Outbreak of African horse sickness in Thailand, 2020

Development and Validation of Three Triplex Real-Time RT-PCR Assays for Typing African Horse Sickness Virus: Utility for Disease Control and Other Laboratory Applications

The African horse sickness virus (AHSV) belongs to the Genus Orbivirus, family Sedoreoviridae, and nine serotypes of the virus have been described to date. The AHSV genome is composed of ten linear segments of double-stranded (ds) RNA, numbered in decreasing size order (Seg-1 to Seg-10). Genome segment 2 (Seg-2) encodes outer-capsid protein VP2, the most variable AHSV protein and the primary target for neutralizing antibodies. Consequently, Seg-2 determines the identity of the virus serotype. An African horse sickness (AHS) outbreak in an AHS-free status country requires identifying the serotype as soon as possible to implement a serotype-specific vaccination program. Considering that nowadays 'polyvalent live attenuated' is the only commercially available vaccination strategy to control the disease, field and vaccine strains of different serotypes could co-circulate. Additionally, in AHS-endemic countries, more than one serotype is often circulating at the same time. Therefore, a strategy to rapidly determine the virus serotype in an AHS-positive sample is strongly recommended in both epidemiological situations. The main objective of this study is to describe the development and validation of three triplex real-time RT-PCR (rRT-PCR) methods for rapid AHSV serotype detection. Samples from recent AHS outbreaks in Kenia (2015-2017), Thailand (2020), and Nigeria (2023), and from the AHS outbreak in Spain (1987-1990), were included in the study for the validation of these methods.

Potential roles of Culicoides spp. (Culicoides imicola, Culicoides oxystoma) as biological vectors of bluetongue virus in Yuanyang of Yunnan, P. R. China

Introduction

Culicoides plays a crucial role as an insect vector in the field of veterinary medicine. The transmission of significant viruses such as bluetongue virus (BTV) and African horse sickness virus (AHSV) by this insect poses a substantial threat, leading to the development of severe diseases in domestic animals. This study aimed to explore the Culicoides species, identify their blood-meal sources, and assess the presence of BTV and AHSV carried by Culicoides in Yuanyang County, Yunnan Province. The aim was to gain insights into the potential vectors of these two viruses and elucidate their potential roles in the transmission of pathogens.

Methods

The midges were collected from cattle (Bos indicus), pig (Sus scrofa), and goat (Capra hircus) pens in Yuanyang County, Yunnan Province in June 2020. Initial identification of midges was conducted through morphological characteristics, followed by molecular identification using the cytochrome C oxidase subunit I (COI) gene. The determination of Culicoides blood-meal sources was accomplished using specific primers targeting the cytochrome b (Cyt b) gene from potential hosts. BTV and AHSV RNA were identified in Culicoides pools through the application of reverse transcriptase PCR and quantitative real-time PCR. Nucleotide homology and phylogenetic analysis were performed using MegAlign (DNAStar) and Mega 6.0 software.

Results

A total of 6,300 Culicoides, consisting of C. oxystoma, C. arakawai, C. imicola, and C. innoxius, were collected from cattle, pigs, and goat pens. The engorgement rates for these species were 30.2%, 54.6%, 75%, and 66.7%, respectively. In the cattle pen, the prevailing species is C. oxystoma (100%). In the pig pen, C. arakawai dominates (70%), with C. oxystoma following at 30%. In the goat pen, C. imicola holds the majority (45.45%), trailed by C. oxystoma (25%), C. innoxius (20.45%), and C. arakawai (9.09%). These Culicoides species were identified as feeding on cattle, pigs, goats, chickens (Gallus gallus), and humans (Homo sapiens). The positivity rates for BTV were 20.00% and 11.54% in blood-fed specimens of C. imicola and C. oxystoma, respectively. Conversely, the positivity rates for BTV in non-blood-fed specimens were 0.00% and 6.67% for C. imicola and C. oxystoma, respectively. BTV was not detected in C. arakawai and C. innoxius. The specimens (YY86) from C. imicola that tested positive for BTV had the closest genetic relationship to YTS-4 isolated from Mangshi, Yunnan Province in 1996. All test results for the nucleic acid of AHSV were negative.

Conclusion

The study reveals variations in the species distribution, community composition, blood sucking rate, and blood-feeding sources of Culicoides across different habitats. Notably, C. imicola and C. oxystoma emerge as potential vectors for the transmission of BTV in local animals. Accordingly, this investigation provides crucial insights that can serve as a valuable reference for the prevention and control of BTV in local animals, particularly from the perspective of vector management.

Molecular identification of Culicoides oxystoma and Culicoides actoni vectors of bluetongue virus

Bluetongue is a non-contagious viral disease causing significant economic losses throughout the world. The bluetongue vectors Culicoides oxystoma and Culicoides actoni, which play a significant role in the transmission of various pathogens, are distributed across different geographical realms. Adults are minute in size with wide phenotypic variation, so morphology-based species identification is severely constrained by preparatory time and shortage of taxonomic expertise. To make the identification process rapid and effective, a specific primer was designed for the identification of C. actoni based on the multiple sequence alignment of ITS1 sequences of 11 Culicoides species. Along with this, a refined version of existing C. oxystoma specific primer was proposed. The primer sets distinguished C. oxystoma and C. actoni from a pooled sample consisting of other Culicoides species as well as closely related genera such as Forcipomyia and Alluaudomyia. Our findings suggest that the primers were species specific, sensitive and have potential to discriminate vector species C. oxystoma and C. actoni from pooled samples. To the best of our knowledge, these are the first ITS1 sequences generated and submitted in GenBank for Culicoides innoxius, Culicoides shortti, Culicoides palpifer and Culicoides anophelis and the first for Culicoides peregrinus, Culicoides fulvus and C. actoni from India.

Longitudinal humoral immune response and maternal immunity in horses after a single live-attenuated vaccination against African horse sickness during the disease outbreak in Thailand

Background and Aim

African horse sickness (AHS) has become a newly emerging disease after an outbreak in northeastern Thailand in March 2020. Mass vaccination in horses with live-attenuated AHS virus (AHSV) vaccine is essential for AHS control and prevention. This study aimed to monitor the longitudinal humoral immune response before and after a single vaccination using a live-attenuated vaccine against AHS in stallions, mares, and pregnant mares, including maternal immunity in foals born from pregnant mares during the outbreak in Thailand.

Materials and Methods

A total of 13 stallions and 23 non-pregnant and 21 pregnant mares were vaccinated with live-attenuated AHSV vaccines. Serum samples from selected horses were collected on the day of vaccination and 1, 6, 8, 9, 10, and 12-months post-vaccination. Furthermore, seven serum samples of foals born from vaccinated pregnant mares were collected on parturition date and 1, 3, and 6-months old. The antibody titer against AHS in all collected serum samples was evaluated using a commercial enzyme-linked immunosorbent assay kit. All data were analyzed for mean and standard deviation for each group of samples using a spreadsheet program. Antibody titers between times were analyzed using a one-way analysis of variance as repeated measurement, and antibody titers between horse groups were analyzed using a general linear model for statistically significant differences when p < 0.05.

Results

In stallion and non-pregnant mare groups, there were no statistically significant differences in antibody titers in all 6 time periods after vaccination. The antibody titer in the pregnant mare group showed a non-statistically significant difference between each gestation stage, except at 8 months post-vaccination. Furthermore, increasing antibody titers on days 1 and 3 after receiving colostrum in foals indicate the major role of transcolostral antibody transfer for AHS.

Conclusion

This study demonstrated that a single AHS vaccination using a live-attenuated vaccine could stimulate high antibody titers sufficient for AHS control and prevention during the outbreak in Thailand. Similarly, the antibody response of vaccinated horses of both genders, including various stages of pregnant mares, was statistically not different.

Molecular Identification of Culicoides Species and Host Preference Blood Meal in the African Horse Sickness Outbreak-Affected Area in Hua Hin District, Prachuap Khiri Khan Province, Thailand

African horse sickness (AHS) was reported as an outbreak in Thailand in 2020. Hematophagous insects from the genus Culicoides are the suspected vector responsible for AHS transmission. Horses in Hua Hin district, Prachuab Khiri Khan province, Thailand, were affected and died from AHS in 2020. However, the potential Culicoides species and its host preference blood meal in the affected areas are unknown. To investigate the potential vectors of AHS, Culicoides were collected using ultraviolet light traps placed near horse stables. Six horse farms, including five farms with AHS history and one farm without AHS history, were included in this study. Morphological and molecular identification of the Culicoides species was performed. Polymerase chain reaction (PCR) targeting the cytochrome b oxidase I (COXI) gene for confirmation of the Culicoides species, identification of the prepronociceptin (PNOC) gene for host preference blood meal, and bidirectional sequencing were conducted. Consequently, 1008 female Culicoides were collected, consisting of 708 and 300 samples captured at positions A and B at a distance of <2 and >5 m from the horse, respectively. Twelve Culicoides species identified by morphology were noted, including C. oxystoma (71.92%), C. imicola (20.44%), C. actoni (2.28%), C. flavipunctatus (1.98%), C. asiana (0.99%), C. peregrinus (0.60%), C. huffi (0.60%), C. brevitarsis (0.40%), C. innoxius (0.30%), C. histrio (0.30%), C. minimus (0.10%), and C. geminus (0.10%). The PCR detection of the Culicoides COXI gene confirmed Culicoides species in 23 DNA samples. PCR targeting the PNOC gene revealed that the Culicoides collected in this study fed on Equus caballus (86.25%), Canis lupus familiaris (6.25%), Sus scrofa (3.75%), and Homo sapiens (3.75%) for their blood meal. Human blood was identified from two samples of C. oxystoma and a sample of C. imicola. Three dominant species including C. oxystoma, C. imicola, and C. actoni that were reported in the Hua Hin area prefer to feed on horse blood. Moreover, C. oxystoma, C. imicola, and C. bravatarsis also feed on canine blood. This study revealed the species of Culicoides in Hua Hin district, Thailand, after the AHS outbreak.

Influence of full-time housing in vector-protected facilities on equine cortisol levels, heart rate, and behavior during the African horse sickness outbreak in Thailand

Horses were provided full-time housing in unfamiliar vector-protected facilities during the African horse sickness (AHS) outbreak in Thailand. This study aimed to investigate the impact of this housing arrangement on the equine stress response. Nine healthy horses were housed in both a traditional barn and a vector-protected barn. Equine behavior and stress response data were collected in association with the housing environment and time of day. The mean behavioral score of horses housed in the vector-protected barn was lower at night than during the day. In addition, the horses' mean heart rate at night was lower than their heart rate during the day, irrespective of housing condition. Furthermore, although blood cortisol peaked at 6:00 AM and was lowest at 6:00 PM under both housing conditions, daily fluctuations in blood cortisol levels were correlated with changes in humidity and temperature in both environments. Finally, horses housed in the traditional barn exhibited earlier decreases in cortisol levels relative to the horses in the vector-protected barn. This result indicates that housing horses in vector-protected facilities may impose stress.

Sensitivity and specificity for African horse sickness antibodies detection using monovalent and polyvalent vaccine antigen-based dot blotting

Background and Aim

The immune responses of animals infected with African horse sickness (AHS) virus are determined by enzyme-linked immunosorbent assay (ELISA), complement fixation, and virus neutralization test. During the outbreaks of AHS in Thailand, the immune response after vaccination has been monitored using commercial test kits such as blocking ELISA, which are expensive imported products unavailable commercially in Thailand. This study aimed to assess the sensitivity and specificity of anti-AHS virus antibodies using dot blotting based on monovalent and polyvalent strains of live attenuated AHS vaccine.

Materials and Methods

A total of 186 horse sera, namely, 93 AHS-unvaccinated samples and 93 AHS-vaccinated samples, were used in this study. All sera underwent antibodies detection using commercial blocking ELISA and in-house dot blotting based on monovalent and polyvalent strains of live attenuated AHS vaccine. The numbers of true positive, false positive, true negative, and false negative results in the dot blotting were compared with those in blocking ELISA and the sensitivity and specificity of dot blotting were assessed.

Results

For the monovalent antigen, there were 78, 19, 74, and 15 true positive, false positive, true negative, and false negative results, respectively, while for the polyvalent antigen, the corresponding numbers were 84, 34, 58, and 9. Meanwhile, the diagnostic sensitivity and specificity for monovalent antigen were 83.87% and 79.57%, respectively, but 90.32% and 62.37% for polyvalent antigen.

Conclusion

Dot blotting for AHS antibodies detection using vaccine antigen showed high sensitivity and rather a high specificity compared with the findings with the commercial ELISA test kit. In countries where commercial ELISA test kits are not available and when the size of a serum sample is small, dot blotting could become a good alternative test given its advantages, including its simplicity, rapidity, and convenience. To the best of our knowledge, these findings are the first report on the use of dot blotting for detecting AHS antibodies in horses. In conclusion, monovalent antigen-based dot blotting could be used as a reliable alternative serodiagnostic test for monitoring AHS humoral immune response, especially in vaccinated horses.

Development of Differentiating Infected from Vaccinated Animals (DIVA) Real-Time PCR for African Horse Sickness Virus Serotype 1

African horse sickness (AHS) is a highly infectious and often fatal disease caused by 9 serotypes of the orbivirus African horse sickness virus (AHSV). In March 2020, an AHS outbreak was reported in Thailand in which AHSV serotype 1 was identified as the causative agent. Trivalent live attenuated vaccines serotype 1, 3, and 4 were used in a targeted vaccination campaign within a 50-km radius surrounding the infected cases, which promptly controlled the spread of the disease. However, AHS-like symptoms in vaccinated horses required laboratory diagnostic methods to differentiate infected horses from vaccinated horses, especially for postvaccination surveillance. We describe a real-time reverse transcription PCR-based assay for rapid characterization of the affecting field strain. The development and validation of this assay should imbue confidence in differentiating AHS-vaccinated horses from nonvaccinated horses. This method should be applied to determining the epidemiology of AHSV in future outbreaks.

Sensitivity of RNA viral nucleic acid-based detection of avian influenza virus, Newcastle disease virus, and African horse sickness virus on flinders technology associates card using conventional reverse-transcription polymerase chain reaction

Background and Aim

The flinders technology associates (FTA) card is a cotton-based cellulose membrane impregnated with a chaotropic agent that inactivates infectious microorganisms, lyses cellular material, and fixes DNA and/or RNA within the fiber matrix. However, little is known about the effectiveness of these cards for detecting RNA viruses in animals. This study aimed to evaluate the sensitivity of RNA virus detection using conventional reverse-transcription polymerase chain reaction (RT-PCR) on FTA cards.

Materials and Methods

A highly virulent Newcastle disease virus (NDV) and an avian influenza virus (AIV) with low pathogenicity were propagated using chicken embryonic eggs. Three days after inoculation, the allantoic fluid was harvested, stored at -80°C, and the stock virus was tested for virus titration. African horse sickness virus (AHSV) was obtained from a live attenuated vaccine that was dissolved and stored at -80°C. For sample preparation, each stock virus was 10-fold serially diluted and each dilution was inoculated onto an FTA card, followed by drying in a Class II safety cabinet. Both the stock virus and infected FTA card were genomically isolated using an extraction kit, FTA purification kit, and extraction kit with Tris-EDTA (TE) buffer. The target genome was then detected by one-step RT-PCR for NDV and AIV, and two-step RT-PCR for African horse sickness, including gel electrophoresis for the detection of specific nucleic acids.

Results

The detection limit of stock AIV was compared on FTA cards, using the FTA purification kit, and with TE buffer with an extraction kit. The corresponding results were 1.47, 1.17, and 2.18 log₁₀ EID₅₀, respectively, while for NDV the results were 4.13, 4.83, and 4.84 log₁₀ ELD₅₀. Finally, detection limit of stock AHSV and AHSV on the FTA card extracted using TE buffer with an extraction kit were 4.30 and 4.01 log₁₀ plaque-forming units, respectively.

Conclusion

This study demonstrated that the detection limit or sensitivity of all tested RNA viruses on FTA cards did not differ when compared with those of the stock virus and in both methods for RNA isolation on FTA cards. These cards are suitable for collecting and transporting samples infected with RNA viruses, particularly AIV, NDV, and AHSV. Flinders technology associates cards also provide hazard-free samples, a reliable source of RNA for molecular characterization, and sufficient quantity for diagnostic applications based on nucleic acid-based detection.

Clinical, Virological and Immunological Responses after Experimental Infection with African Horse Sickness Virus Serotype 9 in Immunologically Naïve and Vaccinated Horses

This study described the clinical, virological, and serological responses of immunologically naïve and vaccinated horses to African horse sickness virus (AHSV) serotype 9. Naïve horses developed a clinical picture resembling the cardiac form of African horse sickness. This was characterized by inappetence, reduced activity, and hyperthermia leading to lethargy and immobility–recumbency by days 9–10 post-infection, an end-point criteria for euthanasia. After challenge, unvaccinated horses were viremic from days 3 or 4 post-infection till euthanasia, as detected by serogroup-specific (GS) real time RT-PCR (rRT-PCR) and virus isolation. Virus isolation, antigen ELISA, and GS-rRT-PCR also demonstrated high sensitivity in the post-mortem detection of the pathogen. After infection, serogroup-specific VP7 antibodies were undetectable by blocking ELISA (b-ELISA) in 2 out of 3 unvaccinated horses during the course of the disease (9–10 dpi). Vaccinated horses did not show significant side effects post-vaccination and were largely asymptomatic after the AHSV-9 challenge. VP7-specific antibodies could not be detected by the b-ELISA until day 21 and day 30 post-inoculation, respectively. Virus neutralizing antibody titres were low or even undetectable for specific serotypes in the vaccinated horses. Virus isolation and GS-rRT-PCR detected the presence of AHSV vaccine strains genomes and infectious vaccine virus after vaccination and challenge. This study established an experimental infection model of AHSV-9 in horses and characterized the main clinical, virological, and immunological parameters in both immunologically naïve and vaccinated horses using standardized bio-assays.

Emergence dynamics of adult Culicoides biting midges at two farms in south-east England

Background

Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of livestock arboviruses that cause diseases with significant economic, social and welfare impacts. Within temperate regions, livestock movement during arbovirus outbreaks can be facilitated by declaring a ‘seasonal vector-free period’ (SVFP) during winter when adult Culicoides are not active. In this study we carry out long-term monitoring of Culicoides adult emergence from larval development habitats at two farms in the UK to validate current definitions of the SVFP and to provide novel bionomic data for known vector species.

Methods

Standard emergence traps were used to collect emerging adult Culicoides from dung heaps at two cattle farms in the south-east of England from June to November 2016 and March 2017 to May 2018. Culicoides were morphologically identified to species or complex level and count data were analysed using a simple population dynamic model for pre-adult Culicoides that included meteorological components.

Results

More than 96,000 Culicoides were identified from 267 emergence trapping events across 2 years, revealing clear evidence of bivoltinism from peaks of male populations of Culicoidesobsoletus emerging from dung heaps. This pattern was also reflected in the emergence of adult female Obsoletus complex populations, which dominated the collections (64.4% of total catch) and emerged throughout the adult active period. Adult male C. obsoletus were observed emerging earlier than females (protandry) and emergence of both sexes occurred throughout the year. Culicoides chiopterus and Culicoides scoticus were also identified in spring emergence collections, providing the first evidence for the overwintering of larvae in dung heaps for these species.

Conclusions

This study demonstrates continual and highly variable rates of emergence of Culicoides throughout the year. A lack of evidence for mass emergence in spring along with the ability to observe male generations highlights the need for complementary surveillance techniques in addition to light-trap data when investigating seasonality and phenology. Evidence was found of other vector species, C. chiopterus and C. scoticus, utilising cattle dung heaps as an overwintering habitat, further highlighting the importance of these habitats on farms.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05370-z.

First detection and phylogenetic analysis of lumpy skin disease virus from Kinmen Island, Taiwan in 2020

Lumpy skin disease is an arthropod-borne bovine disease caused by lumpy skin disease virus. A suspect lumpy skin disease case in a breeding cattle farm on Kinmen Island, Taiwan was reported on July 8, 2020 and later confirmed the first occurrence of lumpy skin disease in the country by molecular biological detections, electron microscopy, and sequence comparison. Implementation of control measures including blanket vaccination on the island effectively ceased the outbreaks. Phylogenetic analyses revealed that the virus discovered in the outbreaks was most similar to those identified in China in 2019. Identifying this virus in the coastal areas in East Asia indicated the rapid eastward spread of lumpy skin disease in Asia.

Predicting the possibility of African horse sickness (AHS) introduction into China using spatial risk analysis and habitat connectivity of Culicoides

African horse sickness (AHS) is a devastating equine infectious disease. On 17 March 2020, it first appeared in Thailand and threatened all the South-East Asia equine industry security. Therefore, it is imperative to carry out risk warnings of the AHS in China. The maximum entropy algorithm was used to model AHS and Culicoides separately by using climate and non-climate variables. The least cost path (LCP) method was used to analyze the habitat connectivity of Culicoides with the reclassified land cover and altitude as cost factors. The models showed the mean area under the curve as 0.918 and 0.964 for AHS and Culicoides. The prediction result map shows that there is a high risk area in the southern part of China while the habitats of the Culicoides are connected to each other. Therefore, the risk of introducing AHS into China is high and control of the border area should be strengthened immediately.

Immobilization of captive plains zebras (Equus quagga) with a combination of etorphine hydrochloride, acepromazine, and xylazine hydrochloride

The plains zebra (Equus quagga) is a zebra species commonly kept in zoos around the world. However, they are not tame like their domestic relatives and are difficult to immobilize. We immobilized 30 captive plains zebra with a combination of etorphine hydrochloride (2-4 mg), acepromazine (8 mg), and xylazine hydrochloride (30 or 50 mg) to perform physical examination and blood sample collection for disease diagnostics. Physiological parameters including heart rate, respiratory rate, body temperature, and hemoglobin oxygen saturation were recorded. All zebras exhibited satisfactory anesthesia and fully recovered without re-narcotization. The results suggest that etorphine hydrochloride-acepromazine-xylazine hydrochloride combination for plains zebra immobilization is a safe and sufficient regimen for short procedures such as wellness examinations and sample collection.

The Absence of Abdominal Pigmentation in Livestock Associated Culicoides following Artificial Blood Feeding and the Epidemiological Implication for Arbovirus Surveillance

Culicoides midges (Diptera: Ceratopogonidae), the vectors of economically important arboviruses such as bluetongue virus and African horse sickness virus, are of global importance. In the absence of transovarial transmission, the parity rate of a Culicoides population provides imperative information regarding the risk of virus dispersal. Abdominal pigmentation, which develops after blood feeding and ovipositioning, is used as an indicator of parity in Culicoides. During oral susceptibility trials over the last three decades, a persistent proportion of blood engorged females did not develop pigment after incubation. The present study, combining a number of feeding trials and different artificial feeding methods, reports on this phenomenon, as observed in various South African and Italian Culicoides species and populations. The absence of pigmentation in artificial blood-fed females was found in at least 23 Culicoides species, including important vectors such as C. imicola, C. bolitinos, C. obsoletus, and C. scoticus. Viruses were repeatedly detected in these unpigmented females after incubation. Blood meal size seems to play a role and this phenomenon could be present in the field and requires consideration, especially regarding the detection of virus in apparent “nulliparous” females and the identification of overwintering mechanisms and seasonally free vector zones.

Evaluation of light emitting diode suction traps for the collection of livestock-associated Culicoides species in South Africa

Risk analysis of pathogens transmitted by Culicoides (Diptera; Ceratopogonidae) depends on the ability to detect all potential vectors attacking livestock in an area. Onderstepoort 220-V ultraviolet (UV) down-draught light traps are considered the gold standard for this purpose. To improve the flexibility of this trap in the field, in the absence of 220-V power, the possibility of using low-energy light emitting diodes (LEDs) was assessed. The efficiency of a standard 220-V Onderstepoort trap (30 cm 8 W fluorescent UV light tube) was compared to that of 220-V Onderstepoort traps fitted with either two, four or eight individual white LEDs. The Onderstepoort 220-V trap was also compared to a 12-V Onderstepoort trap fitted with an 8 W fluorescent UV light tube, a 12-V Onderstepoort trap with 12 individual white LEDs and 12-V and 220-V Onderstepoort traps fitted with 12 individual UV LEDs. Higher numbers of Culicoides as well as species diversity were collected with a brighter light source. The use of UV LEDs in both the 12-V and 220-V combinations was comparable to the Onderstepoort 220-V light trap with ration to species diversity collected. The Onderstepoort 220-V light trap is recommended if large numbers of Culicoides need to be collected.

African Horse Sickness Virus Serotype 1 on Horse Farm, Thailand, 2020

To investigate an outbreak of African horse sickness (AHS) on a horse farm in northeastern Thailand, we used whole-genome sequencing to detect and characterize the virus. The viruses belonged to serotype 1 and contained unique amino acids (95V,166S, 660I in virus capsid protein 2), suggesting a single virus introduction to Thailand.

Isothermal Nucleic Acid Amplification Technologies for the Detection of Equine Viral Pathogens

Simple Summary

Equine viral diseases remain a prominent concern for human and equine health globally. Many of these viruses are of primary biosecurity concern to countries that import equines where these viruses are not present. In addition, several equine viruses are zoonotic, which can have a significant impact on human health. Current diagnostic techniques are both time consuming and laboratory-based. The ability to accurately detect diseases will lead to better management, treatment strategies, and health outcomes. This review outlines the current modern isothermal techniques for diagnostics, such as loop-mediated isothermal amplification and insulated isothermal polymerase chain reaction, and their application as point-of-care diagnostics for the equine industry.

Abstract

The global equine industry provides significant economic contributions worldwide, producing approximately USD $300 billion annually. However, with the continuous national and international movement and importation of horses, there is an ongoing threat of a viral outbreak causing large epidemics and subsequent significant economic losses. Additionally, horses serve as a host for several zoonotic diseases that could cause significant human health problems. The ability to rapidly diagnose equine viral diseases early could lead to better management, treatment, and biosecurity strategies. Current serological and molecular methods cannot be field-deployable and are not suitable for resource-poor laboratories due to the requirement of expensive equipment and trained personnel. Recently, isothermal nucleic acid amplification technologies, such as loop-mediated isothermal amplification (LAMP) and insulated isothermal polymerase chain reaction (iiPCR), have been developed to be utilized in-field, and provide rapid results within an hour. We will review current isothermal diagnostic techniques available to diagnose equine viruses of biosecurity and zoonotic concern and provide insight into their potential for in-field deployment.

Transboundary Animal Diseases, an Overview of 17 Diseases with Potential for Global Spread and Serious Consequences

Animals provide food and other critical resources to most of the global population. As such, diseases of animals can cause dire consequences, especially disease with high rates of morbidity or mortality. Transboundary animal diseases (TADs) are highly contagious or transmissible, epidemic diseases, with the potential to spread rapidly across the globe and the potential to cause substantial socioeconomic and public health consequences. Transboundary animal diseases can threaten the global food supply, reduce the availability of non-food animal products, or cause the loss of human productivity or life. Further, TADs result in socioeconomic consequences from costs of control or preventative measures, and from trade restrictions. A greater understanding of the transmission, spread, and pathogenesis of these diseases is required. Further work is also needed to improve the efficacy and cost of both diagnostics and vaccines. This review aims to give a broad overview of 17 TADs, providing researchers and veterinarians with a current, succinct resource of salient details regarding these significant diseases. For each disease, we provide a synopsis of the disease and its status, species and geographic areas affected, a summary of in vitro or in vivo research models, and when available, information regarding prevention or treatment.

Use of nanopore sequencing to characterize african horse sickness virus (AHSV) from the African horse sickness outbreak in thailand in 2020

African horse sickness (AHS) is a highly infectious and deadly disease despite availability of vaccines. Molecular characterization of African horse sickness virus (AHSV) detected from the March 2020 Thailand outbreak was carried out by whole-genome sequencing using Nanopore with a Sequence-Independent Single Primer Amplification (SISPA) approach. Nucleotide sequence of the whole genome was compared with closest matching AHSV strains using phylogenetic analyses and the AHSV-1 virus shared high sequence identity with isolates from the same outbreak. Substitution analysis revealed non-synonymous and synonymous substitutions in the VP2 gene as compared to circulating South African strains. The use of sequencing technologies, such as Nanopore with SISPA, has enabled rapid detection, identification and detailed genetic characterization of the AHS virus for informed decision-making and implementation of disease control measures. Active genetic information sharing has also allowed emergence of AHSV to be better monitored on a global basis.

Scientific Opinion on the assessment of the control measures of the category A diseases of Animal Health Law: African Horse Sickness

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases (‘Animal Health Law’). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for African Horse Sickness (AHS). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radius of the protection and surveillance zone, and the minimum duration of measures in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, specific details of the transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones are shown. Several scenarios for which these control measures were assessed were designed and agreed prior to the start of the assessment. In summary, sampling procedures described in the diagnostic manual for AHS were considered efficient for all Equidae considering the high case fatality rate expected. The monitoring period (14 days) was assessed as effective in every scenario, except for those relating to the epidemiological enquiry where the risk manager should consider increasing the monitoring period, based on the awareness of keepers, environmental conditions and the vector abundance in the region. The current protection zone (100 km) comprises more than 95% of the infections from an affected establishment. Both the radius and duration of the zones could be reduced, based on local environmental conditions and the time of year of the first index case. Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation relating to AHS.

Current Arboviral Threats and Their Potential Vectors in Thailand

Arthropod-borne viral diseases (arboviruses) are a public-health concern in many regions of the world, including Thailand. This review describes the potential vectors and important human and/or veterinary arboviruses in Thailand. The medically important arboviruses affect humans, while veterinary arboviruses affect livestock and the economy. The main vectors described are mosquitoes, but other arthropods have been reported. Important mosquito-borne arboviruses are transmitted mainly by members of the genus Aedes (e.g., dengue, chikungunya, and Zika virus) and Culex (e.g., Japanese encephalitis, Tembusu and West Nile virus). While mosquitoes are important vectors, arboviruses are transmitted via other vectors, such as sand flies, ticks, cimicids (Family Cimicidae) and Culicoides. Veterinary arboviruses are reported in this review, e.g., duck Tembusu virus (DTMUV), Kaeng Khoi virus (KKV), and African horse sickness virus (AHSV). During arbovirus outbreaks, to target control interventions appropriately, it is critical to identify the vector(s) involved and their ecology. Knowledge of the prevalence of these viruses, and the potential for viral infections to co-circulate in mosquitoes, is also important for outbreak prediction.

Next-generation tools to control biting midge populations and reduce pathogen transmission

Biting midges of the genus Culicoides transmit disease-causing agents resulting in a significant economic impact on livestock industries in many parts of the world. Localized control efforts, such as removal of larval habitat or pesticide application, can be logistically difficult, expensive and ineffective if not instituted and maintained properly. With these limitations, a population-level approach to the management of Culicoides midges should be investigated as a means to replace or supplement existing control strategies. Next-generation control methods such as Wolbachia- and genetic-based population suppression and replacement are being investigated in several vector species. Here we assess the feasibility and applicability of these approaches for use against biting midges. We also discuss the technical and logistical hurdles needing to be addressed for each method to be successful, as well as emphasize the importance of addressing community engagement and involving stakeholders in the investigation and development of these approaches.