Trials of an inactivated equid herpesvirus 1 vaccine: challenge with a subtype 2 virus.

The research article focuses on testing an inactivated equid herpesvirus 1 (EHV-1) vaccine in yearling ponies and the subsequent immune responses elicited by it, especially when faced with a subtype 2 of the virus challenge.

Subject and Vaccine Administered

• The research carried out trials with a vaccine against equid herpesvirus 1 (EHV-1), a significant pathogen in horses, mules, and donkeys leading to much economic loss due to its detrimental effects. The subtype 1 strain of the EHV-1 was incorporated into the inactivated vaccine.
• The trials were conducted on ponies that were a year old to observe the immune response to vaccination.
• Two groups received the vaccine: one group got two doses, while the other got three doses. The timing of the doses and the subsequent challenge with subtype 2 of the virus varied for each group.

Serological Response

• The serological responses, or the production of antibodies in response to the vaccine, were studied.
• A significant increase in complement fixing antibodies was observed against the subtype 1 virus included in the vaccine. These antibodies are involved in eliminating infected cells and combatting the virus.
• An interesting observation was that these antibodies declined rapidly after the second dose and almost reverted to pre-vaccination levels eight weeks post the second dose.
• The amount of complement fixing antibodies against the subtype 2 virus showed an increase with each additional dose of vaccine.
• The vaccine-induced neutralising antibody responses were weak, suggesting lower effectiveness of the vaccine against neutralising the virus. However, this response was less strain-specific than the complement fixing ones.

Challenge Infection Outcomes

• The vaccinated ponies were then challenged with a subtype 2 virus to study the vaccine’s effectiveness.
• Ponies administered three doses of the vaccine showed resistance to the subtype 2 virus, indicating the benefits of a third dose in providing immunity against a heterologous virus.
• Conversely, out of the ponies that received two doses, most were still susceptible to subtype 2 virus infection, indicating that two doses may not offer complete protection.
• While two doses did not lower the duration of virus excretion or fever responses when ponies were faced with a subtype 2 challenge, the viral load was significantly reduced.

Implications

• The study provides insights on EHV-1 vaccine’s effectiveness, showing the benefit of a three-dose regimen in equine immunity against homologous and heterologous viruses.
• The findings highlight the need for further research to optimize the vaccine dosage and its delivery schedule for comprehensive protection against EHV-1 and its subtypes.