Leptospirosis – One of the cattle industry’s hidden production losses
Julia Herman, DVM, MS Beef Cattle Specialist Veterinarian, NCBA, a contractor to the Beef Checkoff | December 12, 2023
Leptospirosis (commonly known as “Lepto”) is one of many diseases that cattle producers may recognize that is a zoonotic disease, meaning an infectious disease can that be passed between animals to humans. It is caused by the bacteria Leptospira which has a characteristic corkscrew-like shape (spirochete) that helps its motility. There are hundreds of pathogenic serovars (distinct variants of Leptospira with unique surface structures) that can infect many different mammals, humans included. These serovars can be adapted to specific host species, such as Leptospira borgpetersenii serovar Hardjo (previously known as L. hardjo-bovis) which is specific to cattle, or nonhost-adapted, meaning they can infect multiple host species, such as L. interrogans serovar Pomona. Leptospira infect the kidney and/or reproductive tract of farm animals. It can be transmitted directly from animal to animal (or animal to human) via urine or indirectly through the environment. Dogs, rodents, livestock, and horses can become carrier animals, which have no outwards signs of infection. It is an important reproductive disease, causing reproductive failures such as bovine abortions and early pregnancy loss. Acute infections are seen less frequently and usually present as reproductive failures. Infected animals can also suffer from weight loss, milk loss, and death. Chronically infected animals can become an important reservoir to continually contaminate the environment and increase the risk of other animals becoming infected.
Vaccines have historically been used to minimize the effects of leptospirosis infections in cattle and is the cheapest option for most cattle producers, costing $2.50-5.00 per dose. However, these vaccines have short-term protection and chronic infections are not completely prevented. Even when using commercial Leptospira vaccines, chronic kidney infections can still occur, which creates carrier animals that continue to infect the environment, other animals, and potentially humans. These carrier animals continue to have poorer reproductive success after infection. In addition, existing vaccines are only covering about seven of over 300 serovars and are not cross-protective (a vaccine for one serovar does not provide protection from other serovars). New technologies are being researched to determine how better Leptospira vaccines can be developed and best help cattle producers from suffering preventable production losses.
To properly treat cattle for this disease, an accurate diagnosis needs to occur, which generally involves an investigation by the herd veterinarian, physical exam(s) of affected cattle, and submitting samples to a diagnostic laboratory for serovar identification. Leptospira bacteria are difficult to grow even with the best conditions. Thus, one obstacle for improving diagnostics is the lack of genomic data from diverse pathogenic Leptospira strains because live isolates are very difficult to obtain. Another test that can be used is Polymerase Chain Reaction (PCR), which detects specific genes of the Leptospira genome in samples. These are not foolproof as the specific genes may not be present in all serovars and so some infections may be misidentified as a negative sample (false-negative test). Identifying the genomic diversity of the serovars will improve diagnostic test development, reduce false negative results, and better detect and distinguish strains.
Optimizing culture and laboratory isolation of this bacteria has been an ongoing goal for Jarlath Nally, a research microbiologist with USDA Agricultural Research Service. He has worked with several host species and sample types to improve current diagnostic techniques for Leptospira. The novel techniques his lab uses has helped discover a new Leptospira serovar in a dairy cow in Minnesota, L. borgpetersenii serovar Tarassovi, which is not covered in any U.S. vaccine. Similarly, a new species was identified in soil and water samples from Puerto Rico. “Finding leptospirosis in these soil and water samples was challenging,” Nally describes. “It has helped us understand the environmental sources of infection for animals and humans to better reduce transmission.”
David Wagner, a professor of biological sciences at Northern Arizona University, and his lab have been studying which Leptospira strains are found in different areas through DNA analysis. Through previous projects, his lab has helped identify new Leptospira strains not previously known to infect cattle. “We really do not understand the true burden of leptospirosis in the livestock industry,” explains Wagner. “Subclinical cases are common in cattle and can occur in vaccinated herds but based on current diagnostics we are unable to fully quantify that true burden and what the industry is losing.”
Together, these researchers are providing a unique approach to understanding leptospirosis in the U.S. cattle population. Using Nally’s culturing and isolation techniques and Wagner’s genetic analysis, they want to generate new genomic information for Leptospira species infecting U.S. agricultural animals and use that information to improve diagnostic tools for detection and characterization of these species. The genomic information will be sequenced to help improve diagnostics and vaccine development using new technologies. “We know that leptospirosis is a widespread problem in both the beef and dairy industries,” Wagner adds. “Our goal is to reduce these production losses by improving detection, investigation, and control of the disease in the livestock industry.”
Because Leptospira infections in U.S. agricultural animals are underreported, these types of samples are not readily available. Nally and Wagner are collaborating with cattle producers, veterinarians, and state diagnostic laboratories to send Leptospira-suspect PCR samples collected from livestock to the USDA National Veterinary Services Laboratories (NVSL). Any positive samples will be transferred to Wagner’s lab for genetic analysis. These samples will add to the growing database of recently described pathogenic species of Leptospira and contribute to developing better surveillance and control options in the future. For more information on diagnostic testing completed at NVSL, visit:
https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/lab-info-services/sa_diagnostic_tests/ct_diagnostic_tests.
Until newer detection and surveillance methods are developed, cattle producers are encouraged to continue using prevention practices described in the BQA program that are specific to zoonotic diseases. If any of your operation’s animals are diagnosed with leptospirosis, your herd veterinarian will provide a treatment plan that may include antibiotics and isolating infected animals. Using proper personal protective equipment when handling known infected animals will protect farm workers from potential transmission. Minimize environmental transmission through good sanitation, reducing access to collected water or puddles, and reducing exposure to rodents. If your herd is not already using leptospirosis vaccines in the pre-breeding plan for bulls, cows, and replacement heifers, talk with your herd veterinarian about your herd’s specific risks. Vaccines should be provided at least six to eight weeks before breeding season, after the initial primary and booster vaccinations have been completed (always follow label instructions).
“This practical research is industry driven and we are eager to partner with the cattle industry to develop a solution,” says Nally. In collaborations like this project, cattle producers can directly contribute to new research that will positively impact their industry in the future. The value in examining samples from all over the country is understanding the dynamics of the Leptospira species in different regions and environments. This will benefit future herd health planning and risk management for cattle herds as the true consequence of leptospirosis is better described.
This article was originally published in the December 2022 issue of NCBA National Cattlemen newsletter.
Share This Page