Abstract
Culicoides biting midges (Diptera: Ceratopogonidae) are vectors responsible for the transmission of several viruses of veterinary importance. Previous screens of Culicoides have described the presence of the endosymbiont Candidatus Cardinium hertigii (Bacteroidetes). However, any impacts of this microbe on vectorial capacity, akin to those conferred by Wolbachia in mosquitoes, are yet to be uncovered and await a suitable system to study Cardinium-midge interactions. To identify potential candidate species to investigate these interactions, accurate knowledge of the distribution of the endosymbiont within Culicoides populations is needed. We used conventional and nested PCR assays to screen Cardinium infection in 337 individuals of 25 Culicoides species from both Palearctic and Afrotropical regions. Infections were observed in several vector species including C. imicola and the Pulicaris complex (C. pulicaris, C.bysta, C. newsteadi and C. punctatus) with varying prevalence. Phylogenetic analysis based on the Gyrase B gene grouped all new isolates within 'group C' of the genus, a clade that has to date been exclusively described in Culicoides. Through a comparison of our results with previous screens, we suggest C. imicola and C. sonorensis represent good candidates for onward study of Cardinium-midge interactions.
Highlights
Worldwide, biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are known to transmit more than 50 arboviruses (Mellor et al, 2000)
Vaccines have been very effective in halting the transmission of Culicoides-borne viruses but take significant time and resources to get into at-risk populations
The endosymbiont Wolbachia (Rickettsiales: Anaplasmataceae) leads to an arbovirus blocking effect in Aedes aegypti mosquitoes, which has led to their successful deployment as a dengue fever control strategy in field trials (Nazni et al, 2019)
Summary
Meijerehelea Monoculicoides Oecacta Silvaticulicoides Silvicola Synhelea Wirthomyia. C. tuttifrutti C. obsoletus C. salinarius C. sphagnumensis C. bystaa C. impunctatus. The infection patterns within the Pulicaris complex species (C. bysta, C. newsteadi, C. pulicaris and C. punctatus) suggest field populations could be suitable for future Cardinium work. A low prevalence indicates Cardinium is likely not relevant to vector biology at a population level and this species complex does not appear to be a suitable candidate for investigation. C. imicola from South Africa (Onderstepoort), whereas specimens of two populations from Corsica were negative for the presence of Cardinium, a pattern likely associated with properties of founder individuals (Pilgrim et al, 2021). These species appear to be the most promising candidate species for investigating Cardinium effects on vectorial capacity. To screen other Culicoides species, which may become colonised in the near future, such as C. stellifer (Erram & Burkett-Cadena, 2020)
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