Bluetongue virus serotype 1 in wild mouflons in Spain

A serological survey of pathogens associated with the respiratory and digestive system in the Polish European bison (Bison bonasus) population in 2017-2022

BACKGROUND

The European bison (Bison bonasus) is a near threatened species and requires health monitoring. The aim of the present study was to determine the prevalence of antibodies to pathogens known to cause respiratory and digestive illness in ruminants.

RESULTS

In the studied 328 European bison, the highest seroprevalence was observed for Bovine herpesvirus-1 (BoHV-1) (50.27%), Bovine Coronavirus (BCoV) (26.36%), and Bluetongue Virus (BTV) (12.83%). For Mycoplasma bovis strains and Bovine Viral Diarrhea Virus (BVDV), positive results were rare. Interestingly, a higher prevalence of BTV antibodies was noted in the northeastern populations and older animals.

CONCLUSIONS

Our findings indicate that the Polish European bison population appears to have considerable contact with BoHV-1; however, this does not appear to be of great significance, as clinical symptoms and post-mortem lesions are rarely noted in Polish European bison population. The high seroprevalence of BTV in the north-east of Poland is an ongoing trend, also noted in previous studies. It is possible that European bison may perpetuate the virus in this region. This is the first report of antibodies for BCoV in European bison.

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

Long-term determinants of the seroprevalence of the bluetongue virus in deer species in southern Spain

Bluetongue is a vector-borne disease affecting domestic and wild ruminants, with a major socioeconomic impact. Endemic circulation of the bluetongue virus serotype 4 (BTV-4) and BTV-1 have occurred in Spain since 2004 and 2007, respectively. However, epidemiological studies have seldom been approached from a long-term perspective in wild ruminants. A total of 881 deer (red deer and fallow deer) were necropsied from 2005 to 2018 as part of the DNP health-monitoring program. Serum samples were tested for antibodies against BTV with the aims of assessing the temporal trend and to evaluate the modulating factors: individual, populational, environmental, and stochastic. Red deer displayed statistically significant higher seroprevalences of BTV (SBT; 78.6 ± 3.8%) than fallow deer (53.1 ± 4.7%). The detection of BTV-1 and BTV-4 by the serum neutralization test in calves suggested the circulation of both serotypes over the study period. For red deer, wet years together with high densities could provide suitable conditions for vector borne BTV transmission. Moreover, proximity to high suitability habitat for Culicoides, permanent pasturelands, was associated with higher SBT. The differences in the ecology and behaviour of deer species influencing the exposure to the vectors could determine the differences found in the SBT patterns. This study evidences the role that deer species may play in the maintenance of BTV, however, elucidating the epidemiological role of host in different contexts as well as the consequences of climate change on the competent vector populations and its potential effect on the dynamics of BTV infection in hosts communities deserve further research.

Monitoring of bluetongue virus in zoo animals in Spain, 2007-2019

Bluetongue (BT) is an emerging and re-emerging communicable vector-borne disease of animal health concern. A serosurvey was performed to assess exposure to BT virus (BTV) in zoo animals in Spain and to determine the dynamics of seropositivity in longitudinally sampled individuals during the study period. Serum samples were collected from 241 zoo animals belonging to 71 different species in five urban zoos (A-E) in Spain between 2007 and 2019. Twenty-four of these animals were longitudinally surveyed at three of the sampled zoos (zoos B, C and E) during the study period. Anti-BTV antibodies were found in 46 (19.1%; 95% CI: 14.1-24.1) of the 241 captive animals analysed by commercial ELISA. A virus neutralization test confirmed specific antibodies against BTV-1 and BTV-4 in 25 (10.7%; 95% CI: 6.7-14.6) and five (3.0%; 95% CI: 0.3-4.0) animals, respectively. Two of the 24 longitudinally sampled individuals (one African elephant (Loxodanta africana) and one aoudad (Ammotragus lervia)) showed anti-BTV antibodies at all samplings, whereas seroconversions were detected in one mouflon (Ovis aries musimon) in 2016, and one Asian elephant (Elephas maximus) in 2019. To the best of the authors' knowledge, this is the first large-scale survey on BTV conducted in both artiodactyl and non-artiodactyl zoo species worldwide. The results confirm BTV exposure in urban zoo parks in Spain, which could be of animal health and conservation concern. Circulation of BTV was detected in yearling animals in years when there were no reports of BTV outbreaks in livestock. Surveillance in artiodactyl and non-artiodactyl zoo species could be a valuable tool for epidemiological monitoring of BTV.

Co-Circulation of Multiple Serotypes of Bluetongue Virus in Zambia

Bluetongue (BT) is an arthropod-borne viral disease of ruminants with serious trade and socio-economic implications. Although the disease has been reported in a number of countries in sub-Saharan Africa, there is currently no information on circulating serotypes and disease distribution in Zambia. Following surveillance for BT in domestic and wild ruminants in Zambia, BT virus (BTV) nucleic acid and antibodies were detected in eight of the 10 provinces of the country. About 40% (87/215) of pooled blood samples from cattle and goats were positive for BTV nucleic acid, while one hartebeest pool (1/43) was positive among wildlife samples. Sequence analysis of segment 2 revealed presence of serotypes 3, 5, 7, 12 and 15, with five nucleotypes (B, E, F, G and J) being identified. Segment 10 phylogeny showed Zambian BTV sequences clustering with Western topotype strains from South Africa, intimating likely transboundary spread of BTV in Southern Africa. Interestingly, two Zambian viruses and one isolate from Israel formed a novel clade, which we designated as Western topotype 4. The high seroprevalence (96.2%) in cattle from Lusaka and Central provinces and co-circulation of multiple serotypes showed that BT is widespread, underscoring the need for prevention and control strategies.

Re-emergence of bluetongue virus serotype 4 in Iberian ibex (Capra pyrenaica) and sympatric livestock in Spain, 2018-2019

Between early October and mid-December 2018, mortalities were detected in Iberian ibex (Capra pyrenaica) populations in southern Spain. In the same region and period, bluetongue virus (BTV) circulation was also reported in sentinel and clinically affected domestic ruminant herds. Molecular analyses confirmed BTV serotype 4 (BTV-4) infection in eight Iberian ibexes from six hunting areas, and in 46 domestic ruminants from seven herds in close proximity to affected hunting estates. Histopathological analyses revealed vascular changes in several organs, pneumonia, lymphoid depletion, inflammatory mononuclear cell infiltrate and fibrosis as the most frequently observed lesions in the affected Iberian ibexes. Epidemiological and laboratory results indicate that BTV-4 was the main aetiological agent involved in outbreaks detected in Iberian ibex populations during the study period. Sequence analyses indicated that the BTV-4 strain detected in Iberian ibex had high homology (99.4%-100%) with strains isolated in livestock during the same period, and with previous isolates (≥98.9%) from Spain and Mediterranean Basin countries. Further studies are warranted to determine the impact of BTV-4 on the health status of Iberian ibex populations after the outbreaks. The inclusion of this species in the surveillance programme may be useful for early detection of BTV, especially in epidemiological scenarios at the wildlife-livestock interface.

RECENT CHANGES IN INFECTIOUS DISEASES IN EUROPEAN WILDLIFE

Many infectious diseases originating from, or carried by, wildlife affect wildlife conservation and biodiversity, livestock health, or human health. We provide an update on changes in the epidemiology of 25 selected infectious, wildlife-related diseases in Europe (from 2010-16) that had an impact, or may have a future impact, on the health of wildlife, livestock, and humans. These pathogens were selected based on their: 1) identification in recent Europe-wide projects as important surveillance targets, 2) inclusion in European Union legislation as pathogens requiring obligatory surveillance, 3) presence in recent literature on wildlife-related diseases in Europe since 2010, 4) inclusion in key pathogen lists released by the Office International des Epizooties, 5) identification in conference presentations and informal discussions on a group email list by a European network of wildlife disease scientists from the European Wildlife Disease Association, or 6) identification as pathogens with changes in their epidemiology during 2010-16. The wildlife pathogens or diseases included in this review are: avian influenza virus, seal influenza virus, lagoviruses, rabies virus, bat lyssaviruses, filoviruses, canine distemper virus, morbilliviruses in aquatic mammals, bluetongue virus, West Nile virus, hantaviruses, Schmallenberg virus, Crimean-Congo hemorrhagic fever virus, African swine fever virus, amphibian ranavirus, hepatitis E virus, bovine tuberculosis ( Mycobacterium bovis), tularemia ( Francisella tularensis), brucellosis ( Brucella spp.), salmonellosis ( Salmonella spp.), Coxiella burnetii, chytridiomycosis, Echinococcus multilocularis, Leishmania infantum, and chronic wasting disease. Further work is needed to identify all of the key drivers of disease change and emergence, as they appear to be influencing the incidence and spread of these pathogens in Europe. We present a summary of these recent changes during 2010-16 to discuss possible commonalities and drivers of disease change and to identify directions for future work on wildlife-related diseases in Europe. Many of the pathogens are entering Europe from other continents while others are expanding their ranges inside and beyond Europe. Surveillance for these wildlife-related diseases at a continental scale is therefore important for planet-wide assessment, awareness of, and preparedness for the risks they may pose to wildlife, domestic animal, and human health.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bluetongue

A specific concept of strain was developed in order to classify the BTV serotypes ever reported in Europe based on their properties of animal health impact: the genotype, morbidity, mortality, speed of spread, period and geographical area of occurrence were considered as classification parameters. According to this methodology the strain groups identified were (i) the BTV strains belonging to serotypes BTV‐1–24, (ii) some strains of serotypes BTV‐16 and (iii) small ruminant‐adapted strains belonging to serotypes BTV‐25, ‐27, ‐30. Those strain groups were assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7, Article 5 on the eligibility of bluetongue to be listed, Article 9 for the categorisation according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to bluetongue. The assessment has been performed following a methodology composed of information collection, expert judgement at individual and collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. The strain group BTV (1–24) can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL, while the strain group BTV‐25–30 and BTV‐16 cannot. The strain group BTV‐1–24 meets the criteria as in Sections 2 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (b) and (e) of Article 9(1) of the AHL. The animal species that can be considered to be listed for BTV‐1–24 according to Article 8(3) are several species of Bovidae, Cervidae and Camelidae as susceptible species; domestic cattle, sheep and red deer as reservoir hosts, midges insect of genus Culicoides spp. as vector species.

Bluetongue: control, surveillance and safe movement of animals

The performance of different bluetongue control measures related to both vaccination and protection from bluetongue virus (BTV) vectors was assessed. By means of a mathematical model, it was concluded that when vaccination is applied on 95% of animals even for 3 years, bluetongue cannot be eradicated and is able to re‐emerge. Only after 5 years of vaccination, the infection may be close to the eradication levels. In the absence of vaccination, the disease can persist for several years, reaching an endemic condition with low level of prevalence of infection. Among the mechanisms for bluetongue persistence, the persistence in the wildlife, the transplacental transmission in the host, the duration of viraemia and the possible vertical transmission in vectors were assessed. The criteria of the current surveillance scheme in place in the EU for demonstration of the virus absence need revision, because it was highlighted that under the current surveillance policy bluetongue circulation might occur undetected. For the safe movement of animals, newborn ruminants from vaccinated mothers with neutralising antibodies can be considered protected against infection, although a protective titre threshold cannot be identified. The presence of colostral antibodies interferes with the vaccine immunisation in the newborn for more than 3 months after birth, whereas the minimum time after vaccination of animal to be considered immune can be up to 48 days. The knowledge about vectors ecology, mechanisms of over‐wintering and criteria for the seasonally vector‐free period was updated. Some Culicoides species are active throughout the year and an absolute vector‐free period may not exist at least in some areas in Europe. To date, there is no evidence that the use of insecticides and repellents reduce the transmission of BTV in the field, although this may reduce host/vector contact. By only using pour‐on insecticides, protection of animals is lower than the one provided by vector‐proof establishments.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1182/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1171/full

Bluetongue Virus: From BTV-1 to BTV-27

Bluetongue virus (BTV) is the type species of genus Orbivirus within family Reoviridae. Bluetongue virus is transmitted between its ruminant hosts by the bite of Culicoides spp. midges. Severe BT cases are characterized by symptoms including hemorrhagic fever, particularly in sheep, loss of productivity, and death. To date, 27 BTV serotypes have been documented. These include novel isolates of atypical BTV, which have been almost fully characterized using deep sequencing technologies and do not rely on Culicoides vectors for their transmission among hosts. Due to its high economic impact, BT is an Office International des Epizooties (OIE) listed disease that is strictly controlled in international commercial exchanges. During the 20th century, BTV has been endemic in subtropical regions. In the last 15 years, novel strains of nine "typical" BTV serotypes (1, 2, 4, 6, 8, 9, 11, 14, and 16) invaded Europe, some of which caused disease in naive sheep and unexpectedly in bovine herds (particularly serotype 8). Over the past few years, three novel "atypical" serotypes (25-27) were characterized during sequencing studies of animal samples from Switzerland, Kuwait, and France, respectively. Classical serotype-specific inactivated vaccines, although expensive, were very successful in controlling outbreaks as shown with the northern European BTV-8 outbreak which started in the summer of 2006. Technological jumps in deep sequencing methodologies made rapid full characterizations of BTV genome from isolates/tissues feasible. Next-generation sequencing (NGS) approaches are powerful tools to study the variability of BTV genomes on a fine scale. This paper provides information on how NGS impacted our knowledge of the BTV genome.

Detection in and circulation of Bluetongue virus among domestic ruminants in Madagascar

So far, no published data was available concerning the circulation of Bluetongue virus (BTV) in Madagascar. During a survey on Rift Valley Fever, we were able to detect a virus belonging to BTV. Therefore, we conducted a study aiming at characterizing molecularly the BTV isolated and assess the importance of circulation of BTV in Madagascar. A total of 4393 sera from ruminants selected randomly by stratification and sampled in 30 districts of Madagascar were tested for BTV. Moreover, 175 cattle were followed during 11 months. Phylogenetic analyses were performed from virus isolated from unfed pools of mosquitoes. Overall, the estimated mean seroprevalence of infection at the national level was 95.9% (95% CI: [95.2-96.5]) in cattle and 83.7% (95% CI: [81.4-85.9]) in small ruminants. Estimation of incidence rate was 54 per 100 cattle-years assuming that the incidence rate is constant all year along. Phylogenetic analyses revealed that BTV detected belong to serotype 2. In conclusion, our results showed that BTV is endemic in Madagascar and highly prevalent among cattle. In our study we did not work on the vector involved in transmission of BTV in cattle. Thus, research should be conducted to better describe epidemiology of BTV in Madagascar including vectors and assess economic impact of the disease associated to BTV infections.

Spatial-temporal Trends and Factors Associated with the Bluetongue Virus Seropositivity in Large Game Hunting Areas from Southern Spain

An epidemiological study was carried out to determine the spatial-temporal trends and risk factors potentially involved in the seropositivity to bluetongue virus (BTV) in hunting areas with presence of red deer (Cervus elaphus). A total of 60 of 98 (61.2%; CI95% : 51.6-70.9) hunting areas sampled presented at least one seropositive red deer. Antibodies against BTV were detected in juvenile animals during the hunting seasons 2007/2008 to 2013/2014 in 15 of 98 (15.3%) hunting areas, which indicates an uninterrupted circulation of BTV in this period. A multivariate logistic regression model showed that the red deer density at hunting area level (>22 individuals/km(2) ), the annual abundance of Culicoides imicola (>1.4 mosquitoes/sampling) and the goat density at municipality level (>24.1 individuals/km(2) ) were factors significantly associated with BTV seropositivity in hunting areas. Control measures against BTV in the studied area include vaccination programmes in wild and domestic ruminants, movement control in areas with high densities and abundance of red deer and C. imicola, respectively. Considering the potential risk of BTV re-emergence, red deer should be included in the BT surveillance programmes in regions where these species share habitats with livestock.

Long-term dynamics of bluetongue virus in wild ruminants: relationship with outbreaks in livestock in Spain, 2006-2011

Wild and domestic ruminants are susceptible to Bluetongue virus (BTV) infection. Three BTV serotypes (BTV-4, BTV-1 and BTV-8) have been detected in Spain in the last decade. Even though control strategies have been applied to livestock, BTV circulation has been frequently detected in wild ruminant populations in Spain. The aim of the present study is to assess the role for wild ruminants in maintaining BTV after the vaccination programs in livestock in mainland Spain. A total of 931 out 1,914 (48.6%) serum samples, collected from eight different wild ruminant species between 2006 and 2011, were BTV positive by ELISA. In order to detect specific antibodies against BTV-1, BTV-4 and BTV-8, positive sera were also tested by serumneutralisation test (SNT). From the ELISA positive samples that could be tested by SNT (687 out of 931), 292 (42.5%) showed neutralising antibodies against one or two BTV serotypes. For each BTV seroptype, the number of outbreaks in livestock (11,857 outbreaks in total) was modelled with pure autoregressive models and the resulting smoothed values, representing the predicted number of BTV outbreaks in livestock at municipality level, were positively correlated with BTV persistence in wild species. The strength of this relationship significantly decreased as red deer (Cervus elaphus) population abundance increased. In addition, BTV RNA was detected by real time RT-PCR in 32 out of 311 (10.3%) spleen samples from seropositive animals. Although BT outbreaks in livestock have decreased substantially after vaccination campaigns, our results indicated that wild ruminants have been exposed to BTV in territories where outbreaks in domestic animals occurred. The detection of BTV RNA and spatial association between BT outbreaks in livestock and BTV rates in red deer are consistent with the hypothesis of virus circulation and BTV maintenance within Iberian wild ruminant populations.

Advances in diagnosis of respiratory diseases of small ruminants

Irrespective of aetiology, infectious respiratory diseases of sheep and goats contribute to 5.6 percent of the total diseases of small ruminants. These infectious respiratory disorders are divided into two groups: the diseases of upper respiratory tract, namely, nasal myiasis and enzootic nasal tumors, and diseases of lower respiratory tract, namely, peste des petits ruminants (PPR), parainfluenza, Pasteurellosis, Ovine progressive pneumonia, mycoplasmosis, caprine arthritis encephalitis virus, caseous lymphadenitis, verminous pneumonia, and many others. Depending upon aetiology, many of them are acute and fatal in nature. Early, rapid, and specific diagnosis of such diseases holds great importance to reduce the losses. The advanced enzyme-linked immunosorbent assays (ELISAs) for the detection of antigen as well as antibodies directly from the samples and molecular diagnostic assays along with microsatellites comprehensively assist in diagnosis as well as treatment and epidemiological studies. The present review discusses the advancements made in the diagnosis of common infectious respiratory diseases of sheep and goats. It would update the knowledge and help in adapting and implementing appropriate, timely, and confirmatory diagnostic procedures. Moreover, it would assist in designing appropriate prevention protocols and devising suitable control strategies to overcome respiratory diseases and alleviate the economic losses.

The role of wildlife in bluetongue virus maintenance in Europe: lessons learned after the natural infection in Spain

Bluetongue (BT) is a re-emergent vector-borne viral disease of domestic and wild ruminants caused by bluetongue virus (BTV), a member of the genus Orbivirus. A complex multi-host, multi-vector and multi-pathogen (26 serotypes) transmission and maintenance network has recently emerged in Europe, and wild ruminants are regarded as an important node in this network. This review analyses the reservoir role of wild ruminants in Europe, identifying gaps in knowledge and proposing actions. Wild ruminant species are indicators of BTV circulation. Excepting the mouflon (Ovis aries musimon), European wild ungulates do not develop clinical disease. Diagnostic techniques used in wildlife do not differ from those used in domestic ruminants provided they are validated. Demographic, behavioural and physiological traits of wild hosts modulate their relationship with BTV vectors and with the virus itself. While BTV has been eradicated from central and northern Europe, it is still circulating in the Mediterranean Basin. We propose that currently two BTV cycles coexist in certain regions of the Mediterranean Basin, a wild one largely driven by deer of the subfamily Cervinae and a domestic one. These are probably linked through shared Culicoides vectors of several species. We suggest that wildlife might be contributing to this situation through vector maintenance and virus maintenance. Additionally, differences in temperature and other environmental factors add complexity to the Mediterranean habitats as compared to central and northern European ones. Intervention options in wildlife populations are limited. There is a need to know the role of wildlife in maintaining Culicoides populations, and to know which Culicoides species mediate the wildlife-livestock-BTV transmission events. There is also a clear need to study more in depth the links between Cervinae deer densities, environmental factors and BTV maintenance. Regarding disease control, we suggest that research efforts should be focused on wildlife population and wildlife disease monitoring.

Survey of bluetongue virus infection in free-ranging wild ruminants in Switzerland

Background

In 2006, bluetongue virus serotype 8 (BTV-8) was detected for the first time in central Europe. Measures to control the infection in livestock were implemented in Switzerland but the question was raised whether free-ranging wildlife could be a maintenance host for BTV-8. Furthermore Toggenburg orbivirus (TOV), considered as a potential 25^th BTV serotype, was detected in 2007 in domestic goats in Switzerland and wild ruminants were considered a potential source of infection. To assess prevalences of BTV-8 and TOV infections in wildlife, we conducted a serological and virological survey in red deer, roe deer, Alpine chamois and Alpine ibex between 2009 and 2011. Because samples originating from wildlife carcasses are often of poor quality, we also documented the influence of hemolysis on test results, and evaluated the usefulness of confirmatory tests.

Results

Ten out of 1,898 animals (0.5%, 95% confidence interval 0.3-1.0%) had detectable antibodies against BTV-8 and BTV-8 RNA was found in two chamois and one roe deer (0.3%, 0.1-0.8%). Seroprevalence was highest among red deer, and the majority of positive wild animals were sampled close to areas where outbreaks had been reported in livestock. Most samples were hemolytic and the range of the optical density percentage values obtained in the screening test increased with increasing hemolysis. Confirmatory tests significantly increased specificity of the testing procedure and proved to be applicable even on poor quality samples. Nearly all samples confirmed as positive had an optical density percentage value greater than 50% in the ELISA screening.

Conclusions

Prevalence of BTV-8 infection was low, and none of the tested animals were positive for TOV. Currently, wild ruminants are apparently not a reservoir for these viruses in Switzerland. However, we report for the first time BTV-8 RNA in Alpine chamois. This animal was found at high altitude and far from a domestic outbreak, which suggests that the virus could spread into/through the Alps. Regarding testing procedures, hemolysis did not significantly affect test results but confirmatory tests proved to be necessary to obtain reliable prevalence estimates. The cut-off value recommended by the manufacturer for the screening test was applicable for wildlife samples.

Bluetongue dynamics in French wildlife: exploring the driving forces

Bluetongue (BT) was monitored in wildlife in France during two consecutive years corresponding to contrasting incidence rates in livestock: in 2008 at the peak of domestic outbreaks and in 2009 when very few outbreaks were observed. The disease status of 2 798 ruminants comprising 837 red deer (Cervus elaphus) was explored using ELISA test on serum and real-time RT-PCR test on blood or spleen. A large proportion of red deer were seropositive and positive to RT-PCR in 2008, but also in 2009 (seroprevalence: 47.1% and 24.3%), suggesting that red deer could maintain infection when domestic incidence was negligible. By contrast, low seroprevalence (<3%) and few RT-PCR positive results were observed in other wild ruminant species, which rather appeared thus as dead-end hosts. The risk factors of bluetongue circulation during the periods of high (2008) and low (2009) domestic incidence were explored in red deer using logistic mixed models. In this species, prevalence has been mainly influenced by the initial peak of BT in livestock, but also by environmental factor such as elevation and edge density between forest and pastures. Surprisingly, cattle density has a negative influence on prevalence in red deer, possibly due to the protective effect of cattle regarding midges' bites and/or to still unexplained factors dealing with the host/midge interface. To our knowledge, this study is the first attempt at measuring the effect of landscape and wildlife/domestic interface on BT prevalence in wildlife in Europe.

Animal viral diseases and global change: bluetongue and West Nile fever as paradigms

Environmental changes have an undoubted influence on the appearance, distribution, and evolution of infectious diseases, and notably on those transmitted by vectors. Global change refers to environmental changes arising from human activities affecting the fundamental mechanisms operating in the biosphere. This paper discusses the changes observed in recent times with regard to some important arboviral (arthropod-borne viral) diseases of animals, and the role global change could have played in these variations. Two of the most important arboviral diseases of animals, bluetongue (BT) and West Nile fever/encephalitis (WNF), have been selected as models. In both cases, in the last 15 years an important leap forward has been observed, which has lead to considering them emerging diseases in different parts of the world. BT, affecting domestic ruminants, has recently afflicted livestock in Europe in an unprecedented epizootic, causing enormous economic losses. WNF affects wildlife (birds), domestic animals (equines), and humans, thus, beyond the economic consequences of its occurrence, as a zoonotic disease, it poses an important public health threat. West Nile virus (WNV) has expanded in the last 12 years worldwide, and particularly in the Americas, where it first occurred in 1999, extending throughout the Americas relentlessly since then, causing a severe epidemic of disastrous consequences for public health, wildlife, and livestock. In Europe, WNV is known long time ago, but it is since the last years of the twentieth century that its incidence has risen substantially. Circumstances such as global warming, changes in land use and water management, increase in travel, trade of animals, and others, can have an important influence in the observed changes in both diseases. The following question is raised: What is the contribution of global changes to the current increase of these diseases in the world?

Protection of Spanish Ibex (Capra pyrenaica) against Bluetongue virus serotypes 1 and 8 in a subclinical experimental infection

Many wild ruminants such as Spanish ibex (Capra pyrenaica) are susceptible to Bluetongue virus (BTV) infection, which causes disease mainly in domestic sheep and cattle. Outbreaks involving either BTV serotypes 1 (BTV-1) and 8 (BTV-8) are currently challenging Europe. Inclusion of wildlife vaccination among BTV control measures should be considered in certain species. In the present study, four out of fifteen seronegative Spanish ibexes were immunized with a single dose of inactivated vaccine against BTV-1, four against BTV-8 and seven ibexes were non vaccinated controls. Seven ibexes (four vaccinated and three controls) were inoculated with each BTV serotype. Antibody and IFN-gamma responses were evaluated until 28 days after inoculation (dpi). The vaccinated ibexes showed significant (P<0.05) neutralizing antibody levels after vaccination compared to non vaccinated ibexes. The non vaccinated ibexes remained seronegative until challenge and showed neutralizing antibodies from 7 dpi. BTV RNA was detected in the blood of non vaccinated ibexes from 2 to the end of the study (28 dpi) and in target tissue samples obtained at necropsy (8 and 28 dpi). BTV-1 was successfully isolated on cell culture from blood and target tissues of non vaccinated ibexes. Clinical signs were unapparent and no gross lesions were found at necropsy. Our results show for the first time that Spanish ibex is susceptible and asymptomatic to BTV infection and also that a single dose of vaccine prevents viraemia against BTV-1 and BTV-8 replication.

Identification and differentiation of the twenty six bluetongue virus serotypes by RT-PCR amplification of the serotype-specific genome segment 2

Bluetongue (BT) is an arthropod-borne viral disease, which primarily affects ruminants in tropical and temperate regions of the world. Twenty six bluetongue virus (BTV) serotypes have been recognised worldwide, including nine from Europe and fifteen in the United States. Identification of BTV serotype is important for vaccination programmes and for BTV epidemiology studies. Traditional typing methods (virus isolation and serum or virus neutralisation tests (SNT or VNT)) are slow (taking weeks, depend on availability of reference virus-strains or antisera) and can be inconclusive. Nucleotide sequence analyses and phylogenetic comparisons of genome segment 2 (Seg-2) encoding BTV outer-capsid protein VP2 (the primary determinant of virus serotype) were completed for reference strains of BTV-1 to 26, as well as multiple additional isolates from different geographic and temporal origins. The resulting Seg-2 database has been used to develop rapid (within 24 h) and reliable RT-PCR-based typing assays for each BTV type. Multiple primer-pairs (at least three designed for each serotype) were widely tested, providing an initial identification of serotype by amplification of a cDNA product of the expected size. Serotype was confirmed by sequencing of the cDNA amplicons and phylogenetic comparisons to previously characterised reference strains. The results from RT-PCR and sequencing were in perfect agreement with VNT for reference strains of all 26 BTV serotypes, as well as the field isolates tested. The serotype-specific primers showed no cross-amplification with reference strains of the remaining 25 serotypes, or multiple other isolates of the more closely related heterologous BTV types. The primers and RT-PCR assays developed in this study provide a rapid, sensitive and reliable method for the identification and differentiation of the twenty-six BTV serotypes, and will be updated periodically to maintain their relevance to current BTV distribution and epidemiology (http://www.reoviridae.org/dsRNA_virus_proteins/ReoID/rt-pcr-primers.htm).

Role of wild ruminants in the epidemiology of bluetongue virus serotypes 1, 4 and 8 in Spain

Although the importance of wild ruminants as potential reservoirs of bluetongue virus (BTV) has been suggested, the role played by these species in the epidemiology of BT in Europe is still unclear. We carried out a serologic and virologic survey to assess the role of wild ruminants in the transmission and maintenance of BTV in Andalusia (southern Spain) between 2006 and 2010.

A total of 473 out of 1339 (35.3%) wild ruminants analyzed showed antibodies against BTV by both ELISA and serum neutralization test (SNT). The presence of neutralizing antibodies to BTV-1 and BTV-4 were detected in the four species analyzed (red deer, roe deer, fallow deer and mouflon), while seropositivity against BTV-8 was found in red deer, fallow deer and mouflon but not in roe deer. Statistically significant differences were found among species, ages and sampling regions. BTV RNA was detected in twenty-one out of 1013 wild ruminants (2.1%) tested. BTV-1 and BTV-4 RNA were confirmed in red deer and mouflon by specific rRT-PCR.

BTV-1 and BTV-4 seropositive and RNA positive wild ruminants, including juveniles and sub-adults, were detected years after the last outbreak was reported in livestock. In addition, between the 2008/2009 and the 2010/2011 hunting seasons, the seroprevalence against BTV-1, BTV-4 and BTV-8 increased in the majority of provinces, and these serotypes were detected in many areas where BTV outbreaks were not reported in domestic ruminants. The results indicate that wild ruminants seem to be implicated in the dissemination and persistence of BTV in Spain.

A survey of the transmission of infectious diseases/infections between wild and domestic ungulates in Europe

The domestic animals/wildlife interface is becoming a global issue of growing interest. However, despite studies on wildlife diseases being in expansion, the epidemiological role of wild animals in the transmission of infectious diseases remains unclear most of the time. Multiple diseases affecting livestock have already been identified in wildlife, especially in wild ungulates. The first objective of this paper was to establish a list of infections already reported in European wild ungulates. For each disease/infection, three additional materials develop examples already published, specifying the epidemiological role of the species as assigned by the authors. Furthermore, risk factors associated with interactions between wild and domestic animals and regarding emerging infectious diseases are summarized. Finally, the wildlife surveillance measures implemented in different European countries are presented. New research areas are proposed in order to provide efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

BTV infection in wild ruminants, with emphasis on red deer: a review

The distribution of bluetongue virus has changed, possibly related to climate change. Vaccination of domestic ruminants is taking place throughout Europe to control BT expansion. The high density of wild red deer (Cervus elaphus) in some European regions has raised concerns about the potential role that unvaccinated European wild ungulates might play in maintaining or spreading the virus. Most species of wild ruminants are susceptible to BTV infection, although frequently asymptomatically. The red deer population density in Europe is similar to that of domestic livestock in some areas, and red deer could account for a significant percentage of the BTV-infection susceptible ruminant population in certain regions. High serum antibody prevalence has been found in red deer, and BTV RNA (BTV-1, BTV-4 and BTV-8) has been repeatedly detected in naturally infected European red deer by means of RT-PCR. Moreover, red deer may carry the virus asymptomatically for long periods. Epidemiological studies suggest that there are more BT cases in domestic ungulates in those areas where red deer are present. Vector and host density and environmental factors are implicated in the spatial distribution of BT. As in domestic ruminants, BTV transmission among wild ruminants depends almost exclusively on Culicoides vectors, mainly C. imicola but also members of the C. obsoletus and C. pulicaris complex. However, BTV transmission from red deer to the vector remains to be demonstrated. Transplacental, oral, and mechanical transmissions are also suspected. Thus, wild red deer contribute to the still unclear epidemiology of BTV in Europe, and could complicate BTV control in domestic ruminants. However, further research at the wildlife host-vector-pathogen interface and regarding the epidemiology of BT and BT vectors in wildlife habitats is needed to confirm this hypothesis. Moreover, red deer could be used as BT sentinels. Serum and spleen tissue of calves sampled from late autumn onwards should be the target samples when establishing a BTV surveillance program.

Bluetongue virus serotypes 1 and 4 in red deer, Spain

We studied the potential of red deer as bluetongue maintenance hosts and sentinels. Deer maintained detectable bluetongue virus (BTV) serotype 4 RNA for 1 year after the virus was cleared from livestock. However, the virus was not transmitted to yearlings. BTV serotype 1 RNA was detected in red deer immediately after its first detection in cattle.

Full genome characterisation of bluetongue virus serotype 6 from the Netherlands 2008 and comparison to other field and vaccine strains

In mid September 2008, clinical signs of bluetongue (particularly coronitis) were observed in cows on three different farms in eastern Netherlands (Luttenberg, Heeten, and Barchem), two of which had been vaccinated with an inactivated BTV-8 vaccine (during May-June 2008). Bluetongue virus (BTV) infection was also detected on a fourth farm (Oldenzaal) in the same area while testing for export. BTV RNA was subsequently identified by real time RT-PCR targeting genome-segment (Seg-) 10, in blood samples from each farm. The virus was isolated from the Heeten sample (IAH "dsRNA virus reference collection" [dsRNA-VRC] isolate number NET2008/05) and typed as BTV-6 by RT-PCR targeting Seg-2. Sequencing confirmed the virus type, showing an identical Seg-2 sequence to that of the South African BTV-6 live-vaccine-strain. Although most of the other genome segments also showed very high levels of identity to the BTV-6 vaccine (99.7 to 100%), Seg-10 showed greatest identity (98.4%) to the BTV-2 vaccine (RSAvvv2/02), indicating that NET2008/05 had acquired a different Seg-10 by reassortment. Although Seg-7 from NET2008/05 was also most closely related to the BTV-6 vaccine (99.7/100% nt/aa identity), the Seg-7 sequence derived from the blood sample of the same animal (NET2008/06) was identical to that of the Netherlands BTV-8 (NET2006/04 and NET2007/01). This indicates that the blood contained two different Seg-7 sequences, one of which (from the BTV-6 vaccine) was selected during virus isolation in cell-culture. The predominance of the BTV-8 Seg-7 in the blood sample suggests that the virus was in the process of reassorting with the northern field strain of BTV-8. Two genome segments of the virus showed significant differences from the BTV-6 vaccine, indicating that they had been acquired by reassortment event with BTV-8, and another unknown parental-strain. However, the route by which BTV-6 and BTV-8 entered northern Europe was not established.

Discrimination of Culicoides obsoletus and Culicoides scoticus, potential bluetongue vectors, by morphometrical and mitochondrial cytochrome oxidase subunit I analysis

Biting midges of the Culicoides obsoletus Meigen species complex (Diptera: Ceratopogonidae) are increasingly suspected as vectors of the recent emergence of bluetongue virus in Europe. Within this complex, identification of the C. obsoletus and Culicoides scoticus females is considered as difficult or sometimes not possible while the identification of males is easy, based on genitalia observation. Nolan et al. (2007) concluded that the distinction of C. obsoletus and C. scoticus females is not possible according to morphology but require molecular analyses. In 2010, the identification of biting midges is done under a stereomicroscope without specific identification within the C. obsoletus species complex. However, such a specific identification distinguishing C. obsoletus s. str. and C. scoticus s. str. is crucial to identify the European competent vectors of the virus, their relative abundances and then accurately assess the risk. We performed morphometric analyses of head, genitalia and thorax of females combined with sequencing of the cytochrome oxidase I barcode fragment of mitochondrial DNA on 88 specimens in order to have a molecular identification of our sampled species. As we knew the actual species of individuals thanks to molecular results, we explored the discriminant power of 15 morphometric variables to distinguish the females according to their species. Multivariate analyses were performed on the morphometric measurements to identify and validate a combination of variables leading to an accurate species identification. It appears that females of C. obsoletus and C. scoticus can be accurately distinguished based on only four variables: width between chitinous plates, length and width of spermathecae1 and length of spermatheca2. This approach should improve the accuracy of morphologically-based species identification.

Experimental infection of European red deer (Cervus elaphus) with bluetongue virus serotypes 1 and 8

Bluetongue (BT) is a climate change-related emerging infectious disease in Europe. Outbreaks of serotypes 1, 2, 4, 6, 8, 9, 11, and 16 are challenging Central and Western Europe since 1998. Measures to control or eradicate bluetongue virus (BTV) from Europe have been implemented, including movement restrictions and vaccination of domestic BTV-susceptible ruminants. However, these measures are difficult to apply in wild free-ranging hosts of the virus, like red deer (Cervus elaphus), which could play a role in the still unclear epidemiology of BT in Europe. We show for the first time that BTV RNA can be detected in European red deer blood for long periods, comparable to those of domestic ruminants, after experimental infection with BTV-1 and BTV-8. BTV RNA was detected in experimentally infected red deer blood up to the end of the study (98-112 dpi). BTV-specific antibodies were found in serum both by enzyme-linked immunosorbent assay (ELISA) and virus neutralization (VNT) from 8 to 12 dpi to the end of the study, peaking at 17-28 dpi. Our results indicate that red deer can be infected with BTV and maintain BTV RNA for long periods, remaining essentially asymptomatic. Thus, unvaccinated red deer populations have the potential to be a BT reservoir in Europe, and could threaten the success of the European BTV control strategy. Therefore, wild and farmed red deer should be taken into account for BTV surveillance, and movement restrictions and vaccination schemes applied to domestic animals should be adapted to include farmed or translocated red deer.

Bovine infection with bluetongue virus with special emphasis on European serotype 8

Bluetongue virus (BTV) is an arthropod-borne virus infecting domestic and wild ruminants. Infection in cattle is commonly asymptomatic and characterised by a long viraemia. Associated with the emergence and the recrudescence of BTV serotype 8 (BTV-8) in Northern and Central Europe, remarkable differences have been noticed in the transmission and in the clinical expression of the disease, with cattle showing clinical illness and reproductive disorders such as abortion, stillbirth and fetal abnormalities. Several investigations have already indicated the putative ability of the European BTV-8 strain to cross the bovine placenta and to cause congenital infections. The current epidemiological and pathological findings present an unusual picture of the disease in affected bovines.