1. Human RetrovirusesHuman Retroviruses

2. RetrovirusesRetroviruses
RNA virusesRNA viruses
single stranded, positive sense, enveloped, icosahedral.single stranded, positive sense, enveloped, icosahedral.
Distinguished from all other RNA viruses by presence of an unusualDistinguished from all other RNA viruses by presence of an unusual
enzyme, reverse transcriptase.enzyme, reverse transcriptase.
Retro = reversalRetro = reversal
RNA is serving as a template for DNA synthesis.RNA is serving as a template for DNA synthesis.
Two genera of human interestTwo genera of human interest
LentivirusLentivirus Lentus = slowLentus = slow
Human immunodeficiency viruses 1 & 2 (HIV-1 & -2)Human immunodeficiency viruses 1 & 2 (HIV-1 & -2)
Human T-cell lymphotropic virus-bovine leukemia virus groupHuman T-cell lymphotropic virus-bovine leukemia virus group
(HTLV-BLV)(HTLV-BLV)
Human T-cell leukemia viruses 1 & 2 (HTLV-1 & -2)Human T-cell leukemia viruses 1 & 2 (HTLV-1 & -2)

3. StructureStructure
The viral envelope formed from host cell membrane;The viral envelope formed from host cell membrane;
contains 72 spiked knobs. These consist of acontains 72 spiked knobs. These consist of a
transmembrane protein TMtransmembrane protein TM ((gp 41gp 41), which is linked to), which is linked to
surface protein SUsurface protein SU ((gp 120gp 120) that binds to a cell receptor) that binds to a cell receptor
during infection. The virion has cone-shaped,during infection. The virion has cone-shaped,
icosahedral core, containing theicosahedral core, containing the major capsid protein CAmajor capsid protein CA
((p24p24). Between capsid and envelope is an). Between capsid and envelope is an outer matrixouter matrix
proteinprotein,, MAMA ((p17p17).).
Two identical copies of positive sense ssRNA genomeTwo identical copies of positive sense ssRNA genome
((retroviruses are diploidretroviruses are diploid).).
Enzymes:Enzymes: reverse transcriptasereverse transcriptase,, integraseintegrase andand proteaseprotease..

4. HIV particlesHIV particles

5. HIV particlesHIV particles

7. HIV GenomeHIV Genome
Three major genesThree major genes
 Gag geneGag gene codes for CA, MA and NC proteinscodes for CA, MA and NC proteins
 Pol genePol gene codes for reverse transcriptase,codes for reverse transcriptase,
protease, integrase and ribonuclease.protease, integrase and ribonuclease.
 Env geneEnv gene codes for TM and SUcodes for TM and SU

8. HIV ReplicationHIV Replication
TheThe first phasefirst phase of viral entery, reverse transcription and integration intoof viral entery, reverse transcription and integration into
host genome is accomplished byhost genome is accomplished by viral proteinsviral proteins..
TheThe second phasesecond phase of synthesis and processing of viral genomes,of synthesis and processing of viral genomes,
mRNAs and structural proteins, usesmRNAs and structural proteins, uses host cell machineryhost cell machinery..
 AttachmentAttachment to specific cell surface receptor:to specific cell surface receptor: gp120 binds CD4gp120 binds CD4
molecule on the helper T cells, monocytes and dendritic cellsmolecule on the helper T cells, monocytes and dendritic cells
 Viral enteryViral entery..
 Reverse transcriptionReverse transcription of viral RNA into DNAof viral RNA into DNA. The resulting double. The resulting double
stranded DNA is called provirus.stranded DNA is called provirus.
 Integration of provirus into host cell DNAIntegration of provirus into host cell DNA. The viral integrase cleaves. The viral integrase cleaves
the chromosomal DNA and covalently inserts the provirus. Thethe chromosomal DNA and covalently inserts the provirus. The
insertion site is random.insertion site is random.
 Transcription and translation of viral DNA sequencesTranscription and translation of viral DNA sequences. The provirus is. The provirus is
transcribed into a full length mRNA by the cell RNA polymerase II.transcribed into a full length mRNA by the cell RNA polymerase II.
 Assembly and maturationAssembly and maturation of progeny virusof progeny virus..

10. HIVHIV
Acquired immunodeficiency syndromeAcquired immunodeficiency syndrome
(AIDS) was first reported in US in(AIDS) was first reported in US in 19811981..
ByBy 19841984, AIDS was recognized as an, AIDS was recognized as an
infectious disease caused by a virus.infectious disease caused by a virus.

11. Transmission of HIVTransmission of HIV
 Sexual contactSexual contact: HIV is present in semen and vaginal: HIV is present in semen and vaginal
secretions; either homoxesual or heterosexual contactsecretions; either homoxesual or heterosexual contact
 TransfusionsTransfusions: whole blood, plasma, clotting factors or: whole blood, plasma, clotting factors or
cellular fractions of blood.cellular fractions of blood.
 Contaminated needlesContaminated needles: accidentally or sharing needles: accidentally or sharing needles
by drug users.by drug users.
 PerinatalPerinatal: Transplacental, during delivery or via breast: Transplacental, during delivery or via breast
milk.milk.

12. Pathogenesis and clinical significancePathogenesis and clinical significance
(1)(1)
 Initial infectionInitial infection::
 genital tract macrophagesgenital tract macrophages
 HIV disseminates via bloodHIV disseminates via blood
 Dendritic cells in lymphoid tissueDendritic cells in lymphoid tissue
 CD4+ lymphocytesCD4+ lymphocytes
 Acute phase viremiaAcute phase viremia: several weeks after the initial infection, 1/3 – 2/3 of: several weeks after the initial infection, 1/3 – 2/3 of
individuals experience an acute disease syndrome similar to infectiousindividuals experience an acute disease syndrome similar to infectious
mononucleosis. Circulating antibody appears in 1 – 10 weeks after themononucleosis. Circulating antibody appears in 1 – 10 weeks after the
initial infection (initial infection (seroconversionseroconversion).).
 Latent periodLatent period: lasts from months to many years (average 10 years).: lasts from months to many years (average 10 years).
During this period, 90% of HIV proviruses are transcriptionally silent.During this period, 90% of HIV proviruses are transcriptionally silent.
Although there is continous loss of CD4+ cells in which HIV isAlthough there is continous loss of CD4+ cells in which HIV is
replicating, active replacement through stem cell multiplication isreplicating, active replacement through stem cell multiplication is
occurring. The infection remains clinically asymptomatic as long as theoccurring. The infection remains clinically asymptomatic as long as the
immune system is functional.immune system is functional.

13. Pathogenesis and clinical significancePathogenesis and clinical significance
(2)(2)
 Clinical complications during the latent periodClinical complications during the latent period: there are multiple: there are multiple
non-specific conditions such as persistent generalizednon-specific conditions such as persistent generalized
lymadenopathy, diarrhea, chronic fevers, night sweats and weightlymadenopathy, diarrhea, chronic fevers, night sweats and weight
loss. The more common opportunistic infections such as herpesloss. The more common opportunistic infections such as herpes
zoster and candidiasis may occur repeatedly during this period.zoster and candidiasis may occur repeatedly during this period.
The CD4+ cell count remains normal or gradually declines but isThe CD4+ cell count remains normal or gradually declines but is
greater than 200 / ul. Progression from asymptomatic infection togreater than 200 / ul. Progression from asymptomatic infection to
AIDS is not sudden.AIDS is not sudden.
 AIDSAIDS: Coinfection with HHV-6 can transactivate transcription from: Coinfection with HHV-6 can transactivate transcription from
the silent HIV provirus, increasing HIV replication. Any stimulationthe silent HIV provirus, increasing HIV replication. Any stimulation
of an immune response causing activation of resting T cells alsoof an immune response causing activation of resting T cells also
activates HIV replication. Appearance of HIV mutants with alteredactivates HIV replication. Appearance of HIV mutants with altered
antigenic specificity which are not recognized by the existingantigenic specificity which are not recognized by the existing
humoral antibody or cytotoxic T lymphocytes; also contributes tohumoral antibody or cytotoxic T lymphocytes; also contributes to
progression with CD4+ count falling below 200 / ul andprogression with CD4+ count falling below 200 / ul and
appearance of serious diseases and opportunistic infections.appearance of serious diseases and opportunistic infections.

14. Opportunistic Infections (1)Opportunistic Infections (1)
Bacteria:Bacteria:
 Mycobacterium avium complexMycobacterium avium complex
 Disseminated miliary diseaseDisseminated miliary disease
 Chronic bronchitis, pneumoniaChronic bronchitis, pneumonia
 Chronic osteomyelitis, renal infectionChronic osteomyelitis, renal infection
 Mycobacterium tuberculosisMycobacterium tuberculosis
 Chronic pneumonitis, osteomyelitisChronic pneumonitis, osteomyelitis
 Meningitis, miliary diseaseMeningitis, miliary disease
 Streptococcus pneumoniaeStreptococcus pneumoniae
 Salmonella spp.Salmonella spp.
 Haemophilus influenza (pneumonia)Haemophilus influenza (pneumonia)
 Campylobacter spp. (diarrhea)Campylobacter spp. (diarrhea)
 Shigella spp. (diarrhea)Shigella spp. (diarrhea)

15. Opportunistic Infections (2)Opportunistic Infections (2)
Fungi:Fungi:
 Candida spp. Oral, vaginal or systemic candidiasisCandida spp. Oral, vaginal or systemic candidiasis
 Histoplasma capsulatum (disseminated disease)Histoplasma capsulatum (disseminated disease)
 Cryptococcus neoformans (meningitis)Cryptococcus neoformans (meningitis)
Pneumocystis cariniiPneumocystis carinii
 Unicellular eukaryoteUnicellular eukaryote
 Taxonomic status is uncertainTaxonomic status is uncertain
 Most common opportunistic pathogen in AIDSMost common opportunistic pathogen in AIDS
patientspatients
 Fatal pneumoniaFatal pneumonia

16. Opportunistic Infections (3)Opportunistic Infections (3)
Parasites:Parasites:
 Toxoplasma gondii (focal encephalitits)Toxoplasma gondii (focal encephalitits)
Viruses:Viruses:
 HHV-8 (Kaposi’s sarcoma-associated herpesvirus)HHV-8 (Kaposi’s sarcoma-associated herpesvirus)
 HSV (oral, genital ulcers)HSV (oral, genital ulcers)
 JCV (progressive multifocal leukoencephalopathy,JCV (progressive multifocal leukoencephalopathy,
affect the white matter of the brain)affect the white matter of the brain)
 CMV (Chorioretinitis, encephalitis, enterocolitis,CMV (Chorioretinitis, encephalitis, enterocolitis,
gastritis)gastritis)

17. Malignancies associated with AIDSMalignancies associated with AIDS
 Kaposi’s sarcomaKaposi’s sarcoma HHV-8HHV-8
 LymphomasLymphomas EBVEBV

20. Laboratory DiagnosisLaboratory Diagnosis
Antigen / antibody detectionAntigen / antibody detection
 ELISA, serumELISA, serum
 HIV-1 & -2 antibodies, HIV-1 CA (p24) antigenHIV-1 & -2 antibodies, HIV-1 CA (p24) antigen
 Screening of blood donorsScreening of blood donors
 Western BlottingWestern Blotting
PCRPCR
 Viral RNA or DNA provirusViral RNA or DNA provirus
 Blood or tissue specimensBlood or tissue specimens
 Quantitative PCR (viral load): to determine diseaseQuantitative PCR (viral load): to determine disease
stage and treatment follow up.stage and treatment follow up.

21. ELISA for HIV antibodyELISA for HIV antibody
Microplate ELISA for HIV antibody: coloured wellsMicroplate ELISA for HIV antibody: coloured wells
indicate reactivityindicate reactivity

22. Western blot for HIV antibodyWestern blot for HIV antibody
 There are different criteriaThere are different criteria
for the interpretation of HIVfor the interpretation of HIV
Western blot results e.g.Western blot results e.g.
CDC, WHO, American RedCDC, WHO, American Red
Cross.Cross.
 The most importantThe most important
antibodies are those againstantibodies are those against
the envelope glycoproteinsthe envelope glycoproteins
gp120, and gp41gp120, and gp41
 p24 antibody is usuallyp24 antibody is usually
present but may be absent inpresent but may be absent in
the later stages of HIVthe later stages of HIV
infectioninfection

24. TreatmentTreatment
 Anti-retroviral drugsAnti-retroviral drugs
 Reverse transcriptase inhibitorsReverse transcriptase inhibitors
 Protease inhibitorsProtease inhibitors
 Multidrug therapyMultidrug therapy
 RT has no proofreading activity, resulting in production of manyRT has no proofreading activity, resulting in production of many
errors during viral DNA synthesis which leads to mutations in allerrors during viral DNA synthesis which leads to mutations in all
HIV genes and accumulation of mutant viral strains. In presenceHIV genes and accumulation of mutant viral strains. In presence
of an antiviral drug, there is strong selection for mutations thatof an antiviral drug, there is strong selection for mutations that
confer resistance to that drug.confer resistance to that drug. Use multidrug therapyUse multidrug therapy
 Early therapyEarly therapy
 Viral load is a prognostic indicator of the rate of progression toViral load is a prognostic indicator of the rate of progression to
AIDS. Infection should be treated as aggressively and as earlyAIDS. Infection should be treated as aggressively and as early
as possible to minimize initial spread of the virus and give aas possible to minimize initial spread of the virus and give a
lower chance for mutants to arise.lower chance for mutants to arise.

25. Highly active antiretroviral therapy (HAART)Highly active antiretroviral therapy (HAART)
Nucleoside analog reverse transcriptase inhibitorsNucleoside analog reverse transcriptase inhibitors
 Act by serving as a chain terminatorAct by serving as a chain terminator
 Zidovudine (AZT)Zidovudine (AZT)
 Didanosine (ddi)Didanosine (ddi)
 Lamivudine (3TC)Lamivudine (3TC)
Non-nucleoside reverse transcriptase inhibitorsNon-nucleoside reverse transcriptase inhibitors
 Act by targeting the enzyme itselfAct by targeting the enzyme itself
 EfavirenzEfavirenz
 DelaviridineDelaviridine
 NevirapineNevirapine
Protease inhibitorsProtease inhibitors
 Interfere with the processing of polyproteins in the budding virion,Interfere with the processing of polyproteins in the budding virion,
resulting in non-infectious particle.resulting in non-infectious particle.
 RitonavirRitonavir
 AmprenavirAmprenavir
 IndinavirIndinavir
 LopinavirLopinavir

26. Drug resistance through viral mutations is a major
problem in treatment of HIV patients

27. PreventionPrevention
 VaccineVaccine: not yet available: not yet available
 Blood supply screeningBlood supply screening
 Perinatal transmissionPerinatal transmission: AZT therapy: AZT therapy

28. HTLVHTLV
 HTLV-1 and -2 have 65% nucleotideHTLV-1 and -2 have 65% nucleotide
sequence homologysequence homology
 Genetically and biologically similarGenetically and biologically similar
HTLV-1HTLV-1
 Adult T-cell leukemiaAdult T-cell leukemia
 HTLV-associated myelopathy/tropical spasticHTLV-associated myelopathy/tropical spastic
paraparesisparaparesis
HTLV-2HTLV-2
 Hairy cell leukemiaHairy cell leukemia

29. TransmissionTransmission
 Vertical transmissionVertical transmission
 SexualSexual
 Blood productsBlood products

30.  Hairy cell leukemiaHairy cell leukemia
 a rare lymphocytica rare lymphocytic
leukemia, of B cellleukemia, of B cell
origin; caused byorigin; caused by
HTLV-2. it isHTLV-2. it is
characterized bycharacterized by
malignant cells thatmalignant cells that
look ciliated.look ciliated.

31. LaboratoryLaboratory diagnosisdiagnosis
 Screening of blood donors usingScreening of blood donors using ELISAELISA
 Confirmation byConfirmation by western blottingwestern blotting
 PCRPCR