Alabama and federal officials have announced the completion of an investigation regarding a cow that tested positive for bovine spongiform encephalopathy (BSE) or “mad cow disease” this past March.
Meanwhile, the USDA has reported that the prevalence of BSE in the United States is “extraordinarily low,” and as a result, testing for the disease will be scaled back in the coming months.
Results of an epidemiological investigation conducted by the Alabama Department of Agriculture and Industries, the USDA's Animal and Plant Health Inspection Service (APHIS) and the FDA indicate that the Alabama cow was a red crossbreed, and that it was examined by a local veterinarian. The veterinarian returned to the farm the following day, euthanized the animal, and collected a sample which was submitted for BSE testing.
The animal reportedly was buried on the farm at that time and did not enter the animal or human food chain.
Alabama and APHIS officials excavated the index animal's carcass and through an examination of its teeth, determined that it was more than 10 years old. It was born prior to the implementation of FDA's 1997 feed ban that minimizes the risk that a cow might consume feed contaminated with the agent thought to cause BSE.
Officials investigated 36 farms and five auction houses, in addition to conducting DNA tests on herds that may have included relatives of the infected animal. They were unable to find any related animals except for the two most recent calves of the index animal. The most recent calf was located at the same farm as the infected animal and the second calf had died the year before.
Officials reported that no other animals of interest were located, and the living calf of the BSE-positive animal currently is being held at the APHIS National Veterinary Services Laboratory in Ames, Iowa, for observation.
Origin not revealed
The state and federal investigation did not reveal the BSE-positive animal's herd of origin. However, this was not entirely unexpected due to the age of the animal, along with its lack of identifying brands, tattoos or tags. It is highly unusual to find BSE in more than one animal in a herd or in an affected animal's offspring.
To insure that adequate feed controls were in place in the feed facilities in the immediate geographic area of the affected farm, FDA conducted a feed investigation into local feed mills that may have supplied feed to the infected animal after the 1997 feed ban. This investigation found that all local feed mills that handle prohibited materials have been and continue to be in compliance with the FDA's feed ban.
Alabama Gov. Bob Riley recently signed into law a bill that would implement a National Animal Identification System in the state once it becomes mandatory at the federal level. This law also provides that information gathered by the Alabama Department of Agriculture and Industries for the animal identification database will remain confidential.
In a report released in late April, the USDA indicates that the most likely number of BSE cases in the United States is between four and seven animals. The agency concludes that there is less than one case of BSE per million adult cattle in the United States, based on an adult cattle population of 42 million animals in this country.
“We can now say, based on science, that the prevalence of BSE in the United States is extraordinarily low. The testing and analysis reinforce our confidence in the health of the U.S. cattle herd,” says Agriculture Secretary Mike Johanns.
As part of the APHIS BSE-enhanced surveillance program, more than 700,000 samples have been tested since June 2004. To date, only two of these highest risk animals have tested positive for the disease for a total of three cases of BSE in the United States.
“While the APHIS epidemiological investigation did not locate additional animals of interest, it is important to remember that human and animal health in the United States is protected by a system of interlocking safeguards, which insure the safety of U.S. beef,” says Johanns. “The most important of these safeguards is the ban on specified risk materials from the food supply and the FDA's 1997 feed ban.”
The estimate of BSE prevalence in the United States is based on data gathered not only from the enhanced surveillance effort that has been underway since June 2004, but also from surveillance conducted in the United States for the five years prior. USDA experts used two different methods, the BSurvE Prevalence B method and the Bayesian birth-cohort method, to analyze the prevalence of BSE based on all of the surveillance data.
The findings of the two methods were similar, indicating that the most likely number of cases present in the United States is between four and seven animals.
USDA will use the prevalence analysis, once it is peer-reviewed, and international standards set by the World Animal Health Organization, to design an ongoing BSE surveillance program for the United States. The data and analysis will also assist in making science-based policy and regulatory decisions related to the disease.
USDA's enhanced BSE surveillance program followed the detection of BSE in an imported animal in December 2003. The target population of cattle tested included those animals where the disease is most likely to be found if it is present: non ambulatory cattle, cattle exhibiting signs of central nervous disorders or any other signs that may be associated with BSE, including emaciation or injury and dead cattle.
Samples were drawn from more than 5,000 locations across the United States, including slaughter plants, renderers, farms, public health laboratories, veterinary diagnostic laboratories and salvage slaughter facilities.
USDA is providing its analysis to outside experts for a scientific peer review and making it available to the public. The agency announced on April 29 that it plans to scale back its BSE testing during the next several months. USDA currently is testing 5,000 to 7,000 head of cattle each week for BSE, at a cost of $1 million per week. Under the proposed plan, about 800 head per week or 40,000 annually would be tested. USDA will consult with three outside research groups for review before settling on the final number of annual tests to be conducted under the new plan.
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