Mechanical transport and transmission of Cryptosporidium parvum oocysts bywild filth flies

Over the course of six months wild filth Hies were collected from traps lef t for 7-10 days in a barn with or without a calf shedding Cryptosporidium p arvum Genotype 2, oocysts in diarrheic feces. The oocysts of C. parvum tran sported on the flies' exoskeletons and eluted from their droplets left on v isited surfaces es were infectious for mice. The mean number of oocysts car ried by a fly varied from 4 to 131, and the total oocyst number per collect ion varied from 56 to approximately 4.56 X 10(3). Fly abundance and intensi ty of mechanical transmission of infectious C. parvum oocysts were positive ly correlated. and both increased significantly when an infected calf was i n the barn. Molecular data showed that the oocysts shed by infected calves were carried by flies for at least 3 weeks. Filth flies can acquire infecti ous: C. parvum oocysts from unsanitary sites, deposit them on visited surfa ces, and therefore may be involved in human or animal cryptosporidiosis.