Dataset Information

Lack of Evidence for Laboratory and Natural Vertical Transmission of Bluetongue Virus in Culicoides sonorensis (Diptera: Ceratopogonidae).

ABSTRACT: Culicoides sonorensis (Wirth & Jones) is the principal North American vector of bluetongue virus (BTV). BTV infection of livestock is distinctly seasonal (late summer and fall) in temperate regions of the world such as California, which has led to speculation regarding vertical transmission of the virus within the midge vector as a potential mechanism for interseasonal maintenance ("overwintering") of the virus. To evaluate potential vertical transmission of BTV in its midge vector, we fed adult midges BTV-spiked blood and used a BTV-specific quantitative reverse transcriptase polymerase chain reaction assay to evaluate parent, egg, and progeny stages of laboratory-reared C. sonorensis for the presence of viral nucleic acid. Whereas BTV nucleic acid was weakly detected in egg batches of virus-fed female midges, virus was never detected in subsequent progeny stages (larvae, pupae, and F1 generation adults). Similarly, BTV was not detected in pools of larvae collected from the waste-water lagoon of a BTV-endemic dairy farm in northern California during the seasonal period of virus transmission. Collectively, these results indicate that BTV is not readily transmitted vertically in C. sonorensis, and that persistence of the virus in long-lived parous female midges is a more likely mechanism for overwintering of BTV in temperate regions.

SUBMITTER: Osborne CJ

PROVIDER: S-EPMC4481717 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Lack of Evidence for Laboratory and Natural Vertical Transmission of Bluetongue Virus in Culicoides sonorensis (Diptera: Ceratopogonidae).

Osborne C J CJ Mayo C E CE Mullens B A BA McDermott E G EG Gerry A C AC Reisen W K WK MacLachlan N J NJ

Journal of medical entomology 20150205 2

Culicoides sonorensis (Wirth & Jones) is the principal North American vector of bluetongue virus (BTV). BTV infection of livestock is distinctly seasonal (late summer and fall) in temperate regions of the world such as California, which has led to speculation regarding vertical transmission of the virus within the midge vector as a potential mechanism for interseasonal maintenance ("overwintering") of the virus. To evaluate potential vertical transmission of BTV in its midge vector, we fed adult ...[more]

PMID: 26336312

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Project description:Climate change is affecting the distribution of pathogens and their arthropod vectors worldwide, particularly at northern latitudes. The distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) plays a key role in affecting the emergence and spread of significant vector borne diseases such as Bluetongue (BT) and Epizootic Hemorrhagic Disease (EHD) at the border between USA and Canada. We used 50 presence points for C. sonorensis collected in Montana (USA) and south-central Alberta (Canada) between 2002 and 2012, together with monthly climatic and environmental predictors to develop a series of alternative maximum entropy distribution models. The best distribution model under current climatic conditions was selected through the Akaike Information Criterion, and included four predictors: Vapour Pressure Deficit of July, standard deviation of Elevation, Land Cover and mean Precipitation of May. This model was then projected into three climate change scenarios adopted by the IPCC in its 5th assessment report and defined as Representative Concentration Pathways (RCP) 2.6, 4.5 and 8.5. Climate change data for each predictor and each RCP were calculated for two time points pooling decadal data around each one of them: 2030 (2021-2040) and 2050 (2041-2060). Our projections showed that the areas predicted to be at moderate-high probability of C. sonorensis occurrence would increase from the baseline scenario to 2030 and from 2030 to 2050 for each RCP. The projection also indicated that the current northern limit of C. sonorensis distribution is expected to move northwards to above 53°N. This may indicate an increased risk of Culicoides-borne diseases occurrence over the next decades, particularly at the USA-Canada border, as a result of changes which favor C. sonorensis presence when associated to other factors (i.e. host and pathogen factors). Recent observations of EHD outbreaks in northern Montana and southern Alberta supported our projections and considerations. The results of this study can inform the development of cost effective surveillance programs, targeting areas within the predicted limits of C. sonorensis geographical occurrence under current and future climatic conditions.

Project description:BackgroundFemale Culicoides sonorensis midges (Diptera: Ceratopogonidae) are vectors of pathogens that impact livestock and wildlife in the United States. Little is known about their biology on a molecular-genetic level, including components of their immune system. Because the insect immune response is involved with important processes such as gut microbial homeostasis and vector competence, our aims were to identify components of the midge innate immune system and examine their expression profiles in response to diet across time.MethodsIn our previous work, we de novo sequenced and analyzed the transcriptional landscape of female midges under several feeding states including teneral (unfed) and early and late time points after blood and sucrose. Here, those transcriptomes were further analyzed to identify insect innate immune orthologs, particularly humoral immune response elements. Additionally, we examined immune gene expression profiles in response to diet over time, on both a transcriptome-wide, whole-midge level and more specifically via qRTPCR analysis of antimicrobial peptide (AMP) expression in the alimentary canal.ResultsWe identified functional units comprising the immune deficiency (Imd), Toll and JAK/STAT pathways, including humoral factors, transmembrane receptors, signaling components, transcription factors/regulators and effectors such as AMPs. Feeding altered the expression of receptors, regulators, AMPs, prophenoloxidase and thioester-containing proteins, where blood had a greater effect than sucrose on the expression profiles of most innate immune components. qRTPCR of AMP genes showed that all five were significantly upregulated in the alimentary canal after blood feeding, possibly in response to proliferating populations of gut bacteria.ConclusionsIdentification and functional insight of humoral/innate immune components in female C. sonorensis updates our knowledge of the molecular biology of this important vector. Because diet alone influenced the expression of immune pathway components, including their effectors, subsequent study of the role of innate immunity in biological processes such as gut homeostasis and life history are being pursued. Furthermore, since the humoral response is a key contributor in gut immunity, manipulating immune gene expression will help in uncovering genetic components of vector competence, including midgut barriers to infection. The results of such studies will serve as a platform for designing novel transmission-blocking strategies.

Project description:BackgroundBluetongue disease, caused by bluetongue virus serotype 8 (BTV-8), appeared for the first time in the northern part of Europe in 2006, and subsequently rapidly spread causing severe economic losses to the farming industry. The implicated vectors of BTV in Europe are Culicoides species within the subgenus Avaritia (C. chiopterus, C. dewulfi, C. obsoletus and C. scoticus). Epidemiological data from Switzerland have shown that BTV, whose spread was eliminated at an early stage by vaccination campaigns, had not been circulating among livestock at higher altitudes where other species dominate the Culicoides fauna. In this study, we investigated the extent that Culicoides spp. prevailing at higher altitudes (mainly C. grisescens) can act as vectors for BTV.MethodsCulicoides were collected at farms in the pre-alpine region (two sites at 1550 m above sea level, masl, referred to as pre-alpine I; one site at 2030 masl, pre-alpine II) and, for comparative purposes, from the Swiss Plateau (one site, 650 masl). They were fed on bovine blood/BTV suspensions (BTV-1, 4 or 8) and incubated for eight days under a fluctuating temperature regime (13-25 °C, mean 19 °C), reflecting a mid-summer warm spell in the pre-alpine region. Susceptibility to BTV transmission was assessed from head homogenates by RT-qPCR and virus isolation.ResultsOverall, 9196 female Culicoides were exposed to the three BTV strains through an artificial membrane, with feeding rates of 14-27%. Survival rates of blood-engorged Culicoides females at eight days post-infection depended on both virus serotype and altitude of origin. Virus dissemination (Cq ≤ the cut-off value as determined by serial virus dilutions) was confirmed only for BTV-1 in C. scoticus (dissemination efficiency 22.5%; 9/40) and C. obsoletus (5.6%; 1/18) from the Swiss Plateau area. There was no strong evidence of susceptibility to infection for Culicoides from the pre-alpine area when fed with all BTV strains (BTV-1, 4 and 8).ConclusionsThis study confirms the susceptibility of C. scoticus and C. obsoletus to BTV-1 infection, including under cooler temperatures. Culicoides grisescens, which is highly abundant at higher altitudes, cannot be considered a potential vector under these temperature conditions.

Dataset Information

Lack of Evidence for Laboratory and Natural Vertical Transmission of Bluetongue Virus in Culicoides sonorensis (Diptera: Ceratopogonidae).

Publications

Lack of Evidence for Laboratory and Natural Vertical Transmission of Bluetongue Virus in Culicoides sonorensis (Diptera: Ceratopogonidae).

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