Stomoxys flies (Diptera, Muscidae) are competent vectors of multiple livestock hemopathogens
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Stomoxys flies are widely distributed and economically significant vectors of various livestock pathogens of veterinary importance. However, the role of Stomoxys spp. in pathogen transmission is poorly understood. Therefore, we studied the feeding patterns of these blood feeders collected from specific locations in Kenya, to identify various vertebrate hosts they fed on, and the livestock hemopathogens they carried, to elucidate their role in pathogens transmission. Our findings show that field-collected Stomoxys flies carried several pathogens including Trypanosoma spp., Anaplasma spp., and Theileria spp. that were also found in the blood of sampled livestock, namely camels and cattle. The findings on blood meal analysis show that Stomoxys flies fed on a variety of domestic and wild vertebrate hosts. We further determined whether Stomoxys spp. are vectors of hemopathogens they harbored by studying the vector competence of S. calcitrans, S. niger niger, and S. boueti species complex, through laboratory and natural experimental in vivo studies. We show that in the process of blood feeding Stomoxys spp. complexes can transmit T. evansi (8.3%) and T. vivax (30%) to Swiss white mice. In addition, field-collected Stomoxy spp. were exposed to healthy mice for blood meal acquisition, and in the process of feeding, they transmitted Theileria mutans and Anaplasma spp. to Swiss white mice (100% infection in the test mice group). All mice infected with both trypanosomes via stomoxys bite died while those infected with Theileria and Anaplasma species did not, demonstrating virulence difference between pathogens. The key finding of this study showing broad feeding host range, cosmopolitan, plethora of pathogens harboured, and efficient vector competence in spreading multiple pathogens suggests profound role of Stomoxys on pathogen transmission and infection prevalence in livestock.
Author summary
Stomoxys flies are highly adaptable to several ecological settings, including metropolitan areas. In contrast, tsetse flies (genus Glossina ), the main biological vectors of African trypanosomes, have a limited distribution to parks and other conservation areas. Stomoxys flies could play a significant role in the spread of animal African trypanosomes, among other hemopathogens, particularly in areas with or without tsetse infestation. Although there have been speculations about the potential role of Stomoxys flies in the transmission of various pathogens, there is lack of data to link hemopathogens occurring in both bloodmeal hosts of Stomoxys and in the flies, and further in vivo experimental studies to confirm the vector competence of Stomoxyine flies. Here, we explored a host and pathogens network, and investigated species diversity at various ecologies, and demonstrated that Stomoxys flies feed on diverse vertebrate hosts and are infected with a plethora of pathogens. We also showed experimentally that they could transmit some of these hemopathogens to mice, for instance, T. vivax, T. evansi, Theileria mutans, and Anaplasma spp. with varying infection success rates. Stomoxys flies could play a significant role in transmitting and spreading various hemopathogens of veterinary importance and possibly maintaining their circulation in livestock, which could explain the occurrence of animal African trypanosomes in the regions outside the tsetse belts.
