College of Public Health - University of the Philippines Manila
Leptospirosis is endemic in the Philippines and is one of the reportable infectious diseases in the country. Understanding the epidemiological features of leptospirosis is a critical step in designing interventions for decreasing the risk of disease transmission. In particular, the typing of isolated leptospires is very useful in the recognition of new patterns of disease transmission and in the surveillance of prevailing local pathogenic serovars. The information that will be derived from the latter is very important especially in the development of potential vaccine candidates that are relevant to our country, as well as assessing the effectiveness of intervention measures. This study aimed to identify the prevalent Leptospira serovars that infect humans and animals in the Philippines. In order to fulfill this objective, the study determined the prevalence of Leptospira serovars among patients and high risk groups from the National Capital Region and seven other regions in the Philippines, as well as animals from the National Capital Region and Nueva Ecija from August 2010 to February 2012. Microscopic agglutination test (MAT) was performed on human and animal sera. Human samples were considered positive if the reactive sera had a titer greater than or equal to 400 for single serum samples and a four-fold rise in titer or seroconversion for paired sera. For animal samples, sera having 50% or more agglutination compared to free leptospires, when compared to a negative control were considered MAT-positive. Among human serum samples, Patoc was found to be the most frequently occurring serovar followed by Semaranga, Copenhageni, Poi, Manilae and Pyrogenes. Twenty-seven out of 1,353 patients were culture-positive, with one patient having positive blood and urine cultures. Isolates from humans were identified as serovars Pyrogenes, Losbanos, Ratnapura, Manilae, and Canicola using monoclonal and/or polyclonal antibodies. As for the MAT results of the animal samples collected, different prevalent serovars were found each type of animal. Serovar Tarassovi was found to be prevalent among cows and water buffaloes, Poi for pigs, Copenhageni for rats, and Manilae among dogs. Among the 51 rat samples collected, 7 were culture-positive, with 4 rats being positive for both urine and kidney cultures. These rat isolates were identified as serovars Manilae, Ratnapura, and Losbanos. However, all culture samples from dogs, water buffaloes, pigs, and cows were negative for leptospires. MAT results from human and animal sera showed high antibody positivity against serovars that are usually different from the ones isolated. The finding that the majority of the serum samples were reactive with Patoc suggests either a high exposure to this serovar which is considered non-pathogenic or infection caused by other Leptospira serovars that were not included in the MAT panel of antigens. Additional studies need to be conducted to further characterize the Leptospira serovars that are most commonly occurring in the Philippines in order to understand better and address the problem of leptospirosis in the country. Results from this study may contribute in establishing preventive and control measures against leptospirosis.