What is HIV?
HIV (human immunodeficiency virus) is a retrovirus that selectively infects and destroys CD4+ T lymphocytes (helper T cells), leading to progressive immunosuppression and, without treatment, ultimately resulting in AIDS (acquired immunodeficiency syndrome).
Viral Structure and Classification
HIV is a complex retrovirus belonging to the lentivirus family 1, 2. There are two types: HIV-1 (the predominant worldwide strain) and HIV-2 (less common and primarily found in West Africa) 3. The virus is a single-stranded, enveloped RNA virus that contains critical structural and regulatory elements distinguishing it from simpler retroviruses 1.
Mechanism of Infection
The virus specifically targets cells expressing the CD4 molecule on their surface, primarily:
- Helper/inducer T lymphocytes (CD4+ T cells) - the main target
- Monocytes and macrophages - which serve as viral reservoirs and are relatively resistant to the virus's cell-killing effects 4
- Brain cells - leading to neuropsychiatric complications 4
The virus infects host cells for life, integrating its genetic material into the host cell's DNA 2. Unlike other viruses, HIV appears to establish permanent infection in virtually every case 2.
Replication Characteristics
HIV exhibits unique replication behavior 2:
- Can remain relatively dormant with slow, steady replication
- Capable of explosive up-regulation when stimulated, releasing large numbers of infectious particles
- Replicates in an error-prone manner, constantly mutating its structure
- This constant mutation improves infectivity while evading the immune system by presenting a "constantly moving target" 2
Transmission Routes
HIV is transmitted through 3:
- Unprotected sexual intercourse (most common route globally)
- Inoculation of HIV-contaminated blood into the bloodstream
- Mother-to-child transmission via prenatal, perinatal, or postnatal routes (breastfeeding)
Clinical Significance
Without antiretroviral treatment, HIV infection progresses over years to AIDS, characterized by severe immunodeficiency that permits life-threatening opportunistic infections and malignancies 3. The virus can exist in latent or chronic forms that can be converted to productive infection by various inductive signals 4.
With modern antiretroviral therapy (ART), persons with HIV can now live near-normal lifespans without progressing to AIDS or transmitting the virus to sexual partners or infants 5.