The role of endosymbiotic bacteria in vectors of Schmallenberg and bluetongue viruses

Lead Research Organisation: University of Liverpool
Department Name: Veterinary Clinical Science

Abstract

Biting midges of the genus Culicoides are the vectors of bluetongue (BT), Schmallenberg (SB) and African horse sickness. There are no effective control methods of the vectors, and disease control therefore relies on vaccines which, given the rapid emergence/spread of the viruses, are often not available. Since 1998 multiple serotypes of bluetongue virus have led to the deaths of millions of sheep in Europe, and Schmallenberg, since its emergence in 2011, has affected livestock on hundreds of thousands of European farms. There is increasing interest in the endosymbiotic bacteria present in many insect species, such as Wolbachia, as they present a novel means to control vector-borne diseases. They have been shown to suppress the infection of mosquitoes with several viruses and, if introduced into an insect vector, the induced cytoplasmic incompatibility phenotype (embryo death when uninfected females mate with infected males) may drive the endosymbiont to 100% frequency in both sexes. We have recently detected, for the first time, endosymbiotic bacteria in European midges. A high frequency (94-100%) of Cardinium was detected in C. punctatus midges, and at 16-35% frequency in the closely related C. pulicaris. Both midge species are implicated as vectors of BT virus in Europe. No Cardinium was detected in other species examined, including midges of the C. obsoletus complex, the primary midge vector in Europe. This project will develop a greater understanding of the role played by Cardinium in the biology of C. punctatus and C. pulicaris, including any effects on their vector competence for SB virus. If effects on their lifespan or vector competence are detected, this may open the door to future introductions of the bacteria into C. obsoletus, and the potential for a new means of disease control. An extensive survey of endosymbionts (5 genera) in UK midges will be undertaken, followed by a morphological and age assessment of C. pulicaris & C. punctatus midges. Individuals will be tested for Cardinium and associations between infection and morphology/lifespan examined. An infection system for SB virus in live midges will then be developed. Field-caught C. pulicaris/punctatus will be fed infectious blood and left to develop infection. Individual midges will then be tested for virus and Cardinium, and effects of Cardinium on vector competence identified.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
BB/M011186/1 01/10/2015 31/03/2024
1644378 Studentship BB/M011186/1 01/10/2015 30/09/2019 Jack Pilgrim
 
Description Heritable bacteria (endosymbionts) can have various important affects on the biology of their insect counterparts including reproduction, acquirement of essential nutrients, and in the case of blood-feeders, their ability to spread diseases to other animals. This project has identified a previously overlooked association between a "Rickettsia" endosymbiont and biting midges, with approximately a third of these blood-feeding flies seemingly infected. In addition, this Rickettsia has been found to reside in the insect's ovaries, suggesting a route of transmission to the next generation, and to the fat body (insect equivalent of a liver) which could alter how well certain animal viruses are spread.
Exploitation Route Due to midges' importance in spreading viruses to livestock, this discovery of a common intimate association with Rickettsia bacteria opens up future work to establish how this interaction affects disease outbreaks, as well as if this bacteria can act as an alternative to/alongside current control methods such as vaccinations.
Sectors Agriculture, Food and Drink,Environment,Leisure Activities, including Sports, Recreation and Tourism
URL https://www.ncbi.nlm.nih.gov/pubmed/28805302
 
Title Torix Rickettsia are widespread in arthropods and reflect a neglected symbiosis 
Description Rickettsia are intracellular bacteria best known as the causative agents of human and animal diseases. Although these medically important Rickettsia are often transmitted via haematophagous arthropods, other Rickettsia, such as those in the Torix group, appear to reside exclusively in invertebrates and protists with no secondary vertebrate host. Importantly, little is known about the diversity or host range of Torix group Rickettsia. This dataset supports a study which describes the serendipitous discovery of Rickettsia amplicons in the Barcode of Life Data System (BOLD), a sequence database specifically designed for the curation of mtDNA barcodes. Out of 184,585 barcode sequences analysed, Rickettsia is observed in approximately 0.41% of barcode submissions and is more likely to be found than Wolbachia (0.17%). The Torix group of Rickettsia are shown to account for 95% of all unintended amplifications from the genus. A further targeted PCR screen of 1,612 individuals from 169 terrestrial and aquatic invertebrate species identified mostly Torix strains and supports the 'aquatic hot spot' hypothesis for Torix infection. Furthermore, the analysis of 1,341 Sequence Read Archive (SRA) deposits indicates Torix infections represent a significant proportion of all Rickettsia symbioses found in arthropod genome projects. This study supports a previous hypothesis which suggests Torix Rickettsia are overrepresented in aquatic insects. In addition, multiple methods reveal further putative hot spots of Torix Rickettsia infection; including in phloem-feeding bugs, parasitoid wasps, spiders, and vectors of disease. The unknown host effects and transmission strategies of these endosymbionts make these newly discovered associations important to inform future directions of investigation involving the understudied Torix Rickettsia. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact This dataset resulted in a manuscript entitled "Torix Rickettsia are widespread in arthropods and reflect a neglected symbiosis" which was accepted by the journal GigaScience on 5/3/21 
URL http://gigadb.org/dataset/100873
 
Description UC Riverside 
Organisation University of California, Riverside
Country United States 
Sector Academic/University 
PI Contribution The assessment of Rickettsia infection status of field-caught Culicoides sonorensis (biting midges) in California
Collaborator Contribution Hosting and the use of lab equipment and reagents.
Impact A single individual from an individual pool was positive through 16S PCR screening which was later confirmed as Rickettsia by Sanger sequencing. Furthermore, through phylogenetic analysis, the isolate recovered clustered in a sister group of Rickettsia clades occasionally known to induce pathogenicity in vertebrates. A similar isolate was also recently reported in Aedes mosquitoes from the demilitarised zone of Korea. Subsequently, the Rickettsia isolate reported here may play a role in animal and/or human health which requires further investigation.
Start Year 2018