Mice experimentally infected with a pathogenic strain of Leptospira interrogans serovar Canicola produced false negative results (prozone effect) in a microscopic agglutination test (MAT). This prozone effect occurred in several serum samples collected at different post-infection times, but it was more prominent in samples collected from seven-42 days post-infection and for 1:50 and 1:100 sample dilutions. This phenomenon was correlated with increased antibody titres in the early post-infection phase. While prozone effects are often observed in serological agglutination assays for the diagnosis of animal brucellosis and human syphilis, they are not widely reported in leptospirosis MATs.

A leptospirose é uma antropozoonose mundialmente distribuída que infecta animais de produção, incluindo as ovelhas como carreadores para outros animais e o homem. O presente estudo objetivou determinar a prevalência de Leptospira spp. em ovinos de dois abatedouros do estado de São Paulo e sua associação com algumas variáveis epidemiológicas estudadas. Amostras de soro de 182 ovinos foram pesquisadas para a presença de anticorpos para Leptospira spp. pela soroaglutinação microscópica (SAM). Os resultados indicaram 34/182 (18,68%; IC95% 13,70-24,98%) amostras positivas, principalmente para o sorovar Copenhageni (17/34; 50%; IC95% 33,99-66,01%). Crescimento bacteriano no meio de Fletcher foi observado em amostras de 13/34 (38,24%; CI95% 23.87-55.08%) animais, e confirmados pela Reação em Cadeia pela Polimerase (PCR) e seqüenciamento para somente duas amostras renais de dois animais. Assim, o tratamento e vacinação dos ovinos, além do controle de roedores, pode ser útil na prevenção da infecção na região estudada, visto que os ovinos são importantes carreadores de Leptospira spp. para o homem, e sua transmissão aos trabalhadores de abatedouros ocorre principalmente pela manipulação das vísceras.

Leptospirosis is a worldwide anthropozoonosis that infects livestock, including sheep as the carriers to other animals and humans. The present study aimed to determine the prevalence of Leptospira spp. in sheep from two slaughterhouses in the state of São Paulo, Brazil and its association with epidemiological variables. Serum samples from 182 sheep were evaluated for Leptospira spp. antibodies by microscopic agglutination test (MAT). Results indicated 34/182 (18.68%; CI95% 13.70-24.98%) positive serum samples, mainly to the serovar Copenhageni (17/34; 50%; CI95% 33.99-66.01%). Bacterial growth in the Fletcher medium was detected for 13/34 (38.24%; CI95% 23.87-55.08%) animals, and confirmed by Polymerase Chain Reaction (PCR) and sequencing for only two kidney samples from two animals. Thus, treatment and vaccination of sheep, besides rodent control, can be useful to prevent the infection in the studied region since sheep are important Leptospira spp. carriers, and its transmission to slaughterhouse workers is mainly through the manipulation of visceral tissues.