Mycobacterium bovis infection in wildlife in New Zealand

Bovine tuberculosis (Tb) is the most important disease of livestock in New Zealand, and it puts at risk the nation's trade in dairy, beef and venison products. Elimination of the disease from livestock is based on a herd test and slaughter programme and carcass inspection at abbatoirs. However, this programme has not been as successful as expected, because the disease also occurs in wild or feral animals acting as vectors of the disease to livestock. Brushtail possums are the major wildlife vector and self-sustaining maintenance host of Tb, and play a role analogous to that of the badger in Great Britain. In contrast, some deer species and ferrets may act as vectors of the disease, but their role in transmitting Tb to livestock is unclear. Hedgehogs, pigs, cats, sheep and goats are now considered to be amplifier hosts, and spread the disease to other species only when inspected or their carcasses scavenged. In the absence of infected possum populations, these species do not appear to be capable of maintaining the infection in their own populations and are not thought to be involved in the maintenance of Tb in livestock. Tuberculosis has also been recorded from stoats, hares, and a rabbit, but the level of infection recorded in their populations indicates these species are unlikely to spread the disease to other animals and hence are not involved in the transmission of Tb to livestock.