Learning Outcome
•Discuss important concepts including
transmission, clinical symptoms, and
laboratory diagnostic methods of
HIV/AIDS.
Human Immunodeficiency Virus (HIV)
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Causative agent of AIDS
Family: Retroviridae
Presence of Reverse Transcriptase
MOT: Sexual contact, Parenteral, Perinatal route
Two types:
1. HIV-1 = found in US, Europe, Worldwide
= also called HTLV-III, LAV and ARV
2. HIV- 2 = it is related but distinct virus from
HIV-1
= endemic in West Africa
MODE OF TRANSMISSION
• The HIV virus has been isolated from blood, semen, vaginal
secretions, saliva, tears, breast milk, cerebrospinal fluid (CSF),
amniotic fluid, and urine.
• Viral transmission of HIV-1 can be cervicovaginal, penile, rectal, oral,
percutaneous, intravenous, in utero or breastfeeding after birth.
• Retroviruses contain a single, positive-stranded ribonucleic
acid (RNA) with the genetic information of the virus and a
special enzyme called reverse transcriptase in their core.
Reverse transcriptase enables the virus to convert viral RNA
into deoxyribonucleic acid (DNA). This reverses the normal
process of transcription in which DNA is converted to RNA—
thus, the term retrovirus.
Viral Replication
• Retroviruses carry a single, positive-stranded RNA and use reverse transcriptase to
convert viral RNA into DNA. The life cycle of the HIV-1 virus consists of five phases (see
Box 25-1):
1. The virus attaches and penetrates target cells (e.g., lymphocytes) that express the CD4
receptor. After penetration, the virus loses its protein coat, exposing the RNA core.
2. Reverse transcriptase converts viral RNA into proviral DNA.
3. The proviral DNA is integrated into the genome (genetic complement of the host cell).
4. New virus particles are produced as a result of normal cellular activities of transcription
and translation.
5. These new particles bud from the cell membrane.
Once the viral genome is integrated into host cell DNA, the potential for viral production
always exists and the viral infection of new cells can continue.
Structural genes of HIV
1. Env (envelope antigen)
- found in the viral
envelope
- codes for gp160
• Gp120 (knobs/spikes)
• Gp41 (spans inner and
outer membrane)
• Involved in the fusion and
attachment of HIV to
CD4+ cells
2. Gag (group antigen)
- Located in the
nucleocapsid of the virus
- Codes for structural
proteins; p55, p24, p51
Structural
genes of HIV
3. Pol (polymerase)
-located in the core close to
the nucleic acids
- Codes for enzymes
necessary for replication
(p66 ad p51)
 Reverse transcriptase
 Integrase
 Protease
Effects of HIV
infection on
Immune System
• Prime targets are the CD4
helper T cells =
HALLMARK
• There is decreased in
cytotoxic T cell activity
• There is decreased
monocyte/macrophage
chemotaxis and decreased
NK cells activity
HIV Infection
• Primary infection – there is high levels of virus, flu-like
symptoms, fever, lymphadenopathy, sore throat, arthralgia,
myalgia, fatigue, rash, weight loss. Symptoms usually
appears 3-6 weeks after infection
• Clinical latency – there is decreased in viremia, however
virus is still present in the plasma at lower levels, absence of
clinical symptoms
• AIDS – there is profound immunosuppression, appearance of
life-threatening infections, Absolute CD4+ cell count <
200/uL
Kaposi’s Sarcoma
• The tumor typically presents with one or more asymptomatic
red, purple, or brown patches; plaque; or nodular skin lesions. The
disease is often limited to single or multiple lesions, usually localized to
one or both lower extremities, especially involving the ankle and soles.
Opportunistic Infections
TESTING METHODS
• Testing assays for HIV (Table 25-4) are categorized into the
following three main types:
• 1. Detection of HIV antibodies
• 2. Detection of antigens, particularly p24
• 3. Detection or quantification of viral nucleic acids
TEST ERRORS
Laboratory Work
A. CD4+ T cell enumeration
- Normal: 500 to 1300 cells/uL
- Ratio of CD4 to CD8 should be 2:1
- The gold standard for enumerating CD4 T cells is
immunophenotyping.
B. HIV antibody detection
1. Screening tests: ELISA, agglutination test
2. Confirmatory test: Western blot (Standard confirmatory),
Immunofluorescence assay, Radioimmunoprecipitation
Western Blot
• Prepared commercially as nitrocellulose or nylon
strips containing individual HIV proteins
• Any HIV antibodies present will bind to their
corresponding antigen on the test membrane.
• A result should be reported as POSITIVE if at
least 2 out of 3 bands are present.
Results
Intepretation
1/3
Indeterminate
0/3
Negative
2/3
Positive
HIV antigen
detection
-P24 antigen testing
Levels of this antigen in
the circulation are thought
to correlate with the
amount of HIV replication
Nucleic Acid
Testing
Reverse Transcriptase
Polymerase Chain
Reaction (RT-PCR)
END…