Epidemiology of vCJD and BSE
Notice to readers: The information below was published in Health Information for International Travel: 2005-2006. The case information and other statistics may have changed since the date of publication.
Description
Since 1996, strong evidence has accumulated for a causal relationship between ongoing outbreaks in Europe of a disease in cattle called bovine spongiform encephalopathy (BSE, or "mad cow disease") and a disease in humans called variant Creutzfeldt-Jakob disease (vCJD). Both disorders, which are caused by an unconventional transmissible agent, are invariably fatal brain diseases with unusually long incubation periods, which are measured in years. Transmission of the BSE agent to humans, leading to vCJD, is believed to occur via ingestion of cattle products contaminated with the BSE agent; however, the specific foods associated with this transmission are unknown. Bioassays have identified the BSE agent in the brain, spinal cord, retina, dorsal root ganglia, distal ileum, and bone marrow of cattle experimentally infected by the oral route, suggesting that these tissues represent the highest risk of transmission.
Occurrence
From 1995 through August 2004, 147 human cases of vCJD were reported in the United Kingdom (UK), 7 in France, and 1 each in Canada, Ireland, Italy, and the United States. The patients from Canada, Ireland, and the United States had lived in the UK during a key exposure period of the UK population to the BSE agent. By year of onset, the incidence of vCJD in the UK appears to have peaked in 1999 and to have been declining thereafter. However, the future pattern of this epidemic, including whether a second wave of cases might occur among a large, genetically less susceptible subgroup of the population, remains uncertain.
From 1986 through 2001, more than 98% of BSE cases worldwide were reported from the UK, where the disease was first described. During this same period, the number of European countries reporting at least one indigenous BSE case increased from 4 through 1993 to 8 through 1998 to18 through 2001. During 2001-2003, three countries outside Europe (Canada, Japan, and Israel) reported their first indigenous BSE cases. The proportion of the annual total number of BSE cases worldwide reported outside the UK increased to more than 25% in 2000 and more than 55% in 2003. This increase reflected the declining large (more than 183,000 total cases) epidemic of BSE in the UK and the increasing number of other countries with improved surveillance and higher rates of BSE.
In 2003, only two countries, the UK and Portugal, reported a BSE incidence rate of more than 100 indigenous cases per million cattle more than 24 months of age. In 2003, the reported BSE rates per million cattle more than 24 months of age were 58 for the Republic of Ireland, 46 for Spain, 25 for Switzerland, 12 for France, 11 for Belgium and the Netherlands, 10 for Italy, 9 for Germany, and 7 for Slovakia. The reported rates for Canada, Czech Republic, Denmark, Japan, Poland, and Slovenia were between 0.3 and 6 cases per million. The reported BSE incidence rates, by country and year, are available on the Internet website of the Office International des Epizooties at http://www.oie.int/eng/info/en_esbincidence.htm. New information is being generated on a regular basis, and updated sources should be consulted.
In addition to the countries with indigenous cases of confirmed BSE in 2003, 6 countries previously had reported one or two BSE cases to the OIE; these countries include Austria, Finland, Greece, Israel, Liechtenstein, and Luxembourg. The European Union's committees on BSE risk assessment have also classified 18 other countries as likely to have BSE, including Albania, Andorra, Belarus, Bulgaria, Croatia, Cyprus, Estonia, Hungary, Latvia, Lithuania, Macedonia, Malta, Mexico, Romania, San Marino, South Africa, Turkey, and the United States.
The identification in 2003 of a BSE case in Canada, and the subsequent identification later that year of a BSE case in the United States that had been imported from Canada led to the concern that indigenous transmission of BSE may be occurring in North America. In response, the US Department of Agriculture (USDA) implemented additional safeguards to minimize the risk for human exposure to BSE and on July 1, 2004, initiated a 12- to 18-month-long intensive testing program for BSE among cattle at relatively high risk for the disease (e.g., non-ambulatory cattle). Further details about this BSE surveillance effort in the United States, including test results, are available at http://www.aphis.usda.gov/lpa/issues/bse_testing/plan.html.
In 2003, a case of vCJD, which is now believed to have resulted from the receipt of transfused blood contaminated with the vCJD agent, was reported in a 62-year-old UK resident. In 2004, a second highly probable instance of transmission of the agent of vCJD through transfused blood was reported in the UK. In response, the British government extended earlier safeguards against transmission of vCJD via blood products and banned all persons receiving a blood transfusion after 1980 in the UK from subsequently donating blood. In January 2002, the US Food and Drug Administration published guidance outlining a geography-based donor deferral policy to reduce the risk of bloodborne transmission of vCJD in the United States. This guidance document included an appendix that listed European countries with BSE or a possible increased risk of BSE for use in determining blood donor deferrals. In addition to European countries cited above in the present chapter, other countries listed included Bosnia-Herzegovina, Liechtenstein, Norway, Sweden, and the former Yugoslavia. One deferral criterion was living cumulatively for 5 or more years in continental Europe from 1980 to the present. New information is regularly generated on the international BSE outbreak, and updated sources should be consulted, including the Internet website of the USDA at http://www.aphis.usda.gov/NCIE/country.html#BSE.
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