BSE Anatomy of A Crisis - bovine spongiform encephalopathy - Statistical Data Included

Choices: The Magazine of Food, Farm and Resource Issues, Spring, 2001 by Jean C. Buzby, Linda R. Detwiler

Around 180,000 cases of bovine spongiform encephalopathy (BSE), or "mad cow disease," have been confirmed in cattle since it was first identified in 1986 in Great Britain. Making matters worse, in 1996 BSE was linked to an invariably fatal human illness called variant Creutzfeldt-Jakob Disease (VCJD).

Understandably, BSE has had a substantial impact on the United Kingdom's livestock industry and altered international trade patterns.

Though there have been no confirmed cases of BSE or vCJD in the United States, the U.S. has imposed trade restrictions on British beef. In addition, the U.S. has increased spending for BSE surveillance and other measures in order to protect animal and human health. Consumer food safety concerns are also increasing, exacerbated perhaps by the recent foot-and-mouth outbreak in the United Kingdom.

The Villain of the Piece

BSE is a chronic, degenerative disease affecting the central nervous system of cattle. Infected animals may display changes in temperament such as nervousness or aggression, abnormal posture, lack of coordination and difficulty in rising, decreased milk production, and loss of body condition.

The incubation period usually ranges from two to eight years. Following the onset of symptoms, the animal's condition deteriorates until it dies or is destroyed. This usually takes from two weeks to six months. Most cases in Great Britain have occurred in dairy cows between three and six years of age. At present there is no vaccine or treatment for BSE.

BSE belongs to the family of diseases in other animals and humans known as the transmissible spongiform encephalopathies (TSEs). Brain tissues of infected animals have a sponge-like appearance when examined under a microscope. Other examples of TSEs include scrapie in sheep and goats, transmissible mink encephalopathy, chronic wasting disease in deer and elk, as well as kuru, Creutzfeldt-Jakob Disease (CJD), and--particularly relevant here--a variant of CJD in humans.

Epidemiological data suggest that BSE in Great Britain may have originally been caused by using meat and bone meal made from scrapie-affected sheep, or from cattle with an undiagnosed TSE, as a protein source in animal feed. Changes in rendering practices in the early 1980s may have enhanced the causative agent's ability to survive in meat and bone meal, resulting in the transmission of the disease back to cattle. This increased the spread of the epidemic. However, there is no evidence that BSE spreads through contact between unrelated adult cattle, or from cattle to other species by contact.

As of late March 2001, 177,812 head of cattle on 35,158 farms had been diagnosed with BSE in Great Britain. These animals have been destroyed.

From Cows to People?

In 1996, Great Britain announced that there was a possible link between BSE in cattle and vCJD in humans. This rare, but always fatal, human disease is characterized by progressive deterioration of brain tissue. The new strain differs from "classical" CJD in that vCJD has an unusually early age of onset of symptoms, an unusual clinical course with psychiatric problems, a prolonged duration of illness, and brain lesions visibly different from those associated with classical CJD.

Classical CJD occurs sporadically, and has no known link to any animal TSE. Investigators found that BSE in cattle and vCJD in humans are related, but vCJD has not been linked to any other TSE.

Scientists are not yet certain how BSE is linked to vCJD. However, many scientists now believe that humans may be infected by eating brain and/or spinal cord bovine products contaminated with some kind of causative agent, such as a "prion" or abnormal protein (Lorains et al., 2001).

Current tests cannot detect the disease in live animals. Microscopic post-mortem examination of brain tissue and tests for prion protein are the primary methods used to confirm a diagnosis of BSE in cattle, or of vCJD in humans.

As of March 30, 2001, vCJD has caused 97 deaths in the U.K. (U.K. Dept. of Health, 2001), two (plus one probable) in France, and one in the Republic of Ireland. No cases of vCJD have been detected in the U.S.

Immediately after the 1996 announcement, domestic sales of beef products in the U.K. fell by 40 percent. Within a month, household beef consumption fell 26 percent from the previous year's level (Atkinson, 1999).

The U.K. had developed a significant export trade in live cattle and beef during the early 1990s; this was hard hit by the European Union's March 1996 ban of U.K. live cattle and bovine products (Table 1). Other export markers followed the E.U.'s lead, lowering real producer cattle prices in the U.K.

In the first year of the crisis, the total economic loss from BSE to the U.K. was estimated at [pound]740-[pound]980 million (Atkinson, 1999) (US$1.07-$1.4 billion assuming [pound]=US$1.444). The cumulative gross budgetary cost of BSE to the U.K. between March 1996 and March 31, 2000 stands at roughly [pound]3.5 billion (US$5.05 billion), and was expected to reach [pound]4 billion (US$5.8 billion) by March 31, 2001.