicrobial prophylactic regimens.

•

•Table 16-4 Opportunistic Infections Commonly Associated with AIDS, cont.

•Laboratory Diagnosis of HIV

•HIV isolated in 1983

–First commercial antibody detection tests were available in 1985

•Today, most clinical labs screen for HIV-1 and HIV-2 using and ELISA test (specimen is patient blood sample)

•All classes of anti-HIV antibodies detected with these assays

•HIV ELISA test

•Requires 2 doctor visits

–1. Blood drawing and pretest counseling

–2. Test results and additional counseling if needed

–See Figure 5-20, Chapter 5.

•Other rapid HIV tests

•Performed by healthcare worker, tests results within 5-30 minutes

–e.g. done on women in labor before delivery to determine infection status

–patients following an accidental needlestick injury

•Positive ELISA tests must be confirmed by Western blot

•HIV Home Testing Systems

•FDA approved first system in 1996

–Home Access HIV-1 Test System

•Uses simple finger prick of blood sample

–Place on filter paper

–Mail in for laboratory testing

•Confidential results obtained through toll-free phone number and post-test counseling is available

•HIV Western Blot

•Confirmatory test to exclude false positive results

–(See Ch. 5, Fig. 5-21, for principles behind Western Blotting procedures)

•Nitrocellulose membrane is probed with patient serum

•If the patient has been exposed to HIV, + bands will be observed on the Western blot

•Mandatory Testing for HIV?

•~ 1 in 4 of the 1 million Americans infected with HIV don’t know they are infected

•This group is most responsible for the spread of HIV

•CDC released voluntary testing guidelines that would apply to every American, ages 13-64

•Genetic Variation/Groups

•HIV mutates rapidly

•3 distinct groups of HIV-1

–M (Major) group

–O (Outlier) group

–N (New) group

•M group is further divided into clades or subtypes: A, B, C, D, F, G, H and K

•HIV Virus Life Cycle
HIV Classification and Virion Structure

•Retroviridae family

•Lentivirus genus (from Latin word lenti, for “slow”)

•HIV particles

•100-200 nm icosahedron-shaped sphere surrounded by an envelope

•Envelope contains glycoproteins gp120 and gp41 spikes

•Matrix proteins located below the envelope

•2 copies of genome (+) ssRNA, cellular tRNAlys bound to each genome which acts as a primer for RT

•Reverse transcriptase (RT, p64) and integrase (p34) bound to viral genome.

•Protease (p10) also found within nucleocapsid of virus particle

•Electron Micrograph Showing Mature HIV Particles

•Schematic of HIV Virion

•HIV-1 Entry

•HIV infects CD4+ T lymphocytes and will lyse them during a productive infection

•HIV infects other cells but does not lyse them:

–Natural killer cells

–CD8+ killer T-cells

–Macrophages

–Cell of the nervous system (e.g. astrocytes, neurons, glial cells and brain macrophages)

–Dendritic cells

•HIV Entry

•Early course of infection: HIV infects macrophages

•Later in the course of infection: HIV infects T cells

•The rapid progression to AIDS is associated with a switch in coreceptor preference.

•HIV enters cells via a cellular receptor and coreceptor

–Major cellular receptor: CD4 present on T-lymphocytes (also present in low concentrations on macrophages)

–Coreceptor on T lymphocytes: CXCR4 (fusion)

–Coreceptor on macrophages: CCR5

•HIV Entry and Uncoating

•gp120 of the virus interacts with CD4

•Subsequently HIV gp120 and gp41 undergo a conformational change, causing a coreceptor reaction

•The virus anchors into the membrane of the CD4+ cell

•HIV gp41 changes into a coiled shape, bringing the virus and cell membrane together, allowing them to fuse, resulting in entry and uncoating

•HIV Receptor/Coreceptor Interaction

•Reverse Transcription of HIV RNA

•HIV RT binds to tRNAlys on the viral genome and initiates DNA synthesis

•When reverse transcription is complete, the final product is dsDNA flanked by LTRs at each end of the viral genome.

•The viral DNA is transported to the nucleus of the cell where the viral genome may be integrated into the host cell’s chromosomal DNA.

•HIV Proviral Integration

•Proviral integration is catalyzed by the integrase (p32) protein.

•p32 is packaged in the original HIV particle.

•HIV can latently infect cells.

•The latent reservoirs are one of the main barriers to elimination of HIV infection.

•During a production infection, HIV-1 is reactivated and the completion of the life cycle occurs.

•HIV Viral Genome is More Complicated than a Typical Retroviral Genome

•HIV-1 Transcription

•HIV-1 utilizes the host cell’s transcription and translational machinery.

•The proviral DNA is transcribed from a single promoter in the 5’ LTR into a 9 kb viral RNA transcript by the cellular RNA polymerase II

•HIV-1 tat and rev regulate gene expression

•

•HIV-1 TAR

•TAR is located at the 5’ end of all HIV RNAs.

•The binding of tat to TAR increases the transcription rate from the HIV LTR at least 1000 fold.

•Rev binds to the RRE element, facilitating the export of unspliced and incompletely spliced viral RNAs from the nucleus to cytoplasm

•Some full-length viral mRNAs are packaged into virions following transport into the cytoplasm.

•Other viral mRNAs are spliced within the nucleus to from mRNAs that are translated into the different viral proteins.

•HIV Accessory Proteins

•Nef, vif, vpu, vpr play a role in virulence.

•Translation of HIV Proteins

•Cellular ribosomes translate proviral mRNA into viral proteins

•Gag gene and the gag and pol genes together are translated into 1 large precursor polyprotein cleaved by a viral encoded protease

•Full-length env, gp160 is transported through the Golgi where it is glycosylated and cleaved by a cellular protease into gp120 and gp41 to form mature envelop proteins

•Mature gp120 and gp41 are targeted to the surface of the infected cell.

•HIV-1 Assembly

•HIV-1 virion components (e.g. the viral RNA, gag, pol, and env proteins) are assembled at budding sites located at the cellular plasma membrane.

•The gag and gag-pol proteins are cleaved by an HIV specific protease to form mature virus particles.

•HIV Virus Life Cycle Overview

•HIV Cellular Pathogenesis

•Ultimately, HIV causes AIDS by depleting CD4+ T helper lymphocytes.

–Weakening of the immune system

–Body can’t stop infections or remove cancer cells

–Opportunistic infections

•HIV causes syncytia formation

•AIDS dementia complex

–Occurs in 20% of infected individuals

–Symptoms:

•Impairment of cognitive reasoning (e.g short term memory problems and concentration

•Behavior changes (apathy, withdrawal, irritability, depression, personality changes)

•Motor performance (clumsiness, tremors, leg weakness)

–

•Lymph Node of a Patient Showing Syncytial Formation of Lymphocytes.

•HIV Human Genetics/Resistance: The Smallpox Hypothesis

•Individuals who are homozygous for a defective CCRD32 gene are virtually resistant to HIV infection

–(two defective copies are inherited, one from each parent)

•Individuals who are heterozygous for the defective CCR5D32 gene progress more slowly to AIDS

–(only 1 defective copy inherited)

•CCR5D32

•CCR5 gene is missing 32 base pairs

•Codes for a truncated protein that is not detected on the cell surface.

•HIV gp120/gp41 cannot attach to it to infect cells

•CCR5D32 Mechanisms for HIV Resistance

•HIV Resistance: Population Statistics

•European populations

–5-14% heterozygous CCR5D32

•1% homozygous in some populations such as Caucasian North Americans

•The CCR5D32 allele is almost absent in African, Asian, Native American Indian and Middle Eastern populations.

•Where Did the Resistance Allele Come From?

•Chemokine receptors play a central role in the immune response against many pathogens.

•Time is needed for natural selection to increase the frequency of a rare allele.

•People with CCR5D32 survive without immune system problems because other chemokines compensate for CCR5 (e.g. CXCR4 or CCR2)

•Major infectious diseases in history

–Bubonic plague

–Smallpox

–Syphilis

–Tuberculosis

•

•Popular Theory

•CCR5D32 led to increased survival during smallpox outbreaks that occurred in 14th century Europe

•During this time, smallpox outbreaks were ongoing, allowing for continuous natural selection

•

•The CCR5D32 genetic variant was an unintended but welcomed consequence of smallpox.

•Variola has a SECRET

•Variola virus encodes a 35 kd secretory protein that binds to several CC-chemokine receptors.

•The C-terminal of the 35 kd protein contains smallpox virus encoded chemokine receptor (SECRET) domain

•Acts as a chemokine inhibitor, allowing the virus to evade the immune system.

•In turn, individuals with a defective receptor resist effects by variola and HIV.

•Managing HIV Patients
Antiviral Therapy

•CD4+ T Lymphocyte Counts

–Less than 200 per µl plasma

•Virus load monitoring

–Used to make recommendations for antiviral treatment of patients

–Measure HIV-1 RNA copies per ml of plasma

•100,000 copies per ml of plasma = clinical AIDS

•An absence of detectable RNA copies suggest a slower progression to AIDS

•

•HIV Antiviral Therapy

•Zidovudine (AZT), a thymine analog, RT inhibitor first approved HIV-1 treatment

•Drug resistance to AZT emerged

•1996 David Ho,

–HAART, Highly Active Retroviral Therapy—use of at least 3 compounds simultaneously to block HIV RT, protease, entry/fusion, integrase etc.

•Antiviral Therapy

1.Nonnucleoside or nucleoside reverse transcriptase (RT) inhibitors of HIV RT

2.Protease inhibitors that inhibit HIV maturation by blocking an HIV-specific protease, resulting in noninfectious virus

3.Fusion inhibitors that block HIV fusion of viral gp41 protein and the host cell membrane

4.Integrase inhibitors block HIV p32 activity, abolishing integration of the proviral DNA copy of HIV into the host cell chromosome

5.CCR5 blocking inhibitor

•HIV Drug Targets

•

•Table 16-9 Approved Retroviral Therapy, cont.

•Progression of HIV Infection Based on T-Cell Counts and Viral Loads

•Is an HIV Vaccine Possible?

•Still no HIV vaccine

•An AIDS patient harbors 100 million genetically distinct variants of HIV

•HIV variants can escape both antibody and T-cell immune responses.

•Will a vaccine be able to cope with this variability?

•The HIV Virion is More Complicated Than Portrayed in Most Textbooks

•HIV particles carry numerous host-derived proteins within the HIV envelope

•Many serum proteins are bound to the HIV particle

•Many of the original gp120 spikes have been lost

–This interferes with host antibody responses toward the virus.

Herpesviridae

2009-11-28T18:06:00.000-08:00

Herpesviruses

Properties of herpesviruses

Enveloped double stranded DNA viruses.

Genome consisits of long and short fragments which may be orientated in either direction, giving a total of 4 isomers.

Three subfamilies:

Alphaherpesviruses - HSV-1, HSV-2, VZV

Betaherpesviruses - CMV, HHV-6, HHV-7

Gammaherpesviruses - EBV, HHV-8

Set up latent or persistent infection following primary infection

Reactivation are more likely to take place during periods of immunosuppression

Herpesvirus Particle

Herpes Simplex Viruses

Properties

Belong to the alpha-herpesvirus subfamily of herpesviruses

Double stranded DNA enveloped virus with a genome of around 150 kb

The genome of HSV-1 and HSV-2 share 50 - 70% homology.

They also share several cross-reactive epitopes with each other. There is also antigenic cross-reaction with VZV.

Man is the only natural host for HSV.

Epidemiology

HSV is spread by contact, as the virus is shed in saliva, tears, genital and other secretions.

By far the most common form of infection results from a kiss given to a child or adult from a person shedding the virus.

Primary infection is subclinical in most individuals. It is a disease mainly of very young children

There are 2 peaks of incidence, the first at 0 - 5 years and the second in the late teens, when sexual activity commences.

About 10% of the population acquires HSV infection through the genital route.

Epidemiology

Generally HSV-1 causes infection above the belt and HSV-2 below the belt. In fact, 40% of clinical isolates from genital sores are HSV-1, and 5% of strains isolated from the facial area are HSV-2. This data is complicated by oral sexual practices.

Following primary infection, 45% of orally infected individuals and 60% of patients with genital herpes will experience recurrences.

The actual frequency of recurrences varies widely between individuals. The mean number of episodes per year is about 1.6.

Pathogenesis

During the primary infection, HSV spreads locally and a short-lived viraemia occurs, whereby the virus is disseminated in the body. Spread to the to craniospinal ganglia occurs.

The virus then establishes latency in the craniospinal ganglia.

The exact mechanism of latency is not known, it may be true latency where there is no viral replication or viral persistence where there is a low level of viral replication.

Reactivation - triggers include physical or psychological stress, infection; especially pneumococcal and meningococcal, fever, irradiation; including sunlight, and menstruation.

Clinical Manifestations

HSV is involved in a variety of clinical manifestations which includes ;-

1. Acute gingivostomatitis

2. Herpes Labialis (cold sore)

3. Ocular Herpes

4. Herpes Genitalis

5. Other forms of cutaneous herpes

7. Meningitis

8. Encephalitis

9. Neonatal herpes

Oral-facial Herpes

Acute Gingivostomatitis

Acute gingivostomatitis is the commonest manifestation of primary herpetic infection.

The patient experiences pain and bleeding of the gums. 1 - 8 mm ulcers with necrotic bases are present. Neck glands are commonly enlarged accompanied by fever.

Usually a self limiting disease which lasts around 13 days.

Herpes labialis (cold sore)

Following primary infection, 45% of orally infected individuals will experience reactivation. The actual frequency of recurrences varies widely between individuals.

Herpes labialis (cold sore) is a recurrence of oral HSV.

A prodrome of tingling, warmth or itching at the site usually heralds the recurrence. About 12 hours later, redness appears followed by papules and then vesicles.

Gingivostomatitis

Ocular Herpes

HSV causes a broad spectrum of ocular disease, ranging from mild superficial lesions involving the external eye, to severe sight-threatening diseases of the inner eye. Diseases caused include the following:-

Primary HSV keratitis – dendritic ulcers

Recurrent HSV keratitis

HSV conjunctivitis

Iridocyclitis, chorioretinitis and cataract

Genital Herpes

Genital lesions may be primary, recurrent or initial.

Many sites can be involved which includes the penis, vagina, cervix, anus, vulva, bladder, the sacral nerve routes, the spinal and the meninges. The lesions of genital herpes are particularly prone to secondary infection.

Dysuria is a common complaint, in severe cases, there may be urinary retention.

Local sensory nerves may be involved leading to the development of a radiculitis. A mild meningitis may be present.

60% of patients with genital herpes will experience recurrences. Recurrent lesions in the perianal area tend to be more numerous and persists longer than their oral HSV-1 counterparts.

Herpes Simplex Encephalitis

Herpes Simplex encephalitis is one of the most serious complications of herpes simplex disease. There are two forms:

Neonatal – there is global involvement and the brain is almost liquefied. The mortality rate approaches 100%.

Focal disease – the temporal lobe is most commonly affected. This form of the disease appears in children and adults. It is possible that many of these cases arise from reactivation of virus. The mortality rate is high (70%) without treatment.

It is of utmost importance to make a diagnosis of HSE early. It is general practice that IV acyclovir is given in all cases of suspected HSE before laboratory results are available.

Neonatal Herpes Simplex

Incidence of neonatal HSV infection varies inexplicably from country to country e.g. from 1 in 4000 live births in the U.S. to 1 in 10000 live births in the UK

The baby is usually infected perinatally during passage through the birth canal.

Premature rupturing of the membranes is a well recognized risk factor.

The risk of perinatal transmission is greatest when there is a florid primary infection in the mother.

There is an appreciably smaller risk from recurrent lesions in the mother, probably because of the lower viral load and the presence of specific antibody

The baby may also be infected from other sources such as oral lesions from the mother or a herpetic whitlow in a nurse.

Neonatal Herpes Simplex

The spectrum of neonatal HSV infection varies from a mild disease localized to the skin to a fatal disseminated infection.

Infection is particularly dangerous in premature infants.

Where dissemination occurs, the organs most commonly involved are the liver, adrenals and the brain.

Where the brain is involved, the prognosis is particularly severe. The encephalitis is global and of such severity that the brain may be liquefied.

A large proportion of survivors of neonatal HSV infection have residual disabilities.

Acyclovir should be promptly given in all suspected cases of neonatal HSV infection.

The only means of prevention is to offer caesarean section to mothers with florid genital HSV lesions.

Other Manifestations

Disseminated herpes simplex are much more likely to occur in immunocompromised individuals. The widespread vesicular resembles that of chickenpox. Many organs other than the skin may be involved e.g. liver, spleen, lungs, and CNS.

Other cutaneous manifestations include

eczema herpeticum which is potentially a serious disease that occurs in patients with eczema.

Herpetic whitlow which arise from implantation of the virus into the skin and typically affect the fingers.

“zosteriform herpes simplex". This is a rare presentation of herpes simplex where HSV lesions appear in a dermatomal distribution similar to herpes zoster.

Laboratory Diagnosis

Direct Detection

Electron microscopy of vesicle fluid - rapid result but cannot distinguish between HSV and VZV

Immunofluorescence of skin scrappings - can distinguish between HSV and VZV

PCR - used routinely for the diagnosis HSV encephalitis

Virus Isolation

HSV-1 and HSV-2 are easy to cultivate. It usually takes only 1 - 5 days for a result to be available.

Serology

Not that useful in the acute phase because it takes 1-2 weeks for before antibodies appear after infection. Used to document to recent infection.

Management

Antiviral chemotherapy is indicated where the primary infection is especially severe, where there is dissemination, where sight is threatened, and herpes simplex encephalitis.

Acyclovir – this the drug of choice for most situations at present. It is available in a number of formulations:-

I.V. (HSV infection in normal and immunocompromised patients)

Oral (treatment and long term suppression of mucocutaneous herpes and prophylaxis of HSV in immunocompromised patients)

Cream (HSV infection of the skin and mucous membranes)

Ophthalmic ointment

Famciclovir and valacyclovir – oral only, more expensive than acyclovir.

Varicella- Zoster Virus

Properties

Belong to the alphaherpesvirus subfamily of herpesviruses

Double stranded DNA enveloped virus

Genome size 125 kbp, long and short fragments with a total of 4 isometric forms.

One antigenic serotype only, although there is some cross reaction with HSV.

Epidemiology

Primary varicella is an endemic disease. Varicella is one of the classic diseases of childhood, with the highest prevalence occurring in the 4 - 10 years old age group.

Varicella is highly communicable, with an attack rate of 90% in close contacts.

Most people become infected before adulthood but 10% of young adults remain susceptible.

Herpes zoster, in contrast, occurs sporadically and evenly throughout the year.

Pathogenesis

The virus is thought to gain entry via the respiratory tract and spreads shortly after to the lymphoid system.

After an incubation period of 14 days, the virus arrives at its main target organ, the skin.

Following the primary infection, the virus remains latent in the cerebral or posterior root ganglia. In 10 - 20% of individuals, a single recurrent infection occurs after several decades.

The virus reactivates in the ganglion and tracks down the sensory nerve to the area of the skin innervated by the nerve, producing a varicellaform rash in the distribution of a dermatome.

Varicella

Primary infection results in varicella (chickenpox)

Incubation period of 14-21 days

Presents fever, lymphadadenopathy. a widespread vesicular rash.

The features are so characteristic that a diagnosis can usually be made on clinical grounds alone.

Complications are rare but occurs more frequently and with greater severity in adults and immunocompromised patients.

Most common complication is secondary bacterial infection of the vesicles.

Severe complications which may be life threatening include viral pneumonia, encephalititis, and haemorrhagic chickenpox.

Rash of Chickenpox

Herpes Zoster (Shingles)

Herpes Zoster mainly affect a single dermatome of the skin.

It may occur at any age but the vast majority of patients are more than 50 years of age.

The latent virus reactivates in a sensory ganglion and tracks down the sensory nerve to the appropriate segment.

There is a characteristic eruption of vesicles in the dermatome which is often accompanied by intensive pain which may last for months (postherpetic neuralgia)

Herpes zoster affecting the eye and face may pose great problems.

As with varicella, herpes zoster in a far greater problem in immunocompromised patients

Complications include encephalitis and dissemination

Shingles

Congenital VZV Infection

90% of pregnant women already immune, therefore primary infection is rare during pregnancy.

Primary infection during pregnancy carries a greater risk of severe disease, in particular pneumonia.

First 20 weeks of Pregnancy

Up to 3% chance of transmission to the fetus, recognised congenital varicella syndrome;

Scarring of skin

Hypoplasia of limbs

CNS and eye defects

Death in infancy normal

Neonatal Varicella

VZV can cross the placenta in the late stages of pregnancy to infect the fetus congenitally.

Neonatal varicella may vary from a mild disease to a fatal disseminated infection.

If rash in mother occurs more than 1 week before delivery, then sufficient immunity would have been transferred to the fetus.

Zoster immunoglobulin should be given to susceptible pregnant women who had contact with suspected cases of varicella.

Zoster immunoglobulin should also be given to infants whose mothers develop varicella during the last 7 days of pregnancy or the first 14 days after delivery.

Laboratory Diagnosis

The clinical presentations of varicella or zoster are so characteristic that laboratory confirmation is rarely required. Laboratory diagnosis is required only for atypical presentations, particularly in the immunocompromised.

Virus Isolation - rarely carried out as it requires 2-3 weeks for a results.

Direct detection - electron microscopy may be used for vesicle fluids but cannot distinguish between HSV and VZV. Immunofluorescense on skin scrappings can distinguish between the two.

Serology - the presence of VZV IgG is indicative of past infection and immunity. The presence of IgM is indicative of recent primary infection.

Management

Uncomplicated varicella is a self limited disease and requires no specific treatment. However, acyclovir had been shown to accelerate the resolution of the disease and is prescribed by some doctors.

Acyclovir should be given promptly immunocompromised individuals with varicella infection and normal individuals with serious complications such as pneumonia and encephalitis.

herpes zoster in a healthy individual is not normally a cause for concern. The main problem is the management of the postherpetic neuralgia.

The International Herpes Management Forum recommends that antiviral therapy should be offered routinely to all patients over 50 years of age presenting with herpes zoster.

Three drugs can be used for the treatment of herpes zoster: acyclovir, valicyclovir, and famciclovir. There appears to be little difference in efficacy between them.

Prevention

Preventive measures should be considered for individuals at risk of contracting severe varicella infection e.g. leukaemic children, neonates, and pregnant women

Where urgent protection is needed, passive immunization should be given. Zoster immunoglobulin (ZIG) is the preparation of choice but it is very expensive. Where ZIG is not available, HNIG should be given instead.

A live attenuated vaccine is available. There had been great reluctance to use it in the past, especially in immunocompromised individuals since the vaccine virus can become latent and reactivate later on.

However, recent data suggests that the vaccine is safe, even in children with leukaemia provided that they are in remission.

It is highly debatable whether universal vaccination should be offered since chickenpox and shingles are normally mild diseases.

Cytomegalovirus

Properties

Belong to the betaherpesvirus subfamily of herpesviruses

double stranded DNA enveloped virus

Nucleocapsid 105nm in diameter, 162 capsomers

The structure of the genome of CMV is similar to other herpesviruses, consisting of long and short segments which may be orientated in either direction, giving a total of 4 isomers.

A large no. of proteins are encoded for, the precise number is unknown.

Epidemiology

CMV is one of the most successful human pathogens, it can be transmitted vertically or horizontally usually with little effect on the host.

Transmission may occur in utero, perinatally or postnatally. Once infected, the person carries the virus for life which may be activated from time to time, during which infectious virions appear in the urine and the saliva.

Reactivation can also lead to vertical transmission. It is also possible for people who have experienced primary infection to be reinfected with another or the same strain of CMV, this reinfection does not differ clinically from reactivation.

In developed countries with a high standard of hygiene, 40% of adolescents are infected and ultimately 70% of the population is infected. In developing countries, over 90% of people are ultimately infected.

Pathogenesis

Once infected, the virus remains in the person for life and my be reactivated from time to time, especially in immunocompromised individuals.

The virus may be transmitted in utero, perinatally, or postnatally. Perinatal transmission occurs.

Perinatal infection is acquired mainly through infected genital secretions, or breast milk. Overall, 2 - 10% of infants are infected by the age of 6 months worldwide. Perinatal infection is thought to be 10 times more common than congenital infection.

Postnatal infection mainly occurs through saliva. Sexual transmission may occur as well as through blood and blood products and transplanted organ.

Clinical Manifestations

Congenital infection - may result in cytomegalic inclusion disease

Perinatal infection - usually asymptomatic

Postnatal infection - usually asymptomatic. However, in a minority of cases, the syndrome of infectious mononucleosis may develop which consists of fever, lymphadenopathy, and splenomegaly. The heterophil antibody test is negative although atypical lymphocytes may be found in the blood.

Immunocompromised patients such as transplant recipients and AIDS patients are prone to severe CMV disease such as pneumonitis, retinitis, colitis, and encephalopathy.

Reactivation or reinfection with CMV is usually asymptomatic except in immunocompromised patients.

Congenital Infection

Defined as the isolation of CMV from the saliva or urine within 3 weeks of birth.

Commonest congenital viral infection, affects 0.3 - 1% of all live births. The second most common cause of mental handicap after Down's syndrome and is responsible for more cases of congenital damage than rubella.

Transmission to the fetus may occur following primary or recurrent CMV infection. 40% chance of transmission to the fetus following a primary infection.

May be transmitted to the fetus during all stages of pregnancy.

No evidence of teratogenecity, damage to the fetus results from destruction of target cells once they are formed.

Cytomegalic Inclusion Disease

CNS abnormalities - microcephaly, mental retardation, spasticity, epilepsy, periventricular calcification.

Eye - choroidoretinitis and optic atrophy

Ear - sensorineural deafness

Liver - hepatosplenomegaly and jaundice which is due to hepatitis.

Lung - pneumonitis

Heart - myocarditis

Thrombocytopenic purpura, Haemolytic anaemia

Late sequelae in individuals asymptomatic at birth - hearing defects and reduced intelligence.

Incidence of Cytomegalic Disease

Laboratory Diagnosis

Direct detection

biopsy specimens may be examined histologically for CMV inclusion antibodies or for the presence of CMV antigens. However, the sensitivity may be low.

The pp65 CMV antigenaemia test is now routinely used for the rapid diagnosis of CMV infection in immunocompromised patients.

PCR for CMV-DNA is used in some centers but there may be problems with interpretation.

CMV pp65 antigenaemia test

Laboratory Diagnosis

Virus Isolation

conventional cell culture is regarded as gold standard but requires up to 4 weeks for result.

More useful are rapid culture methods such as the DEAFF test which can provide a result in 24-48 hours.

Serology

the presence of CMV IgG antibody indicates past infection.

The detection of IgM is indicative of primary infection although it may also be found in immunocompromised patients with reactivation.

Cytopathic Effect of CMV

DEAFF test for CMV

Specimens for Laboratory Diagnosis

Treatment

Congenital infections - it is not usually possible to detect congenital infection unless the mother has symptoms of primary infection. If so, then the mother should be told of the chances of her baby having cytomegalic inclusion disease and perhaps offered the choice of an abortion.

Perinatal and postnatal infection - it is usually not necessary to treat such patients.

Immunocompromised patients - it is necessary to make a diagnosis of CMV infection early and give prompt antiviral therapy. Anti-CMV agents in current use are ganciclovir, forscarnet, and cidofovir.

Prevention

No licensed vaccine is available. There is a candidate live attenuated vaccine known as the Towne strain but there are concerns about administering a live vaccine which could become latent and reactivates.

Prevention of CMV disease in transplant recipients is a very complicated subject and varies from center to center. It may include the following measures.

Screening and matching the CMV status of the donor and recipient

Use of CMV negative blood for transfusions

Administration of CMV immunoglobulin to seronegative recipients prior to transplant

Give antiviral agents such as acyclovir and ganciclovir prophylactically.

Epstein-Barr Virus

Epstein-Barr Virus (EBV)

Belong to the gammaherpesvirus subfamily of herpesviruses

Nucleocapsid 100 nm in diameter, with 162 capsomers

Membrane is derived by budding of immature particles through cell membrane and is required for infectivity.

Genome is a linear double stranded DNA molecule with 172 kbp

The viral genome does not normally integrate into the cellular DNA but forms circular episomes which reside in the nucleus.

The genome is large enough to code for 100 - 200 proteins but only a few have been identified.

Epidemiology

Two epidemiological patterns are seen with EBV.

In developed countries, 2 peaks of infection are seen : the first in very young preschool children aged 1 - 6 and the second in adolescents and young adults aged 14 - 20 Eventually 80-90% of adults are infected.

In developing countries, infection occurs at a much earlier age so that by the age of two, 90% of children are seropositive.

The virus is transmitted by contact with saliva, in particularly through kissing.

Pathogenesis

Once infected, a lifelong carrier state develops whereby a low grade infection is kept in check by the immune defenses.

Low grade virus replication and shedding can be demonstrated in the epithelial cells of the pharynx of all seropositive individuals.

EBV is able to immortalize B-lymphocytes in vitro and in vivo

Furthermore a few EBV-immortalized B-cells can be demonstrated in the circulation which are continually cleared by immune surveillance mechanisms.

EBV is associated with several very different diseases where it may act directly or one of several co-factors.

Disease Association

1. Infectious Mononucleosis

2. Burkitt's lymphoma

3. Nasopharyngeal carcinoma

4. Lymphoproliferative disease and lymphoma in the immunosuppressed.

5. X-linked lymphoproliferative syndrome

6. Chronic infectious mononucleosis

7. Oral leukoplakia in AIDS patients

8. Chronic interstitial pneumonitis in AIDS patients.

Infectious Mononuclosis

Primary EBV infection is usually subclinical in childhood. However in adolescents and adults, there is a 50% chance that the syndrome of infectious mononucleosis (IM) will develop.

IM is usually a self-limited disease which consists of fever, lymphadenopathy and splenomegaly. In some patients jaundice may be seen which is due to hepatitis. Atypical lymphocytes are present in the blood.

Complications occur rarely but may be serious e.g. splenic rupture, meningoencephalitis, and pharyngeal obstruction.

In some patients, chronic IM may occur where eventually the patient dies of lymphoproliferative disease or lymphoma.

Diagnosis of IM is usually made by the heterophil antibody test and/or detection of EBV IgM.

There is no specific treatment.

Burkitt’s Lymphoma

Burkitt's lymphoma (BL)

endemic in parts of Africa and Papua New Guinea.

children aged 3-14 years.

restricted to areas with holoendemic malaria. Therefore it appears that malaria infection is a cofactor.

Multiple copies of EBV genome and some EBV antigens can be found in BL cells and patients with BL have high titers of antibodies against various EBV antigens.

Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC)

malignant tumor of the squamous epithelium of the nasopharynx.

prevalent in S. China, where it is the commonest tumor in men and the second commonest in women.

Multiple copies of EBV genome and EBV EBNA-1 antigen can be found in cells of undifferentiated NPC. Patients with NPC have high titers of antibodies against various EBV antigens.

Immunocompromised Patients

After primary infection, EBV maintains a steady low grade latent infection in the body. Should the person become immunocompromised, the virus will reactivate. In a few cases, lymphoproliferative lesions and lymphoma may develop. These lesions tend to be extranodal and in unusual sites such as the GI tract or the CNS.

Transplant recipients e.g. renal - EBV is associated with the development of lymphoproliferative disease and lymphoma.

AIDS patients - EBV is associated with oral leukoplakia and with various Non-Hodgekin’s lymphoma.

Ducan X-linked lymphoproliferative syndrome - this condition occurs exclusively in males who had inherited a defective gene in the X-chromosome . This condition accounts for half of the fatal cases of IM.

Diagnosis

Acute EBV infection is usually made by the heterophil antibody test and/or detection of anti-EBV VCA IgM.

Cases of Burkitt’s lymphoma should be diagnosed by histology. The tumor can be stained with antibodies to lambda light chains which should reveal a monoclonal tumour of B-cell origin. In over 90% of cases, the cells express IgM at the cell surface.

Cases of NPC should be diagnosed by histology.

The determination of the titer of anti-EBV VCA IgA in screening for early lesions of NPC and also for monitoring treatment.

A patient with with non-specific ENT symptoms who have elevated titers of EBV IgA should be given a thorough examination.

Vaccination

A vaccine against EBV which prevents primary EBV infection should be able to control both BL and NPC.

Such a vaccine must be given early in life. Such a vaccine would also be useful in seronegative organ transplant recipients and those developing severe IM, such as the male offspring of X-linked proliferative syndrome carriers.

The vaccine should not preferably be a subunit vaccine since there is a danger that a live vaccine may still have tumorigenic properties.

The antigen chosen for vaccine development is the MA antigen gp 340/220 as antibodies against this antigen are virus neutralizing.

This vaccine is being tried in Africa.

Other Human Herpes Viruses

Properties of HHV-6 and 7

Belong to the betaherpesvirus subfamily of herpesviruses

Double stranded DNA genome of 170 kbp

The main target cell is the T-lymphocyte, although B-lymphocytes may also be infected.

HHV-6 and HHV-7 share limited nucleotide homology and antigenic cross-reactivity.

It is thought that HHV-6 and HHV-7 are related to each other in a similar manner to HSV-1 and HSV-2.

Epidemiology and Pathogenesis

HHV-6 and HHV-7 are found worldwide.

They are transmitted mainly through contact with saliva and breast feeding.

HHV-6 and HHV-7 infection are acquired rapidly after the age of 4 months. (lack of maternal antibody).

By the time of adulthood, 90-99% of the population had been infected by both viruses.

Like other herpesviruses, HHV-6 and HHV-7 remains latent after primary infection and reactivates.

Clinical Manifestations

Primary HHV-6 infection is associated with Roseala Infantum, which is a classical disease of childhood.

Most cases occur in infants between the ages of 4 months and two years.

A spiking fever develops over a period of 2 days followed by a mild rash. The fever is high enough to cause febrile convulsions.

There are reports that the disease may be complicated by encephalitis.

Clinical Manifestations

If primary infection is delayed until adulthood, there is a small chance that an infectious mononucleosis-like disease may develop in a similar manner to EBV and CMV.

There is no firm evidence linking HHV-6 to lymphomas or lymphoproliferative diseases.

There is no firm disease association with HHV-7 at present.

Although both viruses may be reactivated in immunocompromised patients, it is yet uncertain whether they cause significant disease since CMV is almost invariably present.

Roseala Infantum

Diagnosis and Management

Rosela Infantum has a very characteristic presentation and a diagnosis can usually be made on clinical grounds alone.

Therefore very few virology laboratories offer a diagnostic service for HHV-6 or HHV-7 infection.

The technique for virus isolation is complicated and thus not practicable as a routine diagnostic procedure.

Therefore serology is the mainstay of diagnosis where specific IgM and IgG are detected.

There is no specific antiviral treatment for HHV-6 infection.

Human Herpes Virus 8

Belong to the gammaherpesviruses subfamily of herpesviruses

Originally isolated from cells of Kaposi’s sarcoma (KS)

Now appears to be firmly associated with Kaposi’s sarcoma as well as some lesser known malignancies such as Castleman’s disease and primary effusion lymphomas

HHV-8 DNA is found in almost 100% of cases of Kaposi’s sarcoma

Most patients with KS have antibodies against HHV-8

The seroprevalence of HHV-8 is low among the general population but is high in groups of individuals susceptible to KS, such as homosexuals.

Unlike other herpesviruses, HHV-8 does not have a ubiquitous distribution.

Kaposi’s Sarcoma