Molecular Detection of Filarial and Avian Haemosporidian Parasites in Culicoides Biting Midges (Diptera: Ceratopogonidae) from Laos.

Species of Culicoides Latreille (Diptera: Ceratopogonidae) are important biting pests and vectors of pathogens affecting humans and animals. However, information on Culicoides-parasite associations in Laos is lacking. We used molecular methods to screen 237 specimens representing 27 Culicoides species from Laos for filarial nematodes, avian haemosporidians, Trypanosoma spp., and Leishmania spp. Overall, 59 specimens representing 19 Culicoides species were positive for at least one parasite. Only filarial nematodes and avian haemosporidians were detected. Filarial parasites were found in four Culicoides species (C. actoni, C. guttifer, C. huffi, and C. mahasarakhamense). Analysis of 12S rRNA sequences revealed at least two filarial taxa, one closely related to Onchocerca lienalis and the other to an unidentified onchocercid previously detected in Culicoides. Avian haemosporidians were more prevalent. Leucocytozoon spp. were detected in 40 specimens from 18 Culicoides species, with cyt b sequences identifying Leucocytozoon caulleryi and an unidentified Leucocytozoon sp., the latter accounting for 39 of the 40 positive specimens. Plasmodium juxtanucleare was detected in 27 specimens (11.4%), whereas Haemoproteus spp. were found in only two specimens (0.8%), which represented two distinct lineages previously reported from wild birds. No Trypanosoma or Leishmania DNA was detected. Culicoides mahasarakhamense and C. huffi had the highest infection frequencies. Their high abundance and documented feeding on livestock, particularly chickens and cattle, suggest that they may play important roles in pathogen transmission and should be prioritized for future vector surveillance in Laos.