EPIDEMIOLOGICAL MODELING OF Trypanosoma cruzi TRANSMISSION: REINFECTIONS IN THE CHRONIC PHASE EXPLAINS THE FREQUENCY OF MIXED INFECTIONS IN HUMANS

NICOLÁS TOMASINI; PAULA G. RAGONE; SEBASTIEN GROUBIERE; JUAN P. APARICIO; PATRICIO DIOSQUE

Santa Fe

Congreso; XXVIII Reunión Anual de la Sociedad Argentina de Protozoología y Enfermedades Parasitarias; 2016

Sociedad Argentina de Protozoología

People living in areas with active vector-borne transmission of Chagas disease are subject to multiple contacts with its causative agent, Trypanosoma cruzi. Animal models of the disease showed that reinfections by T. cruzi are possible although they may display lower or undetected parasitaemia. In humans, although reinfections may have major public health implications, as they are thought to increase the risk of chronic manifestations of the disease, there is little quantitative knowledge about their frequency and the timing of parasite re-inoculation in the course of the disease. We implemented stochastic agent-based models to estimate the rate of re-infection in humans and to assess how frequent are secondary infections during the acute and chronic stages of the disease according to several alternative hypotheses on the adaptive immune response following a primary infection. By using a hybrid genetic algorithm, the models were fitted to epidemiological data of Argentinean rural villages where mixed infections by different genotypes of T. cruzi have been reported to reach 56% in humans. To explain such a level of mixed-infections, the best model predicted an average of 0.04 annual reinfection per person with most of secondary infections occurring in the chronic phase. The main reason for this relatively low frequency of annual re-infections is the weak efficiency of the stercorarian mode of transmission of T. cruzi that strongly limit re-inoculation, rather than the adaptive immune response that the parasite was estimated to escape in at least 20% of the events of re-inoculation. Concluding, a few re-infections typically occur per individual, mostly in the chronic phase of the disease. The provided estimates are of particular interest for vaccine development as they provide indirect knowledge on adaptive immunity in the field, and they can help understanding the higher risk of chronic disease manifestations suffered by infected people living in endemic areas.