Assessing familial aggregation of paratuberculosis in beef cattle of unknown pedigree

Pathogenesis of paratuberculosis

Paratuberculosis in ruminants is characterized by oral ingestion of Mycobacterium avium subsp. paratuberculosis (MAP), followed by a long incubation period during which time MAP is able to survive within the host’s macrophages. Initially the infection is held in check by the host’s cell-mediated immune response, but gradually the host loses control of the infection. The infection incites a granulomatous inflammatory response in intestinal tissue and mesenteric lymph nodes, resulting in protein-losing enteropathy, malabsorption, diarrhea, weight loss, and edema.

Familial and herd-level associations with paratuberculosis enzyme-linked immunosorbent assay status in beef cattle

A cross-sectional study was performed to determine the odds of having a positive paratuberculosis ELISA result if the dam was ELISA positive in Texas beef cattle, adjusted for individual and herd-level risk factors for seropositivity. Texas beef cattle (n = 2,621) were tested for paratuberculosis by using a commercial ELISA and microbiologic culture of feces for Mycobacterium avium subsp. paratuberculosis (MAP). Pedigree data were collected to identify dam-and sire-offspring pairs. Bayesian mixed-effects logistic regression was used to estimate the odds of seropositivity associated with age, dam ELISA status, sire ELISA status, herd size, herd history of clinical paratuberculosis, within-herd seroprevalence, within-herd fecal MAP prevalence, and within-herd fecal non-MAP Mycobacterium spp. prevalence. Herd of residence was included as a random effect to account for the correlation of observations within the same herd. Statistically probable associations were observed between ELISA status and herd fecal MAP prevalence [OR (odds ratio) 1.28 per 1% increase; P < 0.001] and herd seroprevalence (OR 1.21 per 1% increase; P < 0.001). The association with dam ELISA status was small (OR 1.35) and not highly probable (P = 0.69). Results indicate that use of dam ELISA status to make culling decisions in beef cattle may not improve the success of paratuberculosis control programs. Alternative strategies may be more effective for reducing the odds of seropositivity.