Prevalence and immunoreactivity of Schistosoma spindale-induced cercarial dermatitis among paddy farmers in Assam, India: A comprehensive molecular and proteomic study.

Cercarial dermatitis is an important occupational health problem among rice farmers in Assam and other parts of India. We surveyed 1657 paddy farmers from sixteen villages across four districts of Assam, Northeast India, to determine the prevalence of cercarial dermatitis. Of these, 555 (33.5%) reported dermatitis during the preceding three months, and a subset of affected farmers from Barpeta district showed a high proportion of moderate-to-severe disease, often complicated by secondary bacterial infection. Snail surveys were conducted in thirteen villages across eight districts. Examination of 13,309 freshwater snails representing six species identified Indoplanorbis exustus as the only intermediate host shedding Schistosome cercariae, with an infection prevalence of 6.3% among I. exustus. Experimental infections in mice yielded adult worms that were used for morphological, molecular, immunological, and proteomic studies. Molecular identification based on partial 28S rDNA sequencing confirmed the Assamese isolates as Schistosoma spindale, and phylogenetic analysis placed them firmly within the S. spindale clade together with reference sequences from Nepal and Sri Lanka. SDS-PAGE and immunoblotting identified four dominant immunoreactive antigens of approximately 25, 38, 60, and 100 kDa. Two-dimensional PAGE coupled with MALDI-TOF/TOF MS identified several conserved proteins, including paramyosin, tropomyosin, actin, and heat shock protein 70, based on best database matches. ELISA developed using adult worm antigen showed high diagnostic performance (96% sensitivity and 100% specificity) and outperformed the cercarial antigen-based ELISA. This integrated epidemiological, malacological, molecular, proteomic, and immunological investigation provides comprehensive insight into S. spindale the causative agent of cercarial dermatitis in Assam. The findings highlight the need to recognize cercarial dermatitis as a neglected occupational and zoonotic disease within a One Health framework.