There are tests to determine the presence of HIV and its strains present in the blood, plasma and lymph samples. By studying the strains of the earliest cases of HIV, a trail of clues points to the appearance of the virus in humans and its evolution.
The first breadcrumb; a plasma sample taken from an adult male, in 1959 from the Democratic Republic of Congo. The Second, HIV found in the samples of tissues take from the body of an American Teenager who died in St. Louis in 1969. The Third, HIV found in the samples from a Norwegian Sailor in 1976.
In 1998 another study showed that the sample take in 1959 had HIV 1 and jumped into humans around the 1940s - 50s. In January 2000, another paper suggested that the first cases of HIV 1 occurred in the year 1931 in Western Africa. These estimates were made on a statistical and genetic study which lead to the building of a complex computer model to suggest the evolution of this virus and the pandemic of AIDS.
Another study in 2008 suggested the origins of the AIDS virus between 1884 to 1924. The scientists compared the earliest known viral sequence of HIV from 1959 to a newly discovered sequence in 1960. And significant genetic difference has been found between them, this demonstrated the diversification in the HIV 1 long before the pandemic struck. Kinshasa in western Africa was the epicenter of the AIDS virus epidemic and the development of colonial cities lead to increase in interaction of people, leading to greater rate of transmission of the virus.
HIV 2 has transmitted into humans via Zoonosis, the SIV infests the Mangabeys, the crossover to humans is suggested happening through the butchering and consumption of monkey meat. HIV 2 infection is rarer and not as aggressive as the HIV 1 hence it infects fewer people and is endemic to western Africa.
A Belgian Research published in May 2003 by Dr. Anne-Mieke Vandamme and her group in the Proceedings of the National Academy of Science suggested another possibility for the pandemic. They analyzed two different subtypes of HIV 2 (A and B) taken from carrier individuals and SIV samples taken from the sooty Mangabeys, after studies the team determined that the Subtype A passed into humans in the 1940s and the subtype B in 1945 - with a margin of 16 years. The virus originated in Guinea-Bissau. It spread during the War of Independence from Portugal. The European cases of HIV 2 were discovered in the Portuguese veterans of the war. The mode of transmission may have been use of unsterilized needles, reception of blood transfusions by the soldiers and relationships with the local infected women.
The question that where, when, and how did HIV originate is still open - many issues like blaming innocent peoples for the pandemic, the social over-reaction, has lead to more research into its origins. Simians from South America and Asia have been tested negative, yet the research continues as it not only leads us to the beginnings but also suggests cures for the disease.