Abundance of mosquitoes (Diptera: Culicidae) and their potential role in hemoplasma transmission and cross-species infection on a pig farm in Loei Province, Thailand

Hemotrophic Mycoplasma, or hemoplasma, is a group of bacteria that cause infectious anemia in mammals, including pigs. These pathogens can potentially be mechanically transmitted by mosquitoes. However, limited data exist on hemoplasma transmission within pig farms via mosquitoes. This study involved monthly mosquito surveillance on a pig farm in Erawan District, Loei Province, Thailand, from November 2021 to October 2022. CO2-baited CDC light traps were used to collect mosquitoes over 2 consecutive days each month. Pig blood samples were collected every other month. Female mosquitoes were sorted under a stereomicroscope, pooled by species, complex or group, and kept individually if blood-fed. All mosquito and pig samples were tested for hemoplasma using PCR targeting the 16S rRNA gene. Positive samples were further analyzed by amplifying a partial 23S rRNA gene fragment, followed by sequencing. Sequences were analyzed using DnaSP6, BLASTn, phylogenetic trees, and network analysis. In total, 5,797 female mosquitoes were collected, representing 5 genera (Aedes, Anopheles, Armigeres, Culex, and Mansonia). Hemoplasma DNA was detected in 18.40% (85/462) of blood-fed mosquitoes, 2.17% (5/230) of mosquito pools, and 21.61% (51/236) of pig blood samples. Sequences from 36 mosquitoes across 4 species and 31 pig samples were recovered. At least 6 hemoplasma species were identified; 4 (Mycoplasma suis, Mycoplasma sp., Mycoplasma parvum, and Mycoplasma wenyonii) were found in both pigs and mosquitoes. These findings suggest mosquitoes may act as mechanical vectors, while other mammals like buffalo may serve as additional reservoirs for hemoplasma in pig farms.