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Human Herpesviruses

Jackie Parker, Ph.D.Department of Pediatrics, Infectious Diseases

CHB 118B, 1600 6th Avenue South(behind Children’s Hospital)

996-7881 (office)996-7875 (lab)

jnparker@uab.edu

Lecture Objectives

• Introduction to the Human herpesviruses• Virus replication• Human herpesviruses

Herpes Simplex Viruses VZV EBV CMV HHV6,7,8 Simian B Virus

*Clinical manifestations*Antiviral treatment*Disease in the Immuno-compromised host

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Herpesviruses: History

• Herpes infections havebeen described sinceancient Greece

• Name derived from theGreek word “herpein”, whichmeans “to creep”

• Hippocrates and otherGreek scholars used theword “herpes” to describespreading cutaneouslesions caused by manytypes of herpesviruses

Herpesviruses: General Features

Family Herpesviridae

Subfamilies Alpha, Beta, Gammaherpesvirinae

Size 180-200 nm

Envelope Yes

Genome linear ds DNA ranges from ~120 kb (VZV)to ~230 kb (CMV)

GenomeReplicated nucleus

Virus nucleusAssembly

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Herpesviruses:Structural Components

Viral glycoproteins, foundembedded within the lipidenvelope, are responsible forseveral functions, includingreceptor-mediated cellular entry.

The tegument, a layer ofproteins between the envelopeand the underlying capsid.Tegument proteins areresponsible for induction of viralgene expression and shutoff ofhost protein synthesisimmediately following infection,in addition to virion assemblyfunctions.

Icosadeltahedral capsid dsDNA core

Herpesviridae Subfamilies

Alphaherpesvirinae (HSV-1, HSV-2, VZV)-variable host range-short reproductive cycle; rapid spread in culture-capacity to establish latent infections primarily (but not

exclusively) in sensory ganglionsBetaherpesvirinae (CMV, HHV-6)

-restricted host range-long reproductive cycle; slow infection in culture-latent virus maintained in secretory glands, lymphoreticularcells, kidneys, and other tissues

Gammaherpesvirinae (EBV)-members replicate in lymphoblastoid cells-latent or lytic infection, but without production of infectiousprogeny

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α

β

γ

(HSV)

(VZV)

(HCMV)

(HHV-6B)

(EBV)

(HHV-8)

Gene organization among representative herpesviruses

encephalitisNeuron*MucoepitheliaSimian B virus (Herpes B)

Tumors, Kaposi’s sarcoma,some B cell tumors

B lymphocytes,others?

B cells,Endothelial cells

HHV-8. Kaposi’s sarcomaassociated virus (KHSV)

Some cases of roseola,possibly Pityriasis rosea

T lymphocytesand others

T lymphocytes andothers

HHV-7

Roseola in infantsT lymphocytesand others

T lymphocytes andothers

Herpes lymphotrophicvirus (HHV-6)

numerousMonocytes,lymphocytes,dendritic cells

Epithelia,monocytes,lymphocytes

Cytomegalovirus (CMV)(HHV-5)

Infectious mononucleosis,tumors

B lymphocytesB lymphocyte,epithelia

Epstein-Barr virus, EBV(HHV-4)

Chicken pox, shinglesNeuronMucoepitheliaVaricella Zoster virus, VZV(HHV-3)

Genital, ocular, disseminatedNeuronMucoepitheliaHSV-2 (HHV-2)

Oral, ocular lesions; encephalitis, etc.

NeuronMucoepitheliaHSV-1 (HHV-1)

DiseaseLatencyTarget cell typeCommon Name(Designation)

Properties of Human Herpesviruses

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HHV Infections in theImmunocompromised Patient

In immune competent patients any clinical illness tends to be mild and self-limiting. HHVs cause severe and atypical clinical illness in immunocompromised patients. Patients may be immunocompromised for many different reasons, most of which are

acquired rather than congenital. These include: Iatrogenic - the consequence of prescribed drugs such as corticosteroids or other

immunosuppressants. Cancer - often associated with dysregulation of the immune system. Infection - patients with T-cell immunodeficiency (e.g. AIDS) generally have more

severe and persistent HHV infections. It is also important to remember that the immune system changes through life:

Neonates have an immature immune system and are particularly susceptible tosevere HHV primary infection that may be fatal.

Primary HHV infection in pregnancy can be severe• HHV infection of the developing fetus can cause severe congenital

abnormalities associated with mortality and high morbidity.• Pregnant women are at increased risk of developing severe primary HHV

infection that can be fatal. The immune system becomes less efficient with increasing age.

• In particular, T-lymphocyte immunity is less effective in old age.

• Herpes simplex virus type 1 (HSV-1)

• Herpes simplex virus type 2 (HSV-2)

• Varicella Zoster virus (VZV)

Alpha herpesviruses

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Herpes Simplex Viruses (HSV-1, HSV-2)

• HSV-1 and HSV-2 are neurotrophic alpha-herpesvirusthat only naturally occur in humans. There are noanimal reservoirs.

• Significant differences between genomes of HSV-1and HSV-2, but both cause similar clinical illnesses

• HSV-1 mostly infects oral mucosa, but can infectgenital mucosa, whereas HSV-2 mostly infectsgenital mucosa, but can infect oral mucosa

• HSV-1 seroprevalence exceeds 90%, whereas HSV-2seroprevalence is ~18%.

• Initially establish a productive infection in epithelialcells, gain access to the sensory nerve endings withinthe infected area, and travel by retrograde axonal flowto neuronal cells bodies within the respective dorsalroot ganglia

• Can establish a latent infection within sensory neuronsand lytic replication in the nervous system is generallylimited

• Reactivates periodically in a fraction of the latentlyinfected neuronal cells

• The newly replicated virus is transported anterograde,usually to a site at or near the portal of entry into thebody, where it may cause a localized lesion

Herpes Simplex Viruses,cont.

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The "a" sequences are important in both circularization of the viral DNA, and inpackaging the DNA in the virion.

The 9,000 bp long repeat (red), which encodes 4 proteins, including an importantimmediate early regulatory protein (α0). Also includes the promoter of and most ofthe "gene" for the latency associated transcript (LAT).

The long unique region (UL),108 kb long, encodes at least 65 distinct proteins(actually more because some ORFs are spliced and expressed in redundant ways).It contains genes for the DNA replication enzymes and the capsid proteins, as wellas many other proteins.

The 6,600 bp short repeats (yellow) encodes a transcriptional activator (α4) thatacts along with α0 and α27 (in the UL) to stimulate the infected cell for all viral geneexpression that leads to viral DNA replication.

Three origins of replication: the oriL is in the middle of the UL region, while the oriSis located within the repeat sequences and thus, is present in two copies.

The 13,000 bp unique short region (US) encodes 14 ORFs, a number of which areglycoproteins important in viral host range and response to host defense.

UL US

ab b’a’a’c’ ca

Herpes simplex virus genome

Herpesvirus Replication (1)

• Initial attachment is mediated by the interaction of viral envelopeglycoproteins with cell surface receptors.

• Tropism of some herpesviruses (e.g. EBV) is restricted as a result ofthe tissue-specific expression of their receptors.

• The nucleocapsid is released into the cytoplasm through fusion ofthe viral envelope and plasma membrane.

• Virally encoded enzymes and transcription factors are carried intothe infected cell in the tegument of the virion.

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Herpesvirus Replication (2)

•The nucleocapsid docks with the nuclear membrane and delivers the viralgenome into the nucleus, the site of viral gene transcription and replication.

•VP16, a structural viral protein, in conjunction with cellular proteins Oct-1and complex forming factor (CFF), interacts with sequence-specificelements within the promoters of five immediate early (IE) (alpha) genes:ICP0, ICP4, ICP22, ICP27 and ICP47.

•Transcription of the viral genome and viral protein synthesis proceeds in acoordinated and regulated manner in the following three phases:

•Immediate early proteins(α genes), which are necessary for the regulation ofgene transcription and takeover of the cell•Early proteins (β genes), includes more transcription factors and enzymes,including the DNA polymerase•Late proteins (γ genes), which includes the viral structural proteins

http://www.dbc.uci.edu/~faculty/wagner/hsvresrch.html

Herpesvirus Replication (3)

The viral genome is transcribed by the cellular DNA-dependentribonucleic acid (RNA) polymerase and is regulated by viralencoded and cellular nuclear factors.

The interplay of these factors determines whether the proteinsnecessary for a lytic, persistent or latent infection are produced.

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Latency: HSV-1 and HSV-2

• The virus establishes latency in sensory neurons.• Some neurons harboring latent virus express an

RNA designated as Latency Associated Transcript(LAT).

• This RNA does not play a role in the establishmentor maintenance of the latent state.

• Viral proteins have not been demonstrated inneurons harboring latent virus.

• DNA is maintained in episomal form (circular non-integrated)

• Establishment of latency may involve a cellularfunction.

Reactivation from latency

• Not all neurons harboring virus reactivate at once.• Reactivation is more frequent than the appearance

of clinical lesions: the phenomenon is known as“shedding” which may occur in a significant fractionof infected individuals.

• The stimulus for reactivation may differ from oneindividual to another: e.g., fever, physical, emotionalstress, intake of hormones, menstruation, etc.Immunosuppression exacerbates the lesions causedby reactivated virus.

• Upon reactivation, the virus multiplies in the sensoryneuron and is transported to a site at or near theportal of entry. On rare occasion, the reactivatedvirus causes ocular or CNS infections.

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HSV-1 and HSV-2: Establishment of Latency and Reactivation

Clinical Manifestations ofHerpes Simplex Infections

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Oral HSVDiseases Caused by HerpesSimplex Viruses

• Orolabial herpes (almost all type 1) Primary – HSV gingivostomatitis Recurrent – herpes labialis (cold sores, fever blisters)

• Ocular infections• Cutaneous herpes• Genital herpes (mostly type 2)

Primary Recurrent

• Herpes proctitis, perianal herpes (type 2)• HSV encephalitis

Oral HSVDiseases Caused by HerpesSimplex: Orolabial

• Mostly caused by HSV-1• In primary herpetic gingivostomatitis, typical clear lesions first

develop, followed by ulcers with white appearance• Infection initially on the lips and spreads to all parts of the mouth

and pharynx• Spectrum of severity of clinical illness ranging from a few intraoral

ulcers and no systemic features, to severe oral ulceration. Clinicalsymptoms include: Painful vesicles that burst to leave ragged ulcers Drooling, from increased saliva production due to inflammation Systemic symptoms including fever, cervical lymphadenitis, etc.

• Risk of autoinoculation to other sites (eye, skin) highest during theacute phase of the primary infection Herpetic whitlow Herpetic keratitis

• Disease is more severe in immunosuppressed people

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• HSV-1 latency in trigeminal ganglia• Reactivation triggers include: UV exposure,

fever, menses, trauma, etc.• Reactivation from trigeminal ganglia often

results in cold sore development at or nearinitial site of infection

• prodrome of itching, tingling; cluster ofpainful vesicles

• External lesions• Lips (90%)• Nose, chin, or cheeks (10%)• Intra-oral lesions can also occur

Diseases Caused by HerpesSimplex: Orolabial (2)

Oral HSVDiseases Caused by HerpesSimplex Viruses: Oral

Gingivostomatitis inan AIDS patient

Herpes simplex cold sore

Herpetic gingivitis

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Herpes Labialis:Epidemiology in the US

• Cold sores affect 1 in 5 people

• ~98 million cases each year

• 35%-60% Caucasians: HSV-1 serology +

• Seroprevalence dependent on age, socioeconomicstatus, and geographic location

• Primary infection occurs almost exclusively beforeage 4 Usually asymptomatic

• 20%-40% of individuals have recurrent outbreaks In only 1% recurrence is severe

Herpes Labialis – Principles OfAntiviral Treatment

• Treat early (during prodrome) – rapid naturalevolution of disease

• Short duration of therapy – period of viralreplication is brief (2-3 days), then controlledby host immunity

• High dose systemic therapy – deliver highdrug concentrations to tissue, preventextension of HSV to uninfected cells

Ref: Spruance et al, J infect Dis 161:185, 1990

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Topical Antiviral Therapyfor Herpes Labialis

• Penciclovir 1% cream (Denavir®) Reduced duration of lesion pain Accelerated lesion healing Apply topically q2h FDA approved September, 1996

• Acyclovir 5% In PEG ointment – not effective In MAC cream

Herpetic whitlow

Diseases Caused by HerpesSimplex Viruses: Whitlow

• Direct contact with bodysecretions

• Infection occurs through smallcuts or abrasions on the fingers,hand or wrist

• HSV-1 or HSV-2

• Often seen in health careworkers treating patients withHSV infections

• Thumb-sucking children are alsomore susceptible

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Diseases Caused by HerpesSimplex Viruses: Bell’s Palsy

• Acute onset of unilateralfacial nerve palsy

• Multiple causes; many ofthe “idiopathic” cases maybe associated with HSVreactivation

• Small studies withprednisone and/oracyclovir have yieldedvariable results – largerstudies ongoing

• Many experts recommendvalacyclovir + prednisone– optimal dose & durationnot known

• Reactivation of HSV-1; 1250 cases/yr in US of HSE

• Presentation: AMS, fever, HA, personality change, seizures

• Diagnosis: MRI – temporal lobe lesion CSF – PCR for HSV DNA

• Therapy: Acyclovir 10-15 mg/kg q8h x 21d

• Outcome (with therapy): mortality 13% at 1 mo., 28% at 18 mo,38% have no/mild impairment at 6 mo

Diseases Caused by HerpesSimplex Viruses: Encephalitis

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• Mostly likely caused by HSV-2• 18-20% of US population is HSV-2 seropositive• Primary infection may be more severe, may be

associated with systemic syndromes, or may beasymptomatic.

• Variable frequency of recurrences – about 90%will have at least 1 recurrence/year

• Vesicles/ulcerations on genitals or perigenitalskin

• Key to natural history – asymptomatic viralshedding

Diseases Caused by HerpesSimplex Viruses: Genital Herpes

Antiviral Therapy forPrimary Genital HSV

• Acyclovir 200 mg po 5x daily for 10 days

• Valacyclovir 1000 mg po bid for 10 days

• Famciclovir* 125 mg po tid for 10 days

*not FDA approved for this indication

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Oral HSVDiseases Caused by Herpes SimplexViruses: Ocular Infections

• HSV-1 usually associated with ocular infections• Leading cause of blindness in the United States• Typically is limited to one eye• A number of manifestations, including blepharitis,

conjunctivitis, keratis, retinitis• Long-term (12 month) suppressive therapy with an

oral antiviral drug (acyclovir) reduces rates ofrecurrence of HSV keratitis and rates of recurrenceof ocular complications

Oral HSVDiseases Caused by Herpes SimplexViruses: Ocular Infections

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Antiviral Drugs

All anti HSV drugs currently licensed are dependent on being activated by

viral enzymes.

Herpes Simplex Viruses:Antiviral Therapy and Drug Resistance

nucleoside analogs

Drugs are activated by a viral enzyme, thymidine kinase

Only activated in herpes-infected cells, few side effects as aconsequence.

The best known nucleoside analog used to treat herpes simplexvirus infections is acycloguanosine (acyclovir); other approveddrugs include famciclovir and valacyclovir.

Drug resistant herpes mutants do arise with all of these, althoughresistant strains are usually less virulent than the wild type.

Drugs act only against replicating virus (incorporated into DNAduring synthesis); are ineffective against latent virus.

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Herpes Simplex Viruses:Antiviral Therapy and Drug Resistance

acycloviracyclo GMP acyclo GTP

Herpes Simplex Viruses:Antiviral Therapy and Drug Resistance

Mechanisms of Action of Acyclovir: Inhibition of DNA Synthesis & Chain

Termination

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Activation of acyclovir (ACV) andgancyclovir (GCG) by viral enzymes

DNA

ACG-TP

ACG-DP

ACG-MPViral

Thymidinekinase

Wide substraterange

ACG

Inhibitspolymerase;

DNA terminator

Anti-HSV drugs

DNA

GCG-TP

GCG-DP

GCG-MPViral

proteinkinase

GCG

Anti-CMV drugs

Inhibitspolymerase

Varicella-Zoster Virus (VZV)

• Primary infection causes chickenpox (varicella)• Reactivated virus causes herpes zoster, or

shingles• Spreads primarily through the respiratory route• Local replication occurs in respiratory tract-

leads to formation of skin lesions over the entirebody

• Latency is established in dorsal root or cranialnerve ganglia

• Antibody immunity limits viremic spread of VZV• Cell-mediated immunity important for limiting

progression and resolving disease

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Varicella-Zoster Virus (VZV)

chickenpox VZV in newborn

shingles

Varicella-Zoster Virus (VZV):treatment

• For children with chickenpox, normally supportive careis sufficient

• Acyclovir, famciclovir and valacyclovir are used toprevent disseminated infection in immunosuppressedpatients

• Protection for immunosuppressed patients also maycome from varicella-zoster immunoglobulin (VZIg).This can prevent viremic spread, but is ineffective forpatients with active varicella or herpes zoster disease.

• An FDA-approved live virus vaccine is available forVZV

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Epstein-Barr Virus (EBV)

• First discovered as the causative agent for African Burkitt’slymphoma (AfBl).

• Later identified as causative agent for infectiousmononucleosis (“kissing disease”) when serum frominfected individual was found to contain antibody to AfBl.

• Tissue tropism is determined by expression of its receptor,which is same receptor for the C3d component of thecomplement system (a.k.a. CR2 or CD21). Infection islimited to only those cell types which express this receptor.

• Encodes more than 70 proteins

• Has both semi-permissive and permissive replicative cycles

EBV Gene Expression

Semi-permissive replication

• In latently infected lymphocytes, a few unintegratedcopies are replicated every time the cell divides. Earlyimmediate genes are expressed, including the EBV nuclearantigens, two latent membrane proteins (LMPs), and twosmall RNA molecules (EBER-1 and EBER-2).

• The LMPs are oncogenes that stimulate growth of andimmortalize the B cell.

Permissive replication

• In epithelial cells or B cells permissive for EBV replication,expression of ZEBRA protein activates early genes,resulting in expression of the polymerase and DNAreplication and rest of the lytic cycle.

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EBV Pathogenesis:B cell transformation

• Taken up by CD21+ B lymphocytes following virusreplication in pharyngeal epithelial cells andshedding in saliva

• Infected B cells become protected fromundergoing apoptosis; cell is transformed

• B cell transformation changes the interaction ofthe cell with other immune system components

EBV Pathogenesis:Burkitt’s lymphoma

• Tumor of the jaw and face found in children, withevidence of EBV DNA and tumor antigens in thetumor cells

• Tumor cells are monoclonal and show acharacteristic translocation betweenchromosomes 8 and 14, which brings the c-mycgene next to the gene for the Ig heavy chain.

• Result is elevated transcription of c-myc• Biopsy shows large multinucleated cells

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EBV Pathogenesis:Burkitt’s lymphoma

EBV Pathogenesis:Nasal Pharyngeal Cancer

• Tumor of the epithelium and upper respiratorytract

• Occurrences seen in south China, Alaska, Tunisia,east Africa

• Genetic predisposition may be involved, orpossibly environmental co-factor

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EBV Pathogenesis:Oral Hairy Leukoplakia

• An unusual manifestation of a productive EBVinfection in HIV-infected patients with AIDS

• Characterized by a nonpainful white plaque alongthe lateral tongue borders.

• May spread to contiguous sites such as the mouthfloor, tonsil, and pharynx.

EBV Pathogenesis:Infectious mononucleosis

• Characterized by malaise, lymphadenopathy,tonsilitis, enlarged spleen and liver, and fever,which may persist for more than a week.

• A rash may also develop• Resolution usually occurs in 1 to 4 weeks• Complications can include neurological disorders,

including meningitis, encephalitis, myelitis andGuillain-Barre syndrome.

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EBV Diagnosis and Treatment

• Blood smears showingatypical lymphocytes ininfectiousmononucleosis

• Serological tests arealso available fordiagnosis

• No drugs are currentlyavailable to treatEpstein-Barr virus, sinceit lacks a thymidinekinase

• A vaccine is underdevelopment

Cytomegalovirus (CMV)

• Largest genome of all herpesviruses• Only replicates in human cells• Productive infection seen in macrophages and

fibroblasts, whereas latent infection is set up inseveral cell types, including T lymphocytes andstromal cells of the bone marrow.

• Found in a significant proportion of the population.• Spread mediated through most secretions, including

saliva, urine, vaginal and semen.• Maternal to fetal spread can occur during pregnancy

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CMV and Disease: Congenital Infection

• Most common viral cause of congenital disease.• Up to 1/40 newborns in the United States are

infected by the virus.• During primary infection of the mother, the virus can

spread via the placenta to the fetus.• Abnormalities include microcephaly, rash, brain

calcification and hepatosplenomegaly.• Can result in hearing loss or retardation• Neonates can also receive virus through blood

transfusion, in which the titer of virus is muchhigher.

CMV: Infection in the immunocompromised host

• Pneumonia and pneumonitis, which is fatal if nottreated

• In 16-19% of patients with terminal AIDS, CMVproduces a hemorrhagic, necrotizing retinitis.

• In 10% of AIDS patients, CMV colitis or esophagitismay develop

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CMV: Diagnosis

• Most infections are asymptomatic and areundetected

• Hallmark of infection is the cytomegalic cell, whichis an enlarged cell that contains a dense, central“owl’s eye” basophilic intranuclear inclusion body

• Viral antigens can be detected usingimmunofluorescent antibodies, ELISA, or PCR

CMV: Antiviral Therapy

• Ganciclovir, valganciclovir, cidofovir and foscarnethave all been approved by the FDA for the treatmentof specific diseases resulting from CMV infection inimmunosuppressed patients

• Progression of CMV retinitis may be delayed in theshort term by intravenous ganciclovir or foscarnet.Both are equally effective; however, foscarnet is notas well tolerated.

• Acyclovir is not effective for CMV infections• A vaccine is currently under development

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HHV-6 and HHV-7

• Human herpesvirus 6 (roseola) has two variants, 6A and 6B.• Is found worldwide and in the saliva of >90% of adults.• Almost all children are infected by the age of two, and the

infection is life-long.• Replicates in T and B cells• HHV-6B causes exanthem subitum, otherwise known as

roseola infantum.• Symptoms include fever and sometimes upper respiratory

tract infection and lymphadenopathy.• 14 day incubation period.• After fever subsides, a macropapular rash appears on trunk

and neck that lasts a few days.• Human herpesvirus 7 is similar to HHV-6 and may be

responsible for some cases of exanthem subitum.• HHV-7 binds to CD4 antigen and replicates in CD4+ T cells.

HHV-6 and HHV-7, Clinical Manifestations

Exanthem Subitum; Roseola Infantum

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HHV-8 (Kaposi’s Sarcoma-associated herpesvirus, or KSHV)

• Initially found in biopsy specimens of Kaposi’s sarcoma inAIDS patients

• Like EBV, B cells are primary target, but also infects othercell types

• HHV-8 is found in ~10% immunocompetent people inperipheral blood lymphocytes

• Encodes several proteins with homology to human proteinsthat promote growth and prevent apoptosis of infected celland surrounding cells.

• Characteristic opportunistic infection associated with AIDS.

Oral KSHV Clinical Manifestations

• Over 50% of AIDS patients with skin KS also have oral KS,while 10-20% of AIDS patients have only oral KS

• Oral KS typically found on the hard and soft palates, but alsocan develop on the gingiva, the anterior palate, the tongueand the buccal mucosa

• Characterized by one or more generally flat areas, with areddish brown or deep purple discoloration

• A hyperplastic, or nodular, variety of KS can also be seen,mostly on the gingiva or tongue. Hyperplastic KS willfrequently bleed.

• As disease progresses, and color can change to darkerreddish brown, even violet

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KSHV Clinical Manifestations

A. Flat Kaposi's sarcomas involving the hard and soft palates. B. Nodulargingival Kaposi's sarcoma (arrows). C. Multiple skin Kaposi's sarcomas

in a patient with advanced AIDS.

Treatment of KSHV Oral Lesions

• Large intraoral lesions of KS can be treated withsystemic chemotherapeutic single-agents such asvinblastine and vincristine.

• Radiation therapy is also used in large lesions(after prior use of chlorhexidine gluconate rinse todiminish severity of glossitis and mucositis thatare side effects of radiation)

• Small intraoral lesions can be treated with surgicaland laser excision. Nonsurgical treatment is alsoeffective, such as intralesional injections ofvinblastine sulfate.

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Herpesvirus simiae (B virus)

• Indigenous to Old World monkeys, such asmacaques.

• Transmitted to humans via monkey bites or saliva,or infected cell tissues

• 75% of human cases result in death• Most survivors have serious neurologic damage.• Both acyclovir and ganciclovir are recommended

for therapy, but efficacy is unknown (someevidence for efficacy in the literature).

The take home message: