African Horse Sickness Fever in Vaccinated Horses: Short Communication

Comparative Genome Analysis of All Nine African Horse Sickness Serotypes Isolated From Equine Fatalities in Kenya and South Africa

African horse sickness (AHS) is a viral disease of equids, caused by a virus of the genus Orbivirus, family Reoviridae. The African horse sickness virus (AHSV) genome is made up of ten double-stranded RNA (dsRNA) segments that together code for seven structural and four nonstructural proteins. AHS is endemic in sub-Saharan countries. The efficacy and safety of inactivated AHS vaccines containing all nine serotypes, produced at the Central Veterinary Research Laboratory (CVRL) in Dubai, United Arab Emirates have been proven in the past. All nine AHSV serotypes were isolated from 102 samples collected in the last 20 years from horse fatalities in seven different area of Kenya, Africa. CVRL inactivated AHS vaccines are used in a few African countries defining the importance of this present study to compare the genome sequences of the nine AHSV serotypes isolated from horse fatalities in Kenya and nine AHSV serotypes isolated in South Africa. The hypothesized serotypes of the newly sequenced AHSV field strains from Kenya were likewise confirmed in this investigation, and they show substantial sequence homologies with recently isolated AHSV field strains.

Comparative immune responses after vaccination with the formulated inactivated African horse sickness vaccine serotype 1 between naïve horses and pretreated horses with the live-attenuated African horse sickness vaccine

Background and Aim: African horse sickness (AHS) is a non-contagious, high mortality, and insect-borne disease caused by a double-stranded RNA virus from the genus Orbivirus. The study aimed to develop inactivated vaccines serotype 1 inactivated AHS vaccine (IAV) and to compare the effect of IAV on antibody responses in young naïve horses and adult horses pre-immunized with live-attenuated AHS virus (AHSV) serotypes 1, 3, and 4 live-attenuated vaccine (LAV). Materials and Methods: A total of 27 horses were vaccinated in two trials. Twelve AHS naïve young horses and 15 adult horses were divided into three groups of 4 and 5 horses each, respectively. Horses in control Group 1 were treated with phosphate-buffered saline. Horses in Group 2 were subcutaneously vaccinated with 2 mL of formulated IAV with 10% Gel 01™ (Seppic, France) on day 0 and horses in Group 3 were subcutaneously vaccinated with 2 mL of IAV on day 0 and a booster on day 28. The IAV vaccine was prepared by isolating the AHSV serotype 1 growing on Vero cells, 10× virus titer was concentrated by ultrafiltration and chemically killed by formalin, using 10% Gel 01™ as an adjuvant. Ethylenediaminetetraacetic acid blood samples were taken for hematology, blood biochemistry, and antibody titers using an immunoperoxidase monolayer assay on 158th day post-vaccination. Results: Vaccination with IAV serotype 1 in adult horses pretreated with LAV increased antibody titers more than in young naïve vaccinated horses. The total leukocyte count and %neutrophils significantly increased, while %lymphocytes and %eosinophils significantly decreased on day 1 after vaccination; no local reactions were observed at the site of injection in any group. All biochemical and electrolyte analyte values were within the normal range after vaccination. Conclusion: The formulation of IAV serotype 1 using Gel 01™ as an adjuvant is safe and induces high antibody titers. This IAV formulation induced a high antibody response in horses without causing local reactions and mild systemic effects. However, AHS naïve horses still required ≥2 vaccinations and an annual booster vaccination to achieve high antibody titers.

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.

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

BACKGROUND

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.

OBJECTIVES

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.

STUDY DESIGN

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 4 weeks and 6 months apart. After 13 months, an annual booster was administered.

METHODS

Blood samples were regularly withdrawn for ELISA and virus neutralisation testing. Additionally, EDTA blood was tested every second day for 14 days post each vaccination for the presence of AHS virus or its RNA.

RESULTS

Results show that ELISA and virus neutralising antibodies appeared after the first booster, declined after 4-6 months and therefore three vaccinations and an annual vaccination are necessary to achieve high protective virus neutralising antibodies.

MAIN LIMITATIONS

No challenge infection was carried out due to the lack of a safe facility in the UAE.

CONCLUSION

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.

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

BACKGROUND

African 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.

RESULTS

A 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.

CONCLUSIONS

Horses 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.