Minding the Dairy

Scientists reveal a killer’s M.O.

By identifying how a deadly strain of bacteria causes Johne's disease in cattle, Luiz Bermudez and Marta Alonso-Hearn, hope to provide the basis for new treatments and shed light on human illness.

Little matters more to dairy farmers than the purity of their product and the health of their animals. So when Warren “Buzz” Gibson, co-owner and herd manager at the Lochmead Dairy in Junction City, Oregon, heard six years ago that an incurable cattle disease called Johne’s (pronounced “yo-knees”) could threaten his reputation for quality, he had all of his cows tested and continues to monitor annually, despite never having had a positive test.

Across the Oregon Coast Range at the Tillamook Creamery Association, Mark Wustenberg works with farmers to test for Johne’s and manage their herds to reduce other disease risks. “Our goal is to make sure this disease does not adversely affect our milk supply,” says the association’s vice president for dairy services.

Statewide, more than 50,000 cows in 200 of Oregon’s 350 herds are tested annually for the disease, according to the Oregon Department of Agriculture. Of herds tested in Oregon, Johne’s appears to be present in 60 to 70 percent at a low level (1 to 2 percent) of infection, says ODA field veterinarian Bruce Mueller. While other cattle diseases such as brucellosis have waned, the Johne’s threat has stimulated a national research and education campaign funded by the U.S. Department of Agriculture (USDA) at universities across the country, including OSU.

Terra Up Close

Paratuberculosis (MAP) and a Host Cell

Paratuberculosis evades a host organism’s defenses — stomach acids, killer T-cells, antibodies — and finds a target in the intestinal tract. As it binds to a cell, the pathogen mounts an attack that spreads the infection with deadly consequences. See an artist’s conception of this process as described in preliminary results of research by Luiz Bermudez, Marta Alonso-Hearn and their colleagues.

Gibson, Wustenberg and their peers have good reason to be vigilant. The cause of Johne’s — a bacterium known as Mycobacterium avium paratuberculosis (or MAP) — can survive for years in soil without losing its ability to infect. The organism lives in manure left by infected animals in pastures and barn stalls. When it reaches a newborn calf, it spreads slowly through the animal’s system with no apparent ill effects. But within two to five years, growing intestinal distress leads to diarrhea, weight loss and reduced milk production. By the time symptoms appear, death is imminent.

The MAP bacterium infects dairy herds worldwide and has been estimated to cost the U.S. industry $200 million annually in lost milk revenues alone. The financial impact soars to $1.5 billion when reduced milk production, decreased feed efficiency and expenses for replacement cattle are taken into account.

Moreover, a possible association between Johne’s in cattle and Crohn’s disease in people raises human health concerns. For now, studies to determine whether the same organism causes both diseases have reached differing conclusions. According to the Johne’s Information Center at the University of Wisconsin, no cases of Crohn’s have been linked to milk consumption.

Before he came to OSU in 2002, microbiologist Luiz Bermudez studied the Johne’s pathogen in wild and domesticated animals. Because of its importance to the animal agriculture industry, he now leads a research team that has discovered new details about how the organism goes about its dirty work in cattle. While a vaccine and other treatments can now reduce the severity of the disease, what Bermudez and his colleagues are learning could lead to more effective medications.

Understanding the tricks that MAP uses to evade an animal’s immune system could also improve treatment for other infectious diseases. That’s because as a class of microorganisms, Mycobacteria are responsible for scourges such as tuberculosis, leprosy, chronic lung problems and secondary infections in AIDS patients. Some Mycobacteria are common in soil and water. Others live harmlessly in humans until stress compromises our immune systems, giving the microbes an opening to multiply and cause further harm.

Most Deadly Infection

Conventional wisdom about Johne’s holds that transmission most commonly occurs through the consumption of manure-contaminated grass and hay. However, in 2006 Bermudez and his colleagues reported in the journal Infection and Immunity that it may be through another route — when a newborn calf first sucks at its mother’s udder — that the most deadly infection occurs. They compared the infectious ability of MAP cells grown in milk to those grown in a standard laboratory broth. The result: Those milk-raised cells were more than 10 times as effective in entering a model animal cell. “This is the most infectious form of the microorganism that the calf can get,” says Bermudez.

That report followed a series of papers describing the ability of Mycobacteria to invade host cells and to thrive inside those cells without being destroyed by the host’s immune system. Now, unconfirmed results of further research suggest that the OSU team has identified a mechanism that could prove to be the organism’s Achilles heel: the genes and proteins involved in binding the pathogen to a host cell and getting it inside the cell. Like a Trojan horse, once inside cell walls, MAP subverts the cell’s own machinery, eventually killing it and releasing a new wave of infection (see sidebar illustration). The new work was conducted by a team including lead author Marta Alonso-Hearn, Lia Danelishvili and Lisbeth Meunier-Goddick at OSU and Dilip Patel, a former OSU scientist now at the University of Tennessee, Knoxville.

“The bacteria are not supposed to get inside those cells,” says Bermudez. “For the first time, we have shown that the bacterium has a mechanism that interacts with the host cell and makes the host cell ingest it. This is a very sophisticated mechanism.”

Until a more effective vaccine or a less costly treatment is found, however, monitoring and prevention through good sanitary practices are still a farmer’s best protection, adds Bermudez. He serves on the scientific advisory board of a national research initiative known as the Joint Integrated Johne’s Disease Program at the University of Minnesota, a collaboration of 21 universities funded by the USDA.

For Buzz Gibson, testing for Johne’s amounts to good insurance. Annually, he insists that his veterinarian take blood and fecal samples from 35 to 40 cows and send them to the ODA Animal Health Lab in Salem for analysis. “I want to be ready. I don’t want to wake up one morning and see a headline linking Johne’s and Crohn’s,” he says.

The Lochmead dairy milks 580 Holsteins daily, supplying the company’s 44 Dari Mart stores from Cottage Grove to Corvallis. The herd is now one of four in Oregon — in addition to those owned by Dean and Patti Tohl in Tillamook, Jack Perrin in Woodburn and OSU in Corvallis — to receive the state’s highest level of certification for those that have tested negative for Johne’s.

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