Survey for Trichinella in wild foxes and boar FSA Project Code M01024

The only record of Trichinella spp. in wildlife in the UK is a single case from 1957. No other wildlife cases, or indigenously acquired human cases have been reported in the literature. This survey proposed to sample muscles from approximately 1100 wild foxes (600 during phase one and 500 during phase two) and sera from 20 wild boar for Trichinella spp. A digestion method for pooled samples of fox muscle was developed for use in this survey to enable the detection of Trichinella. This modified method gave a trichinae recovery rate of 83-84 % for spiked samples. Assuming this recovery rate is applied to all contaminated samples, regardless of the level of contamination, then the test sensitivity would be 83 % for all tissue samples with 1 trichinae per 10 g of foreleg muscle, 97 % for samples with 2 trichinae per 10 g, and 99 % for samples with 3 trichinae per 10 g. During this survey 1048 foxes were analysed for Trichinella. Due to local difficulties, it was not possible to live sample wild boar. All muscle samples were negative for Trichinella. If the 587 fox digests from an earlier survey are included (all were negative) the upper 95 percentile confidence limit for national prevalence of Trichinella is 0.19%. We suggest that further foxes are collected over two winters to obtain a total of 3000 negative results, then a sampling regime of about 400 foxes are analysed per annum