Two cases of mad cow in Texas and Alabama seem to have resulted in a mysterious strain that could occur spontaneously in cattle, researchers say.
Officials are trying to downplay the differences between the two U.S. cases and the mad cow epidemic that has led to the slaughter of thousands of cattle in Britain since the 1980s.
It is precisely these differences that complicate efforts to understand the brain wasting disorder, known medically as bovine spongiform encephalopathy, or BSE for short.
“It is most important right now, until science tells us otherwise, we treat this as BSE regardless,” agriculture department’s chief veterinarian, John Clifford, said in an interview.
The Texas and Alabama cases – confirmed last year and this one, respectively – draws international attention.
At a meeting in London last month, experts presented research on the U.S. cases and similar ones in Europe.
These cows seem to have had an “atypical” strain that scientists are only now beginning to identify. Such cases have been described in a dozen cows in France, Italy and other European countries and in Japan.
In the two U.S. cases, researchers did not find the telltale spongy lesions caused by prions, the misfolded proteins that deposit plaque on the brain and kills brain cells. Furthermore seemed prions in brain tissue samples from Texas and Alabama cows, to be distributed differently from what would be expected to be found in cows with the classic form.
Laboratory studies on mice in France showed that both the classic and atypical strains could spread from one animal to another. But scientists theorize the atypical strain might have infected cattle through an unusual way.
Mad cow disease is not transmitted from cow to cow like a cold or the flu. It is believed to spread through feed, when cows eat contaminated tissues other cattle. Happens when crushed cattle remains set to feed as a protein source. This time, a common practice ended in the USA in 1997.
People can get a disease, variant Creutzfeldt-Jakob disease, the same way – by eating meat contaminated with mad cow disease. Mad cow disease in humans affects younger people, and the average age at death is 28 years.
A more common form of CJD – not associated with mad cow disease – can happen spontaneously and is reported in nearly 300 people in the U.S. each year. This form usually occurs in older people, and the average age at death is 68
Some scientists have to raise the possibility that the atypical strain can also take place spontaneously in cattle. The Texas and Alabama cows were older animals, which were some of the other animals in Europe with seemingly atypical cases.
Linda Detwiler, a former Agriculture Department veterinarian who belong to the big food companies, warned against making this assumption. “I think it’s a little early to say that it would be the case,” Detwiler said.
Other theories, she said, suggest atypical strain might come from a mutation of mad cow disease, or even a disease in sheep.
Mad cow disease has turned up three times in the U.S.: the native animals in Texas and Alabama, and in a Canadian import in Washington state.
In Texas and Alabama cows were test patterns are different from what appeared in an infected cow in Washington State, and a cluster of Canadian cases, researchers say. The Washington and Canadian cases resemble the classic British cases.
Whatever the reasons may be of an atypical strain, the government says there is no reason to change federal testing or measures that protect animals and humans from the disease.
“We still feel comfortable with the safeguards we have,” Clifford said. “We need to base our assumptions about what is scientifically known and understood.”
Meanwhile, mad cow disease research has been arrested by the Agriculture Department laboratory in Ames, Iowa, because of employee allegations that the lab was improperly disposing of animal waste.
The department asked a group of international experts to review Lab disposal practices. The city of Ames also investigating.