VACCINATE TWICE A YEAR TO PREVENT LEPTO IN HERDS

by: Heather Smith Thomas

There are several bacterial infections in cattle that occur worldwide, and one of the most common is leptospirosis. Illness from this type of infection can be mild or severe, but this disease is economically significant because it is one of the most common cause of infectious abortion in cattle.

“Lepto” is caused by spiral shaped bacteria (spirochetes) that affect many kinds of animals, including humans. It is often present in wildlife populations, including rats and mice. The leptospires can survive in surface water, stagnant ponds, streams, or moist soil for long periods at mild temperatures. Thus it is generally a more common problem in moist climates and less problem in arid regions with little surface water. Leptospirosis is a common cause of infertility, delayed breeding and early embryonic death, as well as abortions or birth of premature and weak calves.

Transmission – Dr. Richard Hopper, Professor of Theriogenology in the Pathobiology and Population Medicine Department at Mississippi State University, says that cattle in his part of the country are continually exposed, since this organism is almost always present in the environment. This disease is spread by discharges and secretions (especially urine) of sick and carrier animals, which often contaminate feed and water. Some infected animals, particularly with certain strains of lepto, appear to be healthy, yet harbor the bacteria in their kidneys and reproductive tract, shedding the bacteria in urine or reproductive fluids.

As pointed out by Hopper, biosecurity measures (the person who has a closed herd versus a producer who occasionally brings cattle in from sale barns) won't help prevent exposure to leptospires, since these pathogens are shed by rodents, wildlife and other domestic species on the farm or ranch.

Bacteria may enter a susceptible animal via the nose, mouth or eyes by contact with contaminated feed, water or urine, or through breaks in the skin on feet and legs when walking through contaminated water. Urine or contaminated water splashing into the eyes of susceptible animals can spread the disease, as can breeding. Calves infected before birth (in the uterus) may shed the bacteria. Once the leptospires enter an animal, they multiply in the liver and migrate through the bloodstream to the kidneys; they release toxins that damage red blood cells, liver and kidneys.

Prevention – “We recommend twice a year vaccination of cattle in our region,” says Hopper. “This is not just because of the continual exposure, but also to give good protection during pregnancy. Vaccinating twice a year covers your bases regardless of your breeding season and breeding season length,” he says.

“In an area like ours, where the organism is everywhere and we are basically living with it, the multivalent vaccines are generally recommended. It's not that we are getting rid of carriers but vaccination is good insurance against abortion,” he says.

Diagnosis – “Continual progress is being made in diagnostics, using PCR and some of the newer tests, but there are two things that still complicate a conclusive diagnosis. One is the fragile nature of the spirochetes. If you get an aborted fetus and 24 hours later (when it might make it to a diagnostic lab), the tiny spirochete may be broken down and hard to find,” he says. It may have been there, but you are not sure, at that point.

“Secondly, serology can be confusing due to titers from vaccination and previous exposure. But here in the Southeast, whenever we have an abortion we tend to say that it's leptospirosis until proven otherwise. You may rule it out because you find something else, but some of the very best diagnostic labs tell us that for abortions in general, only 40 to 50 percent are definitively diagnosed,” says Hopper.

“There are likely some other organisms that have not been identified that also cause abortion occasionally. We have been concerned, along with the California dairies, about neospora, and it is also hard to diagnose. I am sure we had losses from that disease before we knew what it was, just as one example. There are also many genetic reasons for fetal losses.”

Clinical Signs Of The Disease In Cattle – Clinical disease in cattle is often mild and may go unnoticed, but in some cases the animal will be obviously ill. Since the spirochetes tend to localize in the liver and/or kidneys and may damage them, one of the things that may happen include liver disease or kidney failure. In that scenario, the animal would show signs of liver problems or kidney disease.

“Early in my career, maybe 30 years ago, I saw some clinical lepto cases, and in one instance a heifer died. The clinical signs in the cattle I observed included jaundice, anemia and high fever. These cattle had never been vaccinated, they were susceptible and also immune depressed. In that herd, several adult cows aborted and some of the breeding age heifers were clinically sick,” says Hopper.

“As another sign of lepto infection, a dairy cow would drop dramatically in milk production. You might not notice this as much in a lactating beef animal. Generally when a late-term abortion occurs, the cow will go ahead and bag up, but with a lepto abortion the cow may not bag up,” he says.

Be Pro-Active If A Cow Aborts – Even though an occasional abortion (maybe one percent of a beef herd) is commonplace, and nothing to worry about, you should be concerned if the herd average becomes higher than one to two percent. In that situation, there may be an underlying problem that needs to be addressed.

“If a cow aborts before your calving season begins, or in the early part of calving, you should take action to find the cause, if possible. If you have several hundred cows, you will generally have a few abortions over the years—perhaps from a freak accident or from one of those organisms we haven't identified yet,” says Hopper.

“But if you find a fetus, don't assume it's just one of those odd things. Go ahead and make an effort to figure it out. You don't know at that point whether it's just an odd-ball situation or the first of a devastating herd event.” You are at a point where it is easier to intervene and try to prevent further losses if you can figure it out at the start.







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