Parasitological screening of vector mosquitoes and molecular biological identification of larval filarial parasites among the wild-caught Mansonia mosquito species at selected areas in the district of Gampaha, Sri Lanka, a re-emerging focus of Brugian filariasis

Abstract

Brugian filariasis, a disease caused by the Protozoan parasite Brugia malayi has re-emerged in Sri Lanka after nearly four decades of quiescence. The Brugia malayi that prevailed in Sri Lanka in the past was the nocturnal periodic human parasitic strain transmitted by mosquitoes of the genus Mansonia. The objective of the present study was to determine the role of transmitting B.malayi parasites by the mosquitoes in Genus Mansonia. Entomological surveys were performed during September/October 2021 in Ragama Medical Officer of Health area using cattle-baited net traps. Mansonia sp. mosquitoes were dissected to detect the presence of larvae of the parasite.The lysate of dissected mosquito’s positive for larvae was used for the extraction of genomic DNA of the parasite, which was subjected to Polymerase Chain Reactions (PCR) using pan-filarial primers specific for the internal transcribed spacer region two (ITS-2) of the ribosomal DNA. Atotal of 1060 mosquitoes were tested, and that included seven mosquito species belonging to four genera. Culex gelidus (n=602; 56.8%) was detected as the predominant mosquito species followed by Armigeres subalbatus (n=420; 39.6%) Cx. tritaeniorynchus (n=2; 0.2%) and Anopheles nigerrimus (n=4; 0.4%). Mansonia mosquitoes represented 2.7% of the total field caught samples (Mansonia annulifera [1.2% (n=20)], Ma. uniformis [0.9% (n= 10)] and Ma. Indiana [0.2% (n= 2)]. About 18.7% (n=6) of Mansonia mosquito collection was positive for filarial larvae. Among them,15.6% (n=5) was Mansonia annulifera while 3.1% (n=1) was Ma. uniformis. The PCR products of all tested samples corresponded to the band size of 625 bp, specific to B. malayi confirming the identity of the parasite. Mansonia annulifera and Ma. uniformis were confirmed as vectors of the re-emerged B. malayi (nocturnally sub-periodic) in Gampaha district. The role of other mosquito vector species would require investigation by vector incrimination and xenomonitoring-based approaches.