Diagnostic DIVA tests accompanying the Disabled Infectious Single Animal (DISA) vaccine platform for African horse sickness.

The research focuses on the development of diagnostic tests that differentiate between infected and vaccinated animals (DIVA) for African Horse Sickness using the Disabled Infectious Single Animal (DISA) vaccine platform.

Understanding African Horse Sickness

• African Horse Sickness Virus (AHSV) belongs to the Orbivirus genus of the Reoviridae family and this virus can cause high fatalities among unvaccinated domestic horses. This has significant economic consequences and can affect the social and emotional livelihood of people who rely on these animals.
• The virus is transmitted through biting midges of the Culicoides species. Nine serotypes of the virus exist, which show limited cross neutralization – meaning immunity to one does not necessarily imply immunity to another.
• Because some Culicoides species found in moderate climates can transmit the closely related bluetongue virus, African Horse Sickness represents a serious threat far beyond Africa.

Necessity of DIVA Vaccines

• Safe and efficacious vaccines are desperately needed to control African Horse Sickness. DIVA (Differentiating Infected from Vaccinated Animals) vaccines, in particular, could accelerate control of the disease by allowing vaccinated animals to be readily distinguished from infected ones.
• Scientists have previously demonstrated that a highly virulent form of AHSV, with a deletion of 77 amino acids in NS3/NS3a, is safe, does not cause viremia (the presence of virus in the bloodstream), and offers protective capacity. This deletion mutant represents a promising Disabled Infectious Single Animal (DISA) vaccine platform.

The Diagnostic Tests

• The researchers developed a prototype NS3 competitive ELISA (cELISA) that is DIVA compliant to African Horse Sickness DISA vaccine platforms, meaning it can differentiate between infected and vaccinated animals.
• However, sensitivity and specificity of this prototype serological DIVA assay need to be further researched, particularly for AHSVs expressing antigenically different NS3/NS3a proteins.
• The researchers also developed an experimental panAHSV PCR test targeting genome segment 10, which successfully detected reference AHSV strains but not AHS DISA vaccine platforms. This new PCR test guarantees genetic DIVA based on in silico (computer simulated) and in vitro (in a laboratory environment) validation, although the test’s sensitivity and specificity have not yet been validated.

Conclusion

• In conclusion, the prototype NS3 cELISA and the new PCR test enable serological and genetic DIVA respectively, in line with AHS DISA vaccine platforms.