Longitudinal study of Mycobacterium avium ssp. Paratuberculosis fecal shedding patterns and concurrent serological patterns in naturally infected dairy cattle

摘要

Mycobacterium avium ssp. paratuberculosis (MAP) isthe etiological agent of paratuberculosis, a disease thataffects ruminants worldwide. Despite global interest inthe control of this disease, gaps exist in our knowledgeof fecal shedding patterns and concurrent serologicalpatterns. This longitudinal study in dairy cattle herdswith high MAP seroprevalence in France aimed at accuratelydescribing fecal shedding patterns over 1 year;relating those shedding patterns to individual animalcharacteristics (age, breed, parity); and exploring theassociation between fecal shedding patterns and serologicalpatterns. To describe temporal fecal sheddingpatterns and continuity of shedding, along with thestandard quantitative PCR (qPCR) threshold cycle weused a cutoff value that related to low or nonculturablefecal shedding. We also defined a threshold cycleindicative of shedding in high quantities to describeinfection progression patterns. Twenty-one herds completedthe study, and 782 cows were tested 4 times each.We obtained 4 sets of paired fecal qPCR and serumELISA results from 757 cows. Although we targetedhighly likely infectious animals, we found a large diversityof shedding patterns, as well as high variabilitybetween herds in the proportion of animals showing agiven pattern. The fecal qPCR results of almost 20%of the final study sample were positioned at least oncein the range that indicated low or nonculturable fecalshedding (between the adjusted and the standard cutoffvalue). Although these animals would typically beclassified as non-shedders, they could be important toinfection dynamics on the farm. Animals that shed atleast twice consecutively and animals that shed in highquantities rarely reverted to negativity. Repeated fecalqPCR can be used to detect temporal fecal sheddingtraits, and the decision to cull an animal could practicallybe based on temporal, semiquantitative results.Overall, we found a mismatch between fecal sheddingand ELISA seropositivity (637 animals were ELISAnegative4 times, but only 13% of those animals wereqPCR-negative 4 times). We found that having morethan 2 ELISA-positive samples was strongly related topersistent and continuous shedding. We suggest thatalthough serological testing is much less sensitive thanqPCR, it can also be used, particularly over the courseof multiple testing events, to identify animals that aremost likely to contribute to the contamination of thefarm environment.