Seasonal variation of Leptospira species in pond and paddy field water samples in Thrissur district

Abstract

Leptospirosis is an acute anthropozoonotic infection occurring worldwide caused by a pathogenic spirochete belonging to the genus Leptospira. The highest occurrence of leptospirosis in tropical countries is directly related to heavy rainfall and flooding. The changing rainfall pattern in the Western Ghats with rainless days during the monsoon months is reportedly affecting normal climatic condition of Kerala. Leptospires are able to survive in an environment with high humidity and moderate temperature.. The present study was undertaken to study the seasonal variation in occurrence of Leptospira spp. in pond and paddy field water in Thrissur district of Kerala. The samples were collected in two seasons i.e. monsoon (June to September) (Season-1) and summer (February to May) (Season-2) for the identification of Leptospira spp. The water samples were subjected to PCR for identification of the organism. The temperature and pH of water samples were recorded at the time of collection. The different physicochemical parameters of water in these two sources were in the range of pH (6.5- 7.9), conductivity (85- 150 µs/cm), salinity (0.02- 0.12 psu), turbidity (5-50NTU), dissolved oxygen (6-8 mg/L). Out of the 80 samples analysed, 52 (23 from monsoon and 29 from summer) samples detected 16Sr RNA at 430 bp and hence was positive for Leptospira species. The pathogenicity of the positive isolates were analysed by detecting the virulence gene viz., lipl 32, lipl 21 and lipl 41 respectively. The results revealed that out of the total isolates of Leptospira, 23 and 21 isolates were positive for lipl 21 and lipl 41 in monsoon and summer seasons respectively. Out of the total 85 paddy field water samples collected, 17 samples were found to be positive for Leptospira spp. The virulence gene lipl 21 was detected in three samples in summer season. However, lipl 32 and lipl 41 genes were not detected in any of the samples. The results of the present study demonstrated the ubiquitous nature of the organism in environment in the both seasons. The contaminated environment can hence be one of the sources for the increase in the frequency of human and animal leptospirosis in Kerala. Keywords: Leptospira spp., Leptospirosis, Paddy field water quality, lipl 32, lipl 21 and lipl 41