Molecular Characterization of a Re-Emergent Brugia Malayi Parasite in Sri Lanka, Suggestive of a Novel Strain With Close Nucleotide Homology to Brugia Pahangi

Background: Brugian filariasis has re-emerged in Sri Lanka after four decades of quiescence. As microscopy alone was insufficient for ascertaining the species identity of the re-emerged sub-periodic Brugia spp . parasite, molecular speciation was performed. The transmission dynamics of the parasite was studied by entomological procedures. Methods: Human blood samples positive for Brugia spp . microfilariae (MF) (n=8) were collected and DNA extracted using ReliaPrep™ Blood DNA Miniprep System (modified). Polymerase chain reaction (PCR) was performed with pan-filarial primers specific for the internal transcribed spacer region 2 (ITS2) of the ribosomal DNA (rDNA) of MF. Results: Of those tested, seven (87.5%) yielded a band at 615bp establishing the species identity of the re-emerged filarial parasite as B. malayi . Comparison of the ITS2 region gene sequences of B. malayi MF isolated from humans (n=2), dogs (n=3) and cats (n=6) with GenBank sequences revealed a higher sequence homology with B. pahangi than B. malayi , but phylogeny was closer to B. malayi . A total of 82 mosquitoes of genus Mansonia comprising of M. annulifera (65), M. uniformis (14) and M. indiana (3) were collected by cattle-baited traps. Mosquito dissections identified 17 infected mosquitoes: one M. uniformis (7.14%) and 16 M. annulifera (24.6%). The DNA extracts of all infected Mansonia mosquitoes elicited the 615bp band on pan-filarial primer specific PCR. Conclusions: The re-emergent B. malayi is a genetic variant or a novel species closely related to B. malayi and B. pahangi. Mansonia spp . mosquitoes were vectors of this zoonotic variant B. malayi circulating among cats, dogs and humans in Sri Lanka.