Zoonoses and veterinary public health

Prion diseases

Bovine spongiform encephalopathy (BSE) is a recently reported transmissible spongiform encephalopathy (TSE) of bovines. The human disease "variant Creutzfeldt-Jakob disease" (vCJD) is believed to be a zoonotic disease caused by the BSE agent. From October 1996 to November 2004, 152 cases of (probable) vCJD have been reported in the United Kingdom (UK), eight in France, two in Ireland and one each in Canada, Italy and the United States of America. Insufficient information is available at present to make any well-founded prediction about the future number of vCJD cases.

The route of transmission of vCJD is not yet fully proven but it is generally accepted that it is transmitted through exposure to food contaminated by the bovine BSE agent. Over 180,000 cases of BSE have been confirmed in cattle in the United Kingdom between 1986 and October 2004. The disease was also found in several other countries. Transmission of BSE occurs when cattle eat meat and bone meal contaminated with the causative agent.

Measures for preventing human exposure have been identified and put into effect in the UK and elsewhere. These measures include the ban on meat and bone meal in animal feed, testing of slaughtered animals, systemic removal of "high-risk material" from carcasses and destruction of suspect and confirmed bovine cases as well as the control of animals potentially exposed at the same time.

Scrapie, another animal TSE is endemic in some sheep and goat flocks of Europe, Asia and North America (possibly elsewhere) with the exception of a small number of countries. During centuries of human and animal cohabitation, there has never been a demonstrated risk to humans from sheep scrapie. Recently other animal TSE's have been found in elk and deer (chronic wasting disease, CWD), mink (Transmissible Mink Encephalopathy, TME) and felines (Feline Spongiform Encephalopathy, FSE), but no human case has been linked so far to these animal diseases.

Human TSEs occur in sporadic, familial, and acquired forms. The most common form, sporadic Creutzfeldt-Jakob disease (CJD), has a worldwide death rate of about 1 case per million people each year and is responsible for about 85% of all CJD cases worldwide. The cause of sporadic CJD remains unknown. Familial Creutzfeldt-Jakob disease (fCJD) is inherited as a result of genetic mutations and counts for 10-15% of the cases worldwide. The remaining cases are iatrogenic and variant Creutzfeldt-Jakob disease.

Kuru was known as a human TSE in a restricted area of Papua New Guinea with a prevalence as high as 2% in some tribes. It is now found rarely. No evidence indicates spread of kuru by any other mechanism except by ritual cannibalism.

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