HIV: the more things change, the more they stay the same.

ABSTRACT

PIP The syndrome known as AIDS is eventually brought on after initial infection with HIV. Infection with either HIV-1 or HIV-2 will lead to AIDS. However, different strains of HIV-1 have been found to exist, varying between continents. The strains, or clades, vary quite significantly in their surface antigens and genetic sequences. HIV-1 subtype B, the initial causative virus of AIDS in Western industrialized countries, is reproducibly different from subtypes C and E, respectively found in sub-Saharan Africa and northwestern Thailand. Each subtype provokes divergent host immune responses substantial enough to affect the course of vaccine development. There are currently two HIV/AIDS epidemics in Thailand, one spawned from the initial outbreak of HIV-1 subtype B in 1988 among IV drug users in Bangkok, and the other involving subtype E in and around Chiang Mai. Max Essex and his group have reported recent data which suggest that HIV-1 subtype E may be capable of more efficient spread than subtype B during vaginal intercourse. Both subtypes were found to replicate in almost the same manner in cells of lymphoid origin. Subtype E, however, thrives in vitro among Langerhans cells from either vaginal mucosa or penile foreskin, while subtype B replicates only sluggishly at best. Infection of the Langerhans cells could not be blocked by soluble CD4, reflecting a differential preference of subtype E for another, as yet unidentified, receptor. Clade E could be considered the heterosexual AIDS virus. Essex's hypothesis is worthy of pursuit. The same experiments need to be conducted with other clades in the laboratory along with ongoing epidemiologic monitoring of the pandemic to potentially spot newly introduced clades capable of altering transmission patterns. It has also been suggested that mixed infection occurs and that HIV-1 recombinations are possible. Regardless of whether or not Essex's findings eventually prove true, however, the author stresses that HIV-1 of all clades can spread through all sexual routes; it is just a question of variable efficiency. Appropriate efforts and precautions to prevent the spread of HIV must continue.^ieng