Leptospirosis may be more common in U.S. cattle than veterinarians may realize. The challenge is that infected cattle do not always look sick, existing diagnostic tests can be difficult to interpret and vaccination does not necessarily mean an animal is free from infection.
For Elsio Wunder, DVM, Ph.D., assistant professor at the University of Connecticut, that combination has created a problem that goes beyond diagnostics. It has made leptospirosis easy to overlook.
“I want people to see that it is a problem that we should be talking about,” he says.
Wunder has spent roughly two decades studying Leptospira, moving from veterinary diagnostics and vaccine development into a One Health approach that considers the connections between animals, people and the environment. His latest work, supported by a three-year, $570,000 grant from the U.S.-Israel Binational Agricultural Research and Development Fund, is aimed at developing better diagnostic tools for bovine leptospirosis.
The goal, however, is bigger than a new test. Wunder wants researchers and veterinarians to take another look at a disease that he believes has been overlooked.
Why Leptospirosis Is Difficult to Detect in Cattle
Leptospirosis can be difficult to recognize at the herd level because cattle with chronic infections may not show obvious clinical signs. Instead, the bacteria can colonize the kidneys and be shed into the environment through urine.
“They colonize the kidney, the animals have no symptoms, and they are spreading to the environment which impacts other animals, including humans,” Wunder explains.
That creates a disconnect between infection and what a veterinarian sees in the barn. Reproductive problems, including abortions and other fertility issues, can prompt investigation, but those signs are nonspecific and can have many causes.
Wunder says the problem is compounded by the fact that leptospirosis has often been treated as though it were primarily a disease of other regions or populations.
His own experience illustrates that attitude. When he was considering coming to the University of Connecticut, Wunder recalls being told that leptospirosis was not a problem in the state and that nobody cared about it.
His response was simple: people were not looking for it.
“I just want people to see that it is a problem that we should be talking about,” Wunder urges.
The work his group has since conducted in Connecticut has challenged that assumption. Wunder says his team has found Leptospira in cattle, including vaccinated animals, demonstrating that vaccination alone cannot be used to assume the organism is absent from a herd. His group has also found vaccinated cows excreting the bacteria into the environment.
That does not mean vaccination is ineffective. Wunder emphasizes that vaccines are valuable for protecting animals from clinical disease. The concern is that protection from clinical disease is not necessarily the same as preventing chronic infection and bacterial shedding.
Vaccination Complicates Leptospirosis Diagnosis in Cattle
If a veterinarian suspects leptospirosis, however, determining what a positive result means can be difficult.
Serologic testing can detect antibodies against Leptospira, but vaccination can complicate interpretation. Current diagnostic approaches also reflect decades of work on the organism, while the Leptospira landscape has continued to change. Many existing tests rely on strain-specific antigens, potentially requiring large panels to account for the diversity of the organism.
“The most problematic thing is that you cannot differentiate the agglutination of positivity from vaccination,” Wunder explains.
That uncertainty can create a practical problem for veterinarians. A positive result does not necessarily answer the question they actually need answered: Is this animal currently infected? Is it carrying and shedding the organism? Or is the result reflecting previous vaccination or exposure?
Wunder says that uncertainty can discourage testing in the first place.
His research is aimed at making the answer more actionable.
New Diagnostic Targets Could Improve Bovine Leptospirosis Testing
Wunder’s diagnostic work grew directly out of his research on leptospirosis vaccines. His team identified proteins that appear to play important biological roles in infection and protection. The new project will investigate whether those same proteins can serve as diagnostic targets.
The approach could eventually allow researchers to move away from testing individually for large numbers of Leptospira strains and instead develop a test based on conserved protein targets.
The need for that broader approach stems from the diversity of Leptospira. Wunder points out that current vaccines cover only a limited number of strains, while isolates outside those groups have been identified in animals.
“The traditional vaccines are behind the game in terms of protection,” he says.
That work is still in the research stage. Wunder’s team first needs to better understand which Leptospira species and serovars are circulating in cattle and identify targets that can reliably distinguish infection from vaccination. His team is collecting samples from farms and slaughterhouses and using culture and sequencing to characterize the organisms they find.
The eventual goal is a diagnostic that can identify infected or carrier animals more clearly, giving veterinarians a better picture of what is happening within a herd and across a region.
Leptospirosis in Cattle Is a One Health Concern
The implications extend beyond cattle.
Leptospira is shed through the urine of infected animals and can contaminate the surrounding environment. Other animals can be exposed, and people can become infected through contact with contaminated environments or animal urine. That makes the presence of apparently healthy carrier cattle relevant not only to herd health, but also to the people working around those animals.
“It’s not just about the farm itself, it’s not just about those animals,” Wunder explains. “It’s about everything else in the environment that leptospirosis impacts and then the spillover to humans as well.”
Wunder also believes the conditions surrounding leptospirosis deserve greater attention. Changes in rainfall, humidity, flooding, temperature and social conditions could influence the environments in which Leptospira persists and spreads. Human leptospirosis cases in several U.S. cities have been rising, and changing environmental conditions could intensify the problem.
This means leptospirosis may deserve a place on the differential even when the clinical picture is not obvious.
What Better Leptospirosis Diagnostics Could Mean
“I’m 110% researching lepto,” Wunder exclaims, indicating that he’s working full speed ahead.
That passion is part of why Wunder has stayed with a disease he considers neglected. He sees the lack of attention as a reason to continue working on it rather than a reason to move on.
The first step, he argues, is simply recognizing that the disease is present.
Cattle can carry Leptospira without obvious clinical signs. Vaccinated cattle can still harbor and shed bacteria. Existing diagnostic tools can leave veterinarians uncertain about what a positive result means. And the strains circulating today may not look exactly like those researchers were studying decades ago.
Better diagnostics could help close those gaps. But for Wunder, the larger goal is awareness.
“I want people to talk about the disease, talk about how important it is, talk about it,” he says.
If veterinarians start looking for leptospirosis differently, Wunder believes they may begin seeing a disease that was never truly absent.
