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Vector Competence of Florida Culicoides insignis (Diptera: Ceratopogonidae) for Epizootic Hemorrhagic Disease Virus Serotype-2.

ABSTRACT: Epizootic hemorrhagic disease virus (EHDV; family Reoviridae, genus Orbivirus) is an arthropod-borne virus of ungulates, primarily white-tailed deer in North America. Culicoides sonorensis, the only confirmed North American vector of EHDV, is rarely collected from Florida despite annual virus outbreaks. Culicoides insignis is an abundant species in Florida and is also a confirmed vector of the closely related Bluetongue virus. In this study, oral challenge of C. insignis was performed to determine vector competence for EHDV serotype-2. Field-collected female midges were provided bovine blood spiked with three different titers of EHDV-2 (5.05, 4.00, or 2.94 log₁₀PFUe/mL). After an incubation period of 10 days or after death, bodies and legs were collected. Saliva was collected daily from all females from 3 days post feeding until their death using honey card assays. All samples were tested for EHDV RNA using RT-qPCR. Our results suggest that C. insignis is a weakly competent vector of EHDV-2 that can support a transmissible infection when it ingests a high virus titer (29% of midges had virus positive saliva when infected at 5.05 log₁₀PFUe/mL), but not lower virus titers. Nevertheless, due to the high density of this species, particularly in peninsular Florida, it is likely that C. insignis plays a role in the transmission of EHDV-2.

SUBMITTER: McGregor BL

PROVIDER: S-EPMC7998304 | biostudies-literature |

REPOSITORIES: biostudies-literature

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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.

Project description:BACKGROUND:Biting midges in the genus Culicoides (Diptera: Ceratopogonidae) transmit bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) to ruminants, thus exerting a significant economic impact on animal agriculture worldwide. However, very little is known about the larval habitat characteristics of Culicoides species associated with BTV/EHDV transmission, particularly in southeastern USA, limiting the establishment of effective midge control strategies. In this study, we examined the habitat associations of Culicoides species abundant on a commercial cervid farm in Florida, USA and quantified several environmental variables of their habitat to identify the key variables associated with midge abundance. METHODS:Mud/substrate samples from three potential larval habitats on the farm (edges of streams, puddles and seepages) were brought to the laboratory and incubated for adult emergence, and the percentage organic matter, macronutrients, micronutrients, pH, electrical conductivity, moisture and microbial concentrations of the substrate were quantified. RESULTS:Strong habitat associations were observed for Culicoides haematopotus (Malloch) (stream edge), Culicoides stellifer (Coquillett) (puddles) and Culicoides loisae (Jamnback) (stream edge), the most commonly emerging midge species from the samples. Suspected vector species of BTV/EHDV on the property, C. stellifer and Culicoides venustus (Hoffman), emerged mainly from habitats with moderate-high levels of pollution (edges of puddles and seepages) as indicated by the relatively higher concentrations/levels of organic matter, nutrients and other environmental variables in these samples. The emergence of C. insignis was too low to form any meaningful conclusions. For each Culicoides species, only weak positive or negative associations were detected between midge abundance and the various environmental variables quantified. CONCLUSIONS:Habitat associations of Culicoides species abundant on a local cervid/animal farm vary, most likely as a function of certain biotic/abiotic characteristics of the habitat. Further studies across a larger spatial and temporal scale will be needed to experimentally evaluate/identify the key factors more strongly associated with the abundance of target Culicoides species. This information, in the long term, can be potentially exploited to render local habitats unsuitable for midge oviposition/larval development.

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Vector Competence of Florida Culicoides insignis (Diptera: Ceratopogonidae) for Epizootic Hemorrhagic Disease Virus Serotype-2.

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