The periodicity of microfilariae XI. The effect of body temperature and other stimuli upon the cycles of Wuchereria bancrofti, Brugia malayi, B. ceylonensis and Dirofilaria repens

Abstract

Investigations were made concerning a possible relationship between the 24-hour cycle of body temperature and that of the migrations of microfilariae. Moderate elevation of the body temperature by night or by day did not alter the microfilaria count of Wuchereria bancrofti or Brugia malayi in man, and had only a slight (depressant) action on the count of B. ceylonensis in dogs. Depression of the body temperature by day did not raise the microfilaria count of W. bancrofti, although it caused a slight rise in the count of B. ceylonensis. Apparently there is no correlation between changes in body temperature and the 24-hour cycle of the microfilariae of W. bancrofti or B. malayi, and only a slight correlation with that of B. ceylonensis. Drugs which depress the cerebrum, e.g. butobarbitone, may have a slight tendency to raise the microfilaria count, and drugs which stimulate it e.g. Methedrine, have a tendency to depress the count, but the effects are limited and inconstant. Previous findings that the administration of oxygen reduces the night-time microfilaria count of W. bancrofti and of B. malayi were confirmed. The level to which the count was reduced, was approximately the same during the different stages of the night; but subsequent recovery of the count was less after 03·00 than before it. The microfilaria count of W. bancrofti was often slightly raised after electro-convulsive treatment (i.e. slight liberation of microfilariae from the lungs occurred). Microfilariae of B. ceylonensis and those of Dirofilaria repens responded differently to the same stimuli (administration of oxygen, and rebreathing into a bag) although both were in the same host (dog). This confirms previous conclusions that the effective stimuli which control the 24-hour cycle of microfilariae are probably different with different species of worms. The periodicity of the microfilariae of W. bancrofti and B. malayi may depend on changes of size in the difference of oxygen tension between venous and arterial blood during day and night. This new hypothesis can be extended with slight modifications to explain most (but not all) of the known facts about the periodicity of other species of microfilariae as well.