The interrelationship between meteorological parameters and leptospirosis incidence in Hambantota district, Sri Lanka 2008–2017 and practical implications

Abstract

Background Leptospirosis is a bacterial zoonosis. Leptospirosis incidence (LI) in Sri Lanka is high. Infected animals pass leptospires to the environment with their urine. Leprospires' survival in the environment to infect a new host depends on meteorological factors. El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) modulate the weather in Sri Lanka. Objectives The determination of interrelationship between the LI in the Hambantota District, and local meteorological parameters, ENSO and IOD. Methods We acquired notified leptospirosis cases in the Hambantota District and population data. We calculated weekly leptospirosis incidences for 2008 to 2017.Weather data from two weather stations was obtained, averaged and converted into weekly data. We plotted time series graphs and observed the correlation between seven aggregated weather parameters and LI. We estimated cross-correlations between those weather parameters and LI. As our principal analysis we determined correlation between LI and seven local weather parameters, Nino 3.4, Nino4 and Dipole Mode Index (DMI) indices using wavelet analysis. Results Our wavelet analysis results showed troughs of minimum, maximum, mean temperatures, soil temperature, the evaporation rate, the duration of sunshine were followed by peaks in LI and peaks of rainfall followed by peaks of LI, all after lag periods. Our time series graphs and cross-correlation determination results are generally in agreement with these results. However there was no significant correlation between rainfall and LI in the cross-correlation analysis. There were peaks of LI following both peaks and troughs of DMI. There was no clear correlation between both Nino indices and LI. Discussion This may be the first long-term study demonstrating soil temperature, evaporation rate and IOD are correlating with LI. The correlation pattern of LI with temperature parameters differs from similar past studies and we explain the reasons. We propose ways to control high LI we observed after periods of weather favorable for transmission of leptospirosis.

Time series models for prediction of leptospirosis in different climate zones in Sri Lanka

“…Two studies done by S. R. Gnanapragasam developed univariate seasonal autoregressive integrated moving average (SARIMA) models to describe the incidence of leptospirosis in Kurunegala, Rathnapura, Colombo, Gampaha and Kaluthara districts and for the western province [20,21]. These studies were focusing mainly on the wet zone, while the dry zone was rarely studied [22,23]. Plouffe Cameron et al performed a comprehensive analysis to predict leptospirosis in Sri Lanka, but the only meteorological variable considered was rainfall and the major results presented were limited to three districts [24].…”

The correlation between three teleconnections and leptospirosis incidence in the Kandy District, Sri Lanka, 2004–2019

“…Most of the time, people get infected by leptospires in damp soil or surface water bodies through breaches of the skin or through mucus membranes [4,5]. Survival of leptospires in the environment until they enter into a host, biofilm making by leptospires that influences the load of infecting bacteria, depends upon several local weather parameters including local rainfall, temperature, humidity, evaporation rate, and duration of sunshine [3]. Overflows after heavy rains disperse leptospires [1,3,5].…”

“…Survival of leptospires in the environment until they enter into a host, biofilm making by leptospires that influences the load of infecting bacteria, depends upon several local weather parameters including local rainfall, temperature, humidity, evaporation rate, and duration of sunshine [3]. Overflows after heavy rains disperse leptospires [1,3,5]. Among non-weather factors that affect the survival of leptospires, pH, salinity, texture, and microbiota of the soil are also modulated by local weather [1,3].…”

“…Overflows after heavy rains disperse leptospires [1,3,5]. Among non-weather factors that affect the survival of leptospires, pH, salinity, texture, and microbiota of the soil are also modulated by local weather [1,3]. Outdoor manual work exposing to damp soil and water, especially working in rice paddies, is a common risk factor of exposure to leptospirosis in Sri Lanka and in other tropical countries [1-3, 5, 8].…”

“…Leptospirosis is an emerging zoonotic disease caused by pathogenic and opportunistic spirochete bacteria belonging to the genus Leptospira [1][2][3][4][5]. A small fraction of infections result in severe leptospirosis (Weil's disease) [5].…”