HIV

This section will cover Human Immunodeficiency Virus (HIV), including its etiology, epidemiology, transmission, disease states, and key aspects of its pathogenesis and diagnosis

Human Immunodeficiency Virus (HIV)

Etiology
- Classification: A member of the Retroviridae family, genus Lentivirus
- Types
  - HIV-1: The most common type worldwide. Further classified into subtypes (or clades), with subtype B being predominant in North America and Europe
  - HIV-2: Primarily found in West Africa. Generally less pathogenic and progresses more slowly than HIV-1
- RNA Virus: HIV is a single-stranded RNA virus that uses reverse transcriptase to convert its RNA into DNA, which is then integrated into the host cell’s genome
Epidemiology
- Global Distribution: Found worldwide, but prevalence varies by region
- Prevalence: Approximately 38 million people worldwide are living with HIV
- Incidence: New HIV infections continue to occur, but rates have declined in many regions due to prevention efforts
- Age Groups: Can affect all age groups, but most new infections occur in adults
- Risk Groups: Certain populations are at higher risk for HIV infection, including men who have sex with men (MSM), injection drug users, sex workers, and transgender individuals
- Geographic Distribution: Sub-Saharan Africa has the highest burden of HIV infection
Transmission
- Sexual Contact: The most common route of transmission, including vaginal, anal, and oral sex
- Bloodborne: Sharing needles or syringes, blood transfusions (rare in developed countries due to screening), and occupational exposure in healthcare settings
- Mother to Child (Vertical Transmission): Can occur during pregnancy, childbirth, or breastfeeding
- Other Body Fluids: HIV can be found in other body fluids, such as semen, vaginal fluids, breast milk, and blood, but transmission is less common
Disease States
- Acute HIV Infection: Occurs within 2-4 weeks of exposure. Characterized by flu-like symptoms, such as fever, fatigue, sore throat, rash, and swollen lymph nodes. High viral load and highly infectious during this stage
- Clinical Latency (Chronic HIV Infection): The virus is active but reproduces at low levels. Individuals may be asymptomatic or have mild symptoms. Can last for many years
- Acquired Immunodeficiency Syndrome (AIDS): The most advanced stage of HIV infection. Characterized by a severely weakened immune system, leading to opportunistic infections, cancers, and other complications
- Opportunistic Infections: Infections caused by pathogens that typically do not cause disease in individuals with healthy immune systems. Common examples include Pneumocystis pneumonia (PCP), Kaposi’s sarcoma, cytomegalovirus (CMV) infection, and tuberculosis (TB)
Pathogenesis
- Target Cells: HIV primarily infects CD4+ T cells, which are essential for immune function
- Viral Replication: HIV enters CD4+ T cells, uses reverse transcriptase to convert its RNA into DNA, and integrates the DNA into the host cell’s genome. The virus then replicates, producing new viral particles that infect other CD4+ T cells
- Immune Destruction: Over time, HIV infection leads to a decline in CD4+ T cell count, weakening the immune system and increasing susceptibility to opportunistic infections and cancers
- Viral Reservoirs: HIV can establish latent reservoirs in various cells and tissues, making it difficult to eradicate the virus completely
Diagnosis
- Screening Tests: Initial tests used to detect HIV infection
  - Antibody Tests: Detect antibodies to HIV in blood or oral fluid. May have a window period (time between infection and antibody detection)
  - Antigen/Antibody Combination Tests: Detect both HIV antibodies and p24 antigen (a viral protein). Shorter window period than antibody tests
- Confirmatory Tests: Used to confirm a positive screening test
  - HIV-1/HIV-2 Antibody Differentiation Assay: Distinguishes between HIV-1 and HIV-2 antibodies
  - HIV-1 Nucleic Acid Amplification Test (NAT): Detects HIV-1 RNA in plasma. Used to confirm HIV-1 infection and measure viral load
- Viral Load Testing: Measures the amount of HIV RNA in plasma. Used to monitor treatment response and disease progression
- CD4+ T Cell Count: Measures the number of CD4+ T cells in blood. Used to assess immune function and guide treatment decisions
- Drug Resistance Testing: Used to identify mutations in the HIV genome that confer resistance to antiretroviral drugs. Helps guide treatment selection
Treatment
- Antiretroviral Therapy (ART): Combination of drugs that suppress HIV replication, reduce viral load, and improve immune function. Does not cure HIV, but can control the virus and prevent disease progression
- Classes of ART Drugs
  - Reverse Transcriptase Inhibitors (RTIs)
    - Nucleoside/Nucleotide RTIs (NRTIs)
    - Non-Nucleoside RTIs (NNRTIs)
  - Protease Inhibitors (PIs)
  - Integrase Inhibitors (INSTIs)
  - Fusion Inhibitors
  - CCR5 Antagonists
  - Post-Attachment Inhibitors
- Goals of ART
  - Achieve and maintain undetectable viral load
  - Restore and preserve immune function
  - Prevent opportunistic infections and cancers
  - Reduce HIV transmission
- Pre-Exposure Prophylaxis (PrEP): Use of antiretroviral drugs by HIV-negative individuals to prevent HIV infection. Highly effective when taken as prescribed
- Post-Exposure Prophylaxis (PEP): Use of antiretroviral drugs after a potential exposure to HIV to prevent infection. Must be started within 72 hours of exposure
Prevention
- Safe Sex Practices: Using condoms consistently and correctly
- Testing and Treatment: Regular HIV testing and prompt treatment for those who are infected
- Needle Exchange Programs: Providing sterile needles and syringes to injection drug users
- Prevention of Mother-to-Child Transmission: Antiretroviral drugs for pregnant women with HIV and their infants
- Pre-Exposure Prophylaxis (PrEP): Use of antiretroviral drugs by HIV-negative individuals to prevent HIV infection
- Post-Exposure Prophylaxis (PEP): Use of antiretroviral drugs after a potential exposure to HIV to prevent infection

Key Terms

Etiology: The cause or origin of a disease or condition
Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems
Transmission: The way a disease is spread from one person or source to another
HIV (Human Immunodeficiency Virus): A virus that attacks the immune system, leading to AIDS
AIDS (Acquired Immunodeficiency Syndrome): The most advanced stage of HIV infection
CD4+ T Cells: Immune cells that are targeted by HIV
Viral Load: The amount of HIV RNA in plasma
Antiretroviral Therapy (ART): Combination of drugs that suppress HIV replication
Opportunistic Infections: Infections caused by pathogens that typically do not cause disease in individuals with healthy immune systems
Reverse Transcriptase: An enzyme used by HIV to convert its RNA into DNA
Integrase: An enzyme used by HIV to integrate its DNA into the host cell’s genome
Protease: An enzyme used by HIV to cleave viral proteins
Pre-Exposure Prophylaxis (PrEP): Use of antiretroviral drugs by HIV-negative individuals to prevent HIV infection
Post-Exposure Prophylaxis (PEP): Use of antiretroviral drugs after a potential exposure to HIV to prevent infection
Seroconversion: The development of detectable antibodies to HIV
Window Period: The time between HIV infection and the development of detectable antibodies
Drug Resistance: The ability of HIV to resist the effects of antiretroviral drugs
Vertical Transmission: Transmission of HIV from mother to child
MSM: Men who have sex with men
RNA Virus: A virus that uses RNA as its genetic material
DNA Virus: A virus that uses DNA as its genetic material

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