Canine Leptospirosis: From Environmental Exposure to Systemic Disease

Leptospirosis is a globally significant zoonotic disease caused by pathogenic Leptospira spp., spirochetes capable of infecting a wide range of mammals. The organism is highly diverse, with more than 300 serovars grouped into serogroups based on antigenic similarity. However, serogroup-based classification often lacks clinical clarity, leading to increased reliance on molecular typing such as sequence types (STs) for epidemiological precision^1,3,4. 

In dogs, most clinically relevant infections are caused by highly virulent species within the P1 subclade, including Leptospira interrogans, L. borgpetersenii, and L. kirschneri⁴. While intermediate pathogenic species (P2) can occasionally cause severe disease, they are less commonly implicated. 

Transmission Dynamics: Beyond Water Exposure 

Infection occurs when leptospires penetrate mucous membranes or compromised skin following exposure to contaminated urine from reservoir hosts. Rodents, especially Rattus norvegicus, remain the most important reservoirs globally, with infection prevalence exceeding 80% in some regions¹. 

A key practical insight for veterinarians is that environmental exposure is not the only risk factor. Direct transmission through predation, bite wounds, venereal routes, and even placental transfer is documented¹. This explains cases occurring in urban indoor dogs with no obvious water exposure. 

Environmental persistence is another critical factor. Leptospires survive in moist environments for weeks to months and can replicate in water-saturated soil. Biofilm formation enhances survival both in the environment and within renal tubules of hosts¹. 

Risk Factors in Modern Practice 

Veterinarians should expand risk assessment beyond traditional “rural exposure” models. Urban risk factors include: 

• Poor sanitation and rodent infestation  

• Backyard poultry or composting setups  

• Dog daycare or kennel environments¹ 

Importantly, all dogs should be considered at risk regardless of lifestyle or geography. This shifts leptospirosis from a “selective suspicion” disease to a routine differential in systemic illness. 

Pathophysiology: Why Multiorgan Disease Occurs 

After entry, leptospires disseminate hematogenously, evading host immunity and penetrating tissues using their corkscrew motility. They disrupt endothelial barriers, contributing to vascular leakage and severe complications such as leptospiral pulmonary hemorrhage syndrome (LPHS)^1,5. 

The hallmark organ damage includes: 

• Kidneys: Acute tubulointerstitial nephritis  

• Liver: Cholestatic hepatopathy due to disrupted hepatocyte junctions  

• Lungs: Hemorrhage without significant inflammation  

• Platelets: Direct cytotoxic effects leading to thrombocytopenia¹ 

This explains why leptospirosis presents as a multisystem disorder rather than isolated organ disease. 

Early Clinical Recognition: A Practical Approach 

The initial phase is often nonspecific, presenting with¹: 

• Fever  

• Lethargy  

• Inappetence  

• Vomiting  

• Polyuria/polydipsia  

A key clinical takeaway is that early disease may lack biochemical abnormalities, making diagnosis challenging. Dogs may present before organ dysfunction is evident. 

Veterinarians should adopt a “watch-and-reassess within 24 hours” approach for febrile dogs, especially if unvaccinated or at risk. Delayed deterioration into acute kidney injury (AKI) is common. 

Clinical Pathology: Patterns That Should Raise Suspicion 

Laboratory findings reflect multisystem involvement¹: 

Hematology 

• Neutrophilia and left shift (27–94%)  

• Thrombocytopenia (14–73%)  

• Mild non-regenerative anemia (18–92%)  

Biochemistry 

• Elevated creatinine and BUN (AKI)  

• Increased ALP, ALT, AST  

• Hyperbilirubinemia without classic liver failure  

• Electrolyte imbalances (hyper/hypokalemia, hyponatremia)  

Urinalysis 

• Isosthenuria or hyposthenuria  

• Glucosuria with normoglycemia (tubular damage)  

• Proteinuria (UPC typically <5 but can be higher)  

These findings should prompt immediate inclusion of leptospirosis as a differential diagnosis. 

Imaging and Hidden Pulmonary Risk 

Thoracic radiography is often underutilized but critical. Pulmonary lesions may be present before clinical respiratory signs appear. Early detection of LPHS can significantly influence fluid therapy decisions. 

Abdominal ultrasound frequently reveals renal and hepatic changes, supporting diagnosis and guiding management¹. 

Key Takeaways for Clinical Practice 

• Do not rely solely on exposure history—urban dogs are equally at risk  

• Include leptospirosis early in febrile illness differentials  

• Monitor patients closely within the first 24–48 hours  

• Use a combination of clinical signs and lab patterns to guide suspicion  

• Always consider the disease as multisystemic, not renal-only  

Early recognition remains the most powerful tool in reducing morbidity and improving outcomes in canine leptospirosis. 

Reference 

1. Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. Journal of veterinary internal medicine. 2023 Nov;37(6):1966-82. https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jvim.16903?utm_source=consensus 

2. Vincent AT, Schiettekatte O, Goarant C, Neela VK, Bernet E, Thibeaux R, Ismail N, Mohd Khalid MK, Amran F, Masuzawa T, Nakao R. Revisiting the taxonomy and evolution of pathogenicity of the genus Leptospira through the prism of genomics. PLoS neglected tropical diseases. 2019 May 23;13(5):e0007270. https://journals.plos.org/plosntds/article/file?id=10.1371/journal.pntd.0007270&type=printable 

3. Sykes JE, Gamage CD, Haake DA, Nally JE. Understanding leptospirosis: application of state-of-the-art molecular typing tools with a One Health lens. American journal of veterinary research. 2022 Oct 1;83(10). https://avmajournals.avma.org/downloadpdf/view/journals/ajvr/83/10/ajvr.22.06.0104.pdf 

4. Abdul Rahman MS, Khor KH, Khairani-Bejo S, Lau SF, Mazlan M, Roslan MA. Risk and predictive factors of leptospirosis in dogs diagnosed with kidney and/or liver disease in Selangor, Malaysia. Animals. 2021 Nov 29;11(12):3405. https://www.mdpi.com/2076-2615/11/12/3405 
5. Surdel MC, Anderson PN, Hahn BL, Coburn J. Hematogenous dissemination of pathogenic and non-pathogenic Leptospira in a short-term murine model of infection. Frontiers in cellular and infection microbiology. 2022 Jul 18;12:917962. https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.917962/pdf