Incidence of hemorrhagic disease in white-tailed deer is associated with winter and summer climatic conditions

Relationship Between Weather and Changes in Annual and Seasonal Abundance of Culicoides sonorensis (Diptera: Ceratopogonidae) in Alberta

Factors influencing annual and seasonal abundance of Culicoides sonorensis (Wirth and Jones) (Diptera; Ceratopogonidae) were examined at 10 sites in southern Alberta using negative binomial regression. Annual abundance varied among locations with greatest abundance in a narrow geographic band between -112.17 and -112.64°W longitude and 49.32 and 50.17°N latitude. Sites were grouped depending on whether abundance was continuous and high; discontinuous and low; or sporadic and low without much loss of information. Maximum annual abundance declined with spring precipitation, increased with spring temperature, and was unrelated to spring relative humidity, suggesting that abundance is highest during years with early drought conditions. Seasonal abundance was associated with the same factors but was further influenced by temperature and relative humidity during the sample intervals. Lagged effects were apparent, suggesting abundance increased with warmer temperatures over a six-week period, and increased when relative humidity declined closer to the sampling period. Predicted values were slightly biased and tended to overestimate observed data, but this could be adjusted using calibration curves. The model can also be used to predict presence/absence of C. sonorensis and will be useful for developing risk assessments.

North American Arboviruses and White-Tailed Deer (Odocoileus virginianus): Associated Diseases and Role in Transmission

Background: Arboviral disease is of increasing concern to human and animal health professionals as emerging and re-emerging arboviruses are more frequently recognized. Wildlife species are known to play a role in the transmission and maintenance of arboviruses and infections can result in morbidity and mortality in wildlife hosts. Materials and Methods: In this review, we detail existing evidence of white-tailed deer (Odocoileus virginianus) as an important host to a diverse collection of arboviruses and evaluate the utility of this species as a resource to better understand the epidemiology of related viral diseases. Results: Relevant veterinary and zoonotic viral pathogens endemic to North America include epizootic hemorrhagic disease virus, bluetongue virus, orthobunyaviruses, vesicular stomatitis virus, Eastern equine encephalitis virus, West Nile virus, and Powassan virus. Exotic viral pathogens that may infect white-tailed deer are also identified with an emphasis on zoonotic disease risks. The utility of this species is attributed to the high degree of contact with humans and domestic livestock and evidence of preferential feeding by various insect vectors. Conclusions: There is mounting evidence that white-tailed deer are a useful, widely available source of information regarding arboviral circulation, and that surveillance and monitoring of deer populations would be of value to the understanding of certain viral transmission dynamics, with implications for improving human and domestic animal health.

Spatio-temporal variation in environmental features predicts the distribution and abundance of Ixodes scapularis

Many species have experienced dramatic changes in both geographic range and population sizes in recent history. Increases in the geographic range or population size of disease vectors have public health relevance as these increases often precipitate the emergence of infectious diseases in human populations. Accurately identifying environmental factors affecting the biogeographic patterns of vector species is a long-standing analytical challenge, stemming from a paucity of data capturing periods of rapid changes in vector demographics. We systematically investigated the occurrence and abundance of nymphal Ixodes scapularis ticks at 532 sampling locations throughout New York State (NY), USA, between 2008 and 2018, a time frame that encompasses the emergence of diseases vectored by these ticks. Analyses of these field-collected data demonstrated a range expansion into northern and western NY during the last decade. Nymphal abundances increased in newly colonised areas, while remaining stable in areas with long-standing populations over the last decade. These trends in the geographic range and abundance of nymphs correspond to both the geographic expansion of human Lyme disease cases and increases in incidence rates. Analytic models fitted to these data incorporating time, space, and environmental factors, accurately identified drivers of the observed changes in nymphal occurrence and abundance. These models accounted for the spatial and temporal variation in the occurrence and abundance of nymphs and can accurately predict nymphal population patterns in future years. Forecasting disease risk at fine spatial scales prior to the transmission season can influence both public health mitigation strategies and individual behaviours, potentially impacting tick-borne disease risk and subsequently human disease incidence.

The role of drought as a determinant of hemorrhagic disease in the eastern United States

Bluetongue virus and epizootic hemorrhagic disease (HD) virus are globally distributed, vector-borne viruses that infect and cause disease in domestic and wild ruminant species. The forces driving increases in resulting HD may be linked to weather conditions and increasing severity has been noted in northerly latitudes. We evaluated the role of drought severity in both space and time on changes in HD reports across the eastern United States for a recent 15 year period. The objectives of this study were to: (a) develop a spatiotemporal model to evaluate if drought severity explains changing patterns of HD presence; and (b) determine whether this potential risk factor varies in importance over the present range of HD in the eastern United States. Historic data (2000-2014) from an annual HD presence-absence survey conducted by the Southeastern Cooperative Wildlife Disease Study and from the United States Drought Monitor were used for this analysis. For every county in 23 states and for each of 15 years, data were based on reported drought status for August, wetland cover, the physiographic region, and the status of HD in the previous year. We used a generalized linear mixed model to explain HD presence and evaluated spatiotemporal predictors across the region. We found that drought severity was a significant predictor of HD presence and the significance of this relationship was dependent on latitude. In more northerly latitudes, where immunological naivety is most likely, we demonstrated the increasing strength of drought severity as a determinant of reported HD and established the importance of variation in drought severity as a risk factor over the present range of HD in the eastern United States. Our research provides spatially explicit evidence for the link between climate forces and emerging disease patterns across latitude for a globally distributed disease.

Management of North American Culicoides Biting Midges: Current Knowledge and Research Needs

Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of two important viruses impacting North American ruminants--bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). These viruses have been identified for over 60 years in North America, but we still lack an adequate understanding of the basic biology and ecology of the confirmed vector, Culicoides sonorensis, and know even less about other putative Culicoides vector species. The major gaps in our knowledge of the biology of Culicoides midges are broad and include an understanding of the ecology of juveniles, the identity of potential alternate vector species, interactions of midges with both pathogens and vertebrates, and the effectiveness of potential control measures. Due to these broad and numerous fundamental knowledge gaps, vector biologists and livestock producers are left with few options to respond to or understand outbreaks of EHD or BT in North America, or respond to emerging or exotic Culicoides-transmitted pathogens. Here we outline current knowledge of vector ecology and control tactics for North American Culicoides species, and delineate research recommendations aimed to fill knowledge gaps.

Transmission and Epidemiology of Bluetongue and Epizootic Hemorrhagic Disease in North America: Current Perspectives, Research Gaps, and Future Directions

Bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) are arthropod-transmitted viruses in the genus Orbivirus of the family Reoviridae. These viruses infect a variety of domestic and wild ruminant hosts, although the susceptibility to clinical disease associated with BTV or EHDV infection varies greatly among host species, as well as between individuals of the same species. Since their initial detection in North America during the 1950s, these viruses have circulated in endemic and epidemic patterns, with occasional incursions to more northern latitudes. In recent years, changes in the pattern of BTV and EHDV infection and disease have forced the scientific community to revisit some fundamental areas related to the epidemiology of these diseases, specifically in relation to virus-vector-host interactions and environmental factors that have potentially enabled the observed changes. The aim of this review is to identify research and surveillance gaps that obscure our understanding of BT and EHD in North America.

Bluetongue in Europe and the role of wildlife in the epidemiology of disease

The article reviews a current bluetongue (BT) epidemiological situation in Europe, BT restricted zones and the role of wild ungulates as a reservoir for bluetongue virus (BTV) and its transmission. BT has been eradicated from central and northern Europe, however it is still circulating in some regions of southern and south-eastern Europe. According to the recent information of the Directoriate General for Health and Consumer Affairs (DG SANCO) disease caused by BTV1 was spreading at the beginning of 2014 in Corsica (France). Moreover, four BTV1 cases were noticed in the west Spain (Cáceres province), 59 BTV4 outbreaks in south Spain (Andalusia), 10 in the region of Algarve in Portugal and about 200 outbreaks of BTV4 in Greece (Peloponesse and Evros regions). On 4th July the first outbreak of BTV4 was also confirmed at the south Bulgarian border and by 5th September 2014 disease was noticed in 21 of 28 administrative districts of Bulgaria. In August 2014 the BTV4 disease was reported in south-east of Romania and as for 8th September 184 outbreaks of BT were confirmed in 17 counties of this country. As of 3 September 2014 in Europe there has been fourteen BT-affected zones, in different regions of Italy, Spain, Portugal, Cyprus, Malta, France (Corsica), Greece, Bulgaria and Romania. Most species of wild ruminants and camelids are susceptible to BTV infection, although frequently asymptomatically. Wild sheep, bighorn and mouflon, are susceptible to BTV infection and can develop fatal clinical disease, as do domestic sheep. Experimental or natural infection of antelope, wapiti, musk, ox, bison, yak, white-tailed deer and African buffalo also produced clinical disease, whereas blesbock, mountain gazelle, roe deer, red deer and Eurasian elk did not show clinical sign after natural or experimental infection and infection was recognized by the presence of BTV viral RNA or specific antibodies. The wildlife due to the long-term carrier state may act as a reservoir for BTV and play an important role in its transmission.

Molecular typing of epizootic hemorrhagic disease virus serotypes by one-step multiplex RT-PCR

Epizootic hemorrhagic disease virus (EHDV) causes a highly infectious noncontagious hemorrhagic disease in wild and captive deer (Cervidae) populations in the US. Although rapid and accurate identification of the disease is important, identification of the serotype is equally important for understanding the epidemiology of the disease in white-tailed deer (Odocoileus virginianus) populations. We developed a one-step multiplex reverse transcriptase PCR assay for rapid differentiation and identification of EHDV serotypes 1, 2, and 6 in cell culture and clinical samples by targeting the viral gene segment 2 (L2) that encodes for the structural protein VP2. From 2009 to 2012, 427 clinical samples including tissue and blood (in ethylenediaminetetraacetic acid) from white-tailed deer, found EHDV positive by real-time PCR, were used to evaluate this subtyping assay. Eighteen percent of the positive samples tested were EHDV-1, 59% were EHDV-2, and 21% were EHDV-6; 2% of the samples were positive for more than one subtype, indicating mixed infection. This assay provides a rapid, sensitive, specific diagnostic tool for differentiation and identification of EHDV serotypes in field samples and virus isolates.

Severe hoof disease in free-ranging Roosevelt elk (Cervus elaphus roosevelti) in southwestern Washington, USA

Reports of free-ranging Roosevelt elk (Cervus elaphus roosevelti) with abnormal hooves and lameness increased significantly in southwestern Washington, USA, during winter 2008. In March 2009 we examined five severely affected elk with clinical lameness from this region to characterize hoof lesions, examine the general health of affected elk, and potentially identify etiologies causing hoof disease. Three clinically normal elk from an adjacent but unaffected region were also collected as normal controls. Grossly, affected elk had deformed hooves that were asymmetrical, markedly elongated, and curved or broken, as well as hooves with sloughed horn. Most affected elk had severe sole ulcers with extensive laminar necrosis and pedal osteomyelitis. Histopathology of normal and abnormal hooves identified acute and chronic laminitis in all affected elk and one control elk. Hepatic copper and selenium levels in all affected and control elk were also deficient, and hoof keratin copper levels were low. No significant underlying systemic or musculoskeletal disease was detected in the affected elk, and attempts to isolate bacterial and viral pathogens were unsuccessful. A primary cause of hoof deformity was not definitively identified in this chronically affected group. Studies to identify infectious hoof disease and to characterize acute and subacute lesions are underway.

Spatial-temporal model of haemorrhagic disease in white-tailed deer in south-east USA, 1983 to 2000

The present study constructed a spatial-temporal statistical model to identify the risk and protective factors for haemorrhagic disease (HD) in white-tailed deer in the five states of Alabama, Georgia, South Carolina, North Carolina and Tennessee. The response variable was binary, indicating the presence or absence of HD in an individual county, measured annually from 1983 to 2000. Predictor variables included climatic factors of temperature, rainfall, wind speed and dew point, remotely sensed data of normalised difference vegetation index (NDVI) and land surface temperature derived from archived remotely sensed advanced very-high-resolution radiometer (AVHRR) satellite data, elevation, a spatial autocorrelation (SA) term and a temporal autocorrelation term. This study first applied principal component factor analysis to reduce the volume of climatic data and remotely sensed data. Then, a generalised linear mixed model framework (GLMM) was used to develop a spatial-temporal statistical model. The results showed that the area under receiver operating characteristic curve (ROC) was 0.728, indicating a good overall fit of the model. The total prediction accuracy over the 18 year period with optimal cut-off probability was 67 per cent. The prediction accuracy for individual years ranged from 48 to 75 per cent.