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New Johne’s test claims accuracy of 95 percent
By ANN HINCH
Tennessee Correspondent

KNOXVILLE, Tenn. — A team of researchers on two continents hopes to revolutionize testing for Johne’s disease in cattle and other ruminants.

Lead researcher Dr. C.A. Speer, director of the University of Tennessee’s Center for Wildlife Health, has two patents pending on the new test he and scientists from Iowa, Pennsylvania and Japan have developed. Speer also said a major veterinary diagnostics company is reviewing the test, which may be available for commercial use within a year.

“We got lucky,” he said of the team hitting upon a fresh approach to running their particular test, which he explained is 95 percent accurate, as opposed to established Johne’s tests with success rates upwards of only 38 percent.

The possibility of Mad Cow gets plenty of press, but Johne’s is a present everyday problem for dairy and beef producers. USDA estimates 22 percent of all dairy and 8 percent of beef herds in the United States are infected with the bacterium Mycobacterium avium subspecies paratuberculosis (or Para-TB, in short) that causes Johne’s.

An animal suffering clinical symptoms of Johne’s may exhibit persistent diarrhea, weight loss and decreased milk production – to the tune of $200 million annually for U.S. dairy farmers, according to USDA – leading to death. It can also incubate Para-TB for years and pass it along to others in its herd(s) through feces.

Dr. John Bannantine, a research microbiologist with the National Animal Disease Center in Ames, Iowa, who has sequenced the Para-TB genome, described how Para-TB is designed, “If you think of a bacterium as a sphere, there’s going to be proteins in the sphere.” These are the antigens – substances that trigger the host body to create antibodies – which current Johne’s tests seek out.

Speer said the traditional tests use harsh chemicals to seek the antigens inside Para-TB. The gold standard of the cattle industry is the fecal culture test, which requires incubating the bacterium 5-16 weeks before reading test results. Even then, it only has a 38 percent sensitivity level, the current best in the industry.

“The key to our test, really, is that we keep the surface antigens (of the Para-TB bacterium), and we got reactions there,” Speer said. Simply put, the research team uses a gentler method to probe certain proteins clinging to the surface of the Para-TB, rather than trying to get at those in its interior. The surface antigens are easier to detect, Bannantine explained.

“Certainly, nobody has come up with a way to shake them loose,” he said.

Samples can be taken from an animal’s blood or milk, rather than the feces, and instead of waiting weeks, Speer said test results are available in about two hours.

As for accuracy, Speer described a test in which the team took serum samples from 21 cows known to be infected with Johne’s, positively identified through fecal cultures, and 30 cows which were fecal-negative. Each sample was divided into thirds so that a state diagnostic lab, another university (neither of which Speer would identify) and Speer’s research team each had the same 51 samples for blind testing.

Of the three, only Speer’s team used its new testing process. All three places tested their cultures multiple times. He said the state lab detected a few “positives” of the known positive samples and the university detected only one, but his team detected all 21 positives each time.

“That’s what the industry is faced with,” Speer said, “these tests that don’t work. You’ll never be able to clear up the herd.”

It may sound as if Speer and fellow researchers – Bannantine and Dr. Ray Waters of Ames; Dr. Robert Whitlock of the University of Pennsylvania; Dr. Yasuyuki Mori of Japan; and Dr. Shigetoshi Eda, Cathy Scott and Brad Elliott of UT – have made their test as simple as possible. But Speer said there is room for improvement.

“I’m never going to invent anything that’s very complicated, anyway,” he laughed.

Bannantine pointed out because the test may be used on all ruminants, it could be of great help to other livestock industries.

Sheep, for example, are not so prevalent in the U.S., but are important to the economies of Australia and European countries. Goats are also vital to more than one foreign national economy, and are gaining popularity in America.

Unfortunately, there’s still no treatment or vaccine for Johne’s, and Para-TB is extremely resistant to termination, including milk pasteurization. But Speer hinted the same method used to probe for Para-TB might eventually be turned to developing its vaccine.

This farm news was published in the April 5, 2006 issue of Farm World.

4/5/2006