Reduced spillover transmission ofMycobacterium bovisto feral pigs (Sus scofa) following population control of brushtail possums (Trichosurus vulpecula)

Abstract

In New Zealand, bovine tuberculosis (bTB) is present in domestic cattle and deer herds primarily as the result of on-going disease transmission from the primary wildlife host, the brushtail possum (Trichosurus vulpecula). However, bTB is also present in other introduced free-ranging mammalian species. Between 1996 and 2007, we conducted a series of studies to determine whether poison control of possum populations would have any effect on the prevalence of Mycobacterium bovis infection in sympatric feral pigs (Sus scrofa). We compared trends in the prevalence of bTB infection in feral pigs in six study areas: possum numbers were reduced in three areas, but not in the other three, effectively providing a thrice-replicated before-after-control-intervention design. Before possum control, the overall prevalence of culture-confirmed M. bovis infection in feral pigs was 16.7-94.4%, depending on area. Infection prevalence varied little between genders but did vary with age, increasing during the first 2-3 years of life but then declining in older pigs. In the areas in which possum control was applied, M. bovis prevalence in feral pigs fell to near zero within 2-3 years, provided control was applied successfully at the whole-landscape scale. In contrast, prevalence changed much less or not at all in the areas with no possum control. We conclude that feral pigs in New Zealand acquire M. bovis infection mainly by inter-species transmission from possums, but then rarely pass the disease on to other pigs and are end hosts. This is in contrast to the purported role of pigs as bTB maintenance hosts in other countries, and we suggest the difference in host status may reflect differences in the relative importance of the oral route of infection in different environments. Despite harbouring M. bovis infection for a number of years, pigs in New Zealand do not sustain bTB independently, but are good sentinels for disease prevalence in possum populations.

Field Trial of an Aerially-Distributed Tuberculosis Vaccine in a Low-Density Wildlife Population of Brushtail Possums (Trichosurus vulpecula)

“…A detailed wildlife disease survey conducted in the study area 4 years prior to the present study recorded a mean prevalence of gross TB lesions among resident possums of 2.7% (n = 450 [28]). Prevalence of disease among wild pigs in the area, as a result of spillover infection from possums, often exceeds 60% [33,34]. …”

“…Captured possums were euthanized and necropsied for TB following the procedure in the supplementary material (S1 File). At the same time, a sample of feral pigs (which are highly sensitive ‘sentinel host’ indicators of TB presence in possums [37]) was obtained from the study area by shooting, and these were also necropsied for TB diagnosis [32,33]. …”

Zoonotic Aspects of Tuberculosis: Disease of the past or re-emerging zoonosis?

“…In the widespread absence of control schemes for M. bovis, an increasing small scale pig production may be accompanied by increased transmission of zoonoses at a highly diffuse animal/human interface where pigs share their habitat with humans (Muwonge et al 2012). Likewise, the presence of a wildlife reservoir for M. bovis can effectively drive pathogen transmission to domestic or feral pigs, as shown for wild boar in Spain and possum in New Zealand (Nugent et al 2012;Parra et al 2003).…”

Evaluating the tuberculosis hazard posed to cattle from wildlife across Europe

“…Infected wild species may be able to infect cattle, helping the disease to persist within the cattle population (Nugent, 2011). Sympatric infected wild species may also infect one another, as is the case for feral pigs acquiring TB from possums in New Zealand (Trichosurus vulpecula) (Nugent et al, 2012). The role of different potential host species may vary geographically with habitat, ecology, land use and consequently, behaviour (Gortázar et al, 2011).…”