Beschreibung
Paratuberculosis is an increasingly important infectious disease of both animal health and economic relevance in small ruminants. To promote animal health and inhibit the further spread of paratuberculosis within affected herds as well as in the goat population in general, the prevention of new infections is crucial. In this thesis, multiple potential vectors were examined to assess the occurrence of Mycobacterium avium subsp. paratuberculosis (MAP), aiming to enhance the understanding of the transmission routes of paratuberculosis in dairy goat herds.
To evaluate the potential risk posed by the barn environment and the suckling on does, two studies were conducted within a paratuberculosis-infected dairy goat herd. In Study 1, the prevalence of MAP in the barn was determined by culture and real-time quantitative polymerase chain reaction (qPCR) analysis of 256 environmental samples, including bedding, dust, water, and feed. The influence of spatial and temporal factors on MAP detection was examined separately for each detection method using logistic regression. Additionally, the kappa coefficient and Spearman's rank correlation coefficient were calculated to assess the concordance between the results obtained by the two detection methods. In Study 2, which aimed to determine the MAP load in colostrum and on the udder skin, 110 individual colostrum samples, 14 bulk colostrum samples and 49 udder skin swabs were collected from the same herd and analyzed. As no established methods were available for the detection of MAP in these sample materials, these methods were developed and evaluated in terms of their minimum detection limit prior to the examination.
MAP could be cultured from 28 bedding and one dust sample, while molecular biological detection was possible in all matrices. Cultural detection of the pathogen was linked to the presence of MAP shedders in the respective barn area. Elevated pathogen load was observed in areas with high animal traffic, in particular the milking parlor, and the kidding area. The percentage of MAP shedders in the herd, which decreased during the study, had no significant effect on the detection rate. In contrast, significantly lower detection rates were observed during grazing seasons compared to seasons without pasturing. Despite the confirmed contamination of the environment, the udder skin revealed only a marginal MAP contamination. Specifically, MAP was detected in three udder skin swabs by qPCR, but cultivation was not possible. Besides, MAP was not detected by molecular biological analysis in either individual or bulk colostrum.
Based on these findings, it can be concluded that the kidding area poses a site with a substantial risk for MAP transmission due to the encounter of viable pathogen and susceptible youngstock. In contrast, the risk of pathogen transmission by colostrum ingestion appears to be of subordinate importance in the infection dynamics of the goat herd studied. However, potential transmission during the suckling act remains possible. The fastest possible separation of the kids from the adult animals in a sanitary and, if possible, MAP-free environment is recommended in order to minimize the uptake of the pathogen from the kidding environment and by preventing suckling. Removal of all identified MAP shedders from the herd is another important measure, as even a few of these animals can lead to a detectable contamination of the barn environment.
The recommendations derived from the studies presented in this thesis should be considered in the on-farm animal health management of dairy goat herds when implementing a control program to successfully interrupt the chains of infection of paratuberculosis.
