Susceptibility and Resistance to Trypanosome Infection

In this series of investigations, we set out to examine the relation of various factors to the resistance or susceptibility of experimental animals to infection with a protozoan--the trypanosome. In previous communications (1, 2) we have reported data bearing on the acquired susceptibility and resistance resulting from the interaction of the parasite and host. In this paper we present our observations on the effect of external environmental factors, as for example, light and moisture, on the susceptibility of the host to the infection and on the severity of the disease imposed. Recent experimental epidemiologic studies by Webster (3) indicate that the virulence of a given strain of pathogenic organisms is constant. In that case variations in malignancy and host susceptibility can only be accounted for by assuming that the resistance of the host is variable, and is modified from time to time by a variety of conditions. Since many diseases have a seasonal character, this variation in resistance must have a seasonal rhythm.