Molecular Characterization of a Reemergent Brugia malayi Parasite in Sri Lanka, Suggestive of a Novel Strain.

Sri Lanka achieved elimination status for lymphatic filariasis in 2016; still, the disease remains a potential public health issue. The present study is aimed at identifying a subperiodic Brugia sp. parasite which has reemerged in Sri Lanka after four decades via molecular-based analysis. Polymerase chain reaction performed with pan-filarial primers specific for the internal transcribed spacer region-2 (ITS-2) of the rDNA of Brugia filarial parasites isolated from human, canine, and feline blood samples yielded a 615 bp band establishing the species identity as Brugia malayi. Comparison of the ITS2 sequences of the reemerged B. malayi isolates with GenBank sequences revealed a higher sequence homology with B. pahangi than B. malayi with similar phylogenetic evidence. However, the mean interspecies Kimura-2-parameter pairwise divergence between the generated Brugia sequences with B. malayi and B. pahangi was less than 3%. During the analysis of parsimony sites of the new ITS2 sequences, substitutions at A36T, A296G, T373A, and G482A made the sequences different from both B. pahangi and B. malayi suggesting the possibility of a new genetic variant or a hybrid strain of B. malayi and B. pahangi. Mosquito dissections and xenomonitoring identified M. uniformis and M. annulifera as vectors of this novel strain of B. malayi circulating among cats, dogs, and humans in Sri Lanka.