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Differential Behavior of Vectors Infected with Chagas' disease

Chagas' disease, caused by certain strains of the parasite Trypanosoma cruzi, is a vector-borne disease, previously thought to be transmitted solely through the fecal matter of the triatomine vectors after feeding on the mammalian host. However, this mode of transmission is inefficient in the vectors, Triatoma Sanguisuga a subspecies of the reduviid family, prevalent in the Southeastern United States, due to the significant delay between feeding and defecation times. The prevalence in this region, 40-60% thus necessitates an alternative explanation. The hosts in the sylvatic cycle of this region, including opossums, raccoons, and armadillos, to name a few, are known to consume the vectors, although this is a traditionally inefficient way of transmitting the parasite. Recently, vector behavior has been observed to be modified during infection, termed differential behavior, such as feeding more frequently and wandering into broad daylight. The extent to which this affects the disease dynamics warrants investigation and could explain the persistence of T.Cruzi in the sylvatic cycle of this region. To include both modes of transmission, a deterministic model of the disease dynamics has been developed, incorporating both vector-host and predator-prey dynamics. This model is studied to examine how the differential behavior affects the disease dynamics, threshold of infection, and the current endemic equilibrium which is presently the case. Numerical simulations are carried out to verify the theoretical results. We have shown that elevation of consumption of the vector decreases infection levels and could possibly drive the vector population to extinction. Vectors increased vulnerability to predation increases consumption of infected vectors, which decreases prevalence levels but only slightly affects the total population size. Also, increased feeding frequently of the vectors boosts infection levels significantly, and could explain the high prevalence of T.Cruzi in the southeastern United States.

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Karyn Sutton, Arizona State University
Priscilla Greenwood, Arizona State University
Christopher Kribs-Zaleta, University of Texas at Arlington
Leon Arriola, University of Wisconsin at Whitewater
Carlos Castillo-Chávez, Arizona State University