Low-tech Prescription for Chagas

CHAGAS DISEASE is a serious and sometimes deadly infection that affects 16-18 million people throughout the Americas. What if there were a simple and inexpensive way to prevent transmission? Rockefeller University and Columbia University Professor Joel E. Cohen and Ricardo Gürtler from the University of Buenos Aires say there is, and they have the scientific data to prove it. Cohen and Gürtler are combining their expertise in applied mathematics and tropical infectious diseases to develop mathematical models to solve health problems.

According to the World Health Organization, Chagas disease is endemic to 21 countries in the Americas, where 100 million people are at risk of contracting the disease. The infection is life-long and in its most severe form can lead to heart failure. Humans get the disease from a parasite named Trypanosoma cruzi. The parasite is transmitted to humans through an infected blood transfusion or through the feces of the blood-sucking reduvid bug, locally known as “kissing” bugs, “cone-nosed” bugs, vinchuca, or barbeiro

Cohen and Gürtler set out to learn how the parasite spreads in rural households. They created a mathematical model based on a decade of data from three rural villages in Northwest Argentina. The first model of its kind, it processes data from household populations of bugs, parasites and their relationship to the numbers of humans, chickens, and dogs living within a household.

The results show that transmission follows a seasonal pattern based on what animals live in the house at what time. The cycle begins in the spring when humans, dogs, and chickens all sleep inside together — a safeguard against chicken theft or predation. The bugs also live inside and they feast on the chickens finding them to be an ideal source of a blood meal. Although chickens can’t be infected with the parasite, their presence in the household increases the bug population that peaks in the summer when the chickens are usually moved outside. The bugs then turn to the dogs as their secondary choice for a blood meal. Not only are the dogs much more infectious than humans, but they are also twice as likely to be chosen for a meal as humans.

Based on this data, Cohen and Gürtler’s mathematical model predicts that letting dogs sleep outside could almost eliminate the transmission of infection —  their official recommendation is to move both dogs and chickens to an outbuilding and keep them out of the bedroom.

“It is important to emphasize that the high technology approach to the control of infectious disease has left this disease behind,” Cohen says. “The problem is that the people who have [Chagas] are poor. There is very little prospect of a pharmaceutical company recouping the research costs required to save the 16 to 20 million people who are infected with this disease. What our work does is give the people who are affected the possibility of improving their health by their own efforts.”

A simple solution such as keeping animals out of the sleeping area is practical for all income levels.  “The ingredient here is knowledge rather than high technology.”

Cohen and Gürtler think a similar approach could help understand how other diseases, such as leishmaniasis and malaria, are related to the presence of animals in the household. They believe that the mathematical model will lead to other low-tech solutions for common health problems found in rural areas.

“We think that there are a lot of problems in developing countries where solutions don’t have to come from high-tech or from outside,” Cohen says. “I do think there is a place for the ecological approach for the prevention of disease.”

—Chris Hardman

Published in Americas magazine

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