Evaluation of 3 Serological Tests for Early Detection Of Leptospira-specific Antibodies in Experimentally Infected Dogs

Serological evidence of exposure of healthy dogs to Leptospira in Sydney, New South Wales, Australia

In 2017, highly fatal canine leptospirosis emerged in Sydney, Australia. Based on results of microscopic agglutination testing (MAT), serovar Copenhageni appeared to be the most common causative serovar. Prior to this, no clinical cases had been reported since 1976. In a serosurvey of healthy dogs in Australian shelters in 2004, 2.4% of 431 New South Wales dogs had serological evidence of exposure to Copenhageni, the most prevalent serovar. The aim of this study was to estimate the current prevalence of Leptospira exposure and associated serovars in healthy Sydney dogs, previously unvaccinated against Leptospira. Serum samples from 411 healthy dogs in leptospirosis hotspots and neighbouring suburbs were collected before vaccination. MAT for 23 serovars was performed at the WHO Leptospirosis Reference Laboratory in Queensland, Australia. The overall seroprevalence was 4.1% (17/411) with low titres (1/50-1/200) detected. Eleven dogs were from known leptospirosis hotspots. Eight dogs were known to hunt rodents. One dog had been in contact with a leptospirosis positive dog 1 year prior. Serovar Topaz was the most prevalent serovar (n = 5) followed by serovars Australis (n = 4), Copenhageni (n = 4), Djasiman (n = 2), Cynopteri (n = 1), Javanica (n = 1), Medanensis (n = 1), and Pomona (n = 1). In conclusion, serological evidence of exposure of dogs in Sydney to Leptospira is low, but apparently has increased since 2004. Positive titres to serovars not previously reported to cause disease in dogs could be due to low virulence of those serovars or cross-reactivity with other serovars.

[Overview on utility of in-house tests for detection of systemic infectious diseases in dogs]

For detection of infectious diseases, several point-of-care (POC) tests are on the market in addition to methods performed in commercial laboratories. These POC tests are based on enzyme-linked immunosorbent assay (ELISA) or other immunochromatographic technologies and present results within few minutes in veterinary practice. This article gives an overview of the utility of numerous POC tests of different manufacturers for detection of parvovirus antigen in feces, Dirofilaria (D.) immitis antigen in blood as well as antibodies against Borrelia (B.) burgdorferi, Anaplasma (A.) spp., Ehrlichia (E.) spp., Leptospira (L.) spp. and Leishmania (L.) infantum in blood (single or in different combinations). Sensitivity and specificity of these tests are important for their usefulness in veterinary practice. Furthermore, presence of antibodies or detection of antigen has to correlate with the presence of clinical signs. POC tests for detection of canine parvovirus antigen have a very high specificity, the sensitivity of all evaluated POC tests, however, is very low. POC tests for detection of D. immitis antigen have a very high sensitivity and specificity. As they detect antigen from the uterus of female adult parasites, test results are negative when only very few female or only male adults are present. POC tests for detection of antibodies against B. burgdorferi only indicate contact with Borrelia spp. and do not prove clinical Lyme disease, as the infection only extremely rarely causes clinical signs. POC tests for detection of antibodies against A. phagocytophilum are also not suitable for diagnosis of clinical anaplasmosis. Infections with A. phagocytophilum only lead to clinical disease in very rare cases and in these, clinical signs occur before the development of antibodies. POC tests for detection of antibodies against E. canis have a very high sensitivity as well as specificity. POC tests for detection of antibodies against L. infantum and Leptospira species (spp.) show a very high specificity and a high sensitivity. However, Leptospira spp. antibody-positive results may occur following vaccination, as the POC tests cannot distinguish between field and vaccination strains.

Updated ACVIM consensus statement on leptospirosis in dogs

Since publication of the last consensus statement on leptospirosis in dogs, there has been revision of leptospiral taxonomy and advancements in typing methods, widespread use of new diagnostic tests and vaccines, and improved understanding of the epidemiology and pathophysiology of the disease. Leptospirosis continues to be prevalent in dogs, including in small breed dogs from urban areas, puppies as young as 11 weeks of age, geriatric dogs, dogs in rural areas, and dogs that have been inadequately vaccinated for leptospirosis (including dogs vaccinated with 2-serovar Leptospira vaccines in some regions). In 2021, the American College of Veterinary Internal Medicine (ACVIM) Board of Regents voted to approve the topic for a revised Consensus Statement. After identification of core panelists, a multidisciplinary group of 6 experts from the fields of veterinary medicine, human medicine, and public health was assembled to vote on the recommendations using the Delphi method. A draft was presented at the 2023 ACVIM Forum, and a written draft posted on the ACVIM website for comment by the membership before submission to the editors of the Journal of Veterinary Internal Medicine. This revised document provides guidance for veterinary practitioners on disease in dogs as well as cats. The level of agreement among the 12 voting members (including core panelists) is provided in association with each recommendation. A denominator lower than 12 reflects abstention of ≥1 panelists either because they considered the recommendation to be outside their scope of expertise or because there was a perceived conflict of interest.

Electrochemical aptasensor detection of electron transfer flavoprotein subunit beta for leptospirosis diagnosis

Electron transfer flavoprotein subunit beta (ETFB) of Leptospira interrogans is a biomarker for diagnosing leptospiral infection. Thus, the ETFB-specific nuclease-resistant RNA aptamer ETFB3-63 was developed and used in an electrochemical aptasensor to assay ETFB. Although the majority of reported biosensors detect various genes and antibodies of L. interrogans, this is the first attempt to construct an electrochemical biosensor to detect ETFB protein for the diagnosis of leptospiral infection. The ETFB protein can be detected without any extraction phase. In this assay, a single-stranded DNA probe complementary to the ETFB3-63 sequence was immobilized on a screen-printed carbon electrode (SPCE). The aptamer was then incubated and hybridized with the antisense probe on the SPCE. In the presence of ETFB, the aptamer dissociates from the aptamer/probe complex on the SPCE to bind with the protein. Methylene blue was then added to intercalate with the remaining hybridized aptamers, and its signal was measured using differential pulse voltammetry. The signal arising from the intercalated methylene blue decreased with increasing concentration of ETFB, showing a linear response in the range of 50-500 nM of ETFB and 10 to 109 leptospira cells per mL, respectively. The aptasensor signal was also specific to L. interrogans but not to 12 related bacteria tested. In addition, the aptasensor showed similar performance in detecting ETFB spiked in human serum to that in buffer, indicating that proteins in the serum do not interfere with the assay. Therefore, this assay has great potential to develop into a point-of-care electrochemical device that is accurate, cost-effective, and user-friendly for leptospirosis diagnosis.

Evaluation of Leptospira infection and exposure in free-roaming cat populations in northern California and southern Texas

OBJECTIVES

Leptospirosis is a re-emergent zoonotic bacterial disease associated with renal and hepatic injury. In free-roaming cats in some regions, a high prevalence of Leptospira antibodies has been identified, and pathogenic leptospires have been detected in renal tissue, indicating that they may play a role in Leptospira epidemiology. The objective of this study was to determine the prevalence of Leptospira seroreactivity and urinary shedding of Leptospira DNA in free-roaming cats from northern California and southern Texas. A secondary objective was to compare the results of a point-of-care (POC) assay, designed to detect Leptospira antibodies, with the results of the microscopic agglutination test (MAT) when applied to serum samples from feral cats.

METHODS

Specimens were obtained from free-roaming cats from northern California (n = 52; 2020) and southern Texas (n = 75; 2017). Leptospira quantitative PCR was performed on blood and urine specimens from Californian cats. Serum samples from Californian and Texan cats were subjected to MAT to categorize them as Leptospira antibody-positive or antibody-negative. The performance of the POC assay was assessed using the MAT as the gold standard.

RESULTS

Leptospira DNA was not detected in the blood or urine of any cats tested. The results of the MAT were positive in 17.3% (n = 9) of Californian cats and 10.7% (n = 8) of Texan cats (P = 0.3). The median MAT titer was 1:100 (range 1:100-1:200) in Californian cats and 1:200 (range 1:100-1:800) in Texan cats. The POC assay was negative in all specimens.

CONCLUSIONS AND RELEVANCE

Free-roaming cats in California and Texas are exposed to Leptospira species and may have the potential to act as sentinel hosts. No cats had evidence of current infection, as determined using PCR on blood and urine specimens. The POC test did not reliably detect anti-Leptospira antibodies in these cats. The role of cats in the maintenance or shedding of pathogenic leptospires requires further investigation.

Leptospiral Leucine-Rich Repeat Protein-Based Lateral Flow for Assessment of Canine Leptospiral Immunoglobulin G

The recombinant, modified leucine-rich repeat protein rhKU_Sej_LRR_2271 has been suggested as a candidate for leptospiral vaccine development since it was predicted to be a transmembrane protein containing leucine-rich repeat motifs and immunogenic epitopes. The immunogenic epitopes showed binding affinities with lower IC₅₀ values than peptides of known antigenic proteins, e.g., LipL32. Moreover, this protein was immunoreactive with hyperimmune sera against several serovars. In this study, we aimed to develop a lateral flow strip test using the rhKU_Sej_LRR_2271 protein for the detection of anti-leptospiral IgG in dogs. The lateral flow assay was performed with 184 dog plasma samples and evaluated with a culture method, 16S ribosomal RNA gene (rss) analysis real-time PCR, and LipL32 ELISA. The culture method failed to detect leptospires in the dog blood samples. Six of nine symptomatic dogs gave positive results with the real-time PCR assay. The lateral flow assay and LipL32 ELISA gave positive results with 59 and 50 dogs, respectively. The sensitivity, specificity, and accuracy of the rhKU_Sej_LRR_2271 lateral flow strip test were 70.00, 82.09, and 78.80%, respectively, when compared with LipL32 ELISA. There was a significant association between the LipL32 ELISA and the rhKU_Sej_LRR_2271 lateral flow assay. The rhKU_Sej_LRR_2271 lateral flow strip test has therefore demonstrated a good potential to detect anti-leptospiral IgG in dogs.

Leptospira seroprevalence and associated risk factors in healthy Swedish dogs

BACKGROUND

Leptospirosis is an emerging zoonotic infection worldwide and a cause of life-threatening disease in dogs. Seroprevalence in Swedish dogs is unknown. The aims of the present study were to estimate seroprevalence of pathogenic Leptospira in healthy dogs in Sweden using the microagglutination test (MAT) and a rapid point-of-care enzyme-linked immunosorbent assay (ELISA), and to evaluate risk factors of Leptospira exposure in Swedish dogs.

RESULTS

Positive MAT titres (≥ 1:50) were detected in 27/369 (7.3%) of included dogs. Five different serovars were represented of which the Saxkoebing serovar was the most common (64.3%), followed by Copenhagi (14.3%), Bratislava (10.7%), Icterohaemorrhagiae (7.1%), and Canicola (3.6%). The ELISA test (SNAP® Lepto) was positive in 3/316 (0.9%) dogs. Living in urban areas and contact with stagnant water were found to be risk factors for Leptospira seropositivity (p < 0.05) in a multivariable logistic regression model.

CONCLUSION

In this first seroprevalence study of Leptospira in Swedish dogs, it was shown that healthy dogs without recent (24 months) travel history and antileptospira vaccination had been exposed to pathogenic Leptospira interrogans serovars. Contact with stagnant water and living in urban areas were independent risk factors for seropositivity.

Canine leptospirosis in Canada, test-positive proportion and risk factors (2009 to 2018): A cross-sectional study

Over the past decade, there has been an apparent increased frequency and widened distribution of canine leptospirosis in Canada, however, this has been minimally investigated. Availability and clinical uptake of Leptospira polymerase chain reaction (PCR)-based testing of dogs in Canada may provide important insight into the epidemiology of this canine and zoonotic infectious disease. Study objectives were to evaluate clinical canine Leptospira PCR test results from a large commercial laboratory to determine temporal and spatial distribution in Canada and identify dog, geographic and temporal risk factors for test-positive dogs. This cross-sectional study analyzed data obtained from IDEXX Laboratories, Inc. on 10,437 canine Leptospira PCR tests (blood and/or urine) submitted by Canada-based veterinarians (July 2009 to May 2018). Multivariable logistic regression was used to identify risk factors for test-positive dogs. Test-positive proportion varied widely annually (4.8–14.0%) and by location. Provinces with the highest test-positive proportion over the study period were Nova Scotia (18.5%) and Ontario (9.6%), with the prairie provinces (Manitoba and Alberta combined) having the lowest proportion (1.0%); the northern territories could not be evaluated due to limited testing. In the final model, dog age, sex, breed, month, and year test performed, and location (urban/rural, province) of the practice submitting the sample were significant predictors of a positive Leptospira PCR test. Dogs less than one year of age (OR = 2.1; 95% CI: 1.6–2.9), male sex (OR = 1.3; 1.1–1.5), toy breed (OR = 3.3; 2.5–4.4), and samples submitted from an urban practice (OR = 1.3; 1.0–1.8) had the greatest odds of a positive Leptospira PCR test as compared to referent groups. Significant two-way interactions between province-month and year-month highlight the complex spatial and temporal influences on leptospirosis occurrence in this region. Our work suggests a high incidence of canine leptospirosis regionally within Canada. Identifiable dog and location factors may assist in future targeted prevention efforts.

A lethal model of Leptospira infection in hamster nasal mucosa

Leptospirosis is a fatal zoonosis caused by contact between skin or a mucosal surface and contaminated soil or water. Hamsters were infected by intraperitoneal injection fto establish experimental leptospirosis, which is not a natural route of infection. There are no reports of nasal mucosal infection in hamsters. In this study, infection of the nasal mucosa was performed to establish a model of natural infection. Both methods of infection can cause lethal models with similar symptoms in the later stages of infection, such as weight loss, blood concentration, increased neutrophils (GRAN), and decreased lymphocytes (LYM) in the blood, severe organ damage and liver function obstruction. The burden of Leptospira in the organs and blood was lower in the mucosal inoculation groups at 1 day after infection. However, mucosal infection induced a higher Leptospira burden in urine than intraperitoneal infection in the late stages of infection. After nasal mucosal infection, antibody levels were higher and lasted longer. These results indicated that the route of nasal mucosal infection is a good choice for studying leptospirosis in hamsters.

The establishment of a leptospirosis experimental model is still key to elucidating the pathogenesis of leptospirosis. Hamsters were infected by intraperitoneal injection to establish experimental leptospirosis, although this is not a natural route of infection. The transmission characteristics of Leptospira and the disease progression in hamsters infected by a natural transmission route (e.g. through mucosal surfaces) had not been explored. In this study, we compared the dynamics of Leptospira infection in hamsters inoculated via the nasal mucosa or by intraperitoneal inoculation, and compared the burden of Leptospira and the level of antibodies produced with disease progression, such as body weight, serology, haematological changes and histopathological changes. Our data suggested that there are significant differences in the dynamics of infection between intraperitoneal and mucosal infection pathways. Although the result was the same in the later stage of infection, the course of mucosal infection was slower, which may better recapitulate the natural history of the disease, assist in studying kidney disease caused by Leptospira, and provide an animal model for the study of leptospirosis mucosal immunity.

Evaluation by polymerase chain reaction assay of persistent shedding of pathogenic leptospires in the urine of dogs with leptospirosis

BACKGROUND

Persistent leptospiruria in naturally infected dogs occurs despite appropriate antibiotic treatment.

HYPOTHESIS/OBJECTIVES

To determine the frequency of persistent leptospiruria in naturally infected dogs and the association of persistent leptospiruria with different antibiotic treatments.

ANIMALS

Thirty-two dogs of varying age and breed diagnosed with leptospirosis via urine polymerase chain reaction assay (PCR).

METHODS

A prospective observational study of dogs diagnosed with leptospirosis was undertaken to determine the frequency of persistent leptospiruria as determined by PCR. Clinical presentation of leptospirosis, antibiotic treatment, serum creatinine concentration, and outcome were recorded.

RESULTS

Fifteen of 32 dogs had a negative urine PCR on the first submission in the study, 5 of 15 received only an aminopenicillin. The remaining 17 dogs had a negative urine PCR on the second (n = 6 dogs), third (n = 5), fourth (n = 5), and eighth (n = 1) submissions. Acute kidney injury was reported in 32/32 dogs. Two of 32 dogs developed chronic kidney disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

Persistent leptospiruria is common despite treatment with antibiotics frequently recommended for treatment. Follow-up urine PCR to confirm clearance of the organism is recommended in all dogs. In dogs with persistent leptospiruria, chronic kidney disease can develop after acute kidney injury.

Clinical, diagnostic, and epidemiological features of a community-wide outbreak of canine leptospirosis in a low-prevalence region (Maricopa County, Arizona)

OBJECTIVE

To describe clinical, diagnostic, and epidemiological features of an outbreak of leptospirosis in dogs in Maricopa County, Ariz, from January 2016 through June 2017.

ANIMALS

71 case and 281 control dogs.

PROCEDURES

Cases were classified as confirmed, probable, suspect, or not a case on the basis of medical record data that fulfilled clinical, diagnostic, and epidemiological criteria. Potential exposures were assessed by owner survey. For the case-control investigation, control dogs were recruited through owner completion of a July 2017 survey. Summary statistics and ORs for case dog lifestyle factors were reported.

RESULTS

54 dogs were classified as confirmed and 17 as probable cases. For 4 dogs of a household cluster (5 confirmed and 3 probable), the highest microscopic agglutination titer was for serovar Djasiman (Leptospira kirschneri detected by PCR assay), and for 13 dogs of a community outbreak (49 confirmed and 14 probable cases), the highest titer was for serovar Canicola (Leptospira interrogans detected by PCR assay). The 44 case dogs included in the case-control investigation were 7.7 (95% CI, 3.5 to 16.7) and 2.9 times (95% CI, 1.3 to 6.6) as likely as control dogs to have visited dog daycare or to have been kenneled overnight at a boarding facility, respectively, 30 days prior to the onset of clinical signs or diagnosis.

CONCLUSIONS AND CLINICAL RELEVANCE

Diagnostic and epidemiological findings indicated 2 outbreaks. Transmission where dogs congregated likely propagated the community outbreak. Outbreaks of leptospiral infections can occur in regions of low prevalence, and a dog's exposure to areas where dogs congregate should be considered when making Leptospira vaccination recommendations.

Histopathology of the kidney and seroprevalence of leptospirosis in wild rats in Baghdad Province, Iraq

Background and Aim: Leptospirosis, caused by pathogenic leptospires, is a globally emerging infectious disease affecting both humans and animals, which act as reservoirs, with large outbreaks worldwide. The role of rats in dispersing leptospirosis was never investigated in Iraq. Because of the seriousness of the disease and the scarce data regarding this disease in Iraq, this study determines the incidence of leptospirosis in rats and its renal histopathological profile. Materials and Methods: Of 211 captured rats, 82 apparently healthy rats were included in this study. After euthanatizing, 3-5-ml blood was collected by cardiac puncture. Approximately 0.5 cm3 of the kidney was collected for routine histopathology and stained using hematoxylin and eosin (H&E) and Warthin–Starry (WS) stains. Blood smears were prepared and stained with the WS stain. Results: All rats (100%) with different age groups were immunoglobulin G (IgG)-positive, and 90.24% of them had the IgG against leptospiral antigens in kidney tissues. The juvenile age group had higher IgG levels than other age groups. Considering sex, no significant differences in the overall results were observed. Serum concentrations of blood urea nitrogen and creatinine showed significant increments in the sub-adult and adult IgG- positive groups compared with the IgG-negative groups. No significant alterations were observed in the juvenile group. Using WS stains, 13 and 1 blood smears and 0 and 8 kidney tissues were positive for leptospires in the sub-adult and adult groups, respectively. Microscopical findings of the renal cortex and medulla in the sub-adult IgG-positive group showed hemorrhage, glomerular deterioration, tubular cell degeneration and necrosis with cast formation, periarterial edema, and focal hemorrhage with congestion of peritubular arteries. The adult IgG-positive group revealed deterioration similar to that in the sub-adult group and tended to be chronic. No leptospires were observed using H&E staining. Conclusion: IgG-positive carrier rats refer to previously exposed or infected rats. Understanding the risk of transmitting the disease to human and animals through a carrier rat's urine is highly predicted and possible mitigation of zoonotic transmission.

Progressive gammopathy and coagulopathy in a young English bulldog

A restricted polyclonal or biclonal gammopathy resulting in bleeding tendencies was diagnosed in a young, neutered male English bulldog with concurrent splenomegaly, anemia, and severe elevations in IgM and, to a lesser degree, IgA immunoglobulins. There was a positive clinical response to treatment with prednisone and chlorambucil. This case bears similarity to a recently published syndrome of polyclonal gammopathy that is not neoplastic in origin in this breed. Key clinical message: The current case describes the management and clinical course of a recently described syndrome of polyclonal gammopathy in English bulldogs.

Detection and modeling of anti-Leptospira IgG prevalence in cats from Lisbon area and its correlation to retroviral infections, lifestyle, clinical and hematologic changes

Leptospirosis is a zoonosis of global importance caused by Leptospira species. Rodents are the main reservoirs, known to shed the bacteria in urine, thus contaminating water and soil and infecting other animals and people. Leptospirosis has been re-emerging in both developing and developed countries including Europe. It has been hypothesized that cats could be asymptomatic carriers of Leptospira. This study aims to evaluate cats' exposure to Leptospira in Lisbon, Portugal, by measuring IgG titres and correlating them with possible factors that may increase the risk of exposure in urban cats. Two hundred and forty-three samples were collected from the biobank. An ELISA test followed by a seroprevalence analysis using a finite mixture model was performed to detect and measure anti-Leptospira IgG antibodies titres. In parallel, a survey was conducted to identify possible risk factors for seropositivity. According to the ELISA test protocol, only twenty-three cats (9.5%; 95% CI =(6.1%;13.9%)) could be considered as seropositive to Leptospira antigens. However, when the same data were analysed by the best different mixture models, one hundred and forty-four cats (59.3%; 95%CI = (52.8%; 65.5%)) could be classified as intermediate and high antibody responders to Leptospira antigens. Seropositivity to Feline Immunodeficiency Virus infection (FIV) was found to be the only significant risk factor associated with anti-Leptospira IgG antibodies. In conclusion, the present studies raises the possibility of a higher exposure of cats to Leptospira than previously thought due to the identification of a subpopulation of cats with intermediate antibody levels.

Leptospira infection and shedding in dogs in Thailand

BACKGROUND

Leptospirosis is a widespread zoonosis and has been recognized as a re-emerging infectious disease in humans and dogs, but prevalence of Leptospira shedding in dogs in Thailand is unknown. The aim of this study was to determine urinary shedding of Leptospira in dogs in Thailand, to evaluate antibody prevalence by microscopic agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA), and to assess risk factors for Leptospira infection. In Northern, Northeastern, and Central Thailand, 273 stray (n = 119) or client-owned (n = 154) dogs from rural (n = 139) or urban (n = 134) areas were randomly included. Dogs that had received antibiotics within 4 weeks prior to sampling were excluded. No dog had received vaccination against Leptospira. Urine was evaluated by real-time polymerase chain reaction (PCR) specific for lipL32 gene of pathogenic Leptospira. Additionally, urine was cultured for 6 months in Ellinghausen-McCullough-Johnson-Harris (EMJH) medium. Antibodies were measured by ELISA and MAT against 24 serovars belonging to 15 serogroups and 1 undesignated serogroup. Risk factor analysis was performed with backwards stepwise selection based on Wald.

RESULTS

Twelve of 273 (4.4%; 95% confidence interval (CI): 2.0-6.8%) urine samples were PCR-positive. In 1/273 dogs (0.4%; 95% CI: 0.01-1.1%) Leptospira could be cultured from urine. MAT detected antibodies in 33/273 dogs (12.1%; 95% CI: 8.2-16.0%) against 19 different serovars (Anhoa, Australis, Ballum, Bataviae, Bratislava, Broomi, Canicola, Copenhageni, Coxi, Grippotyphosa, Haemolytica, Icterohaemorrhagiae, Khorat, Paidjan, Patoc, Pyrogenes, Rachmati, Saxkoebing, Sejroe). In 111/252 dogs (44.0%; 95% CI: 37.9-50.2%) immunoglobulin M (IgM) and/or immunoglobulin G (IgG) antibodies were found by ELISA. Female dogs had a significantly higher risk for Leptospira infection (p = 0.023).

CONCLUSIONS

Leptospira shedding occurs in randomly sampled dogs in Thailand, with infection rates comparable to those of Europe and the USA. Therefore, the potential zoonotic risk should not be underestimated and use of Leptospira vaccines are recommended.

Leptospira spp. and Toxoplasma gondii in stranded representatives of wild cetaceans in the Philippines

Background

The stranding events of cetaceans in the Philippines provide opportunities for gathering biological information and specimens, especially from the pelagic forms. As part of an effort to monitor the health of wild cetaceans, this study detected Leptospira spp. and Toxoplasma gondii, causative agents of the emerging zoonotic diseases leptospirosis and toxoplasmosis respectively, in their stranded representatives. From October 2016–August 2018, 40 cetaceans (representing 14 species) that stranded nationwide were sampled for brain, cardiac muscle, skeletal muscle, kidney, and blood tissues, urine, and sera. These were subjected to molecular, serological, culture, and histopathological analyses to detect the target pathogens.

Results

T. gondii was detected in 20 (71%) of the 28 cetaceans with biological samples subjected to either molecular detection through RE gene amplification or IgG antibodies detection through agglutination-based serological assay. On the other hand, Leptospira was detected in 18 (64%) of 28 cetaceans with biological samples subjected to bacterial culture, molecular detection through 16S rDNA amplification, or IgM antibodies detection through ELISA-based serological assay.

Conclusions

There is the plausibility of toxoplasmosis and leptospirosis in cetacean populations found in the Philippines, however, acute or chronic phases of infections in sampled stranded individuals cannot be confirmed in the absence of supporting pathological observations and corroborating detection tests. Further studies should look for more evidences of pathogenicity, and explore the specific mechanisms by which pelagic cetacean species become infected by Leptospira spp. and T. gondii. As there is growing evidence on the role of cetaceans as sentinels of land-sea movement of emerging pathogens and the diseases they cause, any opportunity, such as their stranding events, should be maximized to investigate the health of their populations. Moreover, the role of leptospirosis or toxoplasmosis in these stranding events must be considered.

Diagnosis of Canine Leptospirosis

Several diagnostic tests are available to aid veterinarians in diagnosis of leptospirosis. Understanding the course of infection is imperative to determining which diagnostic test to order and sample to submit. Diagnostic tests for dogs suspected of having leptospirosis include antibody-based tests and polymerase chain reaction (PCR). Paired acute and convalescent microscopic agglutination test (MAT) are diagnostic for leptospirosis. PCR performed on blood and/or urine can be a valuable tool to aid in diagnosis of leptospirosis. Commercially available rapid point-of-care diagnostics have been validated in dogs and have value early in the course of illness before MAT and PCR results are available.

Antibodies produced by dogs successfully challenged with live Leptospira spp. did not cross-react to Brucella antigen in a commercial rapid slide agglutination test that detects antibodies to Brucella canis

Brucella canis is a cause of canine infertility and abortion. Veterinarians and veterinary laboratorians screen for antibodies to B. canis with serologic tests including a rapid slide agglutination test (RSAT; D-Tec CB, Zoetis, San Diego, CA). False-positive results are possible because of cross-reactivity to antibodies to some gram-negative bacteria. Cross-reactivity has been reported between antibodies of Brucella abortus and Leptospira spp. with serologic tests for bovine brucellosis; however, this has not been documented with serologic tests for canine brucellosis, to the author's knowledge. The RSAT was evaluated with the sera from dogs experimentally challenged with 1 of 4 serovars of Leptospira spp.: L. kirschneri serovar Grippotyphosa, or L. interrogans serovars Canicola, Icterohaemorrhagiae, or Pomona. Experimental infections were confirmed through results of microscopic agglutination testing and/or lateral flow immunochromatography testing. The sera of 32 dogs collected at day 0 and days 7, 10, and 14 yielded negative results with the RSAT. Antibodies produced through experimental infections to these 4 serovars of Leptospira spp. did not cross-react with Brucella antigen with the RSAT; therefore, cross-reactivity of anti-leptospiral antibodies may not be of concern for B. canis rapid slide agglutination testing of dogs.

Prospective evaluation of rapid point-of-care tests for the diagnosis of acute leptospirosis in dogs

The early diagnosis of acute leptospirosis is still a major challenge in dogs. The aim of this prospective study was to evaluate the suitability of two in-clinic tests detecting anti-leptospiral IgM and IgG antibodies in diagnosing canine leptospirosis. The performances of the two rapid tests were compared to the microscopic agglutination test (MAT) carried out on acute sera and to diagnostic criteria adopted in this study to confirm leptospirosis infection (MAT upon admission, convalescent MAT and quantitative real-time PCR on blood and/or urine). The dogs were enrolled on the basis of reported exposure to known risk factors and clinical presentation (acute kidney injury and/or systemic inflammatory response syndrome with multi-organ damage). Eighty-nine dogs included in the study were sub-grouped on the basis of the results of the diagnostic criteria adopted: (1) confirmed leptospirosis cases (42/89 dogs); (2) negative leptospirosis cases (36/89 dogs); and (3) unconfirmed leptospirosis cases (11/89 dogs). The results supported the usefulness of the two rapid diagnostic tests as a first in-clinic screening tool for suspected leptospirosis; positive results in the in-clinic tests in dogs with suggestive clinical and laboratory signs strongly indicated acute leptospirosis, while negative results required additional diagnostic investigation to exclude the infection. Confirmatory tests recommended for canine leptospirosis are still necessary in addition to the use of rapid in-clinic tests.