We conducted cross-sectional studies in the New York City Watershed to ensure a valid estimate of the risk associated with Cryptosporidium infection in dairy herds. Our aims were to obtain species-specific estimates of the prevalence of Cryptosporidium in dairy cattle and to investigate seasonal variations in prevalence. We validated our empirical estimates using a Bayesian approach. Samples were collected on 32 study farms, once in each of 3 different seasons using an age-stratified sampling design. The overall prevalence of Cryptosporidium parvum-like species and Cryptosporidium andersoni among the 1911 animals tested by the flotation method was 5% and 1%, respectively. Among preweaned calves (<65 days of age), the prevalence of C. parvum-like species was twice as high in the summer (26%) compared with the winter (11%). Herd prevalence showed the same seasonal trend. Preweaned calves were also shedding C. andersoni at an average intensity of 20 oocysts per gram of feces. We did not detect C. parvum-like oocysts in cattle older than 5 months. Sequencing of a portion of the 18s rRNA gene revealed that in the summer, 42% of the C. parvum-like oocysts shed by preweaned calves were zoonotic, compared with >74% during the rest of the year. Both empirical and stochastic methods revealed a summer peak in the prevalence of C. parvum-like oocysts in preweaned calves. Determining whether seasonal variation in the prevalence and proportion of Cryptosporidium species shed by preweaned calves is due to management practices or ecological factors will have important implications for effective control of this parasite.
A study was performed to assess the validity of the BAX automated polymerase chain reaction system (DuPont Nutrition & Health, Wilmington, Delaware) to detect the shedding of Salmonella species in bovine fecal samples. A total of 133 bovine fecal samples that were submitted to the Cornell University Animal Health Diagnostic Laboratory for Salmonella culture were also tested in the BAX system with a modified version of the manufacturer’s enrichment protocol. Using culture as the gold standard test, the BAX system was found to have a sensitivity of 85.7% and a specificity of 90.5%. There was excellent agreement (κ = 0.71, standard error = 0.072) and no significant differences between the 2 methods (McNemar χ2 = 0.180).
Salmonella spp. is one of the most important food-and waterborne pathogens implicated in human and animal disease. A repeat cross-sectional study was performed to assess the occurrence of Salmonella in dairy herds in a watershed and determine the factors that play a role in the likelihood of perpetuation of this organism among animals on these farms. A convenience sample of herds in the Delaware County watershed was selected based on farmers' willingness to participate. Fecal samples were collected per rectum from a representative sample of cattle in these herds and tested for the presence of Salmonella using a combination of culturing and molecular detection methods. The significance of association between the putative risk factors and the likelihood of Salmonella spp. was evaluated using the logistic regression analysis. A total of 34 dairy farms were enrolled in the study and 1987 samples were collected coinciding with seasonal variation. Salmonella spp. was detected in 44% (15/34) of the herds in the study population (i.e., from at least one animal in these herds). However, only a small fraction of the entire sampling population (1.7%) was found to be shedding Salmonella. Risk factors that were found to be associated with the presence of the pathogen on the farm in the final multivariable model included concrete flooring for calves, prevention of calf access to the dam, and the lack of a designated calving pen. Two serovars, Salmonella enterica serovar Infantis and Salmonella enterica serovar Oranienburg, were identified among the isolates recovered in this study. Our study demonstrated that there was a potential risk of watershed degradation from Salmonella associated with cattle.
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