During the acute phase of dog´s infection with Leptospira interrogans serovars such as icterohaemorrhagiae, copenhageni or canicola many organs systems are affected. The extension and severity of lesions are related to the organism virulence and host susceptibility. Clinical signs of infection in the acute phase are apparent and in association to risk factors, allow the clinician to make the diagnosis of leptospirosis. As the host´s immune response develops, leptospira organisms are confined within kidney tubular cells and from there they are eliminated in the urine. Many dogs, especially in case of serovar canicola infection, might host the organism for months or years, without overt signs of infection. It is thought that chronic kidney colonization might lead to progressive tubulointersticial nephritis and ultimostly, end stage kidney. The polimerase chain reaction (PCR) is being increasingly used for leptospiral DNA detection in the urine in many domestic or wild hosts. Therefore, it might be a useful tool for identification of carriers dogs as a screening test. The results of serological survey (MAT tests) are conflicting and because of widely use of vaccine, it does not allow to distinguish actual infection and antibodies response as the result of vaccination. Identification of carriers dogs using PCR, and antimicrobial therapy of actually infected dogs would help delaying the progression of chronic kidney disease and minimizing the risks for Public Health.
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