A sero-epidemiological study of leptospirosis in Sarawak, Malaysia

Several recent outbreaks of leptospirosis involving human deaths have alarmed health professionals in Malaysia. The study outlined in this thesis was conducted to increase the understanding of the involvement of wildlife in the disease in Malaysia. A strain of Leptospira (designated Lepto 175 Sarawak) was isolated from water in Sarawak, Malaysia. This strain did not produce any titres towards other known Leptospira sera, and thus represents a novel serovar. This serovar had 99.1% 16S rRNA gene sequence similarity with Leptospira wolffii and was the dominant strain present in the region. In this study eight of the 12 non-human primates sampled (66.6%; 95% CI 34.9- 90.1) and 73 of 155 wild small mammals (47.1%: 95% CI 39.0-55.3) were seropositive to leptospires. The seroprevalence was slightly higher in rats than in squirrels or bats. Seropositive animals were detected in all localities sampled, with the highest prevalence at Mount Singai (64.7%; 95%CI 38.3-85.8). Antibodies were detected to two different serovars in non-human primates, eight serovars were detected in rats, six serovars in bats and five in squirrels. Of 155 kidney samples from individuals, 17 were positive for Leptospira on PCR analysis (11%; 95% CI 6.5-17). A cross-sectional serological survey of 198 humans was conducted in four villages around Kuching, Sarawak with 35.9% (95%CI 29.2-43.0) testing positive on the MAT. Antibodies to serovar Lepto 175 Sarawak were most commonly detected (31.3%; 95%CI 24.9-38.3) and were detected in individuals at all four locations. The presence of skin wounds (OR 3.1), farm animals (OR 2.5) and rats (OR 11.2) were all significantly associated with seropositivity in a multivariable logistic regression model. The results of the current study are important as wildlife may act as reservoirs of leptospires for humans. Health authorities should expand disease control measures to minimise the spill-over from wildlife to humans visiting, living or working in the sampled locations. The pathogenic status of serovar Lepto 175 Sarawak also requires further investigation