Eight-year monitoring of Mycobacterium avium subsp. paratuberculosis (MAP) infection in a herd of farmed sika deer (Cervus nippon) following known pasture contamination.

Paratuberculosis (PTB), a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), results in considerable economic losses in deer farming globally. Transmission mainly occurs via the faecal-oral route when the environment is contaminated by subclinically infected deer shedding MAP. Field studies on the spread of disease in naturally infected sika deer do not exist. In this short communication, we report on the 8-year close monitoring of a small sika deer herd on year-round grazing to investigate MAP transmission after a subclinically MAP infected stag B33 had been inadvertently introduced. On a monthly basis, pooled faecal samples were collected from the pasture between January 2017 and 2019 and analysed for MAP detection. Full postmortems were conducted of all animals from the herd (n = 36) and the infection status was investigated by MAP liquid culture on faeces (n = 36), ileocaecal lymph nodes (n = 33) and ileum samples (n = 29). Further, samples of ileum, ileocaecal lymph nodes and relevant gross lesions were examined by histopathology (n = 36) and ELISA was conducted on serum samples (n = 29). MAP was consistently absent from pooled faecal samples collected from the pasture. Despite identifying the stag B33 as a moderate and low shedder on two occasions, none of the other deer got infected over the 8 years of monitoring. Culture and whole genome sequencing identified the MAP isolate as Type C (cattle) strain. This suggests that a subclinically infected sika deer may pose a lower risk for transmission of MAP than anticipated and raises the question of other possible sources to initiate disease in deer herds.