Immune responses to subclinical paratuberculosis in naturally infected young goats

We have tested for cell-mediated (CMI) and humoral immune (HMI) responses to Mycobacterium aviurn subsp. paratuberculosis (MAP) in naturally exposed young goats. Ten goat kids were born into a herd with a three-year history of paratuberculosis. At the age of five months, the kids were admitted to the Clinic for Swine, Small Ruminants and Forensic Medicine, University of Veterinary Medicine Hannover, Foundation, Germany and kept for one month with a goat with clinical Johne's disease. Blood samples were taken every month and tested for CMI against paratuberculosis via Gamma interferon testing and for HMI using an ELISA antibody test. Faecal samples were collected every month and used to test for MAP shedding using real-time PCR. At the age of 17 months, all ten goats were euthanized and submitted to necropsy to confirm paratuberculosis by macroscopical and histological findings, by immunohistochemistry and via bacterial cultures. Three of the ten goats developed HMI responses and six of them developed CMI responses. None of the goats was found to shed MAP in faeces during the experimental period. MAP infection was confirmed by post mortem examination in two of the three goats with HMI and in five of the six goats with CMI responses. The CMI response was detectable earlier than the HMI response. However, the reactions were not continuous and varied considerably within the individual goats. Repeated sampling and tests for both CMI and HMI are recommended for the reliable diagnosis of MAP infections in young goats.