![]() Many, though not all, human viruses originated by cross-species transmission. "Given the very close genetic relationship between chimpanzees and humans, this prompts the question whether chimpanzees have co-evolved with their virus to reach this non-pathogenic association." Jumping and Recombining "The major difference between SIV infection of chimpanzees and HIV infection of humans is that chimpanzees are not known to develop any disease symptoms," said Sharp. ![]() ![]() Scientists say it will be important to examine whether chimpanzee predation on smaller monkeys has led to additional SIV acquisitions, and possibly coinfection and recombination with SIVcpz, and whether the resulting chimpanzee-adapted SIVs are more likely to infect humans. ![]() If a vaccine can be created, it's still unclear how much diversity it will be able to cope with. This knowledge is imperative in the quest for an AIDS vaccine. Even strains of the same subtype may now differ by up to 20 percent. There are already many subtypes of the HIV-1 strain, and the diversity is growing. The complexity of the HIV virus has increased through constant recombination. The new findings thus show that humans are not the only primate species to acquire two different immunodeficiency viruses by cross-species transmission. It is now widely accepted that humans contracted HIV from chimpanzees, probably by butchering them for bush meat. Chimps prey on both of these species and their ranges overlap in West and central Africa. The study shows that the SIVcpz strain arose in chimps through repeated transmission and recombination of SIVs from the red-capped mangabeys and greater spot-nosed monkeys. While monkeys have been infected with SIVs for a long time, chimps apparently acquired the virus more recently. SIVs are carried by many species of monkeys in Africa, but chimps are the only apes known to be naturally infected. In 1999, the same team of scientists identified the origin of HIV-1 as being the transmission of a virus known as SIVcpz from chimpanzees to humans, but they didn't know how chimps acquired the virus in the first place. Second, international travel brings animals from far-away places to a new place." From SIV to HIV "First, the detection of the virus is easier today because of advances in medical science. "It seems this is happening more frequently because of two reasons," said Michael Lai, a virus expert at the University of Southern California, Los Angeles. Diseases like SARS and monkeypox, which recently hit the northern United States, likely originated by cross-species transmissions. The jumping of viruses from animals to humans occurs all the time. The discovery also spotlights how many of our most virulent viruses were transmitted across species. "Because of the similarity between chimpanzees and humans, any virus that successfully adapts to spreading among chimps would be a candidate for a further jump to humans-a potential HIV-3," said Paul Sharp of the Institute of Genetics at University of Nottingham in England, who led the study. Just as chimps acquired viruses from two different sources, humans are infected by two distinct AIDS viruses: HIV-1 and the less virulent HIV-2, which humans acquired from sooty mangabey monkeys. The study suggests striking parallels between SIV infection of chimps and HIV infection of humans. The hybrid virus then spread through the chimpanzee species, and was later transmitted to humans to become HIV-1. Chimps eat monkeys, which is likely how they acquired the monkey viruses. Researchers believe the chimpanzee virus is a hybrid of the SIVs naturally infecting two different monkeys, the red-capped mangabey ( Cercocebus torquatus) and the greater spot-nosed monkey ( Cercopithecus nictitans). Instead, it was a product of separate viruses jumping from different monkey species into chimps, where they recombined to form a hybrid virus, according to a new study. Scientists now say that the simian immunodeficiency virus (SIV) in chimpanzees ( Pan troglodytes), which is believed to have been transmitted to humans to become HIV-1-the virus that causes AIDS-didn't start its life in chimps.
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