POTENTIAL FORCE OF INFECTION OF HUMAN RABIES TRANSMITTED BY VAMPIRE BATS IN THE AMAZONIAN REGION OF BRAZIL

Human rabies tansmitted by bats has acquired greater epidemiologic rel evance in various Latin American countries, just when cases transmitte d by dogs have decreased. Concern has been heightened by reports of in creased rates of bats biting humans in villlages in the Amazonian regi on of Brazil. The aim of the present work was to estimate the potentia l force of infection (per capita rate at which susceptible individuals acquire infection) of human rabies transmitted by the common vampire bat if the rabies virus were to be introduced to a colony of bats clos e to a village with a high rate of human bites. The potential force of infection could be then used to anticipate the size of a rabies outbr eak in control programs. We present an estimator of potential incidenc e, adapted from models for malaria. To obtain some of the parameters f or the equation, a cross-sectional survey was conducted in Mina Nova, a village of gold prospectors in the Amazonian region of Brazil with h igh rates of bates biting humans. Bats were captured near dwellings an d sent to The Rabies Diagnostic Laboratory at the Center for Control o f Zoonoses (Sao Paulo, Brazil) to be examined. To estimate the force o f infection, a hypothetical rabies outbreak among bats was simulated u sing the actual data obtained in the study area. Of 129 people intervi ewed, 23.33% had been attacked by a vampire bat during the year prior to the study, with an average of 2.8 bites per attacked person. Males (29.41%) were attacked more often than females (11.36%); also, adults (29.35%) were attacked more often than children (8.33%). None of the 1 2 bats captured in Mina Nova tested positive for rabies, but the force of infection for a hypothetical outbreak was estimated to be 0.0096 p er person per year. This risk represents 0.96 cases per 100 area resid ents, giving an incidence of 1.54 cases of bat-transimtted buman rabie s per year in the village of Mina Nova (160 inhabitants). The estimate d risk is comparable with what has been observed in similar Brazilian villages.