The mad cow found in the USA in late April was infected with a rare type of brain disease. On one hand, scientists are concerned with the infectious nature of the disease; on the other, government agencies play down the cow as an 'isolated event'.
The so-termed ‘mad cow disease’ emerged as a serious issue in the UK in the 1990s. The disease in cattle was a probable consequence of feeding herbivores the mashed-up brains of sheep. Here an infectious disease of sheep called scrapie, the result of a microscopic protein called a prion, infected the brains of cows causing the disease Bovine Spongiform Encephalopathy (BSE) in some cattle. A probable link was established from cow to people through infected beef, which in turn posed a risk to blood donation.
The British issue was addressed through the restoration of strict animal feeding controls and vigilance on the part of farmers. The remaining issue remains the number of people infected as a result of consuming contaminated beef. The infection manifests itself as a neurodegenerative disease called vCJD (Creutzfeldt-Jakob disease) and has a long incubation time (of up to twenty years).
The phenomenon of ‘mad cow disease’ has largely been confirmed to the British Isles and was thought, based on the incident rate, to be in decline.
In April 2012, Nature reports on the first case of US mad cow disease in six years have emerged. It is unknown how the cow came to be infected and at present it remains an isolated case.
However, what is troubling scientists is that the research team investigating the incident have discovered that the prion responsible was a rare L-type version, also called an atypical variant, rather than the more common C-type, associated with human transmission of the disease in the United Kingdom.
There is some evidence, from studies conducted in apes and mice, that the L-type is more contagious. It is unknown is such a contagion rate would apply to people.
In response to the finding the California Department of Food and Agriculture have said, via spokesperson Karen Ross:
“The detection of BSE shows that the surveillance program in place in California and around the country is working. Milk and beef remain safe to consume. The disease is not transmitted through milk. Because of the strength of the food protection system, the cow did not enter the food or feed supply. There are numerous safeguards in place to prevent BSE from entering the food chain.
“The atypical BSE designation is important because this is a very rare form of BSE not generally associated with an animal consuming infected feed. CDFA veterinarians are working with the USDA to investigate this case and to identify whether additional cows are at risk. Feed restrictions in place in California and around the country for the last 15 years minimize that risk to the greatest degree possible. We will provide additional information about this case as it becomes available.”
At present the detection of the cow remains worrying, although what the discovery actually means for other cattle and any risk to people is uncertain.