Transmission of pathogens by Stomoxys flies (Diptera, Muscidae): a review.

Stomoxys flies are mechanical vectors of pathogens present in the blood and skin of their animal hosts, especially livestock, but occasionally humans. In livestock, their direct effects are disturbance, skin lesions, reduction of food intake, stress, blood loss, and a global immunosuppressive effect. They also induce the gathering of animals for mutual protection; meanwhile they favor development of pathogens in the hosts and their transmission. Their indirect effect is the mechanical transmission of pathogens. In case of interrupted feeding, Stomoxys can re-start their blood meal on another host. When injecting saliva prior to blood-sucking, they can inoculate some infected blood remaining on their mouthparts. Beside this immediate transmission, it was observed that Stomoxys may keep some blood in their crop, which offers a friendly environment for pathogens that could be regurgitated during the next blood meal; thus a delayed transmission by Stomoxys seems possible. Such a mechanism has a considerable epidemiological impact since it allows inter-herd transmission of pathogens. Equine infectious anemia, African swine fever, West Nile, and Rift Valley viruses are known to be transmitted by Stomoxys, while others are suspected. Rickettsia (Anaplasma, Coxiella), other bacteria and parasites (Trypanosoma spp., Besnoitia spp.) are also transmitted by Stomoxys. Finally, Stomoxys was also found to act as an intermediate host of the helminth Habronema microstoma and may be involved in the transmission of some Onchocerca and Dirofilaria species. Being cosmopolite, Stomoxys calcitrans might have a worldwide and greater impact than previously thought on animal and human pathogen transmission.

Seasonal abundance and distribution of Anopheles larvae in a riparian malaria endemic area of western Thailand.

Three taxonomic groups of Anopheles larvae were morphologically identified within the Funestus Group (Minimus Subgroup and Aconitus Subgroup) (75.63%), Maculatus Group (20.47%), and Barbirostris Group (0.57%) during a two-year period in conjunction with active malaria transmission in a village near the Thai-Myanmar border in Kanchanaburi Province, western Thailand. The remaining 3.33% of anophelines collected were Anopheles culicifacies (3.07%), Anopheles philippinensis (0.17%), and Anopheles vagus (0.09%). Using an allele-specific multiplex molecular identification assay, the Minimus Subgroup consisted of Anopheles minimus (69.83%), and Anopheles harrisoni (0.06%) and 2 genetically-related species belonging to the Aconitus Subgroup, Anopheles aconitus (0.63%) and Anopheles varuna (5.12%). The Minimus and Aconitus Subgroup species were more abundant during the dry season (52.58%) than during the hot (24.95%) and wet (22.46%) seasons. The number of Anopheles larvae collected from the stream habitat was significantly higher during the second year than the first year, believed to be due to human environmental changes in the stream habitat from the building of a small check dam, which provided a more suitable and stable habitat for mosquito larval development. This study illustrates the importance of conducting site-specific studies to accurately determine vector bionomics (eg, larval habitats) and adult activity patterns and linking observations with malaria transmission dynamics in a given area.