Scientists are racing to determine whether the United Kingdom must brace for yet another outbreak in cattle--and whether the pathogen poses a risk to people. Last week, U.K. scientists announced the death of a cow in Cumbria that was euthanized last December after suffering from poliolike symptoms. Their hunt for a pathogen has been fruitless so far, triggering anxiety in a country scarred, emotionally and economically, by two devastating cattle epidemics in 15 years.
Unable to stand after its legs became paralyzed over several days, the Holstein heifer was initially diagnosed with botulism. But studies at the U.K.'s Veterinary Laboratories Agency (VLA) revealed telltale brain lesions of a viral infection. The damage was inconsistent with that caused by two known cattle pathogens, Borna disease virus and lyssavirus, VLA researchers report in the 12 June Veterinary Record. And tests for three other viruses--louping ill, bovine herpesvirus type 1, and West Nile--were negative. One other animal in the Cumbria herd showed moderate but transient weakness. The researchers suspect the culprit is either a new virus or a known virus that sporadically attacks the brain. The U.K.'s Health Protection Agency is mounting an urgent assessment of possible risks to humans.
The case triggered widespread media attention in Britain, whose cattle industry was hardest hit by bovine spongiform encephalopathy (mad cow disease) and was ravaged by a foot-and-mouth epidemic in 2001. "There's a tremendous sensitivity about anything in cattle," says virologist Ernest Gould of the Centre for Ecology and Hydrology in Oxford. But it's not unusual for livestock to get sick or die from unknown causes, he says, and better reporting is bringing more such unexplained cases to light. Indeed, U.K. labs have reported 21 similar poliolike cases in cattle and sheep over the last 10 years, and samples from some of those animals are now being studied.
Other experts are digging further afield for clues. A poliolike ailment appears to have struck cattle in Kansas in the early 1950s, says Jack Woodall, an emerging-diseases expert at the Federal University of Rio de Janeiro in Brazil. Hoping it might shed light on the British culprit, Woodall broadcast a message last week on ProMED, an e-mail list about emerging infections he co-edits, asking veterinarians who remembered that outbreak to come forward. So far, no one has done so.
The ProMED posting including Woodall's query