Download HIV-associated infections

Family Retroviridae.
Genus Lentivirus.
Human Immunodeficiency Virus
2008, Françoise Barré-Sinoussi and Luc A. Montagnier were
awarded Nobel prize medicine for their role in the discovery of “the
virus that causes AIDS”.
More than two decades ago (1983) they identified a virus they
named LAV (lymphadenopathy virus), which later became known
as HIV.
Barré-Sinoussi
Luc A. Montagnier
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HIV and AIDS: a Global Pandemic
First cases identified June, 1981
World estimates (as of 2011):
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> 34 million living with HIV
30 million deaths since 1981
7 000 people become infected and
6 000 people die of AIDS daily.
During 2011: 2,5 million became
infected and 1,7 million people died.
In Ukraine (as of 2011):
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214 000 HIV-infected persons
28 000 deaths since 1987
Global view of HIV infection
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The overwhelming majority of people with HIV live in the developing world.
Sub-Saharan Africa accounts for two-thirds of all infected people (67 %).
South and South-East Asia has the second highest number of infected
people.
Adults and children estimated to be living with HIV,
2011
Western & Eastern Europe
Central Europe & Central Asia
820 000
North America
1.5 million
[720 000 – 910 000]
[1.2 – 2.0 million]
1.4 million
[1.3 – 1.5 million] East Asia
770 000
Middle East & North
Africa
Caribbean
240 000
460 000
[220 000 – 270 000]
[400 000 – 530 000]
[500 000 – 1.0 million]
South & South-East
Asia
Sub-Saharan Africa
Latin America
1.4 million
22.5 million
[20.9 – 24.2 million]
[1.2 – 1.6 million]
Total: 34 million
4.1 million
[3.7Oceania
– 4.6 million]
57 000
[50 000 – 64 000]
Classification of the family Retroviridae
Electron microscopy of HIV
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HIV is a spherical
enveloped virus,
about 90-120 nm
in size.
The nucleocapsid
has an outer
icosahedral shell
and inner
coneshaped core,
enclosing the
ribonucleoproteins.
Fine structure of HIV
Attachment of HIV to a CD4+ cell
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The glycoprotein gp 120 binds to the CD4
protein on T-helper cells and macrophages.
The glycoprotein gp 41 allows fusion of the virus
with the cell membrane.
Target cells:
CD4 cells:
Т-helpers
Monocytes
Macrophages
Other cells:
natural killers
dendritic cells
В-lymphocytes of the memory
neuroglia
astrocytes
colonic epithelium
endothelium
Chemokine receptors CCR5 or CXCR4 are co-receptors for HIV to
enter target cells
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CCR5 is expressed on T cells, macrophages, and microglia, CXCR4 on T cells.
They play a role in inflammatory responses to infection. The natural chemokines bind
to this receptors and activate chemotaxis of immune cells.
When the CD8+ cells effectively make a large quantity of the chemokines, they may
block the CCR5 and suppress HIV infection.
Conversely, when levels of the chemokines are low or absent, the virus is free to
more easily infect cells.
A number of new HIV drugs, called entry inhibitors, have been designed to interfere
with the interaction between CCR5 and HIV.
Resistance to HIV
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CCR5-Δ32 is a genetic variant of CCR5.
CCR5-Δ32 is a deletion mutation of a gene when a portion of it is
missing, and it thus cannot produce a functional CCR5 receptor.
CCR5-Δ32 decreases the number of CCR5 proteins on the outside of the
CD4 cell, which can have a large effect on the HIV disease progression
rates. It is possible that a person with the CCR5-Δ32 receptor allele will
not be infected with HIV R5 strains.
When people inherited a defective version of CCR5 from both parents,
they appeared to be resistant to infection with HIV.
People with the partial CCR5 defect may progress to HIV disease more
slowly than someone without the CCR5 defect.
Process of infection of HIV
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- HIV can cross the epithelial barrier through
a process known as transcytosis by M cell.
- HIV is picked up by Ag-presenting cells,
primarily dendritic cells.
- T helpers are infected by HIV in mucosal
associated lymphoid tissue.
- HIV establishes a fulminant local infection
within a few days, and then spreads quickly
throughout the body.
Infection is transmitted when the
virus enters the blood or tissues of
a person and come into contact
with a suitable host cell.
HIV binding via cell
surface receptors
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Potential
mechanisms
underlying cellassociated HIV
transmission.
(a) Columnar
epithelium
(b) Stratified
squamous
epithelium
HIV entry via immune cells within the vaginal
mucosa and spread to systemic lymphoid organs
Replication of HIV
HIV life cycle
HIV budding from an infected cell
HIV
halflives
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Activated cells that become infected with HIV produce virus immediately and die
within 1 to 2 days.
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The time required to complete a single HIV life-cycle is approximately 1.5 days.
Production of virus by short-lived, activated cells accounts for the vast majority of
virus present in the plasma.
Resting cells that become infected produce virus only after immune stimulation;
these cells have a half-life of at least 5-6 months.
Some cells are infected with defective virus that cannot complete the virus lifecycle. Such cells are very long lived, and have an estimated half-life of
approximately 3 to 6 months.
Pathogenesis of AIDS
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The primary pathogenic mechanism in HIV
infection is the damage the CD4 Tlymphocytes.
The T4 cells decrease in number
T4:T8 (helper:supressor) cell ratio is
reversed.
Ways that HIV can damage T4 cells by:
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budding virus particles,
cyncytium formation,
cytotoxic T-cell-mediated lysis.
Killing of CD 4 cells
The interaction of a
dendritic cell with a
lymphocyte.
HIV bound to the surface of the
dendritic cell is clustered at the
site of interaction between the two
cells (arrow)
Multinucleated cell
(syncytium) in touch
preparation from cut surface of
enlarged lymph node from
patient with HIV-1 infection
Pathogenesis
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Infected T4 cells do not release normal amounts
of interleukin-2, gamma interferon and other
lymphokines.
Polyclonal activation of B-lymphocytes leads to
hypergammalobulinemia. AIDS patients are
unable to respond to new antigens.
Monocyte-macrophage function is also affected.
As a result, chemotaxis, antigen presentation
and intracellular killing by these cells are
diminished.
Monocyte-macrophages escape immune
surveillance and transport the infection to other
organ systems, particularly the lungs and brain.
Cells cooperation in an immune response
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Latent and
active
infection in Thelpers and
macrophages
Transmission of HIV
HIV is transmitted by:
 blood,
 breast milk,
 semen,
 vaginal secretions.
– Saliva, urine, tears have very low titer
HIV.
– Minor mucosal trauma and certain STDs
(HSV for example) facilitate
transmission.
Routes of Transmission of HIV
Sexual Contact
 Blood Contact
- Needle sharing behavior: Injection drug use and
other needle sharing
- Blood and blood products transfusion
 Tissue and organs donation:
- Semen, cornea, bone marrow, kidney etc.
 Perinatal:
- Intrauterine;
- During labor and delivery;
- Breast feeding.
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Shift in HIV transmission patterns in the US based on
estimates from the CDC
Distribution and number of documented cases of
occupational transmission of HIV among health
care workers by occupation
Spectrum of HIV Infection
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1. Acute retroviral syndrome: within 2-4
weeks of acquiring HIV
2. Asymptomatic or latent HIV infection:
variable duration
3. Persistent generalized lymphadenopathy
(PGL)
4. AIDS related complex (ARC):
CD4 count<500
5. Advanced HIV infection or AIDS:
CD4 count<200
HIV Pathogenesis
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In the immediate period following exposure, HIV is present at a high level in the blood.
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It then settles down to a certain low level (set-point) during the asymptomatic period.
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There is a massive turnover of CD4 cells, whereby CD4 cells killed by HIV are
replaced efficiently.
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AIDS develops, when killed CD4 cells can no longer be replaced.
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The profound immunosuppression seen in AIDS is due to the depletion of T4 helpers.
Acute/Early Infection
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Approximately 50% of individuals develop a
flu-like or mononucleosis illness
symptoms:
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fever,
headache,
rash,
myalgia, arthralgia,
gartrointestinal symptoms: diarrhea, nausea or vomiting,
neurologic symptoms: aseptic meningitis, encephalitis
lymphadenopathy, organomegaly.
Associated with very high viral load.
p24 antigen can be demonstrated at the beginning
of this stage.
HIV antibody may be negative.
Main symptoms of acute HIV infection
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Asymptomatic HIV Infection
Variable duration of time (as little as 1 to 2 years to more than
15 years).
Steady state viral load
Persistent generalized lymphadenopathy
Gradual fall in CD4 cell count
Enlarged lymph nodes, at least 1 cm, in diameter, in two or
more noncontagious extrainguinal sites, that persist for at least
three months
AIDS related complex
Generalised lymphadenopathy and splenomegaly
Fever, malaise, night sweats, persistent diarrhea and marked
weigh loss of more than 10 per cent of body weight
Herpes zoster, hairy cell leukoplakia, vaginal candidiasis,
tuberculosis, salmonellosis
Increasing viral load
Decreasing CD4 cell count
HIV and T cells go to “war”
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Continuous and highly productive replication
of HIV occurs in all infected individuals,
although the rates of virus production vary by
up to 70-fold in different individuals
Average T 1/2 of an HIV infected cell in vivo
is 2.1 days
About 10 billion HIV particles are produced daily
About 2.6 billion CD4+ T-cells are produced daily
HIV ultimately reduces T-helpers
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As T-helper is central to many aspects of immune
function there is decreased or altered
function of ALL arms of the immune system.
Clinical manifestations are due not primarily to
viral cytopathology but are secondary to the
failure of immune responses. This renders the
patient susceptible to opportunistic infections and
malignancies.
An exception is the dementia and other
degenerative neurological lesions seen in AIDS.
These may be due to the direct effect of HIV on
the CNS.
HIV-associated infections
Bacteria:
Fungi:
Salmonella spp.
Mycobacterium avium
complex
Mycobacterium
tuberculosis
Candida albicans
Crypticoccus neoformans
Histoplasma capsulatum
Coccidioides immitis
Pneumocystis carinii
Protozoa:
Viruses:
Toxoplasma gondii
Herpes simplex
Isospora belli
Cytomegalovirus
Criptosporidium hominis
HIV-associated infections
Pneumocystis carinii pneumonia
P. carinii is the most frequent opportunistic infection seen with AIDS. It produces a
pulmonary infection, called P.carinii pneumonia (PCP), but rarely disseminates
outside of lung.
The most common clinical findings are acute onset of fever, nonproductive cough, and dyspnea.
Diagnosis is made histologically by finding the organisms in cytologic
(bronchoalveolar lavage) or biopsy material from lung, typically via bronchoscopy.
The cysts of P. carinii stain brown to black with the
Gomori methenamine silver stain.
With Giemsa stain the
dot-like intracystic
bodies are seen.
Cytomegalovirus (CMV) Retinitis
Progressive, painless vision
loss.
- There are extensive areas
of hemorrhage, with white
retinal exudates.
- CMV may also cause fever,
pneumonia, GI bleed,
neutropenia.
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Oral Hairy Leukoplakia
is a white patch on the side of the tongue with a
corrugated or hairy appearance.
Causative agent: Epstein Barr virus
Symptoms
The presence of white or gray
colored patches on tongue, gums,
roof of mouth, or the inside of the
cheeks of mouth.
The patch may have developed
slowly over weeks to months and be
thick, slightly raised, and may
eventually take on a hardened and
rough texture.
It usually is painless, but may be
sensitive to touch, heat, spicy foods,
or other irritation.
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Candida albicans can produce invasive infections in esophagus,
upper respiratory tract, and lung
Herpes simplex virus infection involves the gastrointestinal tract,
mainly the esophagus and the perianal region.
Herpes zoster infection of the skin occurs prior to the onset of clinical
AIDS
Candidiasis
Herpes zoster
Kaposi’s Sarcoma
Kaposi's sarcoma (KS) produces reddish purple patches, plaques, or nodules over the
skin and can be diagnosed with skin biopsy. Visceral organ (lung, gastrointestinal
tract, liver) involvement eventually occurs in 3/4 of patients with KS.
Severe wasting in a patient with human
immunodeficiency infection
Dementia. HIV may cause direct cytopathogenic damage in the CNS. It can
cross the blood-brain barrier and cause encephalopathy leading to loss of
higher functions, progressing to dementia.
Laboratory diagnosis
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1. Antigen detection: ELISA (core antigen p24).
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2. Virus isolation:
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3. Polymerase chain reaction.
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4. Antibody detection:
In the
fist few weeks after infection and in the terminal phase, the test is uniformly
positive.
from the peripheral lymphocytes by cocultivation of the patient’s lymphocytes with uninfected lymphocytes in the
presence of interleukin-2. It is not suitable as a routine diagnostic test.
The gold standard for
diagnosis in all stages of HIV infection. It becomes necessary particularly in
the course of treatment.
IgM antibodies appear in about 4-6
weeks to months after infection, to be followed by IgG antibodies.
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Screening tests: ELISA assay.
Confirmatory test: Western blot.
ELISA for HIV antibody
Microplate ELISA for HIV antibody: coloured wells
indicate reactivity
Western Blot
Strips of blot
Strip А – Positive control
 Strip В – Light positive control
 Strip С – Negative control
 Strip D – Positive specimen
(antibodies against HIV-1 are detected)
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Targets of HIV Therapy
Therapy of HIV Infection
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Nucleoside-Analog Reverse Transcriptase Inhibitors (NRTI) inhibit viral polymerase
by incorporating into viral DNA (they are chain-terminating drugs).
- Zidovudine (ZDV, Retrovir) first approved in 1987
- Stavudine
- Lamivudine etc.
Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) inhibit HIV replication
directly by binding non-competitively to reverse transcriptase (first approved in 1997).
- Nevirapine
- Delavirdine
Protease Inhibitors are specific for the HIV-1 protease and competitively inhibit the
enzyme, preventing the maturation of virions capable of infecting other cells.
- Saquinavir (Invirase) first approved in 1995
- Ritonavir
- Indinavir etc.
Fusion or Entry Inhibitors bind gp41 and prevent HIV from binding to or entering
human immune cells (first approved in 2003).
- Enfuvirtide (Fuzeon)
Integrase Inhibitors interfere with the integrase enzyme, which HIV needs to insert its
genetic material into human cells (first approved in 2007).
- Raltegravir (Isentress)
Chemokine receptor antagonists binds the CCR5 coreceptor and inhibit fusion of the
cellular membranes (first approved in 2007).
- Maraviroc.
Nucleoside-Analog Reverse Transcriptase Inhibitors
RT-inhibitors act as nucleoside analogues - in a sense they
"pretend" to be a nucleoside so that when RT is creating new
DNA it "accidentally" inserts a molecule of zidovudine (or
tenofovir) rather than a nucleoside. This terminates the DNA
chain and no more can be appended to it.
Overarching goals for therapy:
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Reduce HIV infection–related morbidity
and prolong survival
Improve quality of life
Restore and preserve immunologic function
Maximally and durably suppress viral load
Prevent vertical HIV transmission
Highly Active AntiRetroviral Therapy
(HAART)
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Combination therapy with 3 or more agents
Use at least 2 classes of agents
Problems:
– Toxicities, failure, adherence, resistance, cost
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Efficacy:
– HIV not eradicated
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RNA interference (RNAi)
It is a process within living cells that moderates the
activity of their genes by RNA.
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Two types of small RNA molecules – microRNA (miRNA) and
small interfering RNA (siRNA) – are central to RNA
interference.
These small RNAs can bind to other specific messenger
RNA (mRNA) and decrease their activity by preventing
an mRNA from producing a protein.
It may be possible to exploit RNA interference
in therapy of HIV infection:
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inhibition of gene expression of host receptors and
co-receptors for HIV,
inhibition stages of viral replication in a host cell.
Cellular mechanism of RNA interference (RNAi)
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RNAi is initiated by small interfering RNAs
(siRNAs) in a cell's cytoplasm, where they
interact with the catalytic protein complex RISC.
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When the siRNA is exogenous (coming from infection
by a virus with an RNA genome or laboratory
manipulations), the RNA is imported directly into the
cytoplasm and cleaved to short fragments by the
enzyme.
When the siRNA is endogenous (originating in the
cell), pre-microRNAs are expressed in the nucleus,
then exported to the cytoplasm.
After integration into the RISC, siRNAs base-pair
to their target mRNA and induce cleavage of the
mRNA, thereby preventing it from being used as
a translation template.
Stages of
HIV life
cycle that
can be
blocked
by RNA
interference
Cellular mechanism of RNA interference