Leptospirosis

The Organism

Leptospirosis is caused by bacteria in the genus Leptospira. These are spirochetes—thin, spiral-shaped bacteria capable of moving through liquid and moist tissues.

Leptospira organisms are classified by both genetic species and serovar. A serovar is an antigenically distinct type, identified by differences in surface structures recognized by the immune system. More than 300 serovars have been described [1].

Serovars are particularly useful for understanding epidemiology because different serovars tend to be associated with different maintenance hosts and patterns of disease. However, the same serovar may occur in more than one Leptospira species.

Immunity is often serovar-specific, so protection against one serovar may provide limited protection against another. This is why cattle vaccines identify the serovars they contain and why vaccinated animals may remain susceptible to organisms not adequately covered by the product [2].

Five serovars are especially relevant to cattle in the United States:

• Hardjo: Two genetically distinct types are recognized: Leptospira borgpetersenii serovar Hardjo (type hardjo-bovis) and Leptospira interrogans serovar Hardjo (type hardjoprajitno). Both are associated with cattle, which serve as important maintenance hosts. It is strongly associated with persistent infection and reproductive losses. The hardjo-bovis type is particularly relevant to cattle in the United States.
• Pomona: Associated with pigs and wildlife reservoirs and can cause acute illness and abortion in cattle.
• Grippotyphosa: Associated with wildlife, including certain rodents and other mammals.
• Icterohaemorrhagiae: Strongly associated with rats and other rodents.
• Canicola: Traditionally associated with dogs.

Vaccine labels and older publications may use historical species names or designations such as Leptospira borgpetersenii serovar Hardjo, type hardjo-bovis.

Where Leptospira Lives

Many pathogenic Leptospira serovars have characteristic maintenance hosts: animal species in which infection can persist and from which transmission can be sustained.

Maintenance hosts often show little or no clinical illness. Some infected animals carry organisms in their kidneys or reproductive tract and shed them for prolonged periods, although not every infected animal becomes a lifelong carrier [1].

Incidental hosts acquire infection outside the usual maintenance-host relationship. They may develop more obvious or severe illness, although the outcome varies with the host, organism, and circumstances of infection.

Cattle are the principal maintenance host for Hardjo. Persistent infection and transmission within cattle populations can therefore occur without continual introduction from wildlife.

Other serovars may reach cattle through contact with rodents, feral swine, or wildlife, including raccoons, skunks, opossums, and deer. Studies in Arizona have documented leptospiral exposure in wildlife, including coyotes, rodents, and collared peccaries [3].

Infection

Pathogenic leptospires can colonize the renal tubules, the microscopic structures in the kidneys that carry urine. In cattle, infection may also persist in reproductive tissues and the mammary gland.

These sites can permit organisms to remain despite an immune response. Antibodies may be detectable in blood even when infection persists, while other carrier animals develop weak or transient antibody responses [1].

The duration of urinary shedding varies by serovar, host, and individual animal. A veterinary review described an average shedding duration of approximately 36 days across certain infections, compared with about 215 days for Hardjo, with shedding often greatest during the first several months [4]. These are study-derived estimates, not reliable predictions for every infected cow.

A two-year study of six dairy herds identified leptospiral urinary shedding in 194 of 411 cows. None of the shedding animals showed obvious clinical illness, and intermittent shedding was documented in a substantial proportion [2].

This is a central problem in diagnosing bovine leptospirosis: one negative urine sample does not reliably exclude persistent infection.

Blood testing has similar limitations. The microscopic agglutination test, or MAT, detects antibodies, not the organism itself. Cattle carrying Hardjo may develop low or short-lived antibody titers, making some infections difficult to identify serologically [1].

In the dairy study, only a minority of cows with evidence of urinary shedding had positive serologic results [2]. An individual case report also documented a clinically normal Holstein that shed leptospires intermittently over 18 weeks despite repeatedly negative antibody tests, including testing against the organism recovered from its urine [5].

Such findings demonstrate that persistent infection can occur despite negative serology. They do not mean that every negative test is unreliable or that all infected cattle remain carriers indefinitely.

Even when urinary shedding is no longer detected, organisms may occasionally persist in renal tissue [5]. Treatment and vaccination can reduce infection and shedding, but elimination of carriage cannot be assumed in every animal.

The practical lesson is that infection status often requires interpretation of multiple findings—clinical history, herd history, vaccination, serology, and direct detection—rather than reliance on one result.

How Leptospira Spreads

Infected animals can shed pathogenic leptospires in urine. Depending on the host and infection, organisms may also be present in reproductive fluids, milk, semen, and tissues associated with pregnancy [1].

Environmental transmission is particularly important. Urine from an infected animal can contaminate soil, mud, bedding, ponds, or standing water. Other animals become exposed when contaminated material contacts the mouth, eyes, nose, genital mucosa, or damaged skin. Prolonged immersion can also soften skin and increase susceptibility [1].

Environmental survival depends on moisture, temperature, pH, sunlight, and the organism involved.

Pathogenic leptospires generally survive poorly in dry environments and are vulnerable to direct sunlight and unfavorable temperatures. However, specific temperature thresholds should not be treated as universal limits. Under favorable conditions, organisms may survive for prolonged periods in moist soil or freshwater [6].

A six-state study of beef cow-calf operations found associations between leptospiral infection and factors including warmer average temperatures, longer breeding seasons, and the use of ponds as water sources [7].

These associations help identify conditions that may increase exposure, but they do not establish that every pond or warm-weather herd is infected.

Infection Pattern

Clinical signs depend on the age of the animal, the infecting serovar, and whether the animal is a maintenance or incidental host.

In calves and young cattle, infection with certain non-host-adapted serovars, including Pomona, may cause acute systemic disease. Signs include fever, reduced appetite, hemolytic anemia, hemoglobinuria—red or brown urine caused by hemoglobin released from damaged red blood cells—jaundice, and occasionally death [6].

In adult cattle, Hardjo infection is often clinically silent until reproductive losses become apparent. These may include abortion, stillbirth, weak or premature calves, and reduced fertility [4].

Dairy cattle may develop milk drop syndrome, characterized by a sudden reduction in milk production, sometimes involving many animals in the herd. The udder may appear unusually soft or flaccid [4].

The interval between infection and abortion varies. Some acute infections are followed by abortion relatively soon afterward, whereas persistent Hardjo infection may be associated with reproductive losses weeks or months later. By the time abortion occurs, antibody titers may be low or difficult to interpret, particularly in vaccinated cattle [1].

What to Do If You Suspect Leptospirosis

Call your veterinarian when unexplained abortions, stillbirths, sudden milk losses, or compatible illness occur.

Preserve the aborted fetus and placenta for diagnostic testing. Place them in appropriate leakproof containers, refrigerate them, and arrange prompt submission. Do not freeze them unless the receiving laboratory specifically instructs you to do so.

Avoid handling urine, placental material, fetal tissues, or contaminated bedding without protection. Wear gloves, waterproof outer clothing, and eye protection. Pathogenic leptospires can enter through mucous membranes and damaged skin [1].

Record which animals aborted, when abortions occurred, animal ages, vaccination histories, recent purchases, and water sources.

Leptospirosis often requires a herd-level investigation because individual cattle may carry or shed the organism without appearing ill. Nevertheless, testing individual animals and fetuses can provide valuable diagnostic evidence.

Where practical, reduce access to potentially contaminated standing water and flooded areas. Discuss herd management, testing, vaccination, and treatment with your veterinarian.

Diagnostic Differential

Other infectious causes of abortion in cattle include brucellosis, neosporosis, infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), trichomoniasis, campylobacteriosis, listeriosis, salmonellosis, Q fever, fungal abortion, and—in parts of the western range—foothill abortion.

These conditions cannot reliably be distinguished by abortion alone. Laboratory examination is usually necessary, and a cause is not identified in every submission. In one California diagnostic-laboratory series, an etiology was established in approximately 57% of bovine abortion cases [8].

In cattle with hemoglobinuria, other important differentials include babesiosis, anaplasmosis, bacillary hemoglobinuria, and postparturient hemoglobinuria.

Diagnosis

The microscopic agglutination test (MAT) is a widely used serologic test for leptospirosis. It measures antibodies that react with selected Leptospira serovars.

A high MAT titer in an unvaccinated animal with compatible clinical findings may support recent infection, but a single titer does not conclusively establish active disease. Vaccination, previous exposure, and cross-reactions can complicate interpretation [1].

A fourfold rise in antibody titer between acute and convalescent samples is stronger evidence of recent infection. The sampling interval should follow the diagnostic laboratory’s recommendations and allow sufficient time for the antibody response to develop.

Serology is particularly challenging in cattle carrying Hardjo because titers may be low or absent despite persistent infection.

MAT results also do not reliably identify the infecting serovar. The highest-reacting serovar is not necessarily the organism responsible for the infection, especially early in disease or after vaccination [1].

PCR can detect leptospiral DNA in urine, blood, or tissues, depending on the stage of infection. PCR detection does not necessarily demonstrate that viable organisms are present. Culture can demonstrate viable bacteria but is technically demanding, slow, and less routinely available.

For herd investigations, testing multiple animals is generally more informative than testing a single cow. A veterinary review recommends sampling at least 10 animals or approximately 10% of the herd, whichever is greater, depending on the investigation [1]. The number required to detect infection depends on prevalence, test performance, and sampling strategy.

A separate statistical example suggests that testing approximately 15 animals can provide a high probability of detecting at least one positive animal when prevalence is around 20%, assuming suitable test sensitivity and representative sampling [4]. This is a sampling calculation, not a guarantee of detection.

What to Collect

Urine: Collect a clean specimen according to the receiving laboratory’s instructions and submit it promptly. Some protocols use repeated collection or urine obtained after administration of a diuretic, but this should be directed by the veterinarian and laboratory [4].

Abortion: Submit the whole fetus and placenta, chilled, when possible. Fetal kidney and other tissues may be useful for PCR and histopathology. Maternal blood samples may be collected for paired serology [4].

The choice of specimens depends on the suspected stage of infection and the tests available.

Risk to Humans

Leptospirosis is a zoonotic disease. People become infected through contact with urine or tissues from infected animals or with contaminated water and soil. Flooding and heavy rainfall can increase exposure risk [9].

Veterinary personnel, livestock workers, dairy workers, slaughterhouse workers, and people handling contaminated water or animal tissues may be at increased risk.

Symptoms generally begin 2 to 30 days after exposure. Common findings include fever, chills, headache, severe muscle pain, and conjunctival suffusion—redness of the eyes without the typical discharge of conjunctivitis [9].

Some patients experience a biphasic illness, with an initial febrile period followed by temporary improvement and then a second phase. However, not every infection follows this pattern.

Most symptomatic infections are mild to moderate, but a minority progress to severe disease involving the kidneys, liver, lungs, or central nervous system.

Weil’s disease is a severe form characterized by jaundice and kidney dysfunction, often with additional organ involvement. Severe pulmonary hemorrhagic syndrome involves bleeding into the lungs and can have a high fatality rate [6, 10].

The proportion of patients developing severe illness and the associated mortality depend on the population studied, the case definition, and access to treatment. The percentages reported in older fact sheets should not be interpreted as fixed risks for every infected person.

The United States reports relatively few human cases annually compared with many tropical countries. Puerto Rico and Hawaii have historically contributed substantially to reported US cases [10].

Arizona recorded five human cases between 2006 and 2023 in the state surveillance protocol [11].

Human exposure during the Arizona canine outbreak

During the 2016–2017 canine leptospirosis outbreak in Maricopa County, investigators evaluated people who had contact with affected dogs. All 118 tested individuals were negative for evidence of infection, despite some reporting direct contact with potentially infectious urine or blood without gloves [12].

This finding is reassuring for that particular investigation but does not mean that infected dogs cannot transmit leptospirosis to people.

Avoid unprotected contact with animal urine and contaminated materials. People who develop compatible symptoms after an exposure should seek medical evaluation and describe the exposure.

Treatment, Vaccination and Control

Antibiotic treatment can reduce leptospiral infection and urinary shedding, but the likelihood of eliminating persistent carriage varies.

An in-vitro study found reduced tetracycline susceptibility among some bovine leptospiral isolates [13]. Laboratory susceptibility findings do not, by themselves, establish that treatment will fail in infected cattle.

A veterinarian should select treatment based on the animal’s condition, available evidence, drug regulations, and applicable meat or milk withdrawal periods.

Cattle leptospirosis vaccines contain selected serovars. They can reduce clinical disease and reproductive losses, but protection is not uniform across products, serovars, or infection outcomes.

Vaccination may also reduce renal colonization and urinary shedding in some circumstances. However, complete prevention of infection and carriage cannot be assumed [2].

Introducing infected replacement animals is one possible way to bring leptospirosis into a herd. Buying animals from herds with known health histories, isolating incoming stock when practical, and discussing testing and vaccination with a veterinarian can reduce risk [4].

Because a single negative test may miss a carrier, testing should be interpreted in the context of herd history and exposure risk.

Other preventive measures include limiting access to potentially contaminated standing water, improving drainage where feasible, reducing rodent activity, and managing contact with wildlife.

What Leptospirosis Costs Producers

Leptospirosis is not managed through a federal cattle eradication program comparable to bovine brucellosis or tuberculosis. The 2026 national animal-health reporting list does not identify routine bovine leptospirosis as a federally monitored program disease [14].

A diagnosis does not ordinarily trigger the same federal herd quarantine and movement restrictions associated with those eradication programs. However, applicable state rules and any concurrent investigation of an unexplained abortion outbreak still matter.

The principal economic losses are reproductive and productive: abortions, stillbirths, weak calves, open cows, longer calving intervals, and reduced milk production.

Persistent infection may also make the disease difficult to recognize and control because apparently healthy animals can remain sources of exposure.

Where to Report a Case in the Southwest

Leptospirosis is not a federal cattle eradication-program disease. The national animal-health reporting list does not establish a routine federal reporting requirement for bovine leptospirosis [14]. State animal-health and human public-health requirements differ.

Documented Incidence in the Southwest

Several factors associated with leptospirosis exposure—including warmer temperatures, ponds used for livestock water, and contact between cattle and wildlife—occur in the Southwest [7].

Seasonal rainfall and monsoon flooding could increase opportunities for environmental exposure. A quantitative relationship between Southwest monsoon conditions and leptospirosis incidence has not been established by the studies discussed here.

Arizona

Leptospirosis has been documented in people and dogs, and historical serologic evidence of exposure exists in cattle.

A large outbreak among dogs occurred in Maricopa County from January 2016 through June 2017, involving more than 70 reported cases. The source was not identified, and livestock contact was not established as a risk factor [3].

A published serologic survey of Arizona beef cattle was conducted in 1981 [20]. That study demonstrates historical exposure but cannot establish current prevalence in Arizona herds.

Current statewide prevalence of bovine leptospirosis in Arizona is not established by the historical cattle survey.

New Mexico

Published livestock-specific leptospirosis data are limited.

USDA’s National Animal Health Monitoring System included New Mexico operations in broader cattle surveys, but the report did not provide Leptospira serology for those operations [21].

The New Mexico Department of Agriculture’s Veterinary Diagnostic Services lists a five-serovar MAT panel, indicating that diagnostic testing is available, but the fee schedule does not provide statewide case counts [22].

CDC surveillance figures report no confirmed human cases from 2017 through mid-2026, with probable cases recorded in 2020, 2021, and 2022 [23].

Limited published surveillance should not be interpreted as evidence that leptospirosis is absent from New Mexico livestock or wildlife.

Texas

Texas has more published cattle data than Arizona or New Mexico.

In a slaughterhouse study, 22% of 1,193 cattle serum samples reacted to serovar Pomona and 15% to Hardjo. Leptospiral DNA was detected by PCR in 35% of 300 urine samples [24].

These findings indicate substantial evidence of exposure and leptospiral DNA detection in the sampled population. They do not establish that 35% of all Texas cattle were actively shedding viable leptospires.

Texas was also included in a six-state beef cow-calf study that found herd-level results compatible with Hardjo infection and identified environmental and management risk factors [7].

In 2024, the Texas A&M Veterinary Medical Diagnostic Laboratory described a bovine abortion case in which Leptospira DNA was detected in fetal liver and kidney [25].

Other studies provide evidence of exposure or infection in Texas animals:

• A national canine PCR study covering 2009–2016 reported 9.1% positivity among the Texas samples included in its dataset [26].
• In a 2015 survey, 49% of 376 feral swine sampled at two Texas abattoirs had antibodies to Leptospira [27].
• An older study isolated leptospires from desert rodents in West Texas [28].

These studies involve different species, sampling methods, and time periods. Their percentages should not be compared directly as estimates of statewide prevalence.

Human leptospirosis is not included in the 2026 Texas notifiable-conditions list [19]. Historical public-health reports nevertheless documented cases when surveillance requirements differed, including reports from 1978, 1981, 1985, and 1986 [29].

Historical Texas case counts should be interpreted within the reporting practices and surveillance periods of the corresponding annual reports.

References

1. WOAH Terrestrial Manual, Chapter 3.1.12: Leptospirosis. World Organization for Animal Health, 2021. https://www.woah.org/fileadmin/Home/fr/Health_standards/tahm/3.01.12_LEPTO.pdf↑ a b c d e f g h i j k
2. Monti G, Montes V, Tortosa P, Tejeda C, Salgado M. Urine shedding patterns of pathogenic Leptospira spp. in dairy cows. Veterinary Research 2023;54:64. https://doi.org/10.1186/s13567-023-01190-w↑ a b c d
3. Iverson SA, Levy C, Yaglom HD, et al. Clinical, diagnostic, and epidemiological features of a community-wide outbreak of canine leptospirosis in a low-prevalence region. JAVMA 2021;258(6):616–629. https://stacks.cdc.gov/view/cdc/113769/cdc_113769_DS1.pdf↑ a b
4. Hairgrove TB. Leptospirosis in cattle. AABP Proceedings 2004;37. https://bovine-ojs-tamu.tdl.org/aabp/article/view/4897/4788↑ a b c d e f g
5. Hamond C, LeCount K, Putz EJ, et al. Bovine leptospirosis due to persistent renal carriage of Leptospira borgpetersenii serovar Tarassovi. Frontiers in Veterinary Science 2022;9:848664. https://frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.848664/full↑ a b
6. Leptospirosis technical factsheet. Center for Food Security and Public Health, Iowa State University, 2013. https://www.cfsph.iastate.edu/Factsheets/pdfs/leptospirosis.pdf↑ a b c
7. Wikse SE, Rogers GM, Ramachandran S, et al. Herd prevalence and risk factors of Leptospira infection in beef cow/calf operations in the United States. The Bovine Practitioner 2007;41(1):15–23. https://bovine-ojs-tamu.tdl.org/bovine/article/view/2870↑ a b c
8. Clothier K, Anderson M. Evaluation of bovine abortion cases and tissue suitability for identification of infectious agents in California diagnostic laboratory cases from 2007 to 2012. Theriogenology 2016;85:933–938. https://ccfruitandnuts.ucanr.edu/sites/default/files/2023-05/384244.pdf↑
9. About leptospirosis. US Centers for Disease Control and Prevention, updated 10 February 2026. https://www.cdc.gov/leptospirosis/about/index.html↑ a b
10. Leptospirosis fact sheet for clinicians. US Centers for Disease Control and Prevention, 30 January 2018. https://www.cdc.gov/leptospirosis/pdf/fs-leptospirosis-clinicians-eng-508.pdf↑ a b
11. Leptospirosis protocol. Arizona Department of Health Services, revised 18 June 2025. https://azdhs.gov/documents/preparedness/epidemiology-disease-control/investigation-manual/vectorborne/leptospirosis-protocol.pdf↑ a b
12. Guagliardo SAJ, Iverson SA, Sunenshine R, Schafer IJ, et al. Despite high-risk exposures, no evidence of zoonotic transmission during a canine outbreak of leptospirosis. Zoonoses and Public Health 2019;66:223–231. https://stacks.cdc.gov/view/cdc/216983/cdc_216983_DS1.pdf↑
13. Correia L, Loureiro AP, Lilenbaum W. Reduced susceptibility in leptospiral strains of bovine origin might impair antibiotic therapy. Epidemiology & Infection 2019;147. https://www.cambridge.org/core/product/2DA82DDFF2004A560669D5464EFD5584/core-reader↑
14. Voluntary 2026 National Animal Health Reporting System reportable disease list. USDA APHIS, 2026. https://www.aphis.usda.gov/sites/default/files/nlrad-nahrs-disease-list.pdf↑ a b
15. Arizona Administrative Code § R3-2-402: Mandatory disease reporting by veterinarians and veterinary laboratories. https://www.law.cornell.edu/regulations/arizona/Ariz-Admin-Code-SS-R3-2-402↑
16. 21.30.4.9 NMAC: New Mexico reportable disease list. New Mexico Livestock Board, effective 16 July 2024. https://www.srca.nm.gov/parts/title21/21.030.0004.pdf↑
17. 7.4.3.13 NMAC: Notifiable conditions and reporting timeframes. New Mexico Department of Health. https://www.srca.nm.gov/parts/title07/07.004.0003.pdf↑
18. 4 TAC § 45.3: Reportable and actionable disease list. Texas Animal Health Commission. https://www.law.cornell.edu/regulations/texas/4-Tex-Admin-Code-SS-45-3↑
19. Texas notifiable conditions, Rev. 01/01/26. Texas Department of State Health Services. https://www.dshs.texas.gov/sites/default/files/IDCU/investigation/Reporting-forms/notifiable-conditions-2026-black-and-white.pdf↑ a b
20. Songer JG, Chilelli CJ, Marshall MM, Noon TH, Meyer R. Serologic survey for leptospirosis in Arizona beef cattle in 1981. American Journal of Veterinary Research 1983;44(9):1763–1764. https://pubmed.ncbi.nlm.nih.gov/6625331/↑
21. Vaccination of cattle and calves on U.S. beef cow-calf operations. USDA APHIS Veterinary Services, National Animal Health Monitoring System, #564.1209, December 2009. https://www.aphis.usda.gov/sites/default/files/beef0708_is_genvacc_1.pdf↑
22. Fee schedule. New Mexico Department of Agriculture Veterinary Diagnostic Services, Albuquerque. https://nmdeptag.nmsu.edu/labs/vds/fee-schedule.html↑
23. Nationally Notifiable Diseases Surveillance System, weekly and annual tables for leptospirosis, 2017–2026. US Centers for Disease Control and Prevention. https://wonder.cdc.gov/nndss/static/2022/annual/2022-table2i-H.pdf↑
24. Talpada MD, Garvey N, Sprowls R, Eugster AK, Vinetz JM. Prevalence of leptospiral infection in Texas cattle: implications for transmission to humans. Vector-Borne and Zoonotic Diseases 2003;3(3). https://pubmed.ncbi.nlm.nih.gov/14511584/↑
25. Sheppard G, Gomez G, Ferro P, Schroeder M. Bovine abortion caused by Leptospira spp. Texas A&M Veterinary Medical Diagnostic Laboratory case study, 2 August 2024. https://tvmdl.tamu.edu/case-studies/bovine-abortion-caused-by-leptospira-spp/↑
26. Smith AM, Arruda AG, Evason MD, Weese JS, Wittum TE, Szlosek D, Stull JW. A cross-sectional study of environmental, dog, and human-related risk factors for positive canine leptospirosis PCR test results in the United States, 2009 to 2016. BMC Veterinary Research 2019;15:412. https://pmc.ncbi.nlm.nih.gov/articles/PMC6858729/↑
27. Antibodies to various zoonotic pathogens detected in feral swine (Sus scrofa) at abattoirs in Texas, USA. Journal of Food Protection 2017;80(8):1239–1242. https://meridian.allenpress.com/jfp/article/80/8/1239/200132/↑
28. Isolation of Leptospira from desert rodents of West Texas. Journal of Wildlife Diseases 1980;16(3):333. https://pubmed.ncbi.nlm.nih.gov/7411737/↑
29. Reported morbidity and mortality in Texas, annual summaries for 1978, 1981 and 1986. Texas Department of Health. https://www.dshs.texas.gov/sites/default/files/IDCU/data/documents/1981TexasAnnualReport.pdf↑