09. HIV & AIDS Flashcards
HIV Virus Replication
RNA retrovirus: double-stranded RNA undergoes reverse transcription to form double-stranded DNA in cytoplasm of infected cell
- HIV virus attaches to and enters CD4+ cells (T-cells or T-helper cells)
- Viral RNA to Viral DNA via reverse transcription
- Viral DNA incorporated into host cell DNA
- CD4+ cell machinery is used to make HIV proteins
- Newly formed virus is released from host cell
• High replication rate:10 billion virus particles produced daily
HIV has short half-life (estimated at 6 hours) but genome is integrated into immune cells, including long-lived memory T cells.
- Serve as viral reservoir and enable virus to be reactivated even after decades of antiretroviral therapy
measures to monitor progression (2)
CD4+: indicates state of immune system
- Normal: 600 – 1200 cells/mm3
- < 200 cells/mm3:opportunistic and serious infections
Viral load:amount of HIV in blood
- Very high following initial infection
- Falls with development of antibodies
- Rises again with drop of CD4+
- Marker of treatment response
Opportunistic Infections
Weakened immune system of HIV/AIDS patients lead to the development of infections (opportunistic infections or OIs) that are not typically seen in immunocompetent individuals.
Large number of OIs have been identified in immunosuppressed HIV infected individuals, classified as “AIDS-defining illnesses” (CDC lists 28).
Treatment of HIV
Antiretroviral Therapy (ART)
Various classes of drug that decrease viral load in the affected individual.
HIV patients are treated with a combination (typically 3 or more from more than one class) of ART drugs: called HAART (highly active antiretroviral therapy)/
ART is recommended for all HIV positive patients, regardless of CD4+ count
- Reduction of morbidity and mortality
- Reduction of transmission
Treatment challenges
- Drug toxicities
- Expense
- Resistance to adherence
- Development of drug resistance
Modes of Transmission (5)
Sexual Transmission
Injection Drug Use
Perinatal Transmission
Transmission by Blood Transfusion
Transmission in Healthcare Setting
Sexual Transmission
Estimated to account for 75-80% of global HIV infections that have occurred to date:
- Sub-Saharan Africa: predominant means of transmission is heterosexual sex
- US: MSM
Unprotected receptive anal intercourse is the most effective means of sexual transmission.
Factors that increase risk of transmission:
- Presence of STI in either partner
- High viral load in infected partner: Risk high during primary infection prior to immune response
- Rough or traumatic sex (e.g. rape, sex under influence of cocaine or alcohol)
Injection Drug Use
Accounts for an estimated 15-25% of HIV infections globally.
Factors that increase risk of transmission:
- Sharing of contaminated injection equipment (predominant risk behavior)
- Larger number of needle sharing partners
- Social situations that increase likelihood of sharing equipment (e.g. “shooting galleries”)
- Injection drug practices
Harm Reduction Programs:
- To decrease risk of HIV and other adverse consequences of using contaminated equipment
- Offer clean syringes in exchange for used injection equipment
- Politically controversial (some believe they condone/support drug behavior)
- Evaluation by an Institute of Medicine Committee concluded they do reduce transmission of HIV
Perinatal Trans
Factors that increase risk of transmission:
- Internal fetal monitoring
- Prolonged labor & delivery
- Chorioamnionitis (infection of sac & fluid surrounding baby)
- High viral load in mother
- Primary HIV infection during pregnancy
- Advanced HIV infection in mother
Prevention of Mother to Child Transmission (MTCT):
- Universal HIV screening during pregnancy
- Medications during pregnancy
- Medication during labor
- Delivery Method
- Viral load HIV RNA <1000 copies/mL: safe for vaginal delivery
- Viral load HIV RNA ≥1000 copies/mL: cesarean delivery at 38 weeks
- Care of Infant
- Breastfeeding not recommended, even if mother is on ARV drugs
- 6 weeks of zidovudine for infant
- HIV PCR testing of infants
Transmission by Blood Transfusion
“most effective way”
Risk has been significantly decreased by establishing guidelines for donated blood
- Exclusion of potential donors at high risk (utilize extensive interview to screen donors)
- Screening of all donated blood with sensitive ELIZA (enzyme-linked immunosorbent assays) and NAT (nucleic acid testing)
Transmission in Healthcare Setting
Risk for healthcare workers and lab personnel who handle sharp instruments or who may be exposed to body fluid from HIV-infected patients.
Needle-stick accidents pose much higher risk than intact skin or mucous membrane exposure.
Factors that increase risk:
- Patient with advanced HIV disease or high viral load
- Exposure involves a large quantity of blood
- Device is hollow-bore, as compared to a solid needle
- Device placed directly into vein/artery of infected patient
- Deep injury
CDC recommends post-exposure prophylaxis with ART starting within 1-2 hours of exposure and continuing for 28 days
Prevention of HIV
Condoms: Most effective when used correctly every time, but even occasional use has shown to reduce risk with risk reduction being proportionate to amount of usage.
Male circumcision: Circumcision can reduce the risk of female to male transmission, but is not as effective as other means (e.g. condoms).
HIV Pre-exposure Prophylaxis (PrEP): Use of antiretroviral medications among individuals who are HIV-negative but are at high risk of contracting HIV.
HIV Post-exposure Prophylaxis (PEP): Use of antiretroviral medications after potential exposure to HIV. Should be initiated immediately, but no longer than 72 hours after exposure. Should be used only in emergency situations.
Prevention among IVD users
- Best method is to stop injecting drugs
- Use new and sterile needle with each injection (needle exchange programs).
- Don’t share needles
- Use sterile water to prepare drugs
- Clean skin with alcohol prior to injection
- Dispose of needles safely following use
- Yearly HIV testing
- Consider PrEP
Increase HIV testing via “opt-out” strategy
