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

This article discusses the safety and effectiveness of an inactivated vaccine against the African horse sickness virus (AHS), looking at how the formulation of the vaccine with different adjuvants performs in guinea pigs and horses.

African Horse Sickness: Background and Existing Solutions

• African horse sickness (AHS) is a serious contagion affecting horses, caused by the African horse sickness virus (AHSV), a virus species of the Orbivirus genus in the Reoviridae family. The sickness has a very high mortality rate, killing about 95% of unexposed horses.
• This disease is prevalent in sub-Saharan Africa and threatens other regions as horse-biting Culicoides midges, which spread the virus, extend into moderate climate areas.
• The presence of nine serotypes, or different versions, of AHSV makes the disease complex. These serotypes do not produce high amounts of cross-neutralizing antibodies, the immune response that helps protect against multiple related viruses.
• Live-attenuated vaccines (LAVs) are currently used in Africa, but there are concerns about safety. These vaccines are not permitted in countries free of AHS.

Investigating Inactivated Vaccines

• The research focused on an inactivated (dead virus) AHSV vaccine. This type of vaccine works by exposing the immune system to the virus without the risk of causing the disease, helping the body recognize and fight the virus in the future.
• The vaccine was tested with different adjuvants – substances used to boost the body’s response to the vaccine – in both guinea pigs and horses.
• The vaccination was performed through subcutaneous (under skin) and intramuscular (into muscle) methods in horses. Observations were made for local reactions in the animals after primary and booster vaccinations.

Vaccine Outcomes and Future Directions

• Unfortunately, the inactivated AHSV vaccine did not protect all vaccinated horses from a virulent AHSV infection. Most surviving vaccinated horses exhibited temporary clinical signs and viremia (presence of the virus in the blood).
• However, the vaccine proved completely safe with respect to virus spread. The possibility of implementing the DIVA (Differentiating Infected from Vaccinated Animals) principle using serology data and testing the vaccine on other serotypes shows promise.
• The lack of a rapid protective response and the need for multiple booster vaccinations makes the current prototype unsuitable for emergency use. Thus, future research will focus on finding a better adjuvant and refining the vaccine for better efficacy, affordability, and acceptance among consumers.