Infection of the lymphatic system by Wuchereria bancrofti microfilaria is the most common cause of elephantiasis, a disease that affects over 100 million people. The nightly release of microfilaria into the circulation coincides with the feeding activity of its mosquito vector, a synchronization that is presumably an evolutionary adaptation favoring survival and transmission of the parasite. During the daytime hours, the microfilaria are thought to be sequestered in the lungs, and because they are not exposed to the solar light/dark cycle, there must be some other cue that entrains their nightly release into the periphery. I hypothesize that the host's secretion of melatonin synchronizes the nocturnal release of the microfilaria. It follows that exogenous melatonin administration during the day would also trigger release of microfilaria in the blood and could be used as a provocative diagnostic test for filariasis.
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