Regional differences of leptospirosis in Sri Lanka: observations from a flood-associated outbreak in 2011

Abstract

Leptospirosis is known to be an important cause of weather disaster-related infectious disease epidemics. In 2011, an outbreak of leptospirosis occurred in the relatively dry district of Anuradhapura, Sri Lanka where diagnosis was resisted by local practitioners because leptospirosis was not known in the area and the clinical presentation was considered atypical. To identify the causative Leptospira associated with this outbreak, we carried out a cross-sectional study. Consecutive clinically suspected cases in this district were studied during a two-and-a-half-month period. Of 96 clinically suspected cases, 32 (33.3%) were confirmed by qPCR, of which the etiological cause in 26 cases was identified using 16S rDNA sequencing to the species level. Median bacterial load was 4.1 × 10(2)/mL (inter-quartile range 3.1-6.1 × 10(2)/mL). In contrast to a 2008 Sri Lankan leptospirosis outbreak in the districts of Kegalle, Kandy, and Matale, in which a predominance of Leptospira interrogans serovars Lai and Geyaweera was found, most cases in the 2011 outbreak were caused by Leptospira kirschneri. Seven (21.9%) confirmed cases had acute renal failure; five (15.6%) had myocarditis; severe thrombocytopenia (<20,000/uL) was seen in five (15.6%) cases. This outbreak of leptospirosis in the relatively dry zone of Sri Lanka due primarily to L. kirschneri was characterized by markedly different clinical presentations and low leptospiremia. These observations and data demonstrate the public health relevance of molecular diagnostics in such settings, possibly related to the microgeographic variations of different Leptospira species, but of particular value to public health intervention in what appears to have been a regionally neglected tropical disease.

Figure 1. Geography of Anuradhapura showing paddy fields and water reservoirs.

(A)Partially dried water reservoir (Nuwara Wewa) during dry season (B) Females removing weeds in paddy fields (C) Water reservoir during the rainy season (D) Dried up reservoirs during dry season (E) Flooding in Anuradhapura (F) Paddy field during the cultivation season.

Figure 2. Suspected cases of leptospirosis reported to the regional epidemiologist Anuradhapura during 2000–2012 period.

Figure 3. Epidemic curve of post flood leptospirosis outbreak in Anuradhapura, based on the notified cases and the number of cases recruited for the present study (in dark color).

Figure 4. Distribution of Leptospira burden among 32 qPCR positive patients.

Figure 5. Phylogenetic tree based on the region of leptospira rrs gene.

The sequences were aligned in MEGA4 using CLUSTALW, and phylogenetic distances were calculated in MEGA4 using the maximum likelihood. Numbers of nodes were bootstrap support after 500 replicates.