The influence of physical factors on the survival and infectivity of miracidia of Schistosoma manosni and S. haematobium I. Effect of temperature and ultra-violet light.

The influence of temperature and ultra-violet radiation on the degree of activity, survival and infectivity of schistosome miracidia is profound. Miracidia of Schistosoma mansoni and S. haematobium were affect eaually. Only miracidia classified as "active" or "slow" were capable of penetration, a capacity they retained for about 17 hours at 19 degrees C. Miracidia that were "lethargic" as a result of low temperature, old age or ultra-violet radiation lost their infective capacity. The conclusion, however, is that neither the temperatures encountered in the field nor the solar ultra-violet radiation penetrating turbid waters are likely to be harmful to miracidia and thus have no effect on the level of transmission.