• Open Access

The Prevalence of Leptospiral Antibodies in Free Roaming Cats in Worcester County, Massachusetts


Corresponding author: L. Ross, Tufts University Cummings School of Veterinary Medicine, North Grafton, MA; e-mail: linda.ross@tufts.edu.



Serosurveys of cats for exposure to or infection with leptospires have been published from other geographic areas, but none for cats in the United States in the past 4 decades.


The purpose of this pilot study was to determine the prevalence of leptospiral antibodies in a population of free roaming cats in Worcester County, (central) Massachusetts.


Sixty-three free roaming cats presenting to a trap-neuter-return (TNR) program.


Prospective study. Serum was collected from 63 free roaming cats presented to a university associated TNR. Microagglutination titers to Leptospira interrogans serovars Autumnalis, Hardjo, Bratislava, Icterohaemorrhagiae, Canicola, Pomona, and L  kirshneri Grippotyphosa were determined.


A total of 3 of 63 cats (4.8%) had a titer of 1 : 100 or greater to one or more serovars, with Autumnalis being the most common. None of the cats were seropositive to Hardjo, Grippotyphosa, or Canicola.

Conclusions and clinical importance

These results are consistent with previously published seroprevalence rates in feral cats. Additional studies are required to determine the role of leptosporosis in clinical disease in the domestic cat.


microagglutination titer



Leptospirosis in dogs has received increased recognition in the United States over the past 20 years, and several serosurveys of the prevalence of leptospiral antibodies in dogs have been published during that time.[1] The role of cats in the epidemiology of leptospirosis has received little attention. Serosurveys of cats for exposure to or infection with leptospires have been published from other geographic areas, but none for cats in the United States in the past 4 decades. Cats can acquire leptospirosis from the ingestion of infected mice, as well as the ingestion of contaminated water.[2] The northeastern United States has a high incidence of leptospirosis in dogs.[3] The purpose of this study was to determine the seroprevalence of leptospirosis in a free roaming population of cats in an endemic area (central Massachusetts).

Materials and Methods

Subjects of the study were intact cats trapped within an average of 19 miles from the Tufts University Cummings School of Veterinary Medicine campus (range: 9–36 miles), and presented to the veterinary school-associated trap-neuter-return (TNR) clinic on one day in November 2010. Many of the cats were trapped within the same neighborhoods. All cat trappers or caretakers provided permission for inclusion in this study. This study was approved by the Tufts Cummings School Clinical Studies Review Committee.

Cats were sedated with a standard and previously described TNR cat total intravenous anesthesia protocol consisting of telazol, ketamine, and xylazine.[4] After anesthesia induction, a physical exam was performed and blood was obtained from jugular or medial saphenous venipuncture before spay or neuter. The blood was centrifuged and the serum separated and frozen at −80°C. Frozen serum was sent to the Animal Health Diagnostic Center at Cornell University in Ithaca, NY. Microagglutination titers (MAT) were performed to Leptospira interrogans serovars Pomona, Hardjo, Canicola, Icterohemorrhagiae, Autumnalis, and Bratislava and Leptospira kirshneri serovar Grippotyphosa. Microagglutination titers >1 : 100 were considered positive.


A total of 70 cats presented to the spay and neuter clinic and 63 cats were included in the study. Reasons for exclusion included inability to obtain a blood sample; the cat was found to be already sexually altered and thus did not present to the blood sampling station; or the trapper/caretaker did not give permission for inclusion in the study. Of these 63 cats. 33 were intact females, 27 were intact males, 1 cat was a spayed female, and 1 cat was a neutered male. The sex of one cat was not recorded. All 63 cats were domestic short- or long-haired cats. The cats were trapped an average of 19 miles from the Tufts University Cummings School of Veterinary Medicine campus (range: 7–36 miles).

Three of the 63 or 4.8% of the cats were positive for one or more leptospiral serovars (95% confidence interval: 1.6%–13.1%). Confidence limits were calculated with an online calculator (http://faculty.vassar.edu/lowry/prop1.html, accessed October 23rd, 2011). Three cats were seropositive to Autumnalis with titers 1 : 200, 1 : 1600, and 1 : ≥12800. The cat with the highest Autumnalis titer was also seropositive to Pomona at a titer of 1 : 1600, Icterohemorrhagiae at 1 : 400, and Bratislava at 1 : 800. No other cats were found to be positive for Pomona, Icterohemorrhagiae, or Bratislava. None of the cats were seropositive to Hardjo, Grippotyphosa, or Canicola.

All seropositive cats were intact females, which was not statistically significant by Pearson Chi Square analysis (= 0.11). Physical exam findings on these 3 cats were lactation in 1 cat; thin body condition, dental disease, and ear mites in 1 cat; and no abnormalities in 1 juvenile cat. Two of the 3 cats with the highest titers were cats trapped on the same street in the same neighborhood in Worcester, MA.


Seroprevalence in this study was slightly less than that in other recent studies reporting seroprevalence rates of 9.2–12.8%.[5, 6] However, it is consistent with 1 study performed in the United States in 1957 of 350 cats with a prevalence of 4.9%, the majority of which were from rural Pennsylvania.[7] The lower prevalence when compared to previous reports may be due to the cut-off value of 1 : 100 utilized in this study. Many of the previous reports utilized a lower cut-off value, such as 1 : 30 or 1 : 50, thus increasing the sensitivity of their MAT.[5, 8] Other possible reasons could include the time of year, the suburban to urban areas from which the cats in this study were trapped, small sample size, prey species native to this location, or true lower incidence in this geographic location as compared to that in other locations.

Previous reports on domestic cats showed varying serovar prevalence. However, there are at least two previous reports of Autumnalis as the most prevalent serovar.[7, 8] Furthermore, this serovar has recently been found to be one of the more common canine serovars based on seroprevalence studies in the United States.[9] Autumnalis has known cross-reactivity to serovars Grippotyphosa, Pomona, and Bratislava.[1] However, only one of the cats in this study was positive for Pomona and Bratislava, and no cats were positive for Grippotyphosa. Although Autumnalis has never been isolated from dogs or cats in the United States, in 1958 it was isolated from raccoons in Georgia.[10] The possibility that this serovar may cause pathogenic disease in cats should be considered and isolation attempts should be made.

There are several views regarding the lower reported seroprevalence rates in cats. Some researchers have postulated that cats respond to infection with a lower MAT than their canine counterparts, and have demonstrated experimental and naturally occurring infections in cats resulting in MATs ≤1 : 100.[2, 5, 11] Others have theorized that cats may have the ability to mount a rapid immune response, followed by a rapid decline in titer.[2] However, it must also be noted that the majority of seroprevalence studies in cats have utilized serovars that are known to be associated with infection in dogs or people. It could instead be that the primary serovars affecting cats are different, or as yet undescribed, and that reported serovar prevalence is due to cross-reaction or paradoxical reactions between serovars rather than true infection. Limitations to this study include the relatively small geographical area from which all subjects originated, the inability to compare clinical signs with presence of infection due to free roaming cat status, as well as the inability to confirm acute infection with a paired convalescent sample. One additional limitation would be that only 7 serovars were evaluated in the cats in this study, and the possibility that cats can be infected by another untested serovar cannot be discounted. This study confirms that cats in the northeastern United States are exposed to leptospirosis, but it does not indicate whether the cat serves as a maintenance or incidental host for this disease.


A portion of this work was presented at the 2011 American College of Veterinary Internal Medicine Forum, Denver, CO.