WASHINGTON – The Agriculture Department acknowledged Wednesday that its testing options for mad cow disease were limited in 9,200 cases despite its effort to expand surveillance throughout the U.S. herd.
In those cases, only one type of test was used – one that failed to detect the disease in an infected Texas cow.
The department posted the information on its Web site because of an inquiry from The Associated Press.
Conducted over the past 14 months, the tests have not been included in the department’s running tally of mad cow disease tests since last summer. That total reached 439,126 on Wednesday.
“There’s no secret program,” the department’s chief veterinarian, John Clifford, said in an interview. “There has been no hiding, I can assure you of that.”
Officials intended to report the tests later in an annual report, Clifford said.
These 9,200 cases were different because brain tissue samples were preserved with formalin, which makes them suitable for only one type of test – immunohistochemistry, or IHC.
In the Texas case, officials had declared the cow free of disease in November after an IHC test came back negative. The department’s inspector general ordered an additional kind of test, which confirmed the animal was infected.
Veterinarians in remote locations have used the preservative on tissue to keep it from degrading on its way to the department’s laboratory in Ames, Iowa. Officials this year asked veterinarians to stop using preservative and send fresh or chilled samples within 48 hours.
The department recently investigated a possible case of mad cow disease that turned up in a preserved sample. Further testing ruled out the disease two weeks ago.
Scientists used two additional tests – rapid screening and Western blot – to help detect mad cow disease in the country’s second confirmed case, in a Texas cow in June. They used IHC and Western blot to confirm the first case, in a Washington state cow in December 2003.
“The IHC test is still an excellent test,” Clifford said. “These are not simple tests, either.”
Clifford pointed out that scientists reran the IHC several times and got conflicting results. That happened, too, with the Western blot test. Both tests are accepted by international animal health officials.