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 4.1×102/mL (inter-quartile range 3.1–6.1×102/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.
Highlights
IntroductionAnnual rainfall varies from ,1,500 mm in ‘‘dry’’ zones, where water reservoirs may dry to completeness, to 5,000 mm in the ‘‘wet’’ zones with a mean annual temperature between 26.5uC to 28.5uC
Sri Lanka is a tropical island located southeast of India
In the present study we use a recently published qPCR assay [4] to attempt to confirm that this outbreak of febrile illness with renal and liver complications was due to leptospirosis, and if so, to quantify the bacterial load and determine whether this flood-associated outbreak was caused by the same strains implicated in the island-wide outbreak of 2008 [5]
Summary
Annual rainfall varies from ,1,500 mm in ‘‘dry’’ zones, where water reservoirs may dry to completeness, to 5,000 mm in the ‘‘wet’’ zones with a mean annual temperature between 26.5uC to 28.5uC. All leptospirosis endemic districts are within wet zones and have an annual rainfall in excess of 2,000 mm. Paddy farming activities, high rainfall, moist soil, year-round water retention in paddy fields, the use of buffalo in agriculture and peridomestic animal farming in rural areas provide ideal environments for the transmission of leptospirosis. Anuradhapura is located in North Central province of Sri Lanka, in the dry zone of the country. The soil structure, water quality and ecological systems in Anuradhapura contrast with those of the wet zones of Sri Lanka where leptospirosis is endemic
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