Mathematical Models and Ecology of Chagas' Disease

RABINOVICH, J. E. AND O. ROSSELL

New Approaches in American Trypanosomiasis Research

Pan American Health Organization. Scientific Publications

Lugar: Washington; Año: 1976; p. 359 - 369

Most of the results of the change in the number of sick people in the acute phase with time show periodic peaks; this is due to the process of natality in the human population, which was the only variable introduced as a discrete variable, a birth assigned to occur every 360 days. A comparative analysis of Figures 6-12, plus others not presented here, allows us to suggest that the following parameters are of critical importance in Chagas´ disease transmission: 1) The carrying capacity of the insect vector population, that is, the num ber of insects that can be supported by a given host population. 2) The probability that a bite by an infected insect will be followed by infection of the host. 3) The proportion of bites that are made on humans and among animals. 4) The proportion of hosts in the chronic phase which may be a source of T. cruzi to biting insects. All the other parameters tested individually seem to produce only minor changes in the transmission of Chagas´ disease. An example of the insight into the problem that this type of model may provide can be observed from Figures 3, 4, and 5. As time elapses, the number of people in the acute phase drops to zero (Figure 5); this drop is soon followed by the ex tinction of the infected insect population (Figure 3), which in turn is followed by the disappearance of the infection rate (Figure 4). Thus, after a couple of years, we are left with a situation where 100 per cen t of the population of the house is in the chronic condition. We know that this is seldom the case. However, if after the disappearance of the infected insects, some births take place in the house, then the expected ratio healthy to chronic people is obtained. This expected ratio could only be attained if there were a total absence of immigration of T. cruzi to the house, either because no infected insects immigrate or because no new acutely ill humans are added to the house population. This analysis points out the importance of migrations, in and out of houses, as a factor in the transmission of Chagas´ disease.