M01024: Survey for trichinella in wild foxes and boar

Study Duration: October 2002 to August 2003

Contractor: Central Science Laboratory

A large body of information exists to suggest that at present the risk of contracting trichinosis from UK pigs appears slight. In a recent survey of 587 fox carcasses collected across Britain, all were negative for trichinella. In this study a further 600 foxes will be tested and if negative would mean that with 95% confidence the prevalence of trichinella in foxes in GB is below 0.3%. This would be significantly lower than any European country where trichinella is known to be endemic in wildlife. Also there is a small breeding population in the UK of wild boar, that have escaped over the years from wild boar farms, as these are a reservoir for the disease in other countries a number of them will be tested for trichinella. If the results are all negative this would permit Britain to approach the EU about declaring the UK a trichinella-free area.

This project is being jointly funded with Defra.

EU regulation requires post-mortem testing of all food animals that are susceptible to trichinella (i.e. pigs, horses). In the UK, this is a significant regulatory burden as no positive results have been found in the last 30 years. Regions can be declared of negligible trichinella risk provided certain conditions are met; one of which is a risk-based surveillance programme of susceptible wildlife.

This research was commissioned to look for trichinella infection in foxes and wild boar across Great Britain. These animals are used as indicator species for infection because they eat other wildlife such as rodents and also scavenge waste food that may contain trichinella. This project was extended to allow 1048 foxes to be tested instead of 600 foxes originally proposed.

• In the initial part of this study, methodology was developed to enable Trichinella to be detected in fox carcasses. This method, a modification of the procedure used to test for trichinella in pigs and horses, provided a trichinae recovery rate of 83-84% for artificially infected fox muscle samples. Assuming these recovery rates apply to all contaminated samples, regardless of the level of contamination, then for tissue samples infected with 1 trichinae larvae per 10 g of foreleg muscle the test would find 83% positive, 97% positive for samples infected with 2 trichinae larvae per 10 g, and 99% positive for samples infected with 3 trichinae larvae per 10 g.
• During this survey, 1048 foxes were collected. All muscle samples were negative for trichinella. It was not possible to sample wild boar due to local difficulties.
• If the 587 fox digests from an earlier survey are included (all were negative) we can be confident that the national prevalence of trichinella is 0.19% or less.
  The results from this survey will be used for applications to exempt the post-mortem testing of all fattening pigs and to provide risk-based information on the risk of Trichinella infection in UK pigs.

Publications:
I.A. Zimmer, S.J. Hunter, C.P. Morgan, K.R. Hunt, G.C. Smith, M. Howell and M.A. Taylor (2007). Detection and Surveillance for Animal Trichinellosis in GB. Veterinary Parasitology. In Press

The final report is available from the Agency’s Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk