2 closely related viruses (HIV 1 and 2) cause the disease known as Aids.
2-6 weeks post exposure, most individuals experience a febrile illness from which they recover, but they remain infectious life long thereafter.
Primary infection: fever, sweats, malaise, muscle pain, sore throat, headache and enlargement of lymph glands.
These symptoms tend to resolve spontaneously.
Asymptomatic infection: Infected patients feel well.
Late HIV infection: unexplained weight loss, chronic diarrhoea, increased susceptibility to normally harmless infections. Also may develop rare forms of cancer.
This requires laboratory tests that detect the presence of HIV antibodies in the patient’s blood (standard HIV test).
HIV antibody is present in a patient’s blood from about 4 weeks after exposure.
Less than 4 weeks after exposure, antibody tests may be negative (Window period).
Other tests can be used to detect infection before this:
P24 antigen is present in the blood about 3 weeks after infection
These days many laboratories use a p24 antigen/HIV antibody combination test to screen patients for HIV infection.
HIV PCR test: HIV DNA is present in the blood from about 2 weeks after infection. PCR test is used to determine whether a baby is infected with HIV.
NB If HIV tests are negative and a person has been recently exposed, a repeat HIV test should be taken 2-6 weeks later.
Infected persons are infectious life long from about 2 weeks after exposure. Virus is present in blood as well as in body fluids such as semen, vaginal secretions and breast milk. HIV is spread by sexual intercourse (vaginal, anal or oral sex), needle sharing in IV drug abuse, mother to child (during pregnancy, delivery and breast feeding) and needle stick injury.
The approximate risk per encounter/exposure:
Sex: 0.5% (maximum)
Needle sharing: 0.67%
Mother to child: 30% (if no prophylaxis is given)
Breastfeeding: 10% additional risk
Needle stick: 0.3%
See elsewhere for guidelines.
There is no vaccine. Regular condom use is protective.
Post exposure prophylaxis: If someone is exposed to HIV, infection may be prevented by immediately beginning a course of anti-retroviral drugs. Treatment should be started as soon as possible (probably ineffective if started >72 hours after exposure).
Recommended therapy (South Africa): Combivir (contains Zidovudine 300 mg PLUS Lamivudine 150 mg) given 12 hourly for 4 weeks.
Mother to child transmission during pregnancy and delivery can be reduced by treating the mother with anti-retroviral drugs during pregnancy and the infant after delivery (see PMCTC guidelines). To reduce the risk further, HIV-infected mothers should not breast feed their infants or should pasteurise their milk.