Exposure to Leptospira spp. in Sick Dogs, Shelter Dogs and Dogs from an Endemic Area: Points to Consider

Background: Leptospirosis is a zoonosis caused by pathogenic spirochetes of the genus Leptospira. Rodents play an important role as maintenance hosts, but dogs can be significant reservoirs for human infection in tropical areas as well as the source of disease outbreaks. Manifestations of disease in dogs vary from asymptomatic carriers to severe clinical signs and death. This study compared leptospiral exposure in dogs suspected to have leptospirosis and presented at a Veterinary Teaching Hospital (VTH), dogs from a Control Center of Zoonoses (CCZ) and dogs from a neighborhood with a high prevalence of human leptospirosis. Also, clinical signs, laboratory abnormalities and environmental risk factors associated with the infection were investigated at a population level and in a case-by-case approach. Materials, Methods & Results: Between May 2007 and February 2009, 253 dogs from Porto Alegre, Brazil, were enrolled in the study. Three populations were evaluated including dogs from and endemic area to human leptospirosis, dogs from a CCZ and dogs presented to a VTH. All dogs' owners from the endemic area and from the VTH answered a questionnaire including dog's information such as breed, age, vaccination status, environment, contact with other domestic animals, presence of rodents in the household, clinical signs, medications and if owners had leptospirosis diagnosed in the previous two years. The investigation of the exposure to pathogenic leptospires was based on serology using the Microscopic Agglutination Test (MAT), and polymerase chain reaction (PCR) using two sets of primers to detect pathogenic leptospiras in blood (leptospiremia) and urine (leptospiruria). Positive results were found in the three populations. The most prevalent serovars were Canicola, Icterohaemorrhagiae and Copenhageni, independent of the dog health condition. Leptospiruria occurred in 20.0%, 8.4% and 30.3% of CCZ, endemic area and VTH dogs, respectively. There was no association between seropositivity and leptospiremia or leptospiruria. The presence of rats in the environment was associated with leptospiruria (P = 0.02). Complete blood count (CBC), serum biochemistry (alanine aminotrasferase and creatinine) and urinalysis were also performed. Although increased serum creatinine (P = 0.009), jaundice (P = 0.004) and glucosuria (P = 0.04) were associated with leptospiruria in the VTH dogs, the absence of clinical signs or clinicopathologic alterations did not exclude the infection, as observed in several dogs from CCZ and from the endemic area. Discussion: As expected, the VTH showed the relatively highest percentage of positive samples (serology, leptospiruria and leptospiremia), since these were clinical cases. However, no statistical differences were found in the percentage of leptospiremia between VTH and the dogs from endemic area, neither in the percentage of leptospiruria or serology between VTH and dogs from CCZ. The most common serovars identified by MAT were consistent with the findings of other studies involving dogs in Southern Brazil. If creatinine is elevated, particularly if jaundice is present, the likelihood of leptospiral infection must be considered; however, normal findings for these parameters do not rule out this diagnosis. Most of the dogs vaccinated the year before showed leptospiremia and/or leptospiruria, suggesting infection with a serovar not included in the vaccine, vaccine inefficacy or a wrong dog vaccination schedule. Subclinical infection is a problem when considering animals with leptospiruria that will likely remain untreated. The control of the environmental dissemination of pathogenic Leptospira spp. in urban settings should include the identification of asymptomatic dogs.