The crayfish cure

WHILE MILLIONS OF DOLLARS are being poured into the development of a vaccine to control schistosomiasis, a disease caused by the parasitic schistosome worm, a group of U.S. and Kenyan researchers is testing a far simpler and more unusual means of control: the Louisiana crayfish. "It's essentially a human-crayfish team," says Armand Kuris, a University of California at Santa Barbara parasite ecologist and a leader of the project, which began in Kenya last summer.

As larvae, schistosomes live only in small freshwater snails. Humans come into contact with the worms when the larvae make their way into the water, usually in small ponds. The tiny larvae burrow through the skin and grow to adulthood in the human body. Eggs laid by the adults (which are in a near permanent state of copulation) then burrow back out of the body through the bladder or intestine. As they do so, they cause internal bleeding, fever, fatigue, and sometimes death. Two million Kenyans, mostly children, suffer from schistosomiasis.

Kuris thinks the key to reducing the transmission of the disease is to reduce snail populations. Pesticides have proved ineffective and costly. Louisiana crayfish, on the other hand, gobble snails like candy; snail shells are loaded with calcium, which the crayfish need to grow shells of their own. And Louisiana crayfish already live in Kenya: they were introduced in the early 1970s as an export crop, and today they are found in all the major rivers.

The crayfish do not, however, have access to the ponds where humans water their cattle and do their wash and are most likely to come into contact with schistosomes. So last summer, Kuris and parasitologist Sam Loker of the University of New Mexico let loose thousands of crayfish in ponds near a few schools in Kenya. At the same time, the researchers started screening schoolchildren for schistosome eggs in their urine, and deworming infected children with a drug called praziquantel. The children and their parents are eager to participate in the program, says Kuris ("When you're peeing red," he explains, "you notice it"), but praziquantel is far too expensive to be used routinely in Kenya, and anyway it doesn't solve the problem. "The day after we have dewormed the children," says Kuris, "some will go out and get new infections."

But they won't if the schistosomes can't find any snails to grow in. The children will be monitored for the next two years, and if the crayfish perform the way they're expected to, the researchers hope to reduce greatly the number of reinfections. If they are successful, it would be a milestone: the first time a biological control has proved effective against a human parasite.

The Instructive Bowels of the Cotton-Top Tamarin

Adolescence is a painful transition for cotton-top tamarins. About 40 percent of these small South American primates develop ulcerative colitis--also known as inflammatory bowel disease--by the time they are two and a half years old. As it happens, about one young human adult in a thousand falls victim to much the same condition. For unknown reasons, the whole length of the colon becomes inflamed, causing bloody diarrhea, pain, and weight loss--and sometimes, if the condition is left untreated, liver disease, colon cancer, and death. Although researchers have long suspected that inflammatory bowel disease is genetic--neither stress nor infection seems to be responsible--that has been hard to prove in humans. But tamarins, says Paul Watkins, a veterinarian at the University of Bristol, are bred in colonies for research, where "it is easy to trace their pedigree and what they've been up to." So his group is teaming up with Sequana Therapeutics, an American biotech firm, to find out whether inflamed bowels are indeed inherited in cotton-top tamarins. If the researchers can find a gene for the disease in the tamarins, it may help them find one in humans as well; after all, the two primates are genetically quite similar.

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