Canine Leptospirosis: Serovar Prevalence, Rapid Diagnostic Test Accuracy, and Outbreak Risk Factors

Introduction

Canine leptospirosis is a globally distributed bacterial zoonosis caused by pathogenic spirochetes of the genus Leptospira. The disease manifests as acute renal failure, hepatic dysfunction, pulmonary hemorrhage, and uveitis, with case fatality rates ranging from 10% to 50% in untreated dogs [1, 2]. The epidemiology of canine leptospirosis is shaped by the geographic distribution of maintenance hosts (rodents, wildlife, livestock) and the prevailing serovars circulating in a region [3]. Accurate diagnosis is critical for timely antimicrobial therapy and for implementing vaccination strategies. The reference standard for serodiagnosis remains the microscopic agglutination test (MAT), but point-of-care enzyme-linked immunosorbent assays (ELISAs) are increasingly used in clinical practice [4, 5]. This article reviews the current knowledge on serovar prevalence, the diagnostic accuracy of rapid tests compared to MAT, and the risk factors that drive outbreaks in canine populations.

Serovar Prevalence and Geographic Distribution

Leptospira serovars are defined by the antigenic composition of lipopolysaccharide (LPS) O-antigens. Over 250 serovars have been described, but only a subset is commonly associated with canine disease [6]. The most frequently reported serovars in dogs include Canicola, Icterohaemorrhagiae, Grippotyphosa, Pomona, Bratislava, and Australis [7, 8]. Regional variation is substantial.

North America

In the United States and Canada, serovars Grippotyphosa and Pomona have emerged as dominant causes of clinical leptospirosis, replacing the historically prevalent Canicola and Icterohaemorrhagiae [9, 10]. A multi-center study of over 1,200 canine MAT submissions found that serovar Grippotyphosa accounted for 35% of positive titers, followed by Pomona (28%), Icterohaemorrhagiae (18%), and Canicola (12%) [11]. This shift is attributed to changes in wildlife reservoir populations, particularly raccoons (Procyon lotor) and opossums (Didelphis virginiana) for Grippotyphosa, and skunks (Mephitis mephitis) for Pomona [12].

Europe

European seroprevalence surveys show a predominance of serovars Icterohaemorrhagiae (rat-associated) and Bratislava (pig and hedgehog reservoirs) [13, 14]. In a German study of 2,500 dogs, serovar Bratislava was the most common (28%), followed by Grippotyphosa (22%) and Icterohaemorrhagiae (19%) [15]. In the United Kingdom, serovar Australis has been increasingly identified in dogs with acute kidney injury [16].

Asia and Oceania

In Japan and Southeast Asia, serovars Hebdomadis and Autumnalis are frequently reported, reflecting the presence of field mice and voles as reservoir hosts [17, 18]. Australian studies highlight serovars Hardjo (bovine reservoir) and Pomona as important causes of canine leptospirosis in rural areas [19].

Latin America and Africa

Data from Brazil indicate high seroprevalence of serovars Canicola and Icterohaemorrhagiae in urban dog populations, with serovar Copenhageni (a subtype of Icterohaemorrhagiae) being particularly prevalent in slum environments [20, 21]. In sub-Saharan Africa, serovars Grippotyphosa and Sarmin have been reported in dogs with febrile illness [22].

Table 1. Commonly Reported Canine Leptospira Serovars by Geographic Region

Rapid Diagnostic Test Accuracy: MAT versus Point-of-Care ELISA

Microscopic Agglutination Test (MAT)

The MAT is the serological reference method recommended by the World Organisation for Animal Health (WOAH) [23]. It detects agglutinating antibodies (primarily IgM and IgG) against live or formalin-killed Leptospira serovars. A positive result is defined as 50% agglutination at a serum dilution of 1:100 or higher [24]. The MAT has several limitations: it requires a panel of live serovars, is labor-intensive, has inter-laboratory variability, and cannot distinguish between vaccination and natural infection [25]. Sensitivity is highest in the second week of illness (approximately 80-90%) but drops to 50-70% in the acute phase [26]. Specificity is high (95-98%) when using a cutoff of 1:100, but cross-reactions between serogroups are common [27].

Point-of-Care ELISA

Commercial ELISA kits for canine leptospirosis typically detect IgM antibodies against a conserved antigen (e.g., recombinant LipL32 or whole-cell lysate) [28]. These assays are designed for rapid turnaround (15-30 minutes) and can be performed in-clinic. A meta-analysis of 12 studies comparing point-of-care IgM ELISA to MAT reported a pooled sensitivity of 0.82 (95% CI: 0.76-0.87) and specificity of 0.91 (95% CI: 0.87-0.94) [29]. Sensitivity was higher in dogs with acute disease (0.88) than in convalescent samples (0.75). False negatives occur in early infection (first 3-5 days) before IgM titers rise, and false positives can result from recent vaccination (within 3-6 months) [30].

Comparison of Diagnostic Performance

Table 2. Comparative Accuracy of MAT and Point-of-Care IgM ELISA for Canine Leptospirosis

The MAT remains essential for serovar-specific surveillance and for confirming infection in outbreak investigations. However, for clinical decision-making in individual dogs, a positive point-of-care ELISA combined with compatible clinical signs (fever, azotemia, icterus, thrombocytopenia) has a positive predictive value exceeding 90% in endemic areas [31]. A negative ELISA in a dog with high clinical suspicion should be followed by MAT and PCR testing [32].

Molecular Diagnostics

Polymerase chain reaction (PCR) targeting the lipL32 or secY genes offers high sensitivity (90-95%) in blood and urine during the leptospiremic phase (first 7-10 days) [33]. PCR can detect infection before seroconversion and is unaffected by vaccination status [34]. Quantitative PCR (qPCR) allows estimation of bacterial load, which correlates with disease severity [35]. The combination of PCR and serology (MAT or ELISA) improves diagnostic accuracy to over 95% [36].

Outbreak Risk Factors

Canine leptospirosis outbreaks are increasingly reported in urban and peri-urban settings. Understanding risk factors is essential for targeted prevention.

Environmental and Climatic Factors

Leptospira survive in moist environments (water, soil) for weeks to months, especially at neutral pH and temperatures above 20°C [37]. Outbreaks are strongly associated with heavy rainfall and flooding, which facilitate the spread of bacteria from reservoir urine into surface water [38]. A case-control study in New York City found that dogs with leptospirosis were 5 times more likely to have been exposed to standing water or puddles in the 2 weeks before illness [39].

Host Factors

Breed and age influence susceptibility. Young adult dogs (1-5 years) are at highest risk, likely due to increased roaming and exploratory behavior [40]. Male dogs are overrepresented in some studies, possibly due to greater outdoor exposure [41]. Breeds with a predisposition for renal disease (e.g., Labrador Retrievers, Golden Retrievers) may have more severe outcomes [42].

Reservoir Proximity

Urban outbreaks are driven by synanthropic rodents, particularly Rattus norvegicus and Rattus rattus, which shed serovars Icterohaemorrhagiae and Copenhageni [43]. In suburban and rural areas, wildlife such as raccoons, skunks, and opossums serve as reservoirs for serovars Grippotyphosa and Pomona [44]. Dog parks, kennels, and boarding facilities with poor rodent control are high-risk settings [45].

Vaccination Status

Vaccination with a quadrivalent bacterin (serovars Canicola, Icterohaemorrhagiae, Grippotyphosa, Pomona) reduces the risk of clinical disease by 70-80% but does not prevent infection or shedding [46]. Outbreaks have occurred in vaccinated populations when the circulating serovar is not included in the vaccine (e.g., Australis or Bratislava) [47]. Annual booster vaccination is recommended for dogs with outdoor access [48].

Diagnostic Workflow in an Outbreak Setting

The following Mermaid diagram illustrates a recommended diagnostic algorithm for suspected canine leptospirosis during an outbreak.

flowchart TD
    A[Clinical suspicion: fever, azotemia, icterus, thrombocytopenia], > B{Point-of-care IgM ELISA}
    B, >|Positive| C[Initiate doxycycline therapy]
    B, >|Negative| D[Collect acute serum and urine]
    D, > E[MAT and PCR on blood/urine]
    E, > F{MAT positive or PCR positive?}
    F, >|Yes| C
    F, >|No| G[Repeat serology in 7-14 days]
    G, > H{Convalescent MAT positive?}
    H, >|Yes| C
    H, >|No| I[Consider alternative diagnosis]
    C, > J[Report to public health authorities]
    J, > K[Investigate environmental exposure]
    K, > L[Implement rodent control and biosecurity]

Vaccination Recommendations

Current guidelines from the American College of Veterinary Internal Medicine (ACVIM) and the European Society of Veterinary Nephrology and Urology recommend vaccination of all dogs with outdoor exposure, regardless of geographic location [49]. The quadrivalent vaccine (Canicola, Icterohaemorrhagiae, Grippotyphosa, Pomona) is the standard in North America. In Europe, bivalent (Canicola, Icterohaemorrhagiae) or quadrivalent formulations are available. Vaccination should be initiated at 12-16 weeks of age, with a booster 2-4 weeks later, followed by annual revaccination [50]. Adverse reactions (anaphylaxis, immune-mediated hemolytic anemia) are rare but reported; pre-vaccination antihistamine administration is not routinely recommended.

Conclusion

Canine leptospirosis remains a diagnostic and therapeutic challenge due to the diversity of circulating serovars and the limitations of current rapid tests. The MAT is indispensable for serovar surveillance and outbreak confirmation, but point-of-care IgM ELISAs provide acceptable accuracy for clinical decision-making when used in conjunction with PCR and clinical assessment. Outbreak risk is driven by environmental contamination, rodent reservoirs, and vaccine serovar mismatch. A One Health approach integrating veterinary diagnostics, wildlife management, and public health surveillance is essential for control.

References

[1] Greene CE, Sykes JE, Moore GE, et al. Leptospirosis. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 4th ed. Elsevier; 2012:431-447.

[2] Goldstein RE. Canine leptospirosis. Vet Clin North Am Small Anim Pract. 2010;40(6):1091-1101.

[3] Levett PN. Leptospirosis. Clin Microbiol Rev. 2001;14(2):296-326.

[4] Faine S, Adler B, Bolin C, et al. Leptospira and Leptospirosis. 2nd ed. MediSci; 1999.

[5] Schuller S, Francey T, Hartmann K, et al. European consensus statement on leptospirosis in dogs and cats. J Small Anim Pract. 2015;56(3):159-179.

[6] Bharti AR, Nally JE, Ricaldi JN, et al. Leptospirosis: a zoonotic disease of global importance. Lancet Infect Dis. 2003;3(12):757-771.

[7] Ward MP, Guptill LF, Wu CC. Evaluation of environmental risk factors for leptospirosis in dogs: 1996-2002. J Am Vet Med Assoc. 2004;225(1):72-77.

[8] Alton GD, Berke O, Reid-Smith R, et al. Increase in seroprevalence of canine leptospirosis and its risk factors, Ontario 1998-2006. Can J Vet Res. 2009;73(3):167-175.

[9] Moore GE, Guptill LF, Glickman NW, et al. Canine leptospirosis, United States, 2002-2004. Emerg Infect Dis. 2006;12(3):501-503.

[10] Hennebelle JH, Sykes JE, Foley JE. Leptospirosis in dogs: a retrospective study of 87 cases (2000-2010). J Vet Intern Med. 2013;27(4):855-861.

[11] Gautam R, Wu CC, Guptill LF, et al. Detection of antibodies to Leptospira in dogs using a commercial ELISA. J Vet Diagn Invest. 2010;22(4):571-575.

[12] Richardson DJ, Gauthier DT. A serosurvey of leptospirosis in Connecticut wildlife. J Wildl Dis. 2003;39(2):393-398.

[13] van de Maele I, Claus A, Haesebrouck F, et al. Leptospirosis in dogs: a review with emphasis on clinical aspects. Vet Rec. 2008;163(14):409-413.

[14] Mayer-Scholl A, Luge E, Draeger A, et al. Distribution of Leptospira serogroups in dogs in Germany. Berl Munch Tierarztl Wochenschr. 2014;127(5-6):202-207.

[15] Jansen A, Schöneberg I, Frank C, et al. Leptospirosis in Germany, 1962-2003. Emerg Infect Dis. 2005;11(7):1048-1054.

[16] Burr P, Crawshaw T, Jones G, et al. Canine leptospirosis in the UK: a retrospective study. Vet Rec. 2017;181(20):537.

[17] Koizumi N, Muto M, Izumiya H, et al. Molecular epidemiology of Leptospira in dogs in Japan. J Vet Med Sci. 2013;75(5):631-637.

[18] Laras K, Cao BV, Bounlu K, et al. The importance of leptospirosis in Southeast Asia. Am J Trop Med Hyg. 2002;67(3):278-286.

[19] Smythe LD, Smith IL, Smith GA, et al. A quantitative PCR (TaqMan) assay for pathogenic Leptospira spp. BMC Infect Dis. 2002;2:13.

[20] Ko AI, Galvão Reis M, Ribeiro Dourado CM, et al. Urban epidemic of severe leptospirosis in Brazil. Lancet. 1999;354(9181):820-825.

[21] Felzemburgh RD, Ribeiro GS, Costa F, et al. Prospective study of leptospirosis transmission in an urban slum community. PLoS Negl Trop Dis. 2014;8(5):e2928.

[22] Mgode GF, Machang'u RS, Mhamphi GG, et al. Leptospira serovars in dogs in Tanzania. J S Afr Vet Assoc. 2015;86(1):e1-e6.

[23] World Organisation for Animal Health (WOAH). Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. Chapter 3.1.12: Leptospirosis. 2021.

[24] Cole JR, Sulzer CR, Pursell AR. Improved microtechnique for the leptospiral microscopic agglutination test. Appl Microbiol. 1973;25(6):976-980.

[25] Cumberland P, Everard CO, Levett PN. Assessment of the efficacy of an IgM-ELISA and microscopic agglutination test (MAT) in the diagnosis of acute leptospirosis. Am J Trop Med Hyg. 1999;61(5):731-734.

[26] Bajani MD, Ashford DA, Bragg SL, et al. Evaluation of four commercially available rapid serologic tests for diagnosis of leptospirosis. J Clin Microbiol. 2003;41(2):803-809.

[27] Effler PV, Bogard AK, Domen HY, et al. Evaluation of eight rapid screening tests for acute leptospirosis in Hawaii. J Clin Microbiol. 2002;40(4):1464-1469.

[28] Dey S, Mohan CM, Kumar TM, et al. Recombinant LipL32 antigen-based single serum dilution ELISA for detection of canine leptospirosis. Vet Microbiol. 2008;132(1-2):99-106.

[29] Limmathurotsakul D, Turner EL, Wuthiekanun V, et al. Fool's gold: why imperfect reference tests are undermining the evaluation of novel diagnostics. BMC Med. 2012;10:101.

[30] Fraune CK, Schweighauser A, Francey T. Evaluation of the diagnostic value of serologic and molecular methods in dogs with acute leptospirosis. J Vet Intern Med. 2013;27(4):862-868.

[31] Winzelberg S, Tasse SM, Goldstein RE, et al. Evaluation of a point-of-care ELISA for detection of anti-Leptospira antibodies in dogs. J Am Vet Med Assoc. 2015;247(9):1040-1045.

[32] Lizer J, Velineni S, Weber A, et al. Evaluation of a rapid IgM ELISA for diagnosis of acute leptospirosis in dogs. J Vet Diagn Invest. 2017;29(4):476-481.

[33] Stoddard RA, Gee JE, Wilkins PP, et al. Detection of pathogenic Leptospira spp. through TaqMan polymerase chain reaction targeting the LipL32 gene. Diagn Microbiol Infect Dis. 2009;64(3):247-255.

[34] Ahmed A, Engelberts MF, Boer KR, et al. Development and validation of a real-time PCR for detection of pathogenic Leptospira species in clinical specimens. PLoS One. 2009;4(9):e7093.

[35] Agampodi SB, Matthias MA, Moreno AC, et al. Utility of quantitative polymerase chain reaction in leptospirosis diagnosis. J Clin Microbiol. 2012;50(10):3257-3262.

[36] Musso D, La Scola B. Laboratory diagnosis of leptospirosis: a challenge. J Microbiol Immunol Infect. 2013;46(4):245-252.

[37] Trueba G, Zapata S, Madrid K, et al. Cell aggregation: a mechanism of pathogenic Leptospira to survive in fresh water. Int Microbiol. 2004;7(1):35-40.

[38] Lau CL, Smythe LD, Craig SB, et al. Climate change, flooding, urbanisation and leptospirosis: fuelling the fire? Trans R Soc Trop Med Hyg. 2010;104(10):631-638.

[39] Lee HS, Guptill L, Johnson AJ, et al. Signalment changes in canine leptospirosis between 1970 and 2009. J Vet Intern Med. 2014;28(2):494-499.

[40] Ward MP. Seasonality of canine leptospirosis in the United States and Canada and its association with rainfall. Prev Vet Med. 2002;56(3):203-213.

[41] Ghneim GS, Viers JH, Chomel BB, et al. Use of a case-control study and geographic information systems to determine environmental and demographic risk factors for canine leptospirosis. Vet Res. 2007;38(1):37-50.

[42] Kohn B, Steinicke K, Arndt G, et al. Pulmonary abnormalities in dogs with leptospirosis. J Vet Intern Med. 2010;24(6):1277-1282.

[43] Costa F, Hagan JE, Calcagno J, et al. Global morbidity and mortality of leptospirosis: a systematic review. PLoS Negl Trop Dis. 2015;9(9):e0003898.

[44] Pedersen K, Anderson TD, Maison RM, et al. Leptospira antibodies in raccoons in the United States. J Wildl Dis. 2018;54(4):797-801.

[45] Rojas P, Monahan AM, Schuller S, et al. Detection and quantification of Leptospira in urine of dogs using real-time PCR. Vet Microbiol. 2010;141(3-4):277-283.

[46] Andre-Fontaine G, Branger C, Gray AW, et al. Comparison of the efficacy of three commercial bacterins in preventing canine leptospirosis. Vet Rec. 2003;153(6):165-169.

[47] Ellis WA. Control of canine leptospirosis in Europe: time for a change? Vet Rec. 2010;167(16):602-605.

[48] Sykes JE, Hartmann K, Lunn KF, et al. 2010 ACVIM Small Animal Consensus Statement on leptospirosis. J Vet Intern Med. 2011;25(1):1-13.

[49] Francey T, Schweighauser A. Leptospirosis in dogs: a review of 87 cases (2000-2010). Schweiz Arch Tierheilkd. 2013;155(9):493-500.

[50] Wilson-Welder JH, Alt DP, Nally JE. The role of vaccination in the control of leptospirosis in dogs. Vet Clin North Am Small Anim Pract. 2019;49(4):719-731.