The phrase "simian immunodeficiency" refers to a type of immunodeficiency virus that affects monkeys and apes. It is similar to the human immunodeficiency virus (HIV) that causes AIDS in humans. Full definition
Characterization of Simian Immunodeficiency Virus Variants Anatomically Compartmentalized in Plasma and Milk in Chronically Infected African Green Monkeys. (bsrisf.org)
In April two studies of simian immunodeficiency virus, a kin of HIV that infects monkeys, reported that the virus swiftly infects and decimates key immune cells in the gut within days, not years, of infection. (discovermagazine.com)
Monkey viruses have contaminated vaccines in the past, and several species, such as African green monkeys, are commonly found to be infected with simian immunodeficiency virus (SIV), a relative of HIV. (newscientist.com)