Culicoides Midge Abundance across Years: Modeling Inter-Annual Variation for an Avian Feeder and a Candidate Vector of Hemorrhagic Diseases in Farmed Wildlife.

(1) Background: Epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) are orbiviruses that cause hemorrhagic disease (HD) with significant economic and population health impacts on domestic livestock and wildlife. In the United States, white-tailed deer (Odocoileus virginianus) are particularly susceptible to these viruses and are a frequent blood meal host for various species of Culicoides biting midges (Diptera: Ceratopogonidae) that transmit orbiviruses. The species of Culicoides that transmit EHDV and BTV vary between regions, and larval habitats can differ widely between vector species. Understanding how midges are distributed across landscapes can inform HD virus transmission risk on a local scale, allowing for improved animal management plans to avoid suspected high-risk areas or target these areas for insecticide control. (2) Methods: We used occupancy modeling to estimate the abundance of gravid (egg-laden) and parous (most likely to transmit the virus) females of two putative vector species, C. stellifer and C. venustus, and one species, C. haematopotus, that was not considered a putative vector. We developed a universal model to determine habitat preferences, then mapped a predicted weekly midge abundance during the HD transmission seasons in 2015 (July-October) and 2016 (May-October) in Florida. (3) Results: We found differences in habitat preferences and spatial distribution between the parous and gravid states for C. haematopotus and C. stellifer. Gravid midges preferred areas close to water on the border of well and poorly drained soil. They also preferred mixed bottomland hardwood habitats, whereas parous midges appeared less selective of habitat. (4) Conclusions: If C. stellifer is confirmed as an EHDV vector in this region, the distinct spatial and abundance patterns between species and physiological states suggest that the HD risk is non-random across the study area.

Modeling Abundance of Culicoides stellifer, a Candidate Orbivirus Vector, Indicates Nonrandom Hemorrhagic Disease Risk for White-Tailed Deer (Odocoileus virginianus).

(1) Background: Hemorrhagic diseases in white-tailed deer (Odocoileus virginianus) are caused by orbiviruses and have significant economic impact on the deer ranching industry in the United States. Culicoides stellifer is a suspected vector of epizootic hemorrhagic disease virus (EHDV), with recent field evidence from Florida, but its natural history is poorly understood. Studying the distribution and abundance of C. stellifer across the landscape can inform our knowledge of how virus transmission can occur locally. We may then target vector management strategies in areas where viral transmission can occur. (2) Methods: Here, we used an occupancy modeling approach to estimate abundance of adult C. stellifer females at various physiological states to determine habitat preferences. We then mapped midge abundance during the orbiviral disease transmission period (May-October) in Florida. (3) Results: We found that overall, midge abundance was positively associated with sites in closer proximity to large-animal feeders. Additionally, midges generally preferred mixed bottomland hardwood and agricultural/sand/water habitats. Female C. stellifer with different physiological states preferred different habitats. (4) Conclusions: The differences in habitat preferences between midges across states indicate that disease risk for deer is heterogeneous across this landscape. This can inform how effective vector management strategies should be implemented.

EVIDENCE OF EPIZOOTIC HEMORRHAGIC DISEASE VIRUS AND BLUETONGUE VIRUS EXPOSURE IN NONNATIVE RUMINANT SPECIES IN NORTHERN FLORIDA.

Epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) are vector-borne viruses of ruminants nearly worldwide. They can affect white-tailed deer (WTD; Odocoileus virginianus), the ranching industry, and nonindigenous hoof stock species managed for conservation. One potential risk factor for ranched WTD is commingling with nonindigenous species on high-fenced properties. Nonindigenous species provide novel viewing and hunting opportunities; however, their presence may create disease hazards. Furthermore, animals within conservation properties may be at a risk from commingling exotics and adjacent wild WTD. Currently, knowledge about EHDV and BTV seroprevalence and transmission is limited in nonindigenous populations in the southeastern United States. The authors conducted a serological survey of 10 Bovidae and 5 Cervidae species residing within two properties in northern Florida. The first site was a conservation property breeding threatened nonindigenous species for conservation. The second property was a private high-fenced game preserve managing WTD and nonindigenous species for breeding, sale, and harvest. Blood samples were tested for titers to three EHDV serotypes (1, 2, and 6) and active circulating viral EHDV and BTV. The private ranch had evidence of EHDV or BTV in one of three (33.3%) Bovidae species and four of five (80%) Cervidae species sampled. At the conservation property, evidence of EHDV infection was found in four of seven (57.1%) Bovidae and one of one (100%) Cervidae species sampled. The presence of antibodies in many nonindigenous species sampled might indicate these species are potential viral hosts and may be a risk to ranched WTD and other species within the same property. Nonindigenous species within the private ranch and conservation properties are at risk of contracting EHDV and BTV, and herd managers should reduce vector-host interactions and consider increased biosecurity measures when translocating animals.

Resource Selection by Wild and Ranched White-Tailed Deer (Odocoileus virginianus) during the Epizootic Hemorrhagic Disease Virus (EHDV) Transmission Season in Florida.

Epizootic hemorrhagic disease virus (EHDV) causes serious disease in wild and privately ranched white-tailed deer (Odocoileus virginianus) in the United States. In Florida, there is high EHDV prevalence, yet no treatments. There are few management strategies for the disease due to limited knowledge of virus-vector-host interactions. We conducted a telemetry study on white-tailed deer to examine resource use by wild and ranched animals in the Florida panhandle during the 2016 transmission risk period. We built generalized linear mixed models (GLMMs) to estimate resource selection and map habitat preferences for wild and ranched deer in the study area to reveal how second-order selection may relate to higher disease prevalence in ranched deer. Wild deer preferred areas closer to tertiary roads and supplementary food sources but farther from permanent water. Ranched deer selected bottomland mixed forest and areas closer to tertiary roads, supplementary food sources, and permanent water. Ranched deer behaviors may increase the likelihood of EHDV vector encounters, as these deer selected preferred habitats of several putative vector species, which may increase vector blood meal success and viral transmission risk. Disparate resource selection behaviors may be a factor in observed differential EHDV exposure risk between ranched and wild white-tailed deer in Florida.

Epizootic Hemorrhagic Disease Virus and Bluetongue Virus Seroprevalence in Wild White-Tailed Deer (Odocoileus virginianus) in Florida, USA.

A wild population of white-tailed deer (Odocoileus virginianus) was surveyed for evidence of past or current epizootic hemorrhagic disease virus (EHDV) and current bluetongue virus (BTV) infections. We collected 121 blood samples from hunter-harvested or live-captured deer from two state-managed properties in northwest Florida, US; live captures were in support of a movement ecology study. Blood samples were tested for antibodies against titers to three EHDV serotypes (EHDV-1, EHDV-2, and EHDV-6), and multiplex quantitative reverse transcription PCR was used to identify the presence of EHDV or BTV viral RNA. Of these samples, 81% (98/121) tested seropositive for at least one of three serotypes of EHDV. Of those testing seropositive, 33% (40/121) contained antibodies for two serotypes, and 19% (24/121) contained antibodies for all three EHDV serotypes. Furthermore, results of generalized linear models indicated that the probability of infection by EHDV serotypes 1 and 6 increased with an animal's age. Our findings indicate that seroprevalence may be high for multiple serotypes in regions where these orbiviruses are endemic. These results could prove useful for managing disease risk in naïve deer populations.

Living la Vida T-LoCoH: site fidelity of Florida ranched and wild white-tailed deer (Odocoileus virginianus) during the epizootic hemorrhagic disease virus (EHDV) transmission period.

BACKGROUND: Epizootic hemorrhagic disease virus (EHDV) is a pathogen vectored by Culicoides midges that causes significant economic loss in the cervid farming industry and affects wild deer as well. Despite this, its ecology is poorly understood. Studying movement and space use by ruminant hosts during the transmission season may elucidate EHDV ecology by identifying behaviors that can increase exposure risk. Here we compared home ranges (HRs) and site fidelity metrics within HRs using the T-LoCoH R package and GPS data from collared deer. METHODS: Here, we tested whether white-tailed deer (Odocoileus virginianus) roaming within a high-fenced, private deer farm (ranched) and native deer from nearby state-managed properties (wild) exhibited differences in home range (HR) size and usage during the 2016 and 2017 EHDV seasons. We captured male and female individuals in both years and derived seasonal HRs for both sexes and both groups for each year. HRs were calculated using a time-scale distance approach in T-LoCoH. We then derived revisitation and duration of visit metrics and compared between years, sexes, and ranched and wild deer. RESULTS: We found that ranched deer of both sexes tended to have smaller activity spaces (95% HR) and revisited sites within their HR more often but stayed for shorter periods than wild deer. However, core area (25% HR) sizes did not significantly differ between these groups. CONCLUSIONS: The contrast in our findings between wild and ranched deer suggest that home range usage, rather than size, in addition to differences in population density, likely drive differences in disease exposure during the transmission period.

Antibodies to Epizootic Hemorrhagic Disease Virus (EHDV) in Farmed and Wild Florida White-Tailed Deer (Odocoileus virginianus).

The transmission of multiple serotypes of epizootic hemorrhagic disease virus (EHDV) between farmed and free-ranging wildlife is of interest to livestock industries and natural resource agencies. We compared the seroprevalence of EHDV-1, -2, and -6 in wild and farmed white-tailed deer (Odocoileus virginianus) herds in Florida, US. We compared serological prevalence, circulating serotypes, antibody titers, and viremia with the use of 171 whole-blood samples from 150 unvaccinated white-tailed deer from farm pens, a farm preserve, and wild deer on adjacent public lands between March 2016 and May 2017. Despite aggressive chemical vector control on the farm, we found higher seroprevalence and titers against the predominant EHDV serotype in farmed deer (in pens and the preserve) than in wild deer. The higher exposure to EHDV of farmed vs. wild deer may have been because of the higher densities of farmed vs. wild deer, the presence of exotic amplifying hosts such as elk (Cervus canadensis) in the preserve, or genetic factors that predisposed farmed deer to disease.

Diversity and Abundance of Mosquitoes Inhabiting Waste Tires in a Subtropical Swamp in Urban Florida.

Automobile tires discarded in urban forest fragments may be a public health hazard, as they can support a population of vector mosquitoes. However, little is known about what factors may affect mosquito abundance and diversity within waste tires in a freshwater wetland forest. This study aimed to determine whether mosquito population dynamics in this environment in Florida differed over a year due to the site of collection and variation in vegetation greenness and elevation. We constructed negative binomial regression models to determine which of these characteristics were significant (α = 0.05) in affecting mosquito count data. Our findings suggest that in this specific environment, none of the covariates scrutinized had significant impacts on modulating overall mosquito and Aedes albopictus (the dominant species) abundance; waste tire habitats in urban freshwater wetland forests may be a year-round public health hazard.