January 1, 2014
Leptospirosis is a common bacterial infection of cattle. Clinical illness can be mild or severe, but the cattle disease is economically important as it can cause abortion, infertility, illness — even death.
Most common in moist climates, lepto is caused by spiral-shaped bacteria (spirochetes) that affect both animals and humans. Often present in wildlife populations, including rats and mice, they survive in surface water, stagnant ponds, streams, or moist soil for long periods at mild temperatures.
Shelie Laflin, a Kansas State University DVM, says the pathogen resides in the kidneys of persistently infected animals. “It can be shed in urine and picked up by other animals through mucous membranes. If cow A urinates in a pond and cow B gets her face in the pond, she can potentially pick it up,” she explains.
Richard Hopper, a DVM and professor in Mississippi State University’s College of Veterinary Medicine, says cattle in his region are continually exposed, as the organism is ubiquitous in the environment. Biosecurity measures won’t prevent exposure, as the pathogens are shed by rodents, wildlife and other domestic species on the farm.
Bacteria can enter a susceptible animal via the nose, mouth, eyes or breaks in water-soaked skin as an animal walks through contaminated water, he adds. It can also spread during breeding, with infected fetuses later shedding the bacteria. Leptospires multiply in the liver and migrate via the blood to the kidneys, releasing toxins that may damage red blood cells, the liver or kidneys.
Mark Anderson, a University of California, Davis, diagnostic pathologist, says a healthy animal starts mounting an immune response after exposure.
“We see a titer rise if we check a blood sample. The organism may localize away from the immune response and hide in the liver or kidneys. Non-adapted strains may cause infection for awhile, but won’t persist in the animal. The hardjo bovis serovar, however [adapted to cattle], may persist for months,” he says. These pathogens have found a way to trick the immune system and survive, he adds.
“In cattle, infection with hardjo bovis causes minimal antibody titer, whereas L. pomona and other non-adapted strains trigger a more obvious rise and serologic response,” he explains. Hardjo bovis and the host can coexist without much problem; on occasion, however, the infection causes abortion and may infect the uterus and oviduct, resulting in breeding problems.
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“This adapted strain is widespread in the U.S. and doesn’t cause abortion storms as much as it causes some reproductive loss — repeat breeders or sporadic abortions,” Anderson says.
Abortion is generally the only obvious clinical sign. It may occur 1-3 months after initial infection with L. hardjo, and 1-6 weeks after infection with L. pomona. Herd abortion rate rarely exceeds 10% with L. hardjo, but may be higher with L. pomona or grippotyphosa infection.
While clinical disease is often mild, some cattle will suffer liver disease or kidney failure. There may be blood in the urine. Hopper has observed such clinical signs as jaundice, anemia and high fever.
Milk production in lactating cows can drop dramatically. “Generally, when a late-term abortion occurs, the cow will bag up. With a lepto abortion, she may not,” he says.
Craig Carter, director of the University of Kentucky’s Livestock Disease and Diagnostic Center, says he regards any case he sees in his lab as the tip of the iceberg. “In one situation, several yearlings went down, and a few of them died. No one suspected lepto until tests confirmed it,” he says.
The signs of acute lepto in cattle generally signal renal (kidney) failure. “This might be seen as poor performance, weight loss, appetite loss, decreased milk production, etc.,” Laflin says. Since the animal looks like a poor-doing cow, lepto might not be your first guess. “Without blood work to indicate high renal values, we might suspect hardware disease, leucosis or several other things,” she explains.
Hopper says diagnostic progress is being made with polymerase chain reaction (PCR) and other newer tests, but two factors complicate a conclusive diagnosis. One is the fragile nature of the tiny spirochetes, which may be broken down and hard to find by the time an aborted fetus gets to the diagnostic lab 24 hours later.
“Second, serology can be confusing due to titers from vaccination and previous exposure. In the Southeast, we tend to consider lepto as the cause of abortions, until proven otherwise. But only 40%-50% of all abortions are definitively diagnosed,” Hopper says.
Anderson says labs only get older fetuses to check, because no one finds early abortions when the embryo or fetus is tiny. On every fetus examined, his lab does a general fluorescent antibody (FA) stain that will reveal any type of leptospire.
“This is a quick, easy test, but depending on the condition of the fetus, it may not show anything. The spirochetes are very delicate, tiny and readily destroyed; we probably miss a lot of them,” he says.
“When someone submits an aborted fetus, we also want a serum sample from the cow. Since many producers vaccinate for lepto with multivalent vaccine, the aborting dam may have background vaccine titers — but these titers usually don’t get very high. If she has a high titer to just one serovar, such as pomona, it is good evidence she had lepto,” Anderson explains.
“The host-adapted serovar doesn’t elicit much of an immune response, however, so the cow may abort from hardjo, and have a negative titer. About 25% of cows that abort won’t have a titer at the time of abortion. This makes our serology tests even tougher,” Anderson says.
Many labs today use a PCR test, which Anderson says is almost too sensitive. “There are hundreds of free-living leptospires in the environment that aren’t pathogenic. Some labs have a generic test; if it comes up positive, they do a more specific test to identify leptospires within the pathogenic group,” Anderson says.
Carter says urine can be PCR-tested to see if an animal is shedding leptospires. “Work in Europe shows lepto also can be identified by PCR on vaginal swabs in an infected cow. We encourage producers and DVMs to send samples to a lab when they see a sick animal. Some of the other things we’d want to rule out might include anaplasmosis, babesiosis, redwater or even snakebite,” Carter says.
Daniel Grooms, a DVM in Michigan State University’s College of Veterinary Medicine, says a DVM can help illuminate the story by asking important questions. “When did the cow abort? How many aborted? Were they vaccinated? Abortion diagnostics is a big puzzle. The more clues we have, the better chance we have of solving it,” he explains.
If cows aren’t getting pregnant, and nutrition or bull problems have been ruled out, L. hardjo might be a suspect. “A common strategy for looking for L. hardjo is to screen the herd using urine samples from some of the open cows. If they’re all negative, we’re confident we don’t have lepto,” Grooms says.
If lepto is detected in a urine sample, it’s indicative of a herd situation and a potential contributor to infertility or breeding problems, he says. That’s particularly true if the herd’s vaccination program is substandard, or newer-generation vaccines haven’t been used.
Herd prevalence is 50%
Herd prevalence studies in North America found 40%-45% of beef herds infected with L. hardjo. “We suspect 50% of herds are infected or have at least one animal carrying L. hardjo. One study found higher rates of infection in southern vs. northern states. The most obvious difference is climate,” Grooms says.
“The northern U.S. or Canada may not have as much, but the prevalence can vary with cattle management. For instance, prevalence in dairy cattle is generally higher because they’re more confined,” he says.
What’s new in vaccines
“Until 10 years ago, we only had multivalent, five-way lepto vaccines that were whole-cell bacterins,” Grooms says. “They stimulated humoral immune response, and probably provided protection against pomona, grippotyphosa, etc., but weren’t effective against L. hardjo, which is host-adapted and carried by cattle. Thus, for many years, we found problems with lepto even in vaccinated animals. In the last 10 years, new vaccines appear to do a much better job of protecting against L. hardjo,” he says.
Newer vaccines also reduce the risk of renal colonization and kidney infection, he adds. When the first L. hardjo vaccines debuted, they were given in addition to the five-way vaccine. Today, several companies combine the serovars in one vaccine.
“The host-adapted serovar in the U.S. in cattle is L. borgpetersenii serovar Hardjo [type hardjo-bovis],” Anderson says. “The new vaccines — by Zoetis and Schering-Plough — have focused on this species.”
Some producers don’t vaccinate young animals for lepto, believing only cows need protection to prevent reproductive loss and abortion. This can leave younger cattle vulnerable, Carter says.
“Lepto vaccine is inexpensive. We also must remember that lepto is a zoonotic disease. If you have kids out there helping, or handling a 4-H calf, potential risk to human health raises the importance of preventing it in cattle,” Carter says.
As lepto vaccines are administered primarily to prevent reproductive losses, they should be given before breeding. Cows should be vaccinated twice a year, especially if likelihood of exposure is high. Grooms advises against vaccinating only at weaning. “The cows may be pregnant for several months at this point, with little protection.”
The important thing with any vaccine program for the breeding herd is establishing good immunity in replacement heifers, to build the foundation for future immunity, he says. Lepto vaccines require two initial doses (a booster 4-6 weeks after the first vaccination). “Make sure heifers get both doses prior to breeding to establish that foundation,” Grooms says.
Heather Smith Thomas is a rancher and freelance writer based in Salmon, ID.
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