Genetic research could lead to vaccine for cattle disease

Dylan Thomas

University researchers recently deciphered the genetic sequence of a major cow pathogen that annually costs the dairy industry several million dollars.

The bacterium responsible for Johne’s disease, a chronic gastro-intestinal infection in cows, is known as one of the most serious health threats to dairy cattle worldwide. Researchers say knowledge of the genetic sequence will lead to better diagnosis of the disease and possibly a vaccine.

Vivek Kapur, a University veterinary pathobiologist, led a team of graduate students who used advanced techniques to sequence the bacterium’s genome, working with the Department of Agriculture’s National Animal Disease Center in Ames, Iowa.

The disease is particularly damaging because it grows slowly in laboratory conditions. It can take scientists up to six months to diagnose infected cattle through a laboratory culture, Kapur said.

But the genetic sequencing of the bacterium, M. paratuberculosis, might lead to faster diagnosis procedures. Scientists discovered several genes which could help distinguish the pathogen from other closely-related species of bacteria and allow them to identify it in days, not months, Kapur said.

John Fetrow, a scientist at the University’s Center for Dairy Health, Management and Food Quality, said Johne’s disease causes a cow’s intestinal wall to grow thicker, limiting its ability to absorb nutrients. The cow begins to lose weight and in the later stages of the disease suffers from severe diarrhea.

Fetrow said cows are probably infected within the first few months of life, although the disease does not display symptoms until the cow is 3 to 5 years old. But even when the cow is not showing outward signs of infection, the disease affects milk production, he said.

Estimates put the financial loss from decreased production at $200 million annually. A National Health Monitoring System study found that infected animals can cost a dairy farmer approximately $60 to $240 per cow, depending on the level of infection in a herd.

While the genetic sequencing of M. paratuberculosis is a major step in combating Johne’s disease, it was no easy task. Although “slightly on the larger side” compared to other microbacteria, the number of repeated sequences within the genome impeded researchers’ attempts to assemble it, Kapur said.

“It’s sort of like putting a Ö jigsaw puzzle together with many pieces that are exactly the same size and with almost the same color,” he said.

Fetrow said it is important to understand that despite its name the bacterium causing Johne’s disease is not similar to the bacterium causing human tuberculosis and cannot be transmitted to humans. But the diseases are similarly insidious: they are both slow-growing infections that are difficult for immune systems to combat.

While some dairy herds don’t have the disease, it is widespread among dairy cattle and is a major problem for the industry as a whole, Fetrow said. At least 22 percent of dairy herds are infected, according to a Department of Agriculture study.

Dairy farmers whose herds are infected can only try and control transmission of Johne’s disease, identifying infected cows spreading the bacterium and keeping young cows away from infected manure, Fetrow said.

The disease is currently untreatable. Cows that show signs of infection and lowered production are typically culled from the herd, Fetrow said.

The seriousness of the threat the bacterium poses has led the U.S. House Agriculture Appropriations Subcommittee to recently approve more than $20 million for a National Johne’s Disease Management and Testing Program. While the program is pending approval by the U.S. Senate, Kapur said his graduate students, who led the University’s research, have already made great progress in combating the disease.

“Here at the University of Minnesota, we’ve taken great pride in making sure that graduate students Ö are able to put together these impressive full genome sequencing programs,” Kapur said.

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