SIVs and Human Crossovers in West and Central Africa
Moderator: Mark Siddall (Division of Invertebrate Zoology, American Museum of Natural History)
Preston A. Marx (Tulane University)
"Instructive Differences between AIDS and Ebola Virus Disease, Two Epidemics with Zoonotic Origins"
Field studies in Western and Central Africa have established the simian origins of all known HIV viruses as from Simian Immunodeficiency Viruses [SIVs], a virus species that is found only on the African continent. All known HIV-1 viruses, groups M, N, O and P, originated from chimpanzees and gorillas in the Congo River basin. Sooty mangabeys, a monkey species native to Western Africa, are the origins of the 9 known HIV-2 groups, A through I. Although the simian origins of AIDS are well established, the means by which HIV types 1 and 2 emerged in the 20th century are not known.
Based on the origin results, HIV has been treated as a zoonosis. However, this view is not supported by findings in Western and Central Africa. First, contact between humans and SIV infected simian species is very common and has been ongoing for thousands of years mainly through hunting and game processing practices. If HIV were a zoonosis, it would be an ancient human disease that was spread during slave trade, but this was not the case. In this presentation, studies will show that SIV causes only transient SIV infections upon crossover to humans exposed to SIV. It will be shown that SIV requires adaptation to humans, and that a simple infection from the simian source is not sufficient to launch an AIDS epidemic.
It is also instructive to compare AIDS to a zoonosis that has launched an epidemic in Western Africa. The talk will contrast SIV human infections to EBOLA virus human infections. The comparison is key to understanding how zoonotic infections can have profoundly different outcomes. Both EBOLA and HIV-2 epidemics emerged and spread in the same small area of the Africa continent. One simian virus, the EBOLA virus, launched a deadly epidemic and the other, SIV, resulted only in self-limiting infections without an epidemic. Theories on how SIV adapted to humans will be briefly covered.
