Columbia Earth Institute Populations Expert Finds Banning Animals From the Bedroom in Rural South America Could Reduce Chagas Disease Risk
By Abigail Beshkin
Keeping chickens and especially dogs out of the bedroom could help reduce the risk of Chagas disease infection in rural areas of Central and South America, according to a new report in the July 27, 2001 issue of the international journal, Science.
The study is the first mathematical model of Chagas disease infection to use data from individual households on a community-wide basis, says lead author Joel E. Cohen, a professor of populations at the Columbia Earth Institute at Columbia and at Rockefeller University.
Chagas disease, or American trypanosomiasis, is a chronic, ultimately fatal infection caused by the parasite Trypanosoma cruzi, an American cousin to the African sleeping sickness parasite. T. cruzi is transmitted through the feces of blood-feeding bugs called triatomines, commonly known as "kissing" bugs, "cone-nosed" bugs, vinchuca, or barbeiro.
According to the World Health Organization, 16-18 million people from Mexico to Argentina are affected by Chagas disease, and another 100 million, or 25 percent of the region's population, are at risk of infection. Infection is lifelong, and can result in fatal heart disease.
Despite national-level insecticide spraying programs and blood screening in Latin America, Chagas disease remains a " serious obstacle to health and economic development," especially for the rural poor say study authors Cohen and Ricardo E. Gurtler of Universidad de Buenos Aires.
To better understand how the T. cruzi parasite is transmitted in rural areas, Cohen and Gurtler created a mathematical model based on household data from three rural villages in northwest Argentina. The model looks at seasonal fluctuations in household bug and parasite populations and their relationship to the numbers of humans, chickens, and dogs living within a household.
Data collected by the Science researchers shows that humans, chickens and dogs all sleep indoors during the spring, with the chickens kept inside to prevent theft or predation. Since chickens provide most of the blood meals for the bugs, the indoor bug population begins to grow in the spring and reaches its peak in the summer.
Although chickens cannot become infected with T. cruzi, they can contribute to the overall population of the parasite by increasing the number of bugs available to feed on infected household members such as dogs and humans.
After chickens, the blood-feeding bugs prefer to take their meals from dogs, selecting them roughly twice as often as humans. Since there are approximately five humans per household in the study villages, the mathematical model predicts that having two infected domestic dogs is probably "the worst thing householders can do" in terms of increasing the T. cruzi population, according to the authors.
The study notes that removing infected dogs from a household is enough to nearly wipe out the transmission of the parasite, barring the reintroduction of any infected dogs, children or bugs.
The researchers suggest that their findings can be used in conjunction with insecticide programs and new construction materials--which decrease the number of domestic bugs--to slow down the Chagas infection rate.
"National level spraying programs in Latin America deserve lots of credit, but budgets in these countries are not always sufficient to keep up the spraying. It might take ten years to get around to spraying all the rural villages, but it only takes five years for bugs to fully recolonize these homes," says Cohen.
Cohen hopes that governments, anthropologists and health educators will help spread the message that keeping domestic animals out of the bedroom can reduce the prevalence of the Chagas parasite in bugs and the risk of infection in humans.
The researchers also suggest that their community-wide, household model could be used to evaluate how the spread of other diseases, such as malaria or leishmaniasis, may be affected by intimate contact with domesticated animals.
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