There is good news and bad news about the “L-type” atypical mad cow phenotype, found in the nearly 11-year-old, dead dairy cow discovered two weeks ago in California.
The good news is no human has ever contracted variant Creutzfeldt-Jakob (vCJD) disease from cattle infected with atypical bovine spongiform encephalopathy (BSE). vCJD is the human version of mad cow disease, a fatal neurodegenerative disorder.
The bad news is peer-reviewed findings by French neuroscientist Thierry Baron published in the January edition of Emerging Infectious Diseases indicate it is too soon to say incidents like the California cow are just a spontaneous cases. Baron found mouse lemurs may contract L-type BSE more easily than the classic version.
But with prion researchers around the world working on the topic, that likely will not be the last word. Spontaneous vCJD occurs in humans in about one in one million cases.
Dr. Michael Hansen, a Consumers Union scientist who has long tracked mad cow disease, thinks there is a possibility L-type BSE is “not necessarily a spontaneous case.”
Hansen, speaking for CU last week, called upon USDA to adopt the following steps in the wake of the atypical BSE finding in a non-ambulatory cow:
– Increase the BSE surveillance program beyond the current 40,000 tests annually that Hansen calls “very small” but USDA says is 10 times more than required by world standards.
– Allow private companies to test for BSE at their own expense. Federal courts have said USDA has power over BSE tests and so far it has blocked private testing.
– Prohibit the use of poultry litter for feed, because birds may have consumed agents harboring the infectious mad cow agent, and prohibit cow blood as a milk replacer for weaning calves. USDA has not seen either practice as high risk.
USDA officials have said, over and over, during the past week that a system of interlocking defenses they’ve erected to combat BSE is working. Among these are:
– Removal of specified risk materials, meaning those parts of the animal that would contain BSE if the animal had the disease. These include brain, spinal cord and digestive tracts.
– The ruminant-to-ruminant feed ban that has been in effect since 1997.
– The BSE surveillance program, which includes those 40,000 tests a year, many conducted at targeted places like the rendering transfer station in Hanford, CA where the cow infected with atypical mad cow was found.
Until recently, many prion researchers believed the L-type BSE strain is probably not posing a danger to human because it is so rare people are typically not exposed to it.
But the University of Edinburgh’s Rona Barron, a molecular biologist, has recently found that the L-type prion has a harder time infecting normal human brain protein.
There are actually two atypical BSE phenotypes, L and K. They are classified according to high and low molecular mass. Classic BSE (C-type) is thought to stem from food chain contamination by a single prion strain.
Feed is a common transmission source for Classic BSE.
The world campaign against mad cow disease has driven the number of BSE cases down to 29 in 2011, a 99 percent reduction since the peak of 37,311 cases in 1992. The U.S. announced the nation’s fourth mad cow discovery on April 24.
Three others turned up in 2003 in Washington state, in 2005 in Texas, and in 2006 in Alabama. The first U.S. mad cow was a classical case, imported from Canada and infected from eating feed contaminated with diseased brain and spinal bits.
Two California dairies were under quarantine, awaiting the USDA investigation into whether the two herds include any birth cohorts of the BSE-infected cow. The diseased cow had two calves in the last two years, one stillborn.
Dr. John Clifford, USDA chief veterinarian, said the surviving calf was euthanized. Tests on it for BSE were negative.
The exact location of the two dairies has not been disclosed. Once any cohorts are identified, the quarantine will be scaled back to those animals or eliminated if none exist on one dairy or the other.
Clifford says about 60 cases of atypical BSE have been identified worldwide.
USDA recently agreed to comply with all World Health Organization protocols for mad cow. As a result, it will provide brain tissues from the latest diseased cow to laboratories in both Canada and Europe.
That participation may have helped the U.S. beef industry avoid any export restrictions in any of its four largest markets –Canada, Mexico, Japan and South Korea — following the latest mad cow discovery. Only tiny Indonesia has suspended U.S. beef.