Detection of Mycobacterium avium ssp. paratuberculosis (MAP) and assessment of widespread infection and pathology in small ruminants with Johne's Disease

Johne’s Disease is a prevalent infection in ruminants caused by Mycobacterium avium subspecies paratuberculosis that has far-reaching impacts on production, largely due to the chronic progressive nature of infection evading detection, the likelihood of environmental contamination with bacteria, and a lack of viable treatment options once diagnosed. While MAP is well studied in dairy cattle, the extent, and mechanisms in small ruminants, especially goats, are less well-known, including evaluation of pregnancy effects on the disease severity. The aim of this study was to establish the extent of infection and disease in goats endemically infected with MAP and evaluate pregnant and non-pregnant goats that are naturally infected. Thirty-eight ELISA-positive goats of 1,058 initially screened were culled and necropsied. Blood and fresh feces were collected prior to euthanasia. Tissues were collected for Real-Time qPCR and histopathology. MAP DNA was detected by qPCR in 36 of 38 goats (94.7%), with detection extending to several tissues outside of the ileum and jejunum. Granulomatous lesions were found in atypical tissues along with the intestinal tract, such as the liver. Correlating pre-mortem clinical disease was only noted in 5 of 38 goats. Results indicated that MAP is detected in tissues beyond the ileum and jejunum, such as the draining lymph nodes, gallbladder, and liver during infection. Despite marked histopathologic changes, especially in the intestinal tract, most infected goats did not have correlating clinical disease. Pregnant goats had significantly more granulomatous inflammation consistent with Johne’s Disease compared to non-pregnant animals that tested positive at the same time. Bacterial DNA was detected from fetal tissues collected from 6 of 10 pregnant goats. The fetal tissues most frequently tested positive for MAP bacterial DNA were the thymus and tonsils. These findings offer insight into the effects of Johne’s Disease within pregnancy and additionally support exposure in utero within MAP ELISA-positive goats. A better understanding of disease mechanisms offers the potential for earlier diagnostic detection or improved control measures that may better improve disease outcomes for these animals and offer insight to develop earlier detection options.