Outlook
Human prion diseases are devastating and incurable, but very rare. Fears that an epidemic of the animal disease (BSE) would lead to an epidemic of the human form (vCJD) have not occurred, even in the UK where entire herds of diseased cattle were destroyed and over 180,000 animals were known to develop the disease.
Yet the general public and researchers alike remain uncertain about the implications of BSE for human disease. If the priondisease takes many years to cause symptoms in people who have been infected and not know it, the number of cases may increase in the years ahead.
According to the CDC, as of December 1, 2003, a total of 153 cases of vCJD had been reported in the world: 143 from the United Kingdom; 6 from France; and one each from Canada, Ireland, Italy, and the United States. (Note: the Canadian, Irish, and US cases were reported in persons who resided in the UK during a key exposure period of the UK population to the BSE agent.)
Computer modeling predicted between fewer than 100 to as many as 136,000 people could die from vCJD in the United Kingdom, while another study predicts that the number of cases has reached its peak. Uncertainty remains about the ultimate course of the outbreak, according to the US Department of Agriculture.
The US government has implemented a number of measures to prevent BSE from entering the US and to prevent the spread of the disease, as outlined by the Food Safety and Inspection Service (FSIS). Some of these measures include the following:
- Since 1989, the USDAβs Animal and Plant Health Inspection Service (APHIS) has prohibited the importation of live cattle and certain cattle products, including rendered protein products, from countries where BSE is known to exist. In 1997, due to concerns about widespread risk factors and inadequate surveillance for BSE in many European countries, these importation restrictions were extended to include all of the countries in Europe.
- As of December 7, 2000, APHIS has prohibited all imports of rendered animal protein products, regardless of species, from BSE-restricted countries because of concern that feed intended for cattle may have been cross-contaminated with the BSE agent.
- In 1997, FDA prohibited the use of most animal protein in the manufacture of animal feeds given to cattle and other hoofed animals (known as ruminants).
- The Centers for Disease Control and Prevention (CDC) leads a surveillance system for vCJD.
- Additional safeguards are evolving as the US deals with the first documented case of BSE in 2003: keeping downer animals out of the human food chain because these are at highest risk for being ill with BSE, tracking cattle from birth to slaughter in case an infected animal is found and its meat can be destroyed, and using less aggressive ways to harvest meat from carcasses to avoid brain and spinal tissues.
Current testing in the US only samples a small number ofbrains from all cattle slaughtered for human consumption. Testing of brain tissue takes more than a week to deliver results. This testing is done only after the animal has been presented for slaughter.
European countries use fast tests to screen many more slaughtered cattle than is done in the US. Results are obtained overnight as carcasses await approval in refrigerated warehouses before entering the food stream.
Live animal tests may provide valuable information about the level of BSE in all animals, including downer cattle and cattle aged 24 months or older (those most at risk and in whom BSE is found). However, currently there is no sensitive and reliable live animal test for BSE.
Thus, given the limitations of the tests available today, certain tissues of cattle infected with BSE may contain the BSE agent before a diagnostic test could indicate that the animal has BSE. Therefore, there is a great need for a sensitive and reliable test that can be done on live animals or on cattle that have been slaughtered.