Endemicity, Clinical Features, Risk Factors, and the Potential for Severe Infection in Leptospira wolffii-Associated Leptospirosis in North-Central Bangladesh

Abstract

Leptospirosis is a zoonotic disease caused by pathogenic Leptospira, prevalent in tropical/sub-tropical regions. This study aimed to clarify the prevailing leptospiral species, clinical features, and risk factors of leptospirosis in north-central Bangladesh in 2024. Venous blood and urine samples were collected from 117 patients with clinically suspected leptospirosis. Among these cases, 75 (64%) tested positive for Leptospira infection by IgM ELISA test and/or PCR. By phylogenetic analysis of the 16S rRNA gene, all the samples tested were classified into L. wolffii (pathogenic group P2), showing high sequence identity to those of the type strain Khorat-H2 (97-99%) and L. wolffii reported in Bangladesh previously. Confirmed leptospirosis patients were mostly male (93%), aged 15-60 years (93%), living in rural areas in low socioeconomic conditions. Variable symptoms were presented by patients, with jaundice (84%), nausea/vomiting (84%), and myalgia (67%) being common. Some patients showed severe symptoms involving the nervous system (disorientation and neck stiffness) and the respiratory tract (cough, shortness of breath, and hemoptysis). Major risk factors for leptospirosis were exposures to mud/wet soil, sanding water, heavy rain, working in a paddy field, and cattle. In conclusion, L. wolffii was revealed to be circulating endemically in north-central Bangladesh, since its first detection in 2018, associated with variable and severe clinical symptoms in humans.

Keywords: 16S rRNA; Bangladesh; IgM ELISA; Leptospira wolffii; P2 subclade; nested PCR.

Figure 1

Location of Mymensingh in Bangladesh (left) and incidence of leptospirosis patients in each place of residence (extracted map in a square).

Figure 2

Number of positive samples by IgM ELISA and nested PCR for urine and serum, among 88 samples. The remaining 29 samples were tested only by PCR (8 samples were positive).

Figure 3

Phylogenetic dendrogram based on partial 16S rRNA gene sequences of Leptospira constructed by the maximum likelihood method using the MEGA6 program, following alignment with the ClustalW algorithm. The trees were statistically supported by bootstrapping with 1000 replicates, and phylogenetic distances were measured by the Kimura 2-parameter model with uniform rates among sites. Samples analyzed in the present study are marked with closed circles, while those in the previous studies in Mymensingh, Bangladesh, are shown with triangles (2022) and diamonds (2018–2016), respectively. L. wolffii prototype strain Khorat-H2 is indicated by a closed square. Bootstrap values more than 80% are shown. The scale bar represents the genetic distance. Subclusters are shown on the right using the designations by Guglielmini et al. (P1, P2, and S1/S2) [24] with former designations (pathogenic, intermediate, and non-pathogenic). A cluster of L. wolffii and closely related species to L. wolffii in the P2 subclade are shown by a vertical line.