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.