Use of Released Pigs as Sentinels for Mycobacterium Bovis

Abstract

Identifying the presence of bovine tuberculosis (TB; Mycobacterium bovis) in wildlife is crucial in guiding management aimed at eradicating the disease from New Zealand. Unfortunately, surveys of the principal wildlife host, the introduced brushtail possum (Trichosurus vulpecula), require large samples (Ͼ95% of the population) before they can provide reasonable confidence that the disease is absent. In this study, we tested the feasibility of using a more wideranging species, feral pig (Sus scrofa), as an alternative sentinel capable of indicating TB presence. In January 2000, 17 pigs in four groups were released into a forested area with a low density of possums in which TB was known to be present. The pigs were radiotracked at 2 wk intervals from February to October 2000, and some of them were killed and necropsied at various intervals after release. Of the 15 pigs successfully recovered and necropsied, one killed 2 mo after release had no gross lesions typical of TB, and the only other pig killed at that time had greatly enlarged mandibular lymph nodes. The remainder were killed at longer intervals after release and all had gross lesions typical of TB. Mycobacterium bovis was isolated from all 15 pigs by mycobacterial culture. Home range sizes of pigs varied widely and increased with the length of time the pigs were in the forest, with minimum convex polygon range-size estimates averaging 10.7 km 2 (range 4.7-20.3 km 2 ) for the pigs killed after 6 mo. A 6 km radius around the kill site of each pig would have encompassed 95% of all of their previous locations at which they could have become infected. However, one pig shifted 35 km, highlighting the main limitation of using unmarked feral pigs as sentinels. This trial indicates use of resident and/or released free-ranging pigs is a feasible alternative to direct prevalence surveys of possums for detecting TB presence.

Epidemiology of Mycobacterium Bovis Infection in Wild Boar (Sus Scrofa) From Portugal

“…Feral pigs were considered spillover hosts in New Zealand and Australia (Corner, 2006). Moreover, wild suids were used in New Zealand as sentinels for M. bovis presence in the environment (Nugent et al, 2002). With respect to the wild boar, its contribution to the epidemiology of tuberculosis in Europe seems variable; it is considered a spillover host in Italy (Serraino et al, 1999) but a maintenance host in Spain (Naranjo et al, 2008).…”

Serologic Tests for Detecting Antibodies against Mycobacterium Bovis and Mycobacterium Avium Subspecies Paratuberculosis in Eurasian Wild Boar (Sus Scrofa Scrofa)

“…15 Due to their rooting habits, omnivorous diet, ability to cross barriers and contact with a broad range of wild and domestic animals, 7,16 and susceptibility to mycobacterial infections, 19 wild boar or their feral pig relatives have been used as disease sentinels. 22 In southwestern Europe, bovine tuberculosis (bTB), caused by Mycobacterium bovis, and paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis infection, are diseases of concern in wild and domestic ruminants.…”

Intraspecific Transmission of Mycobacterium Bovis Among Penned Feral Pigs in New Zealand

“…Evidence from Spain implicates a respiratory route of infection, although it is unclear whether that is more important than infection by ingestion (Parra et al, 2003;Vicente et al, 2006). We therefore measured transmission rates between live pigs, by keeping uninfected susceptible pigs (''sentinels'' [Nugent et al, 2002]) penned with infected ''source'' pigs in natural habitat in two trials in 2003 and 2005. We also released sentinel pigs into the wild, into similar habitat, on both occasions, and we used data from a separate study of Tb in locally resident pigs to determine what proportion of infection in the wild population might be attributable to intraspecific transmission.…”