Three surveillance systems for describing the spatial distribution of Johne's disease seropositivity in Texas cattle
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Johne’s disease is a chronic and debilitating disease of cattle caused by infection with Mycobacterium avium subsp. paratuberculosis (Mptb). This disease affects both dairy and beef cattle, though it is more commonly recognized in dairy cattle. Mptb is able to persist in the environment of cattle for extended periods of time; therefore the distribution of the disease depends on the presence of infected animals and environmental conditions. Three surveillance systems were used to describe the spatial distribution of Johne’s disease seropositivity in Texas cattle. These three systems were hypothesized to describe different spatial patterns. These systems involved sampling, 1) herds throughout Texas, 2) market cattle from four markets each month (one each from northern, southern, eastern, and western regions of Texas) and 3) sick animals submitted by veterinarians throughout Texas. Samples were tested for Johne’s disease at the Texas Veterinary Medical Diagnostic Laboratory using serum ELISA. Spatial distributions were estimated by kriging the sample-to-positive control ratios (S/P). Sera were evaluated for Mptb antibodies from 2358 cattle with 1084 animals in system 1, 1200 from system 2 and 74 from system 3. Total number of positive ELISA results was 51, with 25, 19 and 7 positve ELISA results for systems one, two and three, respectively. Results showed an overall prevalence of 2.16%, and prevalence’s of 2.31%, 1.58% and 9.46% for systems one, two and three, respectively. Differences in the spatial distribution of Johne’s disease seropositvity, based on the three surveillance systems, confirmed our hypothesis that estimation of disease distribution is dependant upon the source of surveillance samples.
Pearce, Brielle H. (2007). Three surveillance systems for describing the spatial distribution of Johne's disease seropositivity in Texas cattle. Master's thesis, Texas A&M University. Available electronically from