HIV-1 from chimpanzees and gorillas to humans
Scientists generally accept that the known strains (or groups) of HIV-1 are most closely related to the simian immunodeficiency viruses (SIV) endemic in wild ape populations of West Central African forests. Particularly, each of the known HIV-1 strains is either closely related to the SIV that infects the chimpanzee subspecies or closely related to the SIV that infects western lowland gorillas.
The pandemic HIV-1 strain (group M) and a very rare strain only found in a few Cameroonian people (group N) are clearly derived from chimpanzee populations living in Cameroon. Another very rare HIV-1 strain (group P) is clearly derived from gorilla populations of Cameroon. The primate ancestor of HIV-1 train (group O) is a strain infecting over 100,000 people mostly in Cameroon but also the neighboring countries.This has been recently confirmed to be derived from gorilla strain.
The pandemic HIV-1 group M is prevalent in the southeastern rain forests of Cameroon (modern East Province) near the Sangha River.
Thus, this region is presumably where the virus was first transmitted from chimpanzees to humans. However, reviews of the epidemiological evidence of early HIV-1 infection in stored blood samples, and of old cases of AIDS in Central Africa have led many scientists to believe that HIV-1 group M early human center was probably not in Cameroon, but rather farther south in the Democratic Republic of the Congo, more probably in its capital city, Kinshasa (formerly Léopoldville).
Using HIV-1 sequences preserved in human biological samples along with estimates of viral mutation rates, scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanization and colonization in equatorial Africa.
Exactly when the zoonosis occurred is not known.
Some molecular dating studies suggest that HIV-1 group M (most recent common ancestor) started to spread in the human population, in the early 20th century, probably between 1915 and 1941.
This happened in between the two World Wars I and II when Germans used African bases, especially the Democratic Republic of Congo as a experimental base for clandestine medical research. They probably used cells derived from simian kidney for cell culture studies.
What was studied by Germans are not known after their fall but it looks like American hijacked the project to America with captured German scientists.
I believe this project is still in USA on a different name and place.
What is now known for certain and the researchers at that time failed to recognize was the accidental infection by simian virus of human (African volunteers were used as guinea pigs) subjects.
There were no established protocols or safety concerns for decades.
The transfer of infection most probably occurred through infected unsterilized needles and syringes.
The aids virus is somewhat similar to hepatitis B virus and it is quite possible that it could carry the virus from man to man (in living lymphocytes) unless something happens in the intestinal system of the mosquitoes. It appears that the saliva and intestinal system inactivate both the virus and the lymphocytes.
Direct inoculation by unsterilized injection needles was the primary mode of infection and not zoonosis.
Ignorance of the natives and their abject poverty made it easy for the colonial masters to hide the facts and figures.
In a way it was a grand conspiracy.
I feel that the biological scientists of the 21st century should study the plausible cover ups.
What intrigued me at the beginning of the aids epidemic was why the adult mosquito did not spread the disease?
A study published in 2008, analyzing viral sequences recovered from a recently discovered biopsy made in Kinshasa, in 1960, along with previously known sequences, suggested a common ancestor transmitted to humans between 1873 and 1933 (with central estimates varying between 1902 and 1921).
The primates being a critically endangered species, further confirmatory research is impractical. However, the researchers were able to hypothesize a phylogeny from the limited available data.
They were able to use the molecular clock of a specific strain of HIV to determine the initial date of transmission, which is estimated to be around 1915-1931.