Equine immunity to viruses.

The research article explores the progress in understanding how horses’ immune systems respond to certain viral infections, and how this knowledge can inform the development of more efficient vaccines. It focuses mainly on three specific viruses: Equine Influenza Virus (EIV), Equine Herpes Virus-1 (EHV-1), and Equine Arteritis Virus (EAV).

Immunity to Equine Influenza Virus (EIV)

• The researchers have made strides in understanding the immune responses triggered by a horse’s body when infected with EIV. Such knowledge is essential in designing immunoprophylactic efforts – such as vaccines – against the virus.
• Once infected, a horse’s immune system can remember the virus, leading to long-term immunity. Scientists can use this knowledge to design vaccines that mimic this natural immune defense mechanism.
• Additionally, new adjuvants (substances that enhance the body’s immune response to an antigen) have been introduced that can stimulate cellular immunity — this means that they can spur the body’s cells to defend against the virus.
• Different methods have also been developed to promote the creation of virus-neutralizing (VN) antibodies at the mucosal surfaces of a horse’s body – these are areas like the nose and mouth, which are often the first point of contact with the virus.

Adenovirus Immunity and Vaccine Development

• The presence of VN antibodies, induced by adenoviruses, appears to protect against reinfection.
• The development of vaccines that can stimulate the production of these antibodies and provide protection from the virus is a crucial next step in this research.

Immunity to Equine Herpes Virus-1 (EHV-1)

• Unlike with EIV and adenoviruses, VN antibodies’ role in preventing EHV-1 is limited, as this virus spreads very swiftly through the body.
• However, antibody-mediated protection can be successful at the initial site of infection — typically the nasopharynx (back of the nose) and upper respiratory tract — indicating that vaccines targeting these areas may be effective.
• The researchers found that cellular immune responses, especially from cytotoxic T lymphocytes (CTLs), are essential not only in initial protection but also in recovery and immune surveillance.
• EHV-1-specific CTL precursors may correlate with immunity to this virus, suggesting that the future EHV-1 vaccine design should focus on how to stimulate CTL responses that recognize the virus.

Persistent Infection and Immunity to Equine Arteritis Virus (EAV)

• EAV infection induces strong immunity in horses, but stallions can continue to carry and spread the virus through the genital tract even after recovery.
• Although inactivated vaccines have been able to induce a potent immunity (which depends upon VN activity of serum antibody) to a first EAV infection, the control of these persistent infections is not yet fully understood.
• Like with EHV-1, CTLs are likely to play a crucial role in controlling persistent EAV infections, providing a possible area for future vaccine development.