Unexpected results from large-scale cryptosporidiosis screening study in calves in Tanzania.

A study was undertaken to investigate Cryptosporidium infection in crossbreed dairy calves in two districts in Tanzania. A total of 943 fecal samples from 601 dairy calves were included in the study, with calves from both smallholder dairy farms and from large-scale and medium-scale dairy farms. The modified Ziehl-Neelsen (mZN) technique was used to examine 710 samples, and 13 of these were considered to be positive for Cryptosporidium. These 13 samples considered positive by mZN, along with the remaining 233 samples, were analysed by immunofluorescent antibody test (IFAT). Of these 246 samples examined by IFAT, 15 samples, 10 of which were considered positive by mZN, were also examined by the auramine phenol technique, and 5 samples, all of which were considered positive by mZN, were analysed by PCR. The results from the IFAT, auramine phenol and PCR analyses demonstrated that none of the samples contained Cryptosporidium oocysts, indicating that, cryptosporidiosis is currently not a problem in dairy calves in these regions of Tanzania. These unexpected results are discussed with respect to other reports on cryptosporidiosis in calves that suggest that this parasite is a serious calf disease globally, and particularly in relation to studies from Tanzania. We suggest that results from studies of cattle in Tanzania, in which mZN has been used as the sole analytical method, should be treated with caution.