Epidemiology and control of Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula), the primary wildlife host of bovine tuberculosis in New Zealand

Figures & data

Figure 1. Relationship between possum abundance, represented by mean (and 95% CI) modified trap catch index (TCI), and mean prevalence of tuberculosis (TB) in possums from five study areas (>5,000 ha) in the North Island of New Zealand in the late 1990s. The modified TCI is likely to be substantially lower than the standard residual trap catch index measure of possum relative abundance, because far longer than normal trap lines were used and multi-kill cyanide baits were additionally placed between traps. Adapted from Nugent (2005).

Table 1. Area surveyed, number of possums necropsied, sampling intensity (possums/ha), possums with tuberculosis (TB)-like lesions and lesions that were culture positive for Mycobacterium bovis, and the percentage prevalence of confirmed TB lesions (with upper 99%CI), in operational surveys conducted by TB free NZ during 2007–2012, in areas with different intensities of possum control (G Knowles, unpublished data).

Year	Area (ha)	Possums necropsied	Sampling intensity^a	Possums with lesions	Culture-positive lesions	Prevalence of TB lesions
Long-sustained intensive possum control^b
2007/08	330,909	6,943	0.042	1	0	0 (0.07)
2008/09	357,619	9,671	0.057	5	0	0 (0.05)
2009/10	702,216	24,937	0.052	9	0	0 (0.02)
2010/11	644,534	13,989	0.035	8	0	0 (0.03)
2011/12	749,170	23,045	0.055	9	0	0 (0.02)
Total^c	2,784,448	78,585	0.050	32	0	0 (0.01)
Less intensive or shorter-term possum control^d
2007/08	100,887	3,467	0.052	5	0	0 (0.13)
2008/09	100,705	7,336	0.077	0	0	0 (0.06)
2009/10	124,115	3,672	0.039	1	0	0 (0.12)
2010/11	182,586	4,936	0.036	5	0	0 (0.09)
2011/12	75,059	6,004	0.048	8	4	0.07 (0.19)
Total	583,352	25,415	0.048	19	4	0.02 (0.05)
Overall Total	3,367,800	104,000	0.050	51	4	0.00 (0.01)

^aAcross area averages.

^bAreas in which possums have been intensively managed for long enough for them to be considered subjectively as being close to TB eradication.

^cThe area totals include substantial duplication of areas between years as a result of re-surveys.

^dAll areas other than those in which possums have been intensively managed for a long time.

*Nugent G. The role of wild deer in the epidemiology and management of bovine tuberculosis in New Zealand. PhD Thesis, Lincoln University, Lincoln, NZ, 2005

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