I thought HIV is a single type of viruses but there are 2 different types. HIV-1 and HIV-2.
SIVsmm virus in sooty mangabeys monkeys and SIVcpz virus in chimpanzees are believed to have crossed the species barrier into humans, resulting in HIV-2 and HIV-1 respectively.
Each virus can be contracted individually, or they can be contracted together in what is referred to as co-infection. HIV-2 seems to have lower mortality rates, less severe symptoms, and slower progression to AIDS than HIV-1 alone or the co-infection. In co-infection, however, this is largely dependent on which virus was contracted first. HIV-1 tends to out-compete HIV-2 for disease progression. Co-infection seems to be a growing problem globally as time progresses, with most cases being identified in West African countries, as well as some cases in the US.
HIV-1 is the most common and pathogenic strain of the virus. Scientists divide HIV-1 into a major group (Group M) and two or more minor groups, namely Group N, O and possibly a group P. Each group is believed to represent an independent transmission of SIV into humans (but subtypes within a group are not). A total of 39 ORFs are found in all six possible reading frames (RFs) of HIV-1 complete genome sequence, but only a few of them are functional.
HIV-2 has not been widely recognized outside of Africa. The first case in the US was in 1987. Many test kits for HIV-1 will also detect HIV-2.
As of 2010, there are 8 known HIV-2 groups (A to H). Of these, only groups A and B are pandemic. Group A is found mainly in West Africa but has also spread globally to Europe, and the US. Despite the presence of HIV-2 globally, Group B is mainly confined to West Africa. Despite its relative confinement, HIV-2 should be considered in all patients exhibiting symptoms of HIV that not only come from West Africa but also anyone who has had any body fluid transfer with a person from West Africa (i.e. needle sharing, sexual contact, etc.)
Even HIV-1 and HIV-2 have many sub-groups.
Viruses like the West Nile virus (WNV), Zika virus, dengue virus, and yellow fever virus are the same family of virus. Dengue virus also has type-1 and type-2.