Transcript Retroviruses

Retroviruses
Retroviruses
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Probably the most studied group of viruses in
molecular biology!!!
Enveloped, positive-strand RNA viruses
Unique morphology and replication
Replicate through a DNA intermediate by
reverse transcriptase (RT)
Retroviruses
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Baltimore and Temin in 1970
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RNA-dependent DNA polymerase (reverse
transcriptase ) encoded by retroviruses
Retroviruses replicate through an DNA
intermediate
This DNA copy of viral genome integrates into
host chromosome
This discovery earned the Nobel prize: contradicted
the central dogma of molecular biology-genetic
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information passed from DNA to RNA and
then to protein
 Here: from RNA to DNA
History
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Rous sarcoma virus: solid tumors in chicken
Other cancer causing retroviruses from
other animal species (oncogenes)
1981: first human retrovirus: Human Tlymphotropic virus (HTLV-1)
1983: Human immunodeficiency virus
(HIV)
Subfamily
Oncovirinae
B
C
D
Lentivirinae
Spumavirinae
Endogenous viruses
Examples
Mouse mammary tumor virus
HTLV-I,HTLV-II, Rous sarcoma
virus
HIV-1,HIV-2
Human foamy virus
Human placental virus
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Oncoviruses:immortalize or transform target cells, A,B,C,D
type according to their core and capsid
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Lentiviruses:slow viruses associated with neurologic and
immunosuppresive disease
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Spumaviruses:no disease
Endogenous viruses:transmitted vertically, 1% of
human chromosome, in many animal species and humans, one
detected in placental tissue which facilitates placental function
Retroviruses
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Enveloped sperical virion
Two copies of positive-strand RNA genome
RT
Provirus integrates randomly into host chromosome
Transcription of the genome is regulated by the
interaction of host transcription factors with promoter
and enchancer elements in the long-terminal repeat
portion (LTR) of the genome
Retroviruses
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Simple retroviruses encode gag,pol and env genes
Complex viruses also encode accessory –regulatory
genes (tat,rev,nef, vif, vpu for HIV)
Assembles and buds from the plasma membrane
Final morphogenesis requires protease cleavage of gag
and gag-pol polypeptides after envelopment.
HIV genome
Gp120
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CD4 surface receptor protein
Initially expressed on cells of the macrophage
lineage (macrophage, dendritic cells, microglial
cells) (M-tropic)+ second receptor CCR5
Later on helper T cells (T-tropic) +fusin
(CXCR4)
Chemokine receptors
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CCR5: binds macrophage-tropic, non-syncytium-inducing (R5)
viruses  mucosal and intravenous transmission of HIV
infection.
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CXCR4: T-cell-tropic, syncytium-inducing (X4) viruses, which
are frequently found during the later stages of disease.
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In up to 13% of individuals of northern European descent, a
naturally occurring deletion of 32 base pairs in the CCR5 gene
results in a mutant CCR5 receptor that never reaches the cell
surface. Individuals homozygous for this mutation (1-2% of the
Caucasian population) are almost completely resistant to HIV
infection.
Transmission
*Blood, semen,vaginal secretions
 Sexual contact
 Exposure to contaminated blood and blood
products
 From infected mother to her baby perinatally
HIV is not transmitted
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Casual contact
Touching, hugging, kissing, coughing, sneezing,
insect bites, water, food, utensils, toilets,
swimming pools, public baths
Transmission
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Inoculation of blood: Transfusion,
needlesharing among intravenous drug abusers,
needlestick, open wound, mucous membrane
exposure, tattoo needles
Sexual trasmission: anal and vaginal intercourse
Perinatal transmission: Intrauterine, peripartum
and breast milk
Population at high risk
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Intravenous drug abusers, sexually active people
with many partners (homosexual, heterosexual),
prostitutes, newborns of HIV infected mothers
Blood and organ recipients and hemophiliacs:
before 1985 (pre-screening programs)
Epidemiology
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Late 1970s-early1980s
Young homosexual men, Haitians, heroin addicts,
hemophiliacs were noted to be dying of normally
benign opportunistic infections
HIV appears to have evolved since 1930s from a simian
virus and then rapidly spread Africa and the world by
an increasinly mobile population.
There is an expanding epidemic worldwide.
AIDS cause by HIV
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Retroviridae family
Lentivirinae genus
Enveloped, positive strand RNA virus
2 identical 9-10kb RNA
AIDS
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Human immunodeficiency virus
type 1 and 2
(HIV-1, HIV-2)
HIV
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HIV-1: isolated in1983
Responsible from AIDS pandemic
HIV-2: isolated in 1986
HIV-2 less pathogenic
slow progression to AIDS
HIV group and subtypes
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Rapid mutation and recombination
HIV-1
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Group M (major): A-J
Group O
Group N
HIV-2
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A-E subtypes
Acute retroviral syndrome
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First signs occur in days to several weeks
Transient
%50-70
Activation of immune system
Multisystem dysfunction
Flu or infectious mononucleosis sydrome like findings
Then a latent period
AIDS
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Continuous viral replication
Immune system dysfunction
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CD4 T lymphocyes
> 500 /µl (> %29) 1
200-499 (% 14-28) 2
< 200 /µl (< %14) 3
Incubation
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Adults with no treatment:
10-11 years
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‘rapid progressors’
: 2-3 years
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‘non-progressor’
CD4 cell count
: 7-10 years Stable
HIV genome
Structural genes: gag/env
 Pol: enzymes -reverse transcriptase
-protease
-integrase
Tat and Rev: necessary for replication
Accessory genes: Vif, Vpr(HIV-1), Vpu, Nef
Vpx(HIV-2)
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HIV
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Viral RNA (in free Virion )
Viral DNA: integrated in host cell DNA
(Provirus)
Seroconversion
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Usually 3 weeks
1.5,3,6,12 months
Viral Kinetics
Laboratory diagnosis
Serology: Adults and children older than 15 months:
 Initial screening: ELISA, latex agglutination
 Confirmation: Western-blot
Molecular techniques:
-qualitative DNA detection: babies younger than 15
months
-quantitative RNA: follow up of HIV infected people
who are on therapy
Western blot (WB)
Other tests
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Immunologic status: CD4:CD8 ratio Low
Antiretroviral resistance tests
Indicators of disease
Opportunistic infections:
 Protozoal:Toxoplasmosis
 Fungal:Candidiasis, Pneumocystis carinii
 Viral :Cytomegalovirus, HSV
 Bacterial:Mycobacterium avium-intracellulare
Opportunistic neoplasias: Kaposi’s sarcoma
CCR5 Antagonist
Maravirıoc (MVC) – Selzentry
 Integrase inhibitor
Raltegravir (RAL)/ Isentress
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Prevention and control
Education
 Blood and blood product screening
 Infection control:
‘Universal Blood and body fluid precautions’:
All patients may be infectious for HIV and other bloodborn infections:
-wear protective clothing(gloves, masks, gown) and other
barriers to prevent exposure to blood products
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Prevention and control
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10% household bleach(% 0.5 chlorine,
5g/litre
5000ppm
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70% ethanol
2% glutaraldehyde
4% formaldehyde
6% Hydrogen peroxide
Washing laundry in hot water with detergent is
sufficient to inactivate HIV.
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Modes of control
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Antiviral drugs limit progression of disease
Vaccines for prevention and treatment are in trials
Safe(Condom!) monogamous sex helps limit spread.
Sterile injection neeedles should be used
Large scale screening programs for blood transfusion,
organs for transplants, clotting factors
Oncovirinae
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RNA tumor viruses
Associated with leukemias, sarcomas and
lymphomas in many animals
Not cytolytic
Distinquished by the mechanism of cell
transformation and length of latency period
between infection and the development of
disease
Oncovirinae
Sarcoma and acute leukemia viruses:
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Protooncogenes(at least 35)
Highly oncogenic, direct effect
No human virus
Leukemia viruses:
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No oncogene
Long latency period
HTLV-I,HTLV-II,HTLV-5
Human T lymphotropic virus
type 1( HTLV-I)
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Adult acute T-cell lymphocytic leukemia (ATLL)
HTLV-associated myelopathy (tropical spastic
paraparesis)
Blood transfusion, sexual intercourse, breast
feeding
Long latency period: approximately 30 years
Human T lymphotropic virus
type 1( HTLV-I)
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Endemic in southern Japan
ATLL (1 in 20 people over a 30-50 years
Diagnosis: ELISA+WB
Viral RNA by RT-PCR
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HTLV-2: Hairy cell leukemia
HTLV-5: malignant cutaneous lymphoma