Johne’s Disease in Cattle
Published on Wed, 10/12/2022 - 2:33pm
Johne’s Disease in Cattle.
By Heather Smith Thomas.
Johne’s is a sneaky disease you won’t notice until it is already established. It doesn’t show up (weight loss and diarrhea) until an animal has been infected a long time.
First described by Heinrich Albert Johne in 1895, the causative organism was isolated in 1911. International experts at a seminar on Johne’s disease at the National Animal Disease Center in Ames, Iowa in 1983 estimated that 10 to 20% of all U.S. cattle at that time (beef and dairy) were infected. An earlier nationwide survey of bovine practitioners conducted by Ohio State University in 1978 showed that veterinarians had positively diagnosed the disease in every cattle breed, including imported exotics, and bison.
Johne’s is caused by Mycobacterium avium paratuberculosis (MAP), a bacterium similar to the one that causes tuberculosis in humans. It affects ruminants (cattle, sheep, goats, deer, elk, antelope, bison, etc.) but these bacteria multiply very slowly; it may take two to 10 years for animals to develop clinical signs, even though they are shedding bacteria into the environment via manure (to infect other animals) long before they appear to be sick.
The animal is usually infected as a calf, and the incubation period averages three to four years, sometimes as long as 10 or more years before the disease produces obvious signs. How soon the animal starts showing signs will depend partly on rate of infection and amount of exposure of young animals, according to Dr. Frank Garry (Department of Clinical Sciences, Colorado State University).
“It’s dose-related. If calves only pick up a few bacteria as babies, they may be able to hold it at bay longer and might not start showing clinical signs until they are four or five or even six years of age,” says Garry.
Infected, healthy-looking cattle can be shedding bacteria, infecting other animals, though the ones with clinical signs (diarrhea) will usually be the most significant shedders, passing millions of bacteria in their manure. Usually about 95% of infected animals within a herd are not showing signs yet; those that do are just the tip of the iceberg.
“It’s unusual to see Johne’s in a cow that’s really old. If she is beyond eight years you generally won’t see the disease because if she’s that old without showing signs she probably escaped infection,” he says. A cow of that age either didn’t become exposed to the disease or was infected in middle age and won’t show signs by the time she is culled.
“On the other hand if I see it in two or three year-olds, I know they became infected at birth. I’ve worked in dairies where we see it in bred heifers at 20 months of age. The earliest I’ve ever seen it was in a young purebred bull. He must have come from a seriously contaminated environment, or his dam was infected,” he says.
There are four stages of disease. Stage one is subclinical and “silent”--and generally not detectable with current tests. The infection progresses slowly and it may take months or years to reach stage two, in which the animal becomes a subclinical shedder. Stage two cattle are usually more than two years old and appear healthy, but shedding enough bacteria to detect by fecal culture, though blood tests may not pick it up yet. Animals in stage two pose a hidden threat to the herd unless a producer is checking for Johne’s with PCR tests—which are now more commonly used than cultures. Stage three is clinical disease, with diarrhea and weight loss. Usually the younger that the animal shows signs, the higher the likelihood of there being a high infection rate within the herd—and greater level of contamination. Stage four is watery diarrhea, emaciation and death.
How It’s Spread
Usual transmission is by ingesting the bacteria--eating or drinking contaminated feed or water or nursing a dirty udder. Young calves are at highest risk of picking up bacteria from manure, and may be infected before birth if the dam has Johne’s disease; about 30% of fetuses from cows in advanced stages of the disease will be born infected. Healthy calves are readily infected by nursing udders contaminated with manure.
They can become infected during birth. “A photo I show producers is of a calf being born, and the calf’s nose emerging from the vulva—which is directly below the anus. The cow often passes manure as she strains, and many calves end up with poop on their nose! It goes right onto the calf’s tongue—so there’s the first dose of bacteria!” says Garry.
“If the dam is infected, it is possible that the calf is already infected before birth, or could become infected during the delivery process, and it’s also possible to get the bacteria via the colostrum or milk.” So even in a very clean environment a calf can still get Johne’s--if his mother has the disease or if he is given colostrum from an infected cow. Beef calves given colostrum from dairy cows may be at risk. Several cases of Johne’s have also been traced to embryo transplant calves with Holstein mothers.
If the calf picks up bacteria before or soon after birth, it seems healthy until signs appear several years later--yet part of that time is shedding bacteria into the environment to infect more calves.
This disease can enter a herd quietly and by the time you realize there’s a problem, it has spread throughout the herd. You might buy an infected animal that looks healthy, and a year or so later it might break with diarrhea. Most people don’t connect the two events, not realizing that the animal was already infected at time of purchase. By the time signs show up in one animal, a number of others have already been infected and are shedding bacteria. If you see one animal in the herd with signs, there are many more animals in various stages of infection.
Effects Of The Disease
At first, these bacteria affect just the lower small intestine, causing gradual thickening of the intestinal lining, making it more difficult to absorb fluid and nutrients, hence weight loss and diarrhea. Body temperature and appetite remain normal, but the animal gradually loses weight and the color of its hair coat may fade. Eventually the bacteria spread to other parts of the body, and in later stages of disease are circulating through the blood stream and lymph system.
There is no effective treatment--the disease is not responsive to antibiotics, and is always fatal. As the animal enters stage four, it becomes more emaciated and then dies. Once an animal is diagnosed with Johne’s disease it should be sent to slaughter before the final stages. In stage four, diarrhea is watery and the animal becomes weak and often develops bottle jaw (edema and swelling between the lower jawbones). The fluid-filled lump under the jaw can also be a sign of parasitism or liver damage, or even brisket disease, however, and not just Johne’s disease.
Sometimes stage three (appearance of signs) is brought on by a period of stress, such as calving. A few animals that break with diarrhea may seem to recover temporarily, relapsing again the next time they are stressed. Diarrhea and weight loss is easily misdiagnosed as a parasite problem. The infected animal might respond for a while to parasite control if it is infested with parasites along with Johne’s disease. The “recovery”, however, is brief and it soon goes downhill again.
Many stockmen are not aware they have Johne’s in their herd, since they often cull subclinical animals before they show actual signs of the disease. Cows harboring bacteria during the long incubation period (before obvious signs of diarrhea and weight loss occur) often have higher rates of mastitis, lower milk production, more infertility and longer calving intervals.
If a person is rigorous in culling any animals in poor body condition, this can help reduce the number of animals that may be shedding bacteria. If you can do some things to minimize the risk of calves being exposed to manure from these individuals, this can help slow down transmission.
Even though some animals get culled before they break with diarrhea, Johne’s disease can eventually affect many animals within a herd, since the shed bacteria can survive in water for up to a year and in feces and soil for more than a year. Left unchecked, infection with Johne’s disease gradually mushrooms; within 10 years of the disease entering a herd, a number of young cows could be dying of Johne’s disease at three to four years of age.
Controlling The Disease
Today there are better tests for Johne’s than we had 25 years ago. “It’s a market-driven thing,” says Garry. “We had some good technology in the mid-1990’s but if no one wants to use the tests, there’s no compelling reason for a company to spend money improving tests that nobody uses.”
After about 1996, when the dairy industry decided it was important, this gave the opportunity to approach the federal government and get funding to improve laboratory function and testing methodologies. “The companies realized there was now a market for better tests. So between the labs, the companies and the federally funding, better testing methods were developed,” Garry says.
“When the federal government agreed to fund projects, we made a major step forward. Now there is a system in which diagnostic labs can validate that their tests are running well, using a check test. If you are doing Johne’s testing you can ask the lab if they’ve passed the check test. They do this through the NVSL – the National Veterinary Services Laboratory. With this process the NVSL sends the lab samples and the lab has to accurately identify which samples are infected and which are not. If they pass this check test, this validates their methods,” Garry says.
“The ELISA test is vastly improved. We used to do fecal culturing, which was very slow. Then we developed the liquid culture media and then the PCR test. The PCR test now has improved enough that it can replace the fecal culture. It is pretty reliable, though it will lie occasionally. All tests have a failure rate but with this PCR test the failure rate is not high,” he says.
There are reasons why it sometime fails. “For example, we must use appropriate sampling techniques. If you use the same rectal sleeve to collect samples from multiple animals, you contaminate all the samples. If multiple animals are in close confinement for 24 hours or more before you test them, you might have animals that are shedding a lot of bacteria and contaminating the feed. Other animals consuming that feed now have the pathogen in their GI tract and it is moving through, and you could pick it up in a fecal sample in what we call a pass through effect,” he explains.
“When we test the herd, if we find a few animals that are highly infected and a lot of animals that only have trace positive samples, and are merely suspect, you need to re-test because the process was flawed. The test itself, however, is really good,” he says.
“What we don’t have yet, and probably won’t in our lifetime, is a good vaccine. TB is closely related to MAP and we still don’t have a good vaccine for TB, even though it is one of the most important human pathogens. If we can’t get a good vaccine for TB, we are probably not going to have a breakthrough for MAP,” he explains.
“What we could do, however, is develop better cell-mediated tests. The body’s early response to the bug, in animals that become infected, is a cell-mediated immune response, which is different from a humoral immune response—which is what we test for with an ELISA serum test. That humoral response does not develop until quite late in the infection progression. When the infection becomes more robust, eventually the ELISA test goes positive. But the cell-mediated test is active from the beginning,” he says.
“When testing for TB, for example, we don’t use serology; we use cell-mediated tests. They are not perfect, but are pretty good. I am optimistic that we will create a cell-mediated test for MAP and once we create one that is reasonably accurate, we could pick up this disease much sooner, when the animal is younger. We could use it in heifers pre-breeding, even potentially in 6-month-old calves. If you could find it at weaning age, you could send all positive animals to a feedlot. They would be harvested before they ever develop infection at a high enough level to be shedding. They would never re-enter the herd, so the next crop of heifers would have high likelihood of not encountering the pathogen and would be free of the disease,” he explains.
You could systematically focus testing on young stock rather than mature cows, to make sure all heifers coming into the herd are free of infection. “This would fast-track the process and eliminate the economic loss of culling productive animals. We wouldn’t be arguing about what to do with offspring of infected animals. If we had tests that could pick up MAP at 6 months to a year of age, we could sell the infected animals before we invest all the time and feed into growing replacement heifers.” This would be a way to work toward a disease-free herd, and probably do it a lot quicker than how we do it today, since we can only find it in mature, heavily-infected animals.
You could remove the disease risk, and over a few years’ time eliminate the disease, compared with how long it takes today. “In the herds I’ve worked with, this has taken about 15 years, even with an aggressive approach. I am confident that we have completely eradicated Johne’s from two dairies. There are only a few people who choose this route and are this diligent, but it can be done.”
“If your herd has a high rate of infection, and you want to be aggressive resolving this, consider removing the most recent calves from any cow that tests positive. Those aren’t the only calves that might be infected, but their risk is much higher. So why wait until those calves are shedding bacteria. Just get rid of those calves because there is a market for them,” says Garry.
Mature animals that have been found positive should be sold for slaughter. It’s also important to keep any suspect animals away from young stock. If there are any suspicious animals, do some testing and track those animals carefully. “If the animal was in a certain pen, don’t put heifers in that pen, and maybe strip up the ground (to get rid of manure) and put down new gravel.” There are ways to reduce likelihood of maintaining the disease in the environment.
For more information, see the Johne’s Information Center website. This is updated frequently and has great resources, videos, and information specific to beef or dairy cattle, sheep and goats. The website is www.johns.org