Recognising Leptospirosis Across Animal Species: Clinical Presentations and Organ-Specific Changes

A dog presents with fever and systemic illness, while cattle experience reproductive failure without obvious signs of disease. Could leptospirosis explain both presentations? Infection with Leptospira can produce different clinical outcomes depending on the animal species, infecting serovar, and host immune status. Recognising these differences helps veterinarians identify suspicious cases and determine when further diagnostic investigation is warranted. 

Acute Illness: Look Beyond Fever 

Acute leptospirosis often begins with nonspecific febrile illness that can resemble other infections. During the initial bacteremic phase, clinical signs may be subtle or go undetected. As infection progresses, animals may develop icteric or anicteric disease^{[1],[2],[3],[4]}. 

Hepatic and renal abnormalities can strengthen clinical suspicion, particularly when laboratory findings indicate organ dysfunction. However, neither abnormality is consistently present across all affected species^[4]. The absence of jaundice or obvious renal involvement should therefore not be the sole reason to dismiss leptospirosis. 

Clinical interpretation should consider the combination of presenting signs, pathology findings, and disease progression. Because early manifestations are nonspecific, relying on a single clinical feature may delay appropriate investigation. 

Hepatic and Renal Findings: Different Patterns of Disease^[4] 

Icteric leptospirosis is associated with jaundice and liver abnormalities, whereas renal abnormalities predominate in anicteric disease. Some animals may show changes involving both organs. 

This distinction is useful when evaluating clinical findings. An animal without jaundice may still warrant investigation when renal dysfunction is evident. Similarly, hepatic abnormalities should prompt consideration of leptospirosis when the broader clinical picture is compatible. 

The variation reflects the progression of infection. Leptospira initially disseminates through the bloodstream, followed by renal colonisation and an immune phase. Clinical findings may consequently differ according to the stage of infection and the host response. 

Chronic Infection: Recognising Less Obvious Presentations^[1] 

In ruminants, chronic infection may involve renal or genital colonisation, intermittent bacterial shedding, and reproductive failure without significant clinical illness. Animals may therefore remain undetected when assessment focuses exclusively on fever or organ dysfunction. 

Reproductive problems should be considered alongside the possibility of chronic infection, particularly when leptospirosis is a plausible explanation for the clinical presentation. 

Horses can develop another distinct manifestation: chronic ocular colonisation associated with recurrent equine uveitis and blindness. Recurrent ocular disease may warrant consideration of leptospiral involvement, alongside other potential explanations. 

Clinical Takeaway 

Leptospirosis can present as acute febrile illness, hepatic or renal dysfunction, reproductive failure, or recurrent ocular disease. The clinical picture varies across species and stages of infection. 

Veterinarians should assess findings in context and recognise that chronic or subclinical infection may occur without obvious systemic illness. When leptospirosis is suspected, appropriate diagnostic testing is necessary because clinical signs alone cannot reliably establish the diagnosis.

References:

1. Larson CR, Dennis M, Nair RV, Llanes A, Peda A, Welcome S, Rajeev S. Isolation and characterization of Leptospira interrogans serovar Copenhageni from a dog from Saint Kitts. JMM Case Reports. 2017 Oct 23;4(10):e005120. https://www.microbiologyresearch.org/content/journal/jmmcr/10.1099/jmmcr.0.005120?crawler=true&mimetype=application/pdf
2. Ramsay L, Eberhardt C, Schoster A. Acute leptospirosis in horses: A retrospective study of 11 cases (2015-2023). Journal of Veterinary Internal Medicine. 2024 Sep;38(5):2729-38. https://academic.oup.com/jvim/article-pdf/38/5/2729/66663403/jvim17184.pdf
3. Machado M, Ciuffo C, Giannitti F, Silveira CD, Perdomo Y, Queiroz-Machado CR, Carriquiry R, Zarantonelli L, Menchaca A. Acute fatal Leptospira kirschneri infection in suckling lambs and calves in Uruguay. Journal of Veterinary Diagnostic Investigation. 2025 Jul;37(4):679-83. https://journals.sagepub.com/doi/pdf/10.1177/10406387251341234
4. Gorman M, Fayne B, Rajeev S. Diagnosis of leptospirosis in animals: Challenges and perspectives. Journal of Clinical Microbiology. 2026 Mar 11;64(3):e01700-24. https://journals.asm.org/doi/pdf/10.1128/jcm.01700-24