House flies (Musca domestica) as transport hosts of Cryptosporidium parvum

Refuse and promiscuous-landing synanthropic filth flies, such as house flie s (Musca domestica), are recognized as transport hosts for a variety of pro tozoan and metazoan parasites in addition to viral and bacterial pathogens of public health importance. Exposure of adult M. domestica to 20 mi of bov ine diarrheal feces containing Cryptosporidium parvum oocysts (2.0 x 10(5) oocysts/ml) resulted in intense deposition of the oocysts through fly feces on the surfaces visited by the flies (mean = 108 oocysts/cm(2)). Cryptospo ridium parvum oocysts were detected by immunofluorescent antibodies on the exoskeleton of adult flies and in their digestive tracts. An average of 267 , 131, 32, 19, and 14 oocysts per adult fly were eluted from its exoskeleto n on days 3, 5, 7, 9, and 11 after they emerged, respectively. Approximatel y 320 C. parvum oocysts per pupa were eluted from the external surface of t he pupae derived from maggots that breed in a substrate contaminated with t he bovine feces; the oocysts were numerous on maggots (approximately 150 oo cysts/maggot). Adult and larval stages of house flies breeding or having ac cess to C. parvum-contaminated substrate will mechanically carry the oocyst s in their digestive tracts and on their external surfaces.