Seroreactivity to Leptospira Serovars among Healthy Pregnant Women in Sri Lanka: Implications for MAT Panel Optimization

Abstract

Background: The Microscopic Agglutination Test (MAT) is the standard for leptospirosis serodiagnosis and seroepidemiology. Most panels are designed for clinical use, yet their performance in healthy populations remains underexplored. Understanding local baseline serogroup reactivity is critical for adapting MAT panels for population-based surveillance. Objective: To identify the most frequently reactive Leptospira serovars using an 11-serovar MAT panel optimized for clinical diagnosis and assess its suitability for seroprevalence studies in a healthy population Methods: Serum from 1,344 healthy pregnant women in the Rajarata Pregnancy Cohort (Anuradhapura, Sri Lanka) was tested using a published, locally optimized MAT panel comprising 11 serovars from three pathogenic and one saprophytic species, representing 10 serogroups (Australis, Canicola, Icterohaemorrhagiae, Mini, Pyrogenes, Bataviae, Sejroe, Autumnalis, Javanica, and Semaranga). Seroreactivity, defined as ≥50% agglutination reduction compared to controls, was assessed to determine frequency and cross-reactivity patterns. Results: Seroreactivity, based on the highest observed MAT titer per individual (ranging from 1:50 to 1:800), was detected in 119 individuals (8.9%). Of these, 105 (88.2%) showed reactivity to a single serovar, and 14 (11.8%) exhibited cross-reactivity. L. interrogans serovar Bratislava (strain Jez-Bratislava) was predominant (106, 89.1%), followed by Icterohaemorrhagiae (11, 9.2%), Pyrogenes (5, 4.2%), Patoc (5, 4.2%), Weerasinghe (3, 2.5%), Georgia (2, 1.7%), Mankaraso (1, 0.8%), and Bataviae (1, 0.8%). No reactivity was observed to serovars Canicola, Ceylonica, or Wolffi. Serovar Bratislava cross-reacted with all reactive serovars except Mankaraso. Conclusions: In this healthy low risk population, a subset of serovars accounted for the majority of MAT reactivity, suggesting that a smaller, regionally tailored MAT panel could potentially capture most seroreactivity in similar populations. However, large scale community studies are needed to select the optimal panel. The dominance of reactivity to serovar Bratislava also commonly detected in clinical cases suggests potential cross reactivity or shared epitopes with circulating strains.