Dr. Madonna Benjamin, extension veterinarian and assistant professor at Michigan State University, says human movement from one farm to another creates the perfect disease vector — especially for diseases that are transferred through manure.
“It’s about disease control and prevention,” said Benjamin. “Not just what comes in, but what we keep from going back out as well. It has a lot to do with animal movement — animals of the same species are more likely to spread disease to the same species. It has a lot to do with people movement. For pathogens that are spread by manure, people can easily be vectors.”
Why the concern about biosecurity? One reason is a regulatory push due to foreign and emerging disease issues. “Diseases that have been somewhat dormant and now express themselves in a completely different strain,” said Benjamin, “and that strain can be highly pathogenic.”
Another factor is the globalization of agriculture. The United States is continuously poising itself for export markets, and is also a food importer. Public perception and awareness of food safety is another concern. “If someone hears of a BSE scare, they think they shouldn’t eat beef,” said Benjamin. “If it’s avian influenza, they think they shouldn’t eat chicken.”
Individual farms are less isolated than they were in the past, with more urban production resulting in people being closer to animals. There are also more backyard, self-sustaining farmers who keep a mixture of species.
Manure is a critical factor when it comes to the biosecurity perspective because of the potential for fecal-oral contamination. The commercial value of manure value is significant, so it’s being moved around from farm to farm. “A high amount of pathogens can survive well in a small amount of manure,” said Benjamin. “It’s the perfect host because it’s nice and wet. It vectors easily – manure gets on your shoes, on your clothes, on the feet of rodents and wildlife, dogs and cats, and is moved around. It can also be moved by birds flying around.”
Johne’s disease is caused by the bacteria Mycobacterium avium paratuberculosis (MAP). The Johne’s Information Center at the University of Wisconsin School of Veterinary Medicine estimates that 68 percent of dairy herds have at least one animal infected with Johne’s. The most common way Johne’s enters a herd is through a purchased animal that appears to be healthy. The animal sheds the MAP organism through manure wherever that animal is housed or moves, including barns, travel lanes and pastures, and other animals are easily contaminated through that manure. Since the intestine is the organ most affected by this disease, manure laden with the causative bacteria makes contamination throughout the farm easy.
Young animals are the group most often infected with Johne’s, but the disease is slow to progress and clinical signs often don’t manifest until the animal is at least two years old, and sometimes older. This means that young, potentially infected animals continue to spread the disease, so it’s important that young stock are not exposed to any animals that might be infected.
Because the largest number of MAP bacteria in infected cows exit the body through the feces, the best way to prevent new Johne’s infections in calves is through sanitation and manure management. Calves are highly susceptible to infection, so it’s critical that they are not exposed to potentially contaminated manure. Separation of young stock from adult cattle for as long as possible is ideal.
Calves should enter the world in a clean, dry setting with little or no fecal contamination. Calves should be removed from the cow promptly after birth to manage a variety of diseases, including Johne’s. Ideally, calves should be moved to an area that is free of adult cow manure as quickly as possible following birth.
Ideally, biosecurity for cattle includes maintaining a closed herd. Whenever possible use animals born on the farm as replacements. Use A.I. rather than bulls, and if bulls are used, insist on fully health-tested stock. Livestock exhibitions are a good place to pick up pathogens, so even if you don’t exhibit your own cattle, take good biosecurity precautions after attending events where livestock of any kind are present, including full change of clothing prior to handling your own animals, disinfecting boots/shoes, and disinfecting vehicle tires and mats inside the vehicle.
Whenever possible, any purchased animals should come from a herd that is tested to be free of Johne’s disease. The next best option is familiarity with the level of Johne’s status of a herd from which an animal is purchased, what steps the owner is taking to ensure infection control and selling only animals that test negative. It’s important to remember that Johne’s is a herd issue, and that the test status of the herd is a more accurate picture than the test of an individual animal.
New animals brought to the farm should appear physically healthy, with a history of appropriate disease testing. Isolate incoming animals and prevent any contact with the farm’s animals for at least 21 to 30 days. Observe isolated animals carefully and watch for signs of illness, and take temperatures if any animals appear to be ill and contact the herd veterinarian immediately in the case of clinically sick animals.
Don’t allow any manure to be moved from the isolation area to the rest of the herd housing area, including travel lanes. Instruct all workers about sanitation and manure movement on the farm, including walking from the isolation area to other areas of the farm.
Veterinarian Dr. Michael Collins, University of Wisconsin School of Veterinary Medicine, says there is an increasing number of MAP-infected species, including deer, bison, feral swine and donkeys. More MAP-infected herds are being reported globally, but it isn’t all bad news.
“We have successfully mapped the MAP genome,” said Collins. “We’ve improved our knowledge of the pathobiology of the MAP infection and devised and validated new diagnostic tests and produced reams of educational materials.”
Collins says the Paratuberculosis paradox is that MAP is not recognized as a zoonotic pathogen by researchers, producers, processors and government regulators. “But we behave as if it is a zoonosis,” he said. “We use this to justify our eradication campaigns, national control programs, use it when requesting heavy government subsidies for these programs, and when asking low-prevalence herds to make sizeable investments in control programs that can’t be economically justified.”
One major problem is that as federal funding for Johne’s testing decreases, producers stop testing because they know Johne’s is not a significant production-limiting disease. “Unless somebody pays them to do something about the problem,” said Collins, “it’s really not in their financial best interest.”