Feline leptospirosis serosurvey from a Quebec referral hospital

Abstract

Epidemiologic studies have linked interactions with cats as a risk factor for human leptospirosis, but serosurveys of feline Leptospira spp. infection are scarce in the veterinary literature. The objective of this study was to conduct a serosurvey of Leptospira spp. infection in cats presenting to an eastern Canadian veterinary teaching hospital (VTH). All serum samples collected from cats presented to the VTH were tested by the microscopic agglutination test (MAT) for the Leptospira serovars Canicola, Grippotyphosa, Icterohaemorrhagiae, Bratislava, Pomona, and Autumnalis. Ten of 40 cats [25%; 95% confidence interval (CI): 12.7% to 41.2%] tested had positive antibody titers (≥ 1:100). All 10 cats with positive titers were positive for Bratislava and 2 were also positive for Autumnalis. This high incidence of seropositivity for Leptospira spp. may suggest that the disease could be of more clinical importance than previously recognized.

Introduction

Leptospirosis is a zoonotic disease encountered worldwide and is known to affect humans, domestic animals, and wildlife. A re-emergence of the disease in companion animals in the 1990s inspired an increase in the frequency of leptospirosis prevalence studies in dogs (1). Although epidemiologic studies have linked interactions with cats as a risk factor for human leptospirosis, serosurveys of feline Leptospira spp. infection are scarce in the veterinary literature. Recently, serosurveys reported that between 4.8% and 35.3% of cats tested were seropositive for Leptospira spp. in various geographic regions (2–8). Because the prevalence and distribution of this disease vary widely, the presence of Leptospira spp. infection in cats in various geographic areas is questionable and thus often disregarded as a potential cause for disease in cats and as a zoonotic risk (1). Recently, 3 cases of clinical feline leptospirosis were reported from our institution (9). Although leptospirosis has been reported in dogs in Canada, no recent serosurveys in cats are available (10,11). The objective of this study was to determine the seroprevalence of Leptospira spp. antibodies in cats presenting to an eastern Canadian veterinary teaching hospital.

Materials and methods

Between October 1 and December 1, 2007, all feline serum samples obtained from referral cases to the specialty services, the primary care service, or from the emergency and critical care services were submitted to the diagnostic laboratory of the Faculté de Médecine Vétérinaire of the Université de Montréal. Our protocol was approved by the Institutional Animal Care and Use Committee and informed owner consent was obtained.

Blood samples were collected in a dry blood collection tube and serum was immediately separated then submitted daily to the Laboratoire d’Expertise en Pathologie Animale du Québec (LEPAQ) of the Ministry of Agriculture, Fisheries and Food of Quebec (MAPAQ). The samples were stored and antibody titers for the serovars Leptospira interrogans Canicola, Icterohaemorrhagiae, Bratislava, Pomona, Autumnalis, and Leptospira kirschneri serovar Grippotyphosa were measured by microscopic agglutination test (MAT) once weekly. Cats were considered seropositive when they had antibody titers ≥ 1:100. Cats with titers ≥ 1:200 were considered as potential clinical cases and underwent further evaluation with a urinary polymerase chain reaction (PCR) and a convalescent titer to assess if they had active infections (2 to 4 wk following initial serologic testing).

Results

Samples from 40 cats were obtained for analysis. Ten of the 40 cats [25.0%; 95% confidence interval (CI): 12.7% to 41.2%] had positive antibody titers (≥ 1:100). Of the 10 seropositive cats, 6 either had an indoor/outdoor lifestyle or had contacts with other cats. This information was unavailable for 3 cats and 1 cat was an exclusively indoor cat that did not have contact with other cats. Of the 30 seronegative cats, 17 either had an indoor/outdoor lifestyle or had contact with other cats. This information was unavailable for 4 cats and the 9 cats that were kept exclusively indoors did not have any contact with other cats. Three of the 10 seropositive cats had evidence of kidney disease in their blood work, 1 had a recent history of polyuria and polydyspsia, 2 had hepatic lipidosis, 1 was treated for a corneal ulcer, 1 for an anal sac abscess, and 1 was presented to the emergency service because he had been hit by a car. The reason for presentation of 1 cat was unknown. Nine of the 30 seronegative cats had evidence of kidney disease based on their blood work and 4 had some degree of liver disease (1 had hepatic lipidosis, 1 had cholangitis, 2 had increased liver enzymes). The reasons for presentation for the seronegative cats were as follows: 8 cats were referred to specialty services for specific reasons [tachypnea, mammary mass, abdominal mass, diabetes mellitus, suspicion of feline infectious peritonitis, broken canine tooth, investigation of chronic kidney disease (CKD)], 6 cats were presented for non-specific signs (decreased appetite, depression, and vomiting), 6 cats were presented to the internal medicine or ophthalmology services for a follow-up of their known chronic conditions (hyperthyroidism, CKD and uroliths, hyperthyroidism and diabetes mellitus, cholangitis/cholangiohepatitis complex, CKD and chronic eye ulcers, uveitis and chorioretinitis), 5 cats were presented for lower urinary tract signs, 3 cats were presented for neurological investigation (meningitis, inflammatory polyp, vestibular ataxia), 1 cat was presented for dental treatment, and 1 cat was presented for a routine health examination.

Of the seropositive cats, only 1 cat had an initial titer of 1:200 and therefore was a candidate for paired titers and urinary PCR. This 23-year-old Persian cat was euthanized upon presentation, but a postmortem examination was not performed; therefore, its active infection status could not be determined. All 10 cats with positive titers were positive for serovar Bratislava and 2 of the 10 cats were also positive for serovar Autumnalis. None of the cats had received immunization against leptospirosis.

Discussion

The aim of this study was to evaluate the presence of antibodies for Leptospira spp. in cats presenting to an eastern Canadian veterinary teaching hospital. Our study suggests that 1 out of 4 cats from the population of cats seen at our referral hospital carries antibodies against Leptospira spp. This high incidence of seropositivity for Leptospira spp. may suggest that the disease could be of more clinical importance than previously recognized. One study reporting seroprevalence of leptospirosis in cats concluded that 12.8% of the study population had antibody titers ≥ 1:100 (12). In that study, as in ours, the authors considered titers of 1:200 or more to be suspicious for an active infection. Therefore, no cat with an initial titer of 1:100 was evaluated with a convalescent titer, as in our study. It is difficult to assess if cats with clinical leptospirosis tend to have low titers or if they mount a significant immunological response, as is the case in dogs (1). The cats in our study may have been previously exposed to the spirochete without contracting the disease, which would explain the low titers. Following experimental inoculation, the majority (90%) of cats mount high immune response as evidenced by an increase in antibody titer as high as 1:3200 without any clinical or clinicopathologic changes other than a transient mild elevation in body temperature (13). However, as recently reported, cats with clinical leptospirosis can also mount a significant immune response (9). Nevertheless, 3 cats presented with kidney disease and 2 cats with hepatic disease; thus the role of leptospirosis, in cats with low titers but with kidney or liver diseases needs to be further investigated. Moreover, it is possible that lower titers represent cross-reactivity with serovars not tested for, but which are present in the environment. To determine the magnitude of titer elevation in cats with natural active leptospirosis, future studies should consider cats with lower titers as being potentially infected and urinary PCR should be performed upon initial presentation.

An interesting finding from our study is that serovar Bratislava was implicated in all cats that tested positive. The only other serovar identified was Autumnalis, which often increases with the serovar Bratislava in canine leptospirosis. The serovar Autumnalis has not been isolated from dogs in North America (1). However, the serovar Bratislava is recognized as causing clinical disease in dogs in North America. Moreover, antibodies to this serovar were also elevated in 3 of 6 recently reported seropositive cats (5,9). This raises the question as to the source of exposure of cats with this serovar. In fact, cats are suspected of acquiring leptospirosis through contact with rodents, and the serovar Bratislava is naturally carried by mice and rats (6,14,15). Most of the cats from our study could have acquired leptospirosis through contact with rodents or by coming in contact with the other cats within the household. This could explain the high prevalence of this serovar in the cats in our study. However, the proximity of those cats to facilities that house pigs, which are also natural carriers for serovar Bratislava, and recognized as possible sources of infection for leptospirosis in cats, is unknown (15). The implication of contacts with other cats as a risk factor for leptospirosis needs to be further investigated.

Limitations of this study are related to the short length of time for data collection, the limited geographical area, and the small number of cats. Moreover, the lack of information on the carrier status of cats that tested positive prevents further analysis of the role of leptospirosis in their clinical disease.

To the authors’ knowledge, this is the first study in which cats presenting to a referral hospital were systematically screened for leptospirosis, and it is the first seroprevalence study of feline leptospirosis in Quebec. The results of our study suggest that Leptospira spp. infection is present among cats in our hospital population. Its zoonotic risk and potential as an etiologic agent for various diseases should be considered and further investigated. CVJ