The natural infection of Hippelates pallipes loew with the spirochaetes of yaws

Treponema pertenue has not been demonstrated in Hippelates pallipes later than 48 hours after the infecting feed, nor has any evidence been found of invasion of the salivary glands or proboscis, or of cyclical development of the spirochaetes in the fly, up to 28 days after the initial meal on a yaws lesion. H. pallipes readily becomes infected with T. pertenue under natural conditions from lesions on any part of the body, though the fly feeds by preference on the perineum or on the lower extremities. Of 500 flies dissected in this portion of the study, 71 per cent. were found naturally infected. Three important factors appear to be necessary to the natural infection of flies seeking food at a yaws lesion (a) The scab should not be intact. (b) The surface of the lesion should be moist, or exuding serum, but not pus, freely through cracks in the scab. (c) T. pertenue must be present in abundance in the lesion itself.