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If cows aren’t getting pregnant, and nutrition or bull problems have been ruled out, Leptospirosis hardjo might be a suspect.
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.