Common brushtail possum in New Zealand

The common brushtail possum (Trichosurus vulpecula) is a major agricultural and conservation pest in New Zealand. In Māori it is called paihamu.

European settlers aiming to establish a wild source for food and fibre and fur pelts for clothing introduced the common brushtail possum from Australia to New Zealand in the 1850s; by the 1980s the peak population had reached an estimated 60-70 million. Through control measures, by 2009 the New Zealand population had been reduced to an estimated 30 million.

Possums are vectors of bovine tuberculosis (mycobacterium bovis), which is a major threat to the dairy, beef, and deer farming industries. The disease is endemic in possums across about 38% of New Zealand (known as ‘vector risk areas’). In these areas, nearly 70% of new herd infections can be traced back to possums or ferrets. The Biosecurity Act 1993, which established a national pest management strategy, is the legislation behind control of the disease in New Zealand. The Animal Health Board operates a nationwide programme of cattle testing and possum control with the goal of eradicating mycobacterium bovis from wild vector species across 2.5 million hectares – or one quarter – of New Zealand’s at-risk areas by 2026 and, eventually, eradicating the disease entirely.

The TB-free New Zealand programme is regarded as "world-leading". It has successfully reduced cattle and deer herd infection rates from more than 1700 in 1994 to fewer than 100 herds in July 2011. Much of this success can be attributed to sustained possum control reducing cross-infection and breaking the disease cycle. For example, at Hohotaka, in New Zealand's central North Island, control work from 1988 to 1994 achieved a sustained mean reduction of 87.5% in the density of Tb‐infected possums. As expected, annual Tb incidence in local cattle herds consequently declined by a similar amount (83.4%).

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