Assessing and Addressing the Public Health Concerns of Mycobacterium avium subspecies paratuberculosis Infection in Cattle and Sheep

Abstract

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease (JD) resulting in significant economic losses to the livestock industries. MAP has also been shown to be associated with Crohn’s disease in humans. This thesis aimed to understand veterinarians’ perceptions regarding this association; to develop methods for detection of MAP in powdered infant formula (PIF) and tissue samples to prevent exposure to humans and to improve the current abattoir surveillance program; and to investigate the efficacy of disinfectants against MAP. The overall purpose of the research was to increase the preparedness of the livestock industries for addressing public health concerns about MAP infection. A survey was conducted among Australian livestock veterinarians. Although only about a third of the respondents considered MAP as a potential zoonotic agent, more than two-thirds agreed with the adoption of the precautionary principle against JD. The high throughput Johne’s direct qPCR test was adapted to develop novel qPCR tests for detecting MAP in PIF and tissue samples. The milk qPCR test detected MAP DNA in 4 of 122 PIF samples. The tissue qPCR test successfully confirmed MAP infection in all of the animals showing clinical signs (25/25) and almost all showing gross lesions on post-mortem (37/38) and was found to be better than culture and histopathology when tests result of both intestine and mesenteric lymph nodes were used. It could be validated for use in abattoir surveillance. Almost all of the commonly used disinfectants were found to be bactericidal against MAP under laboratory conditions but in the presence of organic matter 4% phenol was only effective against MAP suggesting that a review of decontamination protocols is required. The new knowledge and technology generated in this thesis would enable animal health authorities and the livestock industries in making informed decisions to control JD and improve their preparedness to tackle future challenges.