African Horse Sickness Research Articles

Humoral and cell-mediated immune responses to plant-produced African horse sickness virus VP7 quasi-crystals

African horse sickness (AHS) is a devastating viral disease affecting equines and has resulted in many disastrous epizootics. To date, no successful therapeutic treatment exists for AHS, and commercially used live-attenuated vaccines have various undesirable side effects. Previous studies have shown that mice inoculated with insoluble African horse sickness virus (AHSV) VP7 crystals are protected from live challenge with a lethal dose of AHSV. This study investigates the humoral and cell-mediated immune responses in guinea-pigs to a safer monovalent vaccine alternative based on AHSV-5 VP7 quasi-crystals produced in plants. Guinea-pigs received prime- and boost-inoculations of between 10 and 50 μg of purified plant-produced AHSV VP7. Western immunoblot analysis of the humoral response showed stimulation of high titres of anti-VP7 antibodies 28 days after the boost-inoculation in sera from three of the five experimental animals. In addition, RNA-seq transcriptome profiling of guinea-pig spleen-derived RNA highlighted thirty significantly (q ≤ 0.05) differentially expressed genes involved in innate and adaptive immunity. Differential expression of genes involved in Th1, Th2 and Th17 cell differentiation suggest a cell-mediated immune response to AHSV-5 VP7. Upregulation of several important cytokines and cytokine receptors were noted, including TNFSF14, CX3CR1, IFNLR1 and IL17RA. Upregulation of IL17RA suggests a Th17 response which has been reported as a key component in AHSV immunity. While further investigation is needed to validate these findings, these results suggest that AHSV-5 VP7 quasi-crystals produced in N. benthamiana are immunogenic and induce both humoral and cell-mediated responses.

Diagnostic applications of molecular and serological assays for bluetongue and African horse sickness.

The availability of rapid, highly sensitive and specific molecular and serologic diagnostic assays, such as competitive enzyme-linked immunosorbent assay (cELISA), has expedited the diagnosis of emerging transboundary animal diseases, including bluetongue (BT) and African horse sickness (AHS), and facilitated more thorough characterisation of their epidemiology. The development of assays based on real-time, reverse-transcription polymerase chain reaction (RT-PCR) to detect and identify the numerous serotypes of BT virus (BTV) and AHS virus (AHSV) has aided in-depth studies of the epidemiology of BTV infection in California and AHSV infection in South Africa. The subsequent evaluation of pan-serotype, real-time, RT-PCR-positive samples through the use of serotype-specific RT-PCR assays allows the rapid identification of virus serotypes, reducing the need for expensive and time-consuming conventional methods, such as virus isolation and serotype-specific virus neutralisation assays. These molecular assays and cELISA platforms provide tools that have enhanced epidemiologic surveillance strategies and improved our understanding of potentially altered Culicoides midge behaviour when infected with BTV. They have also supported the detection of subclinical AHSV infection of vaccinated horses in South Africa. Moreover, in conjunction with whole genome sequence analysis, these tests have clarified that the mechanism behind recent outbreaks of AHS in the AHS-controlled area of South Africa was the result of the reversion to virulence and/or genome reassortment of live attenuated vaccine viruses. This review focuses on the use of contemporary molecular diagnostic assays in the context of recent epidemiologic studies and explores their advantages over historic virus isolation and serologic techniques.

Pathogen detection and disease diagnosis in wildlife: challenges and opportunities.

The availability of rapid, highly sensitive and specific molecular and serologic diagnostic assays, such as competitive enzyme-linked immunosorbent assay (cELISA), has expedited the diagnosis of emerging transboundary animal diseases, including bluetongue (BT) and African horse sickness (AHS), and facilitated more thorough characterisation of their epidemiology. The development of assays based on real-time, reverse-transcription polymerase chain reaction (RT-PCR) to detect and identify the numerous serotypes of BT virus (BTV) and AHS virus (AHSV) has aided in-depth studies of the epidemiology of BTV infection in California and AHSV infection in South Africa. The subsequent evaluation of pan-serotype, real-time, RT-PCR-positive samples through the use of serotype-specific RT-PCR assays allows the rapid identification of virus serotypes, reducing the need for expensive and time-consuming conventional methods, such as virus isolation and serotype-specific virus neutralisation assays. These molecular assays and cELISA platforms provide tools that have enhanced epidemiologic surveillance strategies and improved our understanding of potentially altered Culicoides midge behaviour when infected with BTV. They have also supported the detection of subclinical AHSV infection of vaccinated horses in South Africa. Moreover, in conjunction with whole genome sequence analysis, these tests have clarified that the mechanism behind recent outbreaks of AHS in the AHS-controlled area of South Africa was the result of the reversion to virulence and/or genome reassortment of live attenuated vaccine viruses. This review focuses on the use of contemporary molecular diagnostic assays in the context of recent epidemiologic studies and explores their advantages over historic virus isolation and serologic techniques.

First seroprevalence investigation of epizootic haemorrhagic disease virus in Libya

Background: Epizootic haemorrhagic disease (EHD) is a vector-borne viral disease of domestic and wild ruminants. Epizootic haemorrhagic disease virus (EHDV) is transmitted by Culicoides spp. EHDV is a member of the Orbivirus genus within the Reoviridae family. It shares many morphological and structural characteristics with other members of the genus, such as the bluetongue virus, African horse sickness virus, and equine encephalosis virus.Aims:The purpose of our study was to investigate the epidemiological situation of EHDV in Libya in order to gain some knowledge about the presence of this virus in the country.Methods:In this study, we investigated the seroprevalence of EHDV in Libya, testing 855 blood samples collected during 2015. The samples were collected from domestic ruminants (cattle, sheep, and goats) originating from 11 provinces of Libya. Sera were tested by competitive enzyme-linked immunosorbent assays and positive samples confirmed by serum neutralization test.Results:The overall seroprevalence of EHDV was estimated to be 4% (95% confidence intervals = 2.8%–5.4%). Small ruminant seroprevalence was significantly (p = 0.016) higher than that found in cattle. Neutralizing antibodies against EHDV-6 were detected in a sheep from the western region of Libya.Conclusion:This study suggests that EHDV has circulated or is circulating in Libya, and sheep could play an important role in the epidemiology of EHDV, and the virus may still be circulating in North Africa.

Африканская чума лошадей и ее эпизоотия в Таиланде

Африканская чума лошадей и ее эпизоотия в Таиланде

Humoral antibody response of 10 horses after vaccination against African horse sickness with an inactivated vaccine containing all 9 serotypes in one injection.

African horse sickness (AHS) is a devastating viral disease of equids that was first recorded in 1327. Currently, prevention and control of the disease are based on attenuated vaccines and midge control. It has been shown that attenuated Orbivirus vaccines are not always safe as they may reverse to virulence. In the Emirate of Dubai, a vaccination experiment was carried out with an inactivated AHS vaccine produced at the Central Veterinary Research Laboratory (CVRL), Dubai, UAE to investigate the humoral antibody response of AHS-naïve horses to this vaccine. Our vaccination experiment was performed to establish an AHS vaccine bank in the UAE to protect horses from the disease in case of an outbreak. Therefore, CVRL established an inactivated AHS vaccine containing all nine serotypes which induce high neutralising antibodies. A total of 10 horses kept in a desert isolation area were subcutaneously and intramuscularly vaccinated with an inactivated vaccine containing all nine AHS serotypes previously isolated from Kenyan horse fatalities. Primary immunisation was followed by two booster immunisations 4weeks and 6months apart. After 13months, an annual booster was administered. Blood samples were regularly withdrawn for ELISA and virus neutralisation testing. Additionally, EDTA blood was tested every second day for 14days post each vaccination for the presence of AHS virus or its RNA. Results show that ELISA and virus neutralising antibodies appeared after the first booster, declined after 4-6months and therefore three vaccinations and an annual vaccination are necessary to achieve high protective virus neutralising antibodies. No challenge infection was carried out due to the lack of a safe facility in the UAE. Before more advanced AHS vaccines become a reality, inactivated vaccines containing all nine serotypes should be used as they produce high ELISA and neutralising antibodies.

Inhibition of Orbivirus Replication by Aurintricarboxylic Acid.

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are vector-borne viruses belonging to the Orbivirus genus, which are transmitted between hosts primarily by biting midges of the genus Culicoides. With recent BTV and AHSV outbreaks causing epidemics and important economy losses, there is a pressing need for efficacious drugs to treat and control the spread of these infections. The polyanionic aromatic compound aurintricarboxylic acid (ATA) has been shown to have a broad-spectrum antiviral activity. Here, we evaluated ATA as a potential antiviral compound against Orbivirus infections in both mammalian and insect cells. Notably, ATA was able to prevent the replication of BTV and AHSV in both cell types in a time- and concentration-dependent manner. In addition, we evaluated the effect of ATA in vivo using a mouse model of infection. ATA did not protect mice against a lethal challenge with BTV or AHSV, most probably due to the in vivo effect of ATA on immune system regulation. Overall, these results demonstrate that ATA has inhibitory activity against Orbivirus replication in vitro, but further in vivo analysis will be required before considering it as a potential therapy for future clinical evaluation.

English

A study was conducted to determine the prevalence and risk factors for African Horse Sickness (AHS) in donkeys in the highland area of Kiambu County, Kenya. Data on the risk factors was collected using semi-structured questionnaires administered to 146 donkey owners while blood samples collected from 398 donkeys both during the rainy and dry seasons. Antibodies against AHS were detected using competitive antibody Enzyme Linked Immuno – Sorbent Assay (c-ELISA). The estimated sero-prevalence of AHS in donkeys was 35.2 and 27.6% during the rainy and the dry seasons, respectively. The sero-prevalence of AHS in the donkeys that were re-examined during both seasons decreased from 60 to 20% indicating a waning immunity. Age of the donkey (P= 0.02) and presence of water streams (P= 0.03) were significant risk factors of AHS among donkeys. Three seropositive donkeys also showed pulmonary clinical signs of AHS. There was poor agreement (k =0.05) between the c-ELISA and clinical diagnosis of AHS. In conclusion, AHS in donkeys is endemic in the highland area of Kenya. This calls for increased adoption of preventive measures against the disease and justifies the need for future research on clinical and epidemiological patterns of AHS in donkeys in other highland areas. Key words: African horse sickness, donkeys, highland area, prevalence, risk factors.

Safety and efficacy of inactivated African horse sickness (AHS) vaccine formulated with different adjuvants

African horse sickness virus (AHSV) is a virus species in the genus Orbivirus of the family Reoviridae causing African Horse Sickness (AHS) in equids with a mortality of about 95% in naïve horses. AHS causes serious losses in developing countries where horses play a central role in draft power and transportation. There are nine AHSV serotypes inducing no or low cross-neutralizing antibodies. AHSV is spread by biting Culicoides midges. AHS is endemic in sub-Saharan Africa, and a serious threat outside Africa, since Culicoides species in moderate climate conditions are spreading the closely related bluetongue virus. AHS outbreaks will be devastating for the equestrian industry in developed countries. Live-attenuated vaccines (LAVs) are licensed, marketed and in use in Africa. Their application is controversial with regard to safety issues. LAVs are not allowed in AHS-free countries. We here studied inactivated AHSV with different adjuvants in guinea pigs and horses. Subcutaneous and intramuscular vaccination were studied in horses. Local reactions were observed after prime and boost vaccination. In general, neutralizing antibodies (nAbs) titres were very low after prime vaccination, whereas boost vaccination resulted in high nAb titres for some adjuvants. Vaccinated horses were selected based on local reactions and nAb titres to study efficacy. Unfortunately, not all vaccinated horses survived virulent AHSV infection. Further, most survivors temporarily developed clinical signs and viremia. Further, the current prototype inactivated AHS vaccine is not suitable as emergency vaccine, because onset of protection is slow and requires boost vaccinations. On the other hand, inactivated AHS vaccine is completely safe with respect to virus spread, and incorporation of the DIVA principle based on NS3/NS3a serology and exploring a vaccine production platform for other serotypes is feasible. A superior adjuvant increasing the protective response without causing local reactions will be required to develop payable and acceptable inactivated AHS vaccines.

Immune response of horses to inactivated African horse sickness vaccines

BackgroundAfrican horse sickness (AHS) is a serious viral disease of equids resulting in the deaths of many equids in sub-Saharan Africa that has been recognized for centuries. This has significant economic impact on the horse industry, despite the good husbandry practices. Currently, prevention and control of the disease is based on administration of live attenuated vaccines and control of the arthropod vectors.ResultsA total of 29 horses in 2 groups, were vaccinated. Eighteen horses in Group 1 were further divided into 9 subgroups of 2 horses each, were individually immunised with one of 1 to 9 AHS serotypes, respectively. The eleven horses of Group 2 were immunised with all 9 serotypes simultaneously with 2 different vaccinations containing 5 serotypes (1, 4, 7–9) and 4 serotypes (2, 3, 5, 6) respectively. The duration of this study was 12 months. Blood samples were periodically withdrawn for serum antibody tests using ELISA and VNT and for 2 weeks after each vaccination for PCR and virus isolation. After the booster vaccination, these 27 horses seroconverted, however 2 horses responded poorly as measured by ELISA. In Group 1 ELISA and VN antibodies declined between 5 to 7 months post vaccination (pv). Twelve months later, the antibody levels in most of the horses decreased to the seronegative range until the annual booster where all horses again seroconverted strongly. In Group 2, ELISA antibodies were positive after the first booster and VN antibodies started to appear for some serotypes after primary vaccination. After booster vaccination, VN antibodies increased in a different pattern for each serotype. Antibodies remained high for 12 months and increased strongly after the annual booster in 78% of the horses. PCR and virus isolation results remained negative.ConclusionsHorses vaccinated with single serotypes need a booster after 6 months and simultaneously immunised horses after 12 months. Due to the non-availability of a facility in the UAE, no challenge infection could be carried out.

Transboundary spread of equine influenza viruses (H3N8) in West and Central Africa: Molecular characterization of identified viruses during outbreaks in Niger and Senegal, in 2019.

Since November 2018, several countries in West and Central Africa have reported mortalities in donkeys and horses. Specifically, more than 66,000 horses and donkeys have succumbed to disease in Burkina Faso, Chad, Cameroon, The Gambia, Ghana, Mali, Niger, Nigeria, and Senegal. Strangles caused by Streptococcus equi subsp equi, African Horse Sickness (AHS) virus, and Equine influenza virus (EIV) were all suspected as potential causative agents. This study reports the identification of EIV in field samples collected in Niger and Senegal. Phylogenetic analysis of the hemagglutinin and neuraminidase genes revealed that the identified viruses belonged to clade 1 of the Florida sublineage and were very similar to viruses identified in Nigeria in 2019. Interestingly, they were also more similar to EIVs from recent outbreaks in South America than to those in Europe and the USA. This is one of the first reports providing detailed description and characterization of EIVs in West and Central Africa region.

Species composition and relative abundance of the genus Culicoides (Diptera: Ceratopogonidae) in Romania

BackgroundCulicoides biting midges are vectors involved in the biological transmission cycle of important animal diseases such as bluetongue and African horse sickness. In Romania, the first outbreaks of bluetongue were reported in 2014, leading to increased activities within the existing entomological surveillance network. The main goals of the surveillance activities were the establishment of the vector free period in relation to animal trade and the identification of Culicoides species involved in the transmission of the pathogen. This study was conducted on the composition and relative abundance of the species belonging to the genus Culicoides (Diptera: Ceratopogonidae) in certain regions of Romania and provided the opportunity to update the existing checklist of Culicoides species of this country.MethodsThe study was conducted in 33 of the 42 administrative units (counties), including a total of 659 catches, in 102 locations. The collections were carried out with UV blacklight suction traps (OVI type). The collected insects were preserved in 70% ethanol. Morphological insect identification was carried out using a stereomicroscope, according to established identification keys. In ten localities the relative abundance of the cryptic species of the Obsoletus complex was determined by multiplex PCR assay based on the ITS2 segment. The identification of the Culicoides chiopterus (Meigen) species by morphological examination was confirmed by PCR assay based on the ITS1 segment.ResultsEleven species were identified using morphological and PCR tools. The rest of the individuals were separated into five taxa. The species of the Obsoletus complex (grouping Culicoides obsoletus (Meigen) and Culicoides scoticus Downes & Kettle) were the most abundant, accounting for 59% of the total number of captured Culicoides spp. Three of the identified species are mentioned, according to our knowledge, for the first time in Romania: Culicoides newsteadi Austen, Culicoides flavipulicaris Dzhafarov and Culicoides bysta Sarvašová, Kočisová, Candolfi & Mathieu.ConclusionsOur study demonstrates that the Culicoides species most commonly cited as being involved in the transmission of arboviruses in Europe (i.e. bluetongue and Schmallenberg viruses) make up a high proportion of adult Culicoides trapped in Romania.

Effect of Environment and Elevation on Seasonal Prevalence of Culicoides in West Bengal

Background: Culicoides, popularly known as ‘biting midges’ is a group of vector insects causing transmission of pathogens to livestock and other closely related mammals leading to animal health deterioration. They are among the smallest and most abundant hematophagous vectors of Blue tongue virus (BTV), Epizootic haemorrhagic disease virus (EHDV), African horse sickness virus (AHSV), Equine encephalitis virus (EEV), protozoans, filarial nematodes throughout the world. They are known to spread livestock diseases in India in the states of Andhra Pradesh, Assam, Gujarat, Haryana, Himachal Pradesh, Jammu and Kashmir, Jharkhand, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Nagaland, Punjab, Rajasthan, Sikkim, Tamil Nadu, Tripura, Uttar Pradesh and West Bengal. 30 Culicoides vectors are reported worldwide, 13 of them from India, of which 11 are found in West Bengal. In the Indian subcontinent, biting midges live throughout the year, with two distinct peaks - one in the monsoon (August-September) and another peak during post-monsoon or beginning of winter (November) and there is a steady decrease during the summer months (May). Adults thrive best at low-temperature range (19-32oC) and rainfall plays an important role in Culicoides breeding and life-cycle. But a detailed account on the ecology, breeding sites, biology and bionomics of immature and adults have been poorly understood with very scanty literature. The present research is aimed to provide an exhaustive detail on the ecological behavior of Culicoides and their prevalence pattern based on the effect of meteorological parameter and elevation across different regions of West Bengal. Methods: Insect samples were collected using sweep nets in the early morning, afternoon and just before sunset for a period of four years from January 2014 to December 2017 in six agro-climatic regions of West Bengal. After collection, they were transferred in 70% ethanol, kept in a cool place, sorted and different parts of the specimen were mounted on glass slides in the phenol-balsam mixture and identified through Leica DFC 295 binocular light microscope. Ecological graph analysis were generated using software PAST 3.0 and MS-EXCEL 2016. Maps on sampling sites was generated using software ARC GIS 10.5). Result: Five Culicoides species-Culicoides oxystoma, C. actoni, C. peregrinus,C. orientalis and C. anophelis were collected. The results show highest prevalence in post-monsoon months at the coastal-saline region, at an of elevation 5-15m with ideal temperature of 14-35oC and rainfall of 1100-2000mm in West Bengal, with the highest dominance of Culicoides oxystoma throughout the year.

Outbreak of African horse sickness in Thailand, 2020.

African horse sickness was confirmed in horses in Thailand during March 2020. The virus was determined to belong to serotype 1 and is phylogenetically closely related to isolates from South Africa. This is the first incidence of African horse sickness occurring in South East Asia and of serotype 1 outside of Africa.

Impact of Climate Change on Animal Production and Expansion of Animal Disease: A Review on Ethiopia Perspective

Climate change is a result of the global increase in average air and ocean temperatures, and rising average sea levels. Livestock production and health are significantly vulnerable to the impact of climate change. Climate change has direct and indirect impacts on emerging and re-emerging animal diseases and zoonoses since it disrupts natural ecosystems and allows disease-causing pathogens to move into new areas where they may harm wildlife and domestic species, as well as humans. Climate change affects diseases and pest distributions, range prevalence, incidence, and seasonality but the degree of change remains highly uncertain. The occurrence and distribution of vector-borne diseases such as bluetongue, west Nile fever, rift valley fever, African horse sickness, etc. are closely associated with weather patterns and long-term climatic factors strongly influence the incidence of outbreaks. The interaction between animal production and climate change is complex and multi-directional since animal production contributes to climate change; but to the reverse and worse condition, climate change highly affects animal production. Climate change, animal production systems, and animal diseases are strongly linked to each other. But what is worse is that both change in climate and the production systems of animals highly affect the occurrence, distribution, emergence, and re-emergence of animal diseases. The close linkage among climate change, animal production, and disease; the increased threat of climate on the animal production and health sectors needs: the hands of stakeholders in the environment, animal production and health to work in an integrated and systematic manner; researches with emphasis given to the state of climate change and the direct and indirect effects it poses on animal production and health; and ensuring development of sustainable animal farming and land use, and climate adaptation and mitigation strategies.

Barcoding of the Genus Culicoides (Diptera: Ceratopogonidae) in Austria-An Update of the Species Inventory Including the First Records of Three Species in Austria.

Ceratopogonidae are small nematoceran Diptera with a worldwide distribution, consisting of more than 5400 described species, divided into 125 genera. The genus Culicoides is known to comprise hematophagous vectors of medical and veterinary importance. Diseases transmitted by Culicoides spp. Such as African horse sickness virus, Bluetongue virus, equine encephalitis virus (Reoviridae) and Schmallenberg virus (Bunyaviridae) affect large parts of Europe and are strongly linked to the spread and abundance of its vectors. However, Culicoides surveillance measures are not implemented regularly nor in the whole of Austria. In this study, 142 morphologically identified individuals were chosen for molecular analyses (barcoding) of the mitochondrial cytochrome c oxidase subunit I gene (mt COI). Molecular analyses mostly supported previous morphologic identification. Mismatches between results of molecular and morphologic analysis revealed three new Culicoides species in Austria, Culicoides gornostaevae Mirzaeva, 1984, which is a member of the Obsoletus group, C. griseidorsum Kieffer, 1918 and C. pallidicornis Kieffer, 1919 as well as possible cryptic species. We present here the first Austrian barcodes of the mt COI region of 26 Culicoides species and conclude that barcoding is a reliable tool with which to support morphologic analysis, especially with regard to the difficult to identify females of the medically and economically important genus Culicoides.

The Implications of EU Regulation 2016/429 on Neglected Diseases of Small Ruminants including Contagious Agalactia with Particular Reference to Italy.

Simple SummaryThis article explains the future application of the EU regulation Animal Health Law (Reg. CE 429/2016), which will be implemented in 2021. The article describes the major changes and modifications related to notifiable diseases of sheep and goats and outlines the approach that will be taken for their surveillance and control. It explains the objective of the European Commission in applying a modern animal health system based on risk assessment, updated scientific knowledge, epidemiology, and a new culture of European diseases prevention. Five categories of diseases are recognized. Category A diseases are not usually present in the EU, which must be immediately eradicated. Category B diseases must be controlled in member states and eventually eradicated while category C diseases are present in some MS, which must be prevented from spreading to disease-free states. Category D diseases only present moderate risk but necessitate measures such as movement control to prevent their spread among MS or their entry into the EU, and category E diseases need surveillance. Lastly, differences between the previous Italian regulations and the new EU law are highlighted.After almost 40 years, the 27 member states (MS) of the European Union (EU) will comply with the European Law 429/2016 in 2021 by completing a process of unification and harmonization of all regulations related to animal health between MS. These new provisions are based on modern scientific principles on animal health, on long-term epidemiological data, and, above all, on the most current risk assessment and analysis. The paper describes all changes and updates, which will impact the Italian current National regulation. A total of 58 animal diseases have been included in the Annex II (“Listing”) and Annex IV (“Categorization”) of the new Delegated Act (DA 2018/1629). Five diseases comprising the great viral epizooties were automatically included on the list because of their primary importance. These diseases include foot and mouth disease (FMD), African swine fever (ASF), classical swine fever (CSF), highly pathogenic avian influenza (HPAI), and African horse sickness (AHS). Another 53 diseases have been identified by the ad hoc assessment on listing and categorization of animal diseases developed by the European Food Safety Association. Seventeen communicable diseases of the Order Artiodactlya (sheep, goats, deer, etc.) have been listed including foot and mouth disease, sheep and goat pox, and pestes de petits ruminants. In addition, other endemic diseases affecting more than one species include blue tongue, tuberculosis, brucellosis, and anthrax. There are five categories (A-E) based on the degree of action to be undertaken throughout the EU for each disease. These vary from complete eradication for diseases not normally found in the EU like FMD (category A) for establishing surveillance for diseases like West Nile that present high risk but lack control tools (category E).

Post-outbreak African horse sickness surveillance: A scenario tree evaluation in South Africa's controlled area.

An African horse sickness (AHS) outbreak occurred in March and April 2016 in the controlled area of South Africa. This extended an existing trade suspension of live equids from South Africa to the European Union. In the post-outbreak period ongoing passive and active surveillance, the latter in the form of monthly sentinel surveillance and a stand-alone freedom from disease survey in March 2017, took place. We describe a stochastic scenario tree analysis of these surveillance components for 24months, starting July 2016, in three distinct geographic areas of the controlled area. Given that AHS was not detected, the probability of being free from AHS was between 98.3% and 99.8% assuming that, if it were present, it would have a prevalence of at least one infected animal in 1% of herds. This high level of freedom probability had been attained in all three areas within the first 9months of the 2-year period. The primary driver of surveillance outcomes was the passive surveillance component. Active surveillance components contributed minimally (<0.2%) to the final probability of freedom. Sensitivity analysis showed that the probability of infected horses showing clinical signs was an important parameter influencing the system surveillance sensitivity. The monthly probability of disease introduction needed to be increased to 20% and greater to decrease the overall probability of freedom to below 90%. Current global standards require a 2-year post-incursion period of AHS freedom before re-evaluation of free zone status. Our findings show that the length of this period could be decreased if adequately sensitive surveillance is performed. In order to comply with international standards, active surveillance will remain a component of AHS surveillance in South Africa. Passive surveillance, however, can provide substantial evidence supporting AHS freedom status declarations, and further investment in this surveillance activity would be beneficial.

Modelling the monthly abundance of Culicoides biting midges in nine European countries using Random Forests machine learning

BackgroundCulicoides biting midges transmit viruses resulting in disease in ruminants and equids such as bluetongue, Schmallenberg disease and African horse sickness. In the past decades, these diseases have led to important economic losses for farmers in Europe. Vector abundance is a key factor in determining the risk of vector-borne disease spread and it is, therefore, important to predict the abundance of Culicoides species involved in the transmission of these pathogens. The objectives of this study were to model and map the monthly abundances of Culicoides in Europe.MethodsWe obtained entomological data from 904 farms in nine European countries (Spain, France, Germany, Switzerland, Austria, Poland, Denmark, Sweden and Norway) from 2007 to 2013. Using environmental and climatic predictors from satellite imagery and the machine learning technique Random Forests, we predicted the monthly average abundance at a 1 km2 resolution. We used independent test sets for validation and to assess model performance.ResultsThe predictive power of the resulting models varied according to month and the Culicoides species/ensembles predicted. Model performance was lower for winter months. Performance was higher for the Obsoletus ensemble, followed by the Pulicaris ensemble, while the model for Culicoides imicola showed a poor performance. Distribution and abundance patterns corresponded well with the known distributions in Europe. The Random Forests model approach was able to distinguish differences in abundance between countries but was not able to predict vector abundance at individual farm level.ConclusionsThe models and maps presented here represent an initial attempt to capture large scale geographical and temporal variations in Culicoides abundance. The models are a first step towards producing abundance inputs for R0 modelling of Culicoides-borne infections at a continental scale.

Culicoides species composition and molecular identification of host blood meals at two zoos in the UK

BackgroundCulicoides biting midges are biological vectors of arboviruses including bluetongue virus (BTV), Schmallenberg virus (SBV) and African horse sickness virus (AHSV). Zoos are home to a wide range of ‘at risk’ exotic and native species of animals. These animals have a high value both in monetary terms, conservation significance and breeding potential. To understand the risk these viruses pose to zoo animals, it is necessary to characterise the Culicoides fauna at zoos and determine which potential vector species are feeding on which hosts.MethodsLight-suction traps were used at two UK zoos: the Zoological Society of London (ZSL) London Zoo (LZ) and ZSL Whipsnade Zoo (WZ). Traps were run one night each week from June 2014 to June 2015. Culicoides were morphologically identified to the species level and any blood-fed Culicoides were processed for blood-meal analysis. DNA from blood meals was extracted and amplified using previously published primers. Sequencing was then carried out to determine the host species.ResultsA total of 11,648 Culicoides were trapped and identified (n = 5880 from ZSL WZ; n = 5768 from ZSL LZ), constituting 25 different species. The six putative vectors of BTV, SBV and AHSV in northern Europe were found at both zoos and made up the majority of the total catch (n = 10,701). A total of 31 host sequences were obtained from blood-fed Culicoides. Culicoides obsoletus/C. scoticus, Culicoides dewulfi, Culicoides parroti and Culicoides punctatus were found to be biting a wide range of mammals including Bactrian camels, Indian rhinoceros, Asian elephants and humans, with Culicoides obsoletus/C. scoticus also biting Darwin’s rhea. The bird-biting species, Culicoides achrayi, was found to be feeding on blackbirds, blue tits, magpies and carrion crows.ConclusionsTo our knowledge, this is the first study to directly confirm blood-feeding of Culicoides on exotic zoo animals in the UK and shows that they are able to utilise a wide range of exotic as well as native host species. Due to the susceptibility of some zoo animals to Culicoides-borne arboviruses, this study demonstrates that in the event of an outbreak of one of these viruses in the UK, preventative and mitigating measures would need to be taken.