Cross-protective immunity between equine encephalomyelitis viruses in equids

Area of Science:

• Veterinary Virology
• Immunology
• Equine Infectious Diseases

Background:

• Equine encephalomyelitis viruses, including Eastern Equine Encephalomyelitis (EEE), Western Equine Encephalomyelitis (WEE), and Venezuelan Equine Encephalomyelitis (VEE), pose significant threats to equine health.
• Previous epizootics, such as the 1971 VEE outbreak in Texas, suggested potential cross-protective immunity between different encephalomyelitis viruses in equids.

Purpose of the Study:

• To investigate the cross-protective immunity conferred by prior immunization with EEE or WEE viruses against a challenge with a virulent VEE virus strain in equids.
• To quantify the impact of pre-existing immunity on VEE virus viremia, mortality, and antibody responses.

Main Methods:

• Equids were experimentally inoculated with EEE or WEE viruses to establish seropositivity.
• Surviving EEE and WEE virus-seropositive equids, along with non-immunized controls, were subsequently challenged with an epizootic strain of VEE virus.
• Mortality rates, VEE virus viremia levels, and plaque-neutralizing antibody responses were monitored post-challenge.

Main Results:

• EEE virus-seropositive equids exhibited complete survival (0% mortality) following VEE virus challenge, while WEE virus-seropositive equids showed reduced mortality (40%) compared to controls (90%).
• Viremia levels of VEE virus were significantly lower in both EEE and WEE virus-seropositive equids compared to non-immunized controls.
• Neutralizing antibody responses to VEE virus in previously immunized equids were comparable in onset and titer to those in control equids, with 19 of 27 equids developing detectable antibodies.

Conclusions:

• Prior immunization with EEE or WEE viruses induces significant cross-protective immunity in equids against virulent VEE virus challenge.
• The findings support the hypothesis of shared antigenic components or cross-reactive immune mechanisms between these equid encephalomyelitis viruses.
• This study validates field observations and provides experimental evidence for cross-protection, relevant for understanding and managing VEE outbreaks.