Hypothesis: HIV Epidemic Blamed on Flies

Blood-sucking flies may have been to blame for the HIV epidemic being unleashed on humans, scientists suggest. Many AIDS researchers believe the HIV virus jumped species from chimpanzees to humans at some point in the first half of the 20th century. They think humans were first exposed when simian immunodeficiency virus (SIV) got into open wounds of game hunters in west or central Africa. However, German scientists think stable flies may be responsible for HIV invading humans, according to an article in New Scientist magazine (March 16, 2002; Vol. 173; 2334).

Most blood-sucking insects pose no risk of passing on HIV, including mosquitoes, which inject saliva through one tube and suck up blood through another. However, stable flies, which bite humans, could be an exception and are known to transmit equine leukemia virus between horses. When feeding, they scrape the skin to make a wound, suck up blood and regurgitate some on the skin next time they feed. Any viruses in the regurgitated blood can invade the body through the wounds made by the flies. Unlike other blood-sucking insects that regurgitate blood, the stable fly does not digest the blood it regurgitates.

If the flies sucked up virus-tainted blood from chimps, they could transmit it when they feed on humans, researchers believe. They speculate that sporadic cases of HIV transmission via stable flies may have happened for years but has gone unrecognized. However, if these rare infections still happen at all, they now pale into insignificance alongside the spread of HIV through unprotected sex -- a point reinforced by Professor David Mabey at the London School of Hygiene and Tropical Medicine. "It is an interesting theory and no more," he said. "The trouble with all these stories is that they distract attention away from the main public health message, which is 90 percent of infections are transmitted by sex or from mothers to infants."

Beatrice Hahn at the University of Alabama, who first reported finding HIV infections in chimps in 1999, does not think the German research should be taken seriously until further research backs it up. "There's no shortage of hypotheses of how SIVcpz made the jump to humans and this is just another one. The task at hand is to find out for sure what happened and back it up by hard evidence," Hahn said.

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