Prion Diseases Health Article

Demographics

Sporadic CJD, with no recognizable pattern of transmission, has an incidence of about one case per million people per year worldwide, making up 85% of total CJD cases, and 80% of all prion disease cases. In the United States, there are approximately 200 sporadic CJD cases per year. Approximately 15% of CJD cases are inherited and associated with a different prion type than that of sporadic CJD. Inherited CJD may show up in geographic clusters. A 60- to 100-fold increase in CJD is seen in Libya- or Slovakia-born Israelis due to a PRNP gene mutation rather than transmission or environmental factors. Other communities genetically at increased risk are found in some areas of Chile. CJD cases caused by accidental transmission routes such as surgical instruments and transplants are extremely rare and make up less than 1% of total cases. In the United States, the CJD cases are almost always in patients older than 30 years of age. In the United States, patients under 30 dying of CJD are less than one case per 100 million people per year, whereas in the United Kingdom, patients dying of a variant CJD (vCJD) in this age group make up over 50% of the CJD cases.

GSS is rarer than CJD, striking one person in every 10 million people. These figures are likely to be underestimated since prion diseases may be misdiagnosed as other neurological disorders. Kuru occurs in approximately 1% of the indigenous New Guinea population it is associated with. Kuru is found mostly in children older than five years and adult females under 40 years of age.

BSE has been transmitted to humans primarily in the United Kingdom, causing vCJD. An epidemic of mad cow disease began in the United Kingdom in 1985 when cattle feed was contaminated with brain tissue from scrapie-infected sheep. More than 170,000 cattle were infected before the disease was brought under control. Cattle feed containing sheep matter was banned in 1988. In 1989, slaughter techniques that allow nervous tissue to be included in beef intended for human consumption were banned. The mad cow disease epidemic of the United Kingdom reached its peak in 1992, but then declined quickly. More than one million cattle may have been infected with BSE in the United Kingdom. However, as of December 2003, only 143 cases of vCJD have been reported in the United Kingdom, out of 153 cases worldwide. The percentage of BSE cases in cattle reported outside of the United Kingdom is steadily increasing as surveillance increases and disease rates rise. The BSE epidemic in the United Kingdom may have peaked, and may now be in decline. How much of the population has vCJD in the incubation phase is yet to be determined.

To prevent the spread of BSE to the United States, severe restrictions were placed on the importation of ruminants and ruminant products from Europe. In 1997, the U.S. Department of Agriculture (USDA) also implemented a ban on the use of ruminant tissue in ruminant feed. In 2002, the CDC reported a case of vCJD in the United States in a 22-year-old patient who was born and grew up in the United Kingdom. Mad cow disease made its first appearance in cattle of the United States in December 2003, when the USDA announced a possible diagnosis in a cow from Washington State. This diagnosis was confirmed within the month at a laboratory in the United Kingdom. The cow was believed to be imported from Canada in the year 2001 and had been slaughtered for human consumption. The USDA recalled all beef slaughtered at the same slaughter plant on the same date as the infected cow.