Acquired Immunodeficiency Syndrome (AIDS) is a severe condition that affects the immune system, leaving individuals susceptible to various infections. While commonly associated with humans, AIDS originated in non-human primates. Understanding this connection provides insights into these viruses and their potential impact across different species.
Simian Immunodeficiency Virus (SIV)
Simian Immunodeficiency Virus (SIV) is a retrovirus that infects various non-human primate species, primarily in sub-Saharan Africa. SIV is closely related to Human Immunodeficiency Virus (HIV), but they are distinct viruses. SIV has been present in monkeys and apes for an extended period.
SIV belongs to the Lentivirus genus, which also includes HIV-1 and HIV-2. There are numerous strains of SIV, with each strain typically found in a specific primate species. For example, SIVsmm is found in sooty mangabeys, and SIVcpz is found in chimpanzees. These viruses establish persistent infections in their primate hosts.
Do Monkeys Get AIDS?
For most natural primate hosts, SIV infection does not lead to AIDS-like disease. These primates, such as sooty mangabeys and African green monkeys, can carry high levels of the virus without developing immunodeficiency. This phenomenon is attributed to a long history of co-evolution between SIV and its natural hosts, allowing them to tolerate the virus. Their immune systems remain largely intact despite chronic infection.
However, SIV can cause a disease similar to AIDS, known as Simian Acquired Immunodeficiency Syndrome (SAIDS), when it infects a non-natural host. For instance, SIV strains from sooty mangabeys can cause SAIDS in rhesus macaques, an Asian primate species that does not naturally carry SIV. This occurs because these non-natural hosts have not co-evolved with the virus. Chimpanzees, while natural hosts for SIVcpz, are an exception, as SIVcpz infection can lead to increased mortality in them.
SIV’s Connection to Human HIV
Human immunodeficiency viruses, HIV-1 and HIV-2, originated from SIV through cross-species transmission. HIV-1 evolved from SIVcpz found in chimpanzees in west-central Africa. This SIVcpz lineage resulted from recombination between different SIV strains from other monkey species that chimpanzees prey on.
HIV-2, which is less prevalent and primarily found in West Africa, originated from SIVsmm, the SIV strain infecting sooty mangabeys. Multiple independent transfers of SIV from chimpanzees and sooty mangabeys to humans occurred. The most accepted transmission route to humans is the “bushmeat” hypothesis, involving exposure to infected primate blood during hunting or butchering. Scratches or bites from infected monkeys or contact with their blood while preparing food facilitated these transmissions. Understanding HIV’s origins from SIV highlights how viruses can jump species barriers and underscores the importance of monitoring zoonotic diseases.