Public healthElusive killer parasite being traced in Peru

Published 28 September 2011

Chagas disease, primarily seen in South America, Central America, and Mexico, is the most deadly parasitic disease in the Americas; Penn epidemiological study takes snap shot of long-term Chagas disease outbreak

Hollywoodwould have you believe that all epidemics involve people suffering from zombie-like symptoms —  but reality is more mundane, with many epidemics that can only be uncovered through door-to-door epidemiology and advanced mathematics.

Michael Levy, Ph.D., assistant professor of Biostatistics and Epidemiology, at the Perelman School of Medicine, University of Pennsylvania, along with other collaborators from Penn, Johns Hopkins University, the Centers for Disease Control and Prevention (CDC), and Universidad Peruana Cayetano Heredia in Peru, are combining tried-and-true epidemiological approaches with new statistical methods to learn more about the course of a dangerous, contagious disease epidemic. Their research was published last week in PLoS Computational Biology.

A University of Pennsylvania School of Medicine release reports that Chagas disease, primarily seen in South America, Central America, and Mexico, is the most deadly parasitic disease in the Americas. Caused by the protozoan parasite, Trypanosoma cruzi, it is spread chiefly via several species of blood-sucking triatomine insects. After an initial acute phase, the disease continues to lurk in the body and can eventually cause a variety of chronic life-threatening problems, particularly in the heart. Although there are some drugs to treat Chagas disease, they become less effective the longer a person is infected. The lack of a vaccine also means that the only effective way to control the disease is to control the disease vectors.

Because the chronic effects of Chagas disease can take decades to manifest themselves, tracking the development and progression of epidemics has been a challenging problem. In the past, Chagas disease was known mostly in rural regions, but has been spreading into more urbanized areas over the last 40 years. Levy’s team has been focusing on one of those areas in the city of Arequipa, Peru. “There is an assumption that Chagas disease is not a problem in Peru because statistics don’t show that more people are dying of cardiac disease in the areas with Chagas transmission compared to the rest of the country,” Levy said. “What we’ve shown calls into question the assumption that the particular parasite that’s circulating in Arequipa is somehow less virulent. We show that there’s really nothing to back that assumption.”

Epicenter regression

The researchers used epicenter regression, which takes a statistical “snapshot” of disease infection in a particular population to track the history of how an infection takes hold and spreads. Epicenter regression considers the duration of an individual’s exposure to infection as a function