While several human TSEs exist, Creutzfeldt-Jakob disease (CJD) is the prototype human TSE. CJD occurs in a form associated with a hereditary predisposition (approximately 5-10% of all cases) and in a more common, sporadic form that accounts for 85-90% of cases.
A small percentage of cases (less than 5%) are iatrogenic (resulting from the accidental transmission of the causative agent via contaminated surgical equipment or as a result of cornea or dura mater transplants.) It has also been shown that CJD can be transmitted to humans as a result of treatment with natural human growth hormone. Replacement of natural human growth hormone by recombinant growth hormone has alleviated this risk.

TSEs are not caused by the micro-organisms usually associated with infectious diseases, but by less conventional agents. This fact led to great difficulties in the diagnosis, control and prevention of BSE. In particular, the disease could not be diagnosed by routine blood and serum tests, because the agent did not appear to evoke the production of antibodies by the host animal. Clinical suspicion of disease could only be confirmed post-mortem, from microscopic examination of the brain.
Our knowledge of CJD goes back to earlier studies of kuru, the so called headhunter disease seen in Papua New Guinea, where people became infected after eating the brains of their foes and preparing their dead relatives for burial.

Since 1991, WHO convened nine scientific consultations on issues related to human and animal TSEs; the ultimate goal of the meetings was to better protect human and animal health. Experts who participated reviewed the possible human public health implications of animal TSEs, with special emphasis on BSE. The consultations also reviewed the evolving state of knowledge on these diseases, evaluated possible means of transmission and identified risk factors for infection.
The group of independent experts assembled by WHO is continually updating the state-of-the-art as more scientific information on BSE and vCJD becomes available. WHO provides a neutral scientific forum in which scientific questions related to BSE and vCJD can be reviewed, evaluated and debated.

Research on all TSEs is promoted by WHO, especially on early diagnostic procedures and epidemiology. WHO has published a comprehensive priority list for new research. One question which needs investigation is whether or not BSE has infected sheep populations. Advancing current knowledge about TSEs through research will permit the best possible decisions to be taken to safeguard public health, while securing consumer confidence so that national economies dependent on the beef industry can be maintained and developed.
WHO published guidelines for infection control of TSEs in 2000. The full text is available at http://www.who.int/emc-documents/ under the heading ‘TSE’.

WHO has produced a list of recommendations to reduce exposure to the BSE agent. All countries must prohibit the use of ruminant tissues in ruminant feed and must exclude tissues that are likely to contain the BSE agent from any animal or human food chain. BSE eradication was recommended during a WHO consultation held in December 1999.

All countries are encouraged to conduct risk assessments to determine if they are at risk for BSE in sheep and goats. The suspected prion diseases occurring in animals consist of: scrapie in sheep and goats; transmissible mink encephalopathy; chronic wasting disease (CWD) of North American mule deer and elk; feline spongiform encephalopathy. It is advised that any tissue which may come from deer or elk with CWD is not used in animal or human food; however, at this time there is no evidence to suggest that CWD in deer and elk can be transmitted to humans.
No infectivity has yet been detected in skeletal muscle tissue. Reassurance can be provided by removal of visible nervous and lymphatic tissue from meat (skeletal muscle). Milk and milk products are considered safe. Tallow and gelatine are considered safe if prepared by a manufacturing process which has been shown experimentally to inactivate the transmissible agent.

Human and veterinary vaccines prepared from bovine materials may carry the risk of transmission of animal TSE agents. The pharmaceutical industry should ideally avoid the use of bovine materials and materials from other animal species in which TSEs naturally occur. If absolutely necessary, bovine materials should be obtained from countries which have a surveillance system for BSE in place and which report either zero or only sporadic cases of BSE. These precautions apply to the manufacture of cosmetics as well.