How AIDS moved from chimpanzees and, now, gorillas.
The diseases that emerge from Africa are many and successful. Now we know from published research that some of them are cross-infections (zoonoses) from our closest relatives living there. The 4 phylogenetic forms of the immunodeficiency virus AIDS are M, the pandemic one, and N and the O and P groups. Chimpanzees, Pan troglodytes are the proven source of M and N, within populations living in the south of Cameroon. In the same area, because of what we know about the place of bushmeat in the human diet there, we now know that the smallest gorilla, the western lowland Gorilla gorilla gorilla in southern Cameroon is the only source. Other gorilla subspecies and some chimpanzees are free of the virus, which indicates either their isolation or the difficulty it normally has in transmission.
The research was carried out by Martine Peeters of Montpelier University and many others including colleagues from the Universities of Pennsylvania and Edinburgh. It is published this week in PNAS as
Origin of the HIV-1 group O epidemic in Western Lowland Gorillas and is freely available as a pdf file.
Faecal samples were examined in as many possible source sites as possible, in Congo, DRC., Gabon, and Uganda. The cross-species transmissions have each been independently developed, possibly over a long period. The virus was found in between 0.8 and 22% of western lowland gorillas in southern Cameroon. The high level of genetic diversity was relevant, but all strains of these gorilla SIV seem related to the single line leading back to the basal chimpanzee radiation of the virus.
In the gorillas infected, HIV-1 group O pointed to this species as the original source. A barrier exits for transmission between the apes in the form of cytidine deaminase, but this does not prevent gorilla to human transmission! There is now an epidemic of group O HIV in Central Africa, with 100,000 people infected. This level of infection is unmatched by group P. The transmission is thought to be directly from chimpanzee or gorilla blood on hunted bushmeat. If we can eradicate the apes from bushmeat, or perhaps provide food aid to countries that are becoming adjusted to killing even rare animals, no further types of AIDS will threaten us with pandemics.
Other disease is obviously sourced in bushmeat too. It is taking up precious medical research time to investigate how easily the animal/human barrier can be breached. These scientists could be involved in very practical relief for those people already suffering known diseases if we removed multiple stresses on the health services in Africa and elsewhere.