Many species of mammals are infected by lentiviruses, which are characteristically responsible for long-duration illnesses with a long incubation period.
Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses.
The risk of acquiring HIV from a needle stick from an HIV-infected person is estimated as 0.3% (about 1 in 333) per act and the risk following mucous membrane exposure to infected blood as 0.09% (about 1 in 1000) per act.
Preventive treatment involves the mother taking antiretrovirals during pregnancy and delivery, an elective caesarean section, avoiding breastfeeding, and administering antiretroviral drugs to the newborn.
The mechanism of CD4 T cell depletion, although apoptosis may also be a factor.
During the chronic phase, the consequences of generalized immune activation coupled with the gradual loss of the ability of the immune system to generate new T cells appear to account for the slow decline in CD4 Immune activation, which is reflected by the increased activation state of immune cells and release of pro-inflammatory cytokines, results from the activity of several HIV gene products and the immune response to ongoing HIV replication.
however, the pattern of transmission varies among countries.