California cow had lone known BSE infection

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Federal agriculture authorities found no threat to human health from a California cow discovered in April to have been infected with an atypical form of bovine spongiform encephalopathy.

Department of Agriculture officials announced in July that an epidemiologic investigation by the department’s Animal and Plant Health Inspection Service concluded without finding any additional infected animals or problematic practices among suppliers who sold feed to the dairy where the infected cow lived.

The infected animal was a 10 1/2-year-old Holstein dairy cow, and it had developed hind limb lameness that had been attributed to a fungal infection that was being treated. The cow was euthanized in mid-April after increasing weakness led to recumbency.

Subsequent immunohistochemical and western blot tests on samples from the cow were positive for atypical BSE, and World Organisation for Animal Health (OIE) laboratories in Canada and England confirmed the findings.

On May 1, the carcass of the infected cow and about 90 other cattle held by the renderer were sealed inside plastic vaults and buried in a landfill.

Atypical BSE is a rare form of the disease, and APHIS officials have said that, unlike most BSE, it is not likely spread through contaminated feed. Information from the Centers for Disease Control and Prevention indicates atypical BSE may be a distinct strain of prion disease that rises spontaneously, but it also may be spread through feed or the environment.

Investigators were not able to identify and test any other cattle born on the same premises as the BSE-infected cow within one year of the infected cow’s birth. The animal’s only living offspring, a 2-year-old cow, was euthanized, and samples from that cow were negative for BSE. That carcass was incinerated.

The Food and Drug Administration and California Department of Food and Agriculture also found no evidence that the infected cow or herd mates on the central California dairy were exposed to contaminated feed, the APHIS announcement states. They also found that the 11 suppliers who sold feed to the dairy where the cow lived and were still in business were complying with state and federal requirements.