Transmissible Mink Encephalopathy (TME)

TME is rare, and has largely been confined to the United States of America, although incidents have also occurred in Canada, Finland, East Germany and Russia. The last outbreak was in the USA in 1985, after an outbreak free period of 22 years.

TME takes the form of a rapidly evolving epidemic, usually involving single mink farms, and appears not to spread from mother to offspring. The disease is fatal, with neurological symptoms including locomotor incoordination, somnolence and debilitation. It appears to be associated with the feeding of contaminated food. Most mink are fed on either commercially produced compound food and/or tissues of animals that have died on neighbouring farms. It had always been assumed that the most likely source of infection was scrapie in sheep fed to them.

Since BSE was first recognised there has been debate as to whether or not one American outbreak may have been caused by the feeding of cow tissue rather than sheep. Anecdotal evidence suggests that one farmer did not feed sheep to his mink, which later developed TME. If this is so, it is argued that cases of BSE may actually occur in the USA, although to date only one case has been reported (in December 2003).

Supporters of the prion theory believe that spontaneous disease may arise in any species that has a PrP gene, even in the absence of recycling of contaminated feed. The theoretical prevalence rate for this is estimated at about one per million population, the rate at which CJD occurs sporadically in humans. It is thought that if a cow affected with spontaneous BSE was fed to mink it could have caused TME.

In scientific experiments brain tissue from British BSE cases have been inoculated into mink, and in a separate experiment fed to them. Although the mink were killed by the resulting disease, the symptoms and pathology produced were not however identical to TME.

Reference: Marsh R. F and Hadlow. W. J. 1992. Transmissible mink encephalopathy. Rev.sci.tech. Off. int. Epiz. 11 (2). 539-550.