Herpes Viruses:Viruses causing latent

infections

Human Herpes Viruses

The herpes viruses are a diverse group of large DNA viruses that share:

• A common virion morphology• A basic mode of replication• The capacity to establish latent and

recurrent infections

The human herpes viruses are grouped into three sub-families on the basis of difference in viral characteristics( genome structure ,

tissue tropism, cytopathogenicity, site of latent infection) as well as the pathogenesis of the disease and disease presentation.

Human Herpes Viruses

Group•Herpes simplex type 1 and 2-Skin lesions and other diseases•Varicella-Zoster virus- varicella and Zoster

Group•Cytomegalovirus- Cytomegalic inclusion disease (CID), disseminated diseases in immunocompromised patients•Herpes type 6-Roseola infantum/exantema subitum•Herpes virus 7-?

Group•Epstein Barr Virus-Infectious mononucleosis, BL, NPC•Herpes virus 8- kaposi’s sarcoma

Herpesviruses have large, enveloped icosadeltahedral capsids containing double-stranded DNA genomes

Herpesviruses encode many proteins that regulate messenger RNA and DNA synthesis and the shutoff of the host cell DNA, RNA, and protein synthesis.

Herpesviruses encode enzymes (DNA polymerase) promote viral DNA replication and that are good targets for antiviral drugs.

DNA replication and assembly occur in the nucleus; virus buds from nuclear membrane and is released by exocytosis and cell lysis.

Herpesviruses can cause lytic, persistent, latent/recrrent, and for EBV, immortalizing infections.

Herpesviruses are ubiquitous*. Cell-mediated immunity is required for control

Unique Features of Herpesvirus

SubfamilyVirusPrimary Target Cell

Site of Latancy

Means of Spread

Alphaherpesvirinae

Human herpesvirus 1

Herpes simplex type 1

Mucoepithelial cells

NeuronClose contact

Human herpesvirus 2

Herpes simplex type 2

Mucoepithelial cells

NeuronClose contact (sexually transmitted disease)

Human herpesvirus 3

Varicella-zosterMucoepithelial cells

NeuronRespiratory and close contact

Properties Distinguishing the Herpesviruses

SubfamilyVirusPrimary Target Cell

Site of Latancy

Means of Spread

Betaherpesvirinae

Human herpesvirus 5

CytomegalovirusMonocyte, lymphocyte and epithelial cells

Monocyte lymphocyte,stromal cells of BMand?

Close contact transfusions, tissue transplant, and congenital

Human herpesvirus 6

Herpes lymphotropic

T cells and monocyte, lymphocyte and epithelial cells?

T cells and monocytes and?

Respiratory and close contact ?

Human herpesvirus 7

Human herpesvirus 7

T cells and ?

T cells and ?

Gammaherpesvirinae

Human herpesvirus 4

Epstein-Barr virus

B cells and epithelial cells

B cellSaliva (kissing disease

Human herpesvirus 8

Koposi’s sarcoma related virus

Lymphocyteand others

?Saliva?, Sexual

Properties Distinguishing the Herpesviruses- cont.

Structure of Herpes Virus Particle

Electron Micrograph (A) and General Structure (B) of the Herpesviruses

162 capsomers

Herpesviruses Genomes

size

125 kbp

152 kbp

186 kbp

229 kbp

162 kbp

Multiplication of Herpes Simplex

HS/HveC/HveA

Shut off of cellular macromolecule synthesis

Trans- Golgi network

(Nectin1a/ TnfR)

Coordinated and regulated transcription

Figure 72-10 Diagram of pathways of egress. HSV capsids bud through the inner nuclear membrane, forming an enveloped virion particle. Egress of the virions from the host cell may occur by either of two general pathways. A: The envelope fuses with the outer nuclear membrane, de-enveloping the capsid and releasing it into the cytoplasm. The capsid then buds into the Golgi apparatus, forming an enveloped virion, which is transported to the surface by vesicular transport. B: The virion particle buds through the outer nuclear membrane and is transported by vesicular movement through the Golgi apparatus to the exterior of the cell. (From Fields Virology, 4th ed, Knipe & Howley, eds, Lippincott Williams & Wilkins, 2001, Fig. 72-10)

Herpesvirus egress

The virus also spreads by cell-cell fusion

1. Viral inhibition of humoral immunity (complement and antibodies)

2. Viral interference with interferon

3. Viral cytokines and cytokine receptors

4. Viral interference with MHC functions

5. Viral inhibitors of apoptosis

Herpes Virus Gene Products Modulate the Immune Response

Virokines VirusVirokineHost functionMechanism

Herpes simplexgE-gIAntibody-mediated Cytolysis

Binds Fc of IgG, preventing complement-mediated cytolysis

C-1ComplementBinds C3b, inhibiting alternative and classical pathways

CytomegalovirusUL18Cytotoxic T cellsHomolog of class I MHC, binds b-microglobulin, preventing translocation to cell surface

UL144TNFR TNFR homolog, unknown function

MC54vIL-18BP. Binds IL-18, Inhibits IL-18 induced IF-J production

US28US28binds cc chemokines

EB VirusBCRF1 Cytokine, cytotoxic T-Cell-

IL-10 homolog inhibits cytokine synthesis suppressing Tc cells and stimulating B cells

BARFCSF-1RBinds CSF-1

Herpes Simplex Type 1

Herpes Simplex Type 2

Oral or genital herpes and other diseases

Disease/Viral Factors

Virus causes lifelong infection

Recurrent disease is source of contagion

Virus may cause asymptomatic shedding

Transmission*

Virus is transmitted in saliva*, in vaginal secretions, and by contact with lesion fluid (MMMM)

Virus is transmitted orally and sexually and by placement into eyes and breaks in skin

HSV-1 is generally transmitted orally; HSV-2 is generally transmitted sexually

Epidemiology of HSV Infection

Disease is initiated by direct contact and depends on infected tissue (e.g., oral, genital, brain).

Virus causes direct cytopathology (several mechanisms

Cell-mediated immunopathology contributes to symptom

Virus blocks IF action and MHCI Ag presentation ( TAP)

Virus avoids antibody by cell-to-cell spread (syncytia) .

Virus established latency in neurons (hides from immune response).

Virus reactivated from latency by stress or immune suppression.

Cell-mediated immunity is required for resolution with limited role for antibody.

Disease Mechanisms for HSV

HSV Latency and Reactivation

Vp26+ Vp5dynein + dynactin

Vp5, Vp16Us11 andKinesin assoc.

Anterogradetransport

Retrogradetransport

HSV1 and HSV2 latency

Neurons Offer Certain Unique Advantages

Express no MHC antigens, shielded from lysis by cytotoxic T lymphocytes. Because the latent viral genome express no protein, also safe from lysis by antibody plus complement or ADCC.

Neurons do not divide, the virus has no need to divide to maintain a fixed number of copies per cell.

The axon provides a direct pathway to the periphery, to susceptible epidermal cells.

Productive infection in epithelial cells of skin and mucous membranes

Latent in cranial or spinal sensory ganglia (trigeminel ganglion, sacral ganglion)

Reactivation caused by stimuli, such as “stress”, ultraviolet light, fever, nerve injury or immunosuppression

Latent in neurons - 10 –100 copies of viral genome, nonintegrated circular, extended concatamers. Cellular proteins bind viral DNA and regulate latency

No standard mRNAs are transcribed. Expression of overlapping non polyadenylated antisense RNA transcipts (latency associated transcripts, LATs), the size of 8,5, 2 and 1.5 Kb. The 2 and 1.5 Kb transcripts are more abundant.

The 2 Kb LAT is partially complementary in sequence to the mRNA for a key regulatory protein, required for transactivation (ICP0).

The role of the LATs in the establishment and maintenance of latent state is not known. LATs regulate the viral genome and interfere with the normal activities of the infected host cell. Stable expression of the abundant LATS in neurons inhibits viral replication and production of immediate early products. Viral mutants that are unable to express LATs are reactivation deficient. Recent studies indicate that LATs inhibit cell death mechanisms and modulate viral chromatin structure.

HSV 1-2 Latency and Reactivation

The Latency Associated Transcripts of Herpes Simplex Virus Type 1

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

Disease Syndromes of

HSV

Primary Herpes Gingivostomatitis

Genital Herpes

Clinical Course of Genital Herpes Infection

PRIMARY

Virus shedding

Herpes Simplex Encephalitis

Cold Sore of Recurrent Herpes

Labialis

Herpetic Whitlow

Diseases Produced by Herpes Simplex Virus

*Including herpes simplex virus infection of burns, eczema herpeticum, etc.

DiseasePrimary (P) or recurrent (R)

AgeFrequencySeverity Type

Gingivostomatis PYoung childrenCommonMild1

Pharyngotonsillitis PAdultsCommonMild1>2

Herpes labialis RAnyCommonMild1>2

Genital herpes P,R>15yearsCommonMild/moderate

2>1

Keratoconjunctivitis P,RAnyCommonMild/moderate

1

Skin infection* P,RAnyRareMild/moderate

1,2

Encephalitis P,RAnyRareSevere1>2

Neonatal herpes PNewbornRareSevere2>1

Disseminated herpes

P,RAnyRareSevere1>2

Laboratory Diagnosis of HSV Infections

ApproachTest/comment

Direct microscopic examination of cells from base of lesion

Tzanck smear shows multinucleated giant cells and cowdry type A inclusion bodies

Cell cultureHSV replicates and causes indentifiable CPE in most cell cultures*

Assay of tissue biopsy, smear, or vesicular fluid for HSV antigen or DNA

Enzyme immunoassay, immunofluorescent stain, in situ DNA probe analysis and PCR are used

HSV type distinction {HSV-1 vs. HSV-2}

Type-specific antibody, DNA maps of restriction enzyme, SDS-gel protein patterns, and DNA probe analysis are used

SerologySerology is not useful except for primary infection/ epidemiology

Cytopathic Effect of HSV in cell culture: Note the ballooning of cells. )Linda Stannard, University

of Cape Town, S.A.(

Positive immunofluorescence test for HSV antigen in epithelial cell. )Virology Laboratory, New-Yale Haven Hospital(

Herpes Encephalitis

ManagementAt present, there are only a few indications of antiviral chemo therapy, with the high cost of antiviral drugs being a main consideration. Generally, 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.

Other older agents – e.g. idoxuridine, trifluorothymidine, Vidarabine )ara-A(.• These agents are highly toxic and is suitable for topical use for opthalmic infection

only

Chemical structure of antiherpes, antiviral agents, acyclovir (ACV), penciclovir (PCV), ganciclovir (GCV), foscarnet (PFA), iodoxuridine (IDU), trifluorothymidine (TFT), vidarabine (Ara-A), and sorivudine (SVD). (Reprinted from ref. 172, with permission.) (From Fields Virology, 4th ed, Knipe & Howley, eds, Lippincott Williams & Wilkins, 2001, Fig. 15-1)

Anti herpesviral drugs

Activation of Acyclovir

Chain Termination

Resistance

TK inactivatingmutations

Mutations of DNA polymerase

Inhibitors of the polymerization reaction of herpesvirus DNA polymerase. (From Fields Virology, 4th ed, Knipe & Howley, eds, Lippincott Williams & Wilkins, 2001, Fig. 15-2)

Mechanism of action of acyclovir

FDA Approved Antiviral Treatments for Herpesvirus Infections

)serious presentations(

No vaccine available.Killed,subunit,vaccinia hybrid.

Disabled infectious single cycle vaccine ( DISC)are beeing developed

Cidofovir, Adefovir

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Varicella-Zoster Virus

VZV

Chickenpox – Varicella

Shingles – Zoster

Properties

• Belong to the alpha herpesvirus subfamily of herpesviruses*

• Double stranded DNA enveloped virus

• Genome size 125 kbp, long and short fragments with a total of 2 isometric forms.

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

• Replicates slower than HSV, in fewer types of cells

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.

Characteristic skin rash of varicella in all stages of Its evolution

Varicella-Chickenpox

• 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.

Mechanism of spread of VZV within the body

Shingles-Zoster

Herpes Zoster in Thoracic Dermatome

Herpes Zoster Ophthalmicus

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 in whom the reactivation occurs earlier in life and multiple attacks occur as well as complications.

• Complications are rare and include encephalitis and disseminated herpes zoster.

Initial replication is in the respiratory tract.

VZV infects epithelial cells and fibroblasts.

VZV can form syncytia and spread directly from cell to cell.

Virus is spread by viremia to skin and causes lesions in successive crops.

VZV can escape antibody clearance, and cell-mediated immune response is essential to control infection. Disseminated, life-threatening disease can occur in immunocompromised people.

Virus establishes latent infection of neurons, usually dorsal root and cranial nerve ganglia.

Herpes zoster may result from depression of cell-mediated immunity and other mechanisms of viral activation.

Disease Mechanism of VZV-summary

Productive infection in epithelial cells of skin and mucosa tissues.

The latency of VZV is maintained tightly. No. asymptomatic shedding. Reactivation is triggered by declining immunity to the virus.

Virus remains latent in sensory ganglia, in the satellite cells which surround the neurons (endothelial and fibroblastic, resembling glia).

There is now a consensus that latent VZV resides predominantly in ganglionic neurons with less frequent infection of non-neuronal satellite cells

Several copies of the viral genome and several species of RNA

transcripts, not equivalent to the HSV LATs, are detected. There is considerable evidence to show that at least five viral genes are transcribed during latency

Upon reactivation, replication of the virus occurs in the satellite cells as well as neurons throughout the ganglion causing severe pain and lesions in the peripheral epidermal cells of the corresponding dermatome.

Varicella-Zoster Latency

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.

.

VZV diagnosis

CytologyCowdry’s A type intra nuclear inclusion bodiesAntigen detection

)Skin lesions, respiratory specimens, organ biopsies(Fluorescent antibody examination for membrane antigens( FAMA)Virus isolationHuman diploid fibroblasts-CPE similar to HSV but after longer incubation periods. Viral antigens can be detected earlier by IF or ELISASerologyUsed for screening of immunity to VZV and documenting VZV infection. IgM and Ab increase can be detected also in zoster patients

Cytopathic Effect of VZV in cell culture: Note the ballooning of cells. )Coutesy of Linda Stannard, University of Cape Town, S.A.(

Cytopathic Effect of VZV

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.

• 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.

FDA Approved Antiviral Treatments for Herpesvirus Infections

)serious presentations(

Penciclovir

Cidofovir, Adefovir

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.

VZV Vaccine- VARIVAX/MERCK

VARIVAX-varicella virus vaccine liveVaricella virus isolated from the blood of a 3 years old

Japanese boy in 1972 . Attenuated by growing it in different human and animal host cells. 1995 approved

by FDA. •Induces protective antibodies and CMI

•Adverse reactions to the vaccine were generally mild

•How long immunity lasts?

•Can the chickenpox vaccine cause shingles?

Cytomegalovirus

CMV

Cytomegalic Inclusion Disease

Infectious Mononucleosis

Post Transfusion Syndrome

Properties• Belong to the betaherpesvirus subfamily of

herpesviruses

• double stranded DNA enveloped virus

• Nucleocapsid 105 nm in diameter, 162 capsomers

• The largest genome. 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.

• Contains RNA mRNAs within the virion

GeneFunction

UL55 (glycoprotein B)Surface glycoprotein and major target for neutralizing antibodies

UL833 (pp65)Major target for CD8 restricted cytotoxic lymphocytes. Major virions structural proteins

US27, US28, UL33, UL75G coupled receptor family members. US28 acts as a promiscuous chemokine receptor

US2, US3, US6 and US11Proteins involved in the downregulation of HLA class I display on infected cells*

UL18class I HLA homologue Binds b2-microglobulin and may function as and NK decoy

UL146CXC chemokine homologue able to chemoattract neutrophils

UL97Protein kinase essential for replication. Activates ganciclovir to its monophosphate Site of action of the benzimidazole classes of drugs

UL54DNA polymerase. Site of action of antiviral Compounds such as ganciclovir (triphosphate), acyclovir (triphosphate), cidofovir (disphosphate), and foscarnet

Key genes encoded by cytomegalovirus (CMV) pertinent to viral pathogenicity

EpidemiologyCMV 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.

CMV is acquired from blood, tissue,and most body secretions.

CMV causes productive infection of epithelial and other cells.

CMV establishes latency in T cells, macrophages, and other cells.

Cell-mediated immunity is required for resolution and contributes to symptoms. Antibody role is limited.

Suppression of cell-mediated immunity allows recurrence and severe presentation.

CMV generally causes sub clinical infection

Disease Mechanisms of CMV

* Diseases shown occur less commonly after reactivation of a latent infection

Age or Immunocompetence

RouteDisease caused by primary infection

PrenatalTransplacentalEncephalitis, hepatitis, thrombocytopenia Long-term sequelae include brain Nerve deafness, retinopathy damage;

PerinatalCervical secretions,

Breast milk, saliva

Blood transfusion

Nil

Pneumonitis, disseminated disease

Any ageSaliva or Sexual Intercourse

Blood transfusion

Mononucleosis Mononucleosis,hepatitis

Immunocompromised* Saliva, sex, organ graftPneumonia,hepatiitis, retinitis, encephalitis myelitis, gastrointestinal disease

Cytomegalovirus Infections

* Diseases shown occur less commonly after reactivation of a latent infection

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.

CMV

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.

Laboratory Diagnosis (1)

• Direct detection

– biopsy specimens may be examined histologically for CMV inclusion bodies ) enlarged cell that contains a dense, central, “owl’s eye” basophilic intranuclear inclusion body( 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

)Virology Laboratory, New-Yale Haven Hospital(

Laboratory Diagnosis (2)

• 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

)Courtesy of Linda Stannard, University of Cape Town, S.A.(

DEAFF test for CMV

)Virology Laboratory, New-Yale Haven Hospital(

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.

VIRUSANTIVIRAL DRUGTRADE NAME

HSVAcyclovirZovirax

Adenosine arobinoside (Ara A)

Vidarabine, Vira

IododeoxyuridineStoxil (idoxurine)

TrifluorothymidineViroptic (trifluridine)

VZVValacylovirValtrex

FamciclovirFamvir

CMVGanciclovirCytovene

PhosphonoformateFoscarnet, Foscavir

Antiviral Drug therapies Approved by the U.S. Food and Drug Administration

HO

O

P

OH

C

OH

O

N

HO-CH2

O

NH2N

CH2 CH2

N

HN

O

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

EBV

Infectious Mononucleosis (Glandular Fever)

African Burkitt’s Lymphoma

Nasopharyngeal Carcinoma

Post Transplant Lymphoproliferative Disorder

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.

Herpesviruses Genomes

size

125 kbp

152 kbp

186 kbp

229 kbp

162 kbp

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.

Disease Association

1. Infectious Mononucleosis

2. Burkitt's lymphoma

3. Nasopharyngeal carcinoma

4. Hodgkin’s disease

5. Lymphoproliferative disease and lymphoma in the immunosuppressed.

6. X-linked lymphoproliferative syndrome

7. Chronic infectious mononucleosis

8. Oral leukoplakia in AIDS patients

9. Chronic interstitial pneumonitis in AIDS patients.

Virus in saliva initiates infection of oral epithelia and spreads to B cells in lymphatic tissue.

There is productive infection in epithelial cells.

Virus promotes growth of B cells (immortalizes).

T cells kill and limit B-cell outgrowth and promote latency in B cells. They are required for controlling infection. Antibody role is limited.

T-cell response (lymphocytosis) contributes to symptoms of infectious mononucleosis.

There is causative association with lymphoma and leukemia in T-cell-deficient people and African children living in malarial regions (African Burkitt’s lymphoma) and with nasopharyngeal carcinoma in China

Disease Mechanisms of EBV

Progression of EBV Infection

LMP-2A Latent infection

EBNA1 BL

C3d-CD21

B cells are semipermissive

EBER 1,2

Epstein-barr Virus Proteins Required for Establishment and Maintenance of Latent Infection

Epstein-Barr Virus protein

Functions

EBNA-1Maintains replication of the latent Epstein-Barr virus genome.

EBNA-2A transcription factor that coordinates Epstien-Barr virus and cell gene expression in the latent infection.

EBNA-LPRequired for cyclin D2 induction in primary B cells in cooperation with EBNA-2.

EBNA-3A and EBNA-3C

Play important roles early in establishment of the latent infection

LMP-1An integral membrane protein.

Stimulates the expression of several surface adhesion molecules in B cells, a calcium-dependent protein kinase and the apoptosis inhibitor Bcl-2.

LMP-2An integral membrane protein required to block activation of the src family signal transduction cascade; an inhibitor of reactivation from latency.

Pathogenesis of EBV

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, pharyngeal obstruction and neurological comlications, GB and miningoencephalitis.

• 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.• EBV persists in memory B cells for lifetime and may be reactivated.

Atypical T-cell (Downey Cell) Characteristic of Infectious Mononucleosis

Clinical Course of Infectious Mononucleosis and Laboratory Findings of Those With the Infection

Clinical Syndrome*

Labortory Data

Time

Serological Data

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, genetic defect in a T-cell gene )SLAM( preventing the T cell from controlling B cell growth. . This condition accounts for half of the fatal cases of IM.

Diagnosis• Acute EBV infection is usually made by the heterophil antibody

( horse monospot test or ELISA) test and/or detection of anti-EBV VCA IgM.

• Cases of Burkitt’s lymphoma should be diagnosed by histology. The tumour 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 non-specific ENT symptoms who has elevated titers of EBV IgA should be given a thorough examination.

Serological profile for EBV infections

-IF ASSAYS

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•IgM Heterophile antibody recognizes the Paull-Bunnell antigen in sheep,horse and bovine RBCs

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.