The chimp subspecies lives in Cameroon, Equatorial Guinea, Congo and Central African Republic, the region where AIDS is thought to have started. The fourth sample, much less like HIV, came from a separate chimp subspecies native to East Africa. Among humans, there are three major groups of HIV, one of which has spread around the world. The others exist in west- Central Africa. She said a French team, headed by Dr. Phillippe Mauclere of the Pasteur Institute, recently found three more chimps infected with SIVcpz at a sanctuary in Cameroon.
Many viruses come from animals.
Flu, for example, comes from ducks and pigs. Often the virus does not make its natural host sick. It must undergo genetic changes to infect another species such as humans, changes that can cause illness. There is a second strain of HIV that infects people, known as HIV-2. It is believed to have started out in a monkey known as a sooty mangabey.