Canine leptospirosis remains a significant, under-recognised cause of acute kidney and liver injury in UK dogs, and accurate diagnosis is critical both for individual case management and for public health. Modern qPCR assays have become central to confirming infection early and safely, but they work best when integrated thoughtfully with serology and clinical assessment.
Leptospirosis in UK dogs: why it still matters
Leptospirosis is a vaccine-preventable zoonotic disease caused by pathogenic Leptospira spp., maintained in wildlife and rodents and transmitted via urine-contaminated water or soil. In the UK, historically important serogroups such as Canicola and Icterohaemorrhagiae have been joined by Australis and others, changing the epidemiology seen in practice and influencing vaccine design. Freedom of Information data from APHA and surveillance summaries highlight serovars including Canicola, Icterohaemorrhagiae/Copenhageni, Pomona, Grippotyphosa, Australis, Bratislava, Autumnalis and Sejroe as relevant in UK dogs, though their relative importance varies regionally. Before widespread vaccination, Canicola and Icterohaemorrhagiae dominated; now disease is more often linked to non-Canicola serogroups, reflecting shifting reservoir hosts and vaccine pressure.
Clinically, dogs typically present with:
- Acute febrile illness
- Lethargy
- Vomiting, diarrhoea
- Jaundice
- Uveitis
- Varying degrees of azotaemia and hepatic dysfunction
However, presentations can be atypical or chronic. Because these signs are non-specific, leptospirosis should remain on the differential list for any acutely azotaemic or icteric dog in the UK, especially with outdoor, rat or water exposure, regardless of vaccination status. Accurate, timely diagnosis is essential to trigger appropriate barrier nursing, protect staff and owners from zoonotic exposure, and implement early supportive and antimicrobial therapy that can be life-saving.
Traditional diagnostics and their limitations
Historically, diagnosis has relied on a combination of microscopic agglutination testing (MAT), culture and, less commonly, immunohistochemistry (IHC).
- MAT detects serogroup-specific antibodies but often requires paired rising titres for confirmation, so early results may be negative or inconclusive in peracute cases.
- Culture is the reference standard but is slow, labour-intensive, and often negative because leptospires are fastidious and may be killed by prior antibiotics.
- IHC on biopsy or necropsy tissues can confirm infection histologically but is not available during the acute clinical window and showed lower sensitivity than qPCR in a recent kidney-focused study.
A 2022 retrospective evaluation comparing PCR and MAT in dogs with suspected leptospirosis found that PCR on blood or urine had high specificity and positive predictive value, but only moderate sensitivity and negative predictive value, underscoring that no single test is perfect. The authors concluded that PCR should be performed on both blood and urine and interpreted alongside MAT, particularly when initial results are equivocal.
How qPCR improves accurate diagnosis
Real-time qPCR assays targeting leptospiral genes now offer rapid, specific detection of Leptospira DNA in blood, urine and tissues. In a 2021 assay validation using challenge-infected dogs, lipL32 qPCR on blood and urine showed very high analytical specificity with no cross-reaction to non-pathogenic leptospires or common canine pathogens, and produced the same overall conclusions about infection status as culture while being vastly faster and safer. Positive agreement with culture was 68% for blood and 83% for urine, and negative agreement was 97% and 84%, respectively, supporting qPCR as a valid alternative to culture in clinical and research settings.
A 2023 clinical study using TaqMan qPCR in suspected canine leptospirosis reported an overall molecular detection rate of 53.2% (66/124 dogs), with 19 dogs positive in blood only, 5 in urine only and 42 positive in both matrices. These data highlight that sampling both blood and urine maximises sensitivity, because bacteraemia dominates early infection while urinary shedding increases as organisms localise to the kidneys. A 2024 retrospective pathology study of canine kidneys also showed that qPCR slightly outperformed IHC for post-mortem confirmation, detecting Leptospira DNA in 29/65 samples versus 27/65 by IHC and identifying additional cases missed histologically.
Crucially for real-world practice, the 2022 PCR–MAT comparison study found that PCR retained clinical utility even when dogs had already received antimicrobial therapy, contradicting the common assumption that antibiotics completely negate PCR value. The authors emphasised the high specificity and positive predictive value of PCR and recommended that clinicians routinely use both blood and urine PCR, integrated with serology, to maximise diagnostic accuracy.
Putting qPCR into practice: getting diagnosis right
Accurate use of qPCR starts with good case selection and sampling technique.
- When to test: qPCR is most informative in acutely ill dogs with compatible clinical signs (acute kidney injury, liver enzyme elevation, fever, myalgia, uveitis) and relevant exposure risk, before seroconversion has fully developed.
- What to sample: Early in disease, submit EDTA whole blood for qPCR to capture leptospiraemia; as the disease progresses or if presentation is delayed, add urine qPCR to detect renal shedding. Ideally, both are submitted concurrently to bridge these phases.
- Timing relative to antibiotics: Where possible, collect samples before starting antimicrobials; however, evidence suggests PCR can still be useful after therapy has begun, and treatment should never be delayed in a highly suspect, unstable dog just to “improve” test sensitivity.
From a practical standpoint, combining qPCR with MAT offers the best balance of early detection and definitive confirmation.
A typical diagnostic pathway for a UK dog
- Day 0: Suspect leptospirosis, collect blood and urine for qPCR and serum for baseline MAT, institute barrier nursing and start appropriate antimicrobials and intensive supportive care.
- Within 24–48 hours: Interpret qPCR results; a positive result in a compatible case is highly supportive of active infection and reinforces the need for continued isolation and owner education about zoonotic risk.
- Day 10–14: If initial MAT was negative or equivocal, collect a convalescent sample; a fourfold titre rise confirms infection even if PCR is now negative, helping to close the diagnostic loop and inform vaccination and epidemiological records.
This integrated approach minimises false negatives, avoids over-reliance on any single method and provides a robust evidential basis for clinical and public-health decisions.
Why accurate diagnosis matters for treatment, vaccination and public health
A firm, early diagnosis of leptospirosis has direct consequences for therapy and infection control. Confirmed cases justify aggressive fluid therapy, monitoring for pulmonary haemorrhage and tailored antibiotic courses, while clearly flagging the need for PPE, careful urine handling and owner counselling about zoonotic transmission, especially in households with children or immunocompromised people. In contrast, ruling out leptospirosis with appropriately timed PCR and MAT allows clinicians to pursue alternative diagnoses for acute azotaemia (e.g., toxin exposure, immune-mediated disease), avoiding unnecessary isolation, client anxiety and sometimes prolonged empirical antimicrobial courses.
At a population level, accurate diagnostic data feed back into our understanding of which serogroups are causing disease in UK dogs, helping to refine vaccine composition and public-health messaging. Observational work in the UK and Ireland shows that, following introduction of bivalent and then multivalent vaccines, the prominence of Canicola has declined while Australis, Icterohaemorrhagiae and other serogroups have become more important, illustrating how diagnostic and vaccination strategies interact over time. Robust qPCR-supported case confirmation also improves surveillance quality, supporting evidence-based recommendations on environmental risk management, rat control and the need for updated vaccines as serogroup patterns evolve.
For UK practitioners, the key message is that leptospirosis remains a dynamic, regionally variable threat, and that high-quality diagnosis—built around thoughtful use of qPCR in combination with serology—underpins everything from individual case survival to zoonotic risk management and rational vaccine use.
References
Blanchard S, Cariou C, Bouvet J, Valfort W, Oberli F, Villard S, Barret-Hilaire F, Poulet H, Cupillard L, de Saint-Vis B. Quantitative Real-Time PCR Assays for the Detection of Pathogenic Leptospira Species in Urine and Blood Samples in Canine Vaccine Clinical Studies: a Rapid Alternative to Classical Culture Methods. J Clin Microbiol. 2021 Jun 18;59(7):e0300620. doi: 10.1128/JCM.03006-20.
Martin EA, Heseltine JC, Creevy KE. The Evaluation of the Diagnostic Value of a PCR Assay When Compared to a Serologic Micro-Agglutination Test for Canine Leptospirosis. Front Vet Sci. 2022 Apr 26;9:815103. doi: 10.3389/fvets.2022.815103.
