Study of homologous and heterologous antibody response in California horses vaccinated with attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83).

This study focuses on the effectiveness of the Venezuelan equine encephalomyelitis (VEE) vaccine in California horses and how the presence of antibodies to other alphaviruses can affect the VEE antibody formation.

Research Methodology

The research involved a sample of 359 horses, all of which were vaccinated with the attenuated VEE vaccine (specifically, the TC-83 strain). The researchers conducted several tests on these vaccinated horses:

• Hemagglutination-inhibition (HI) tests to detect antibodies to VEE virus
• Blood tests on a sub-sample of 101 horses, conducted over a 12-month period
• Tests to detect the presence of VEE-neutralizing (Nt) antibodies and VEE complement-fixing (CF) antibodies

Findings

Within a month of vaccination, the majority of the horses in the sub-sample showed significant developments of VEE HI antibodies (84%), VEE Nt antibodies (87%), and VEE CF antibodies (78%). However, these percentages declined after a year, with 58% of the horses retaining VEE HI antibodies and 73% retaining VEE Nt antibodies.

A key finding was that the VEE CF antibody titers decreased drastically to 46% within 6 months after vaccination, and most horses tested negative for these antibodies after a year.

Antibodies and VEE Antibody Formation

Intriguingly, the presence of antibodies to other alphaviruses like western or eastern equine encephalomyelitis, had a suppressing effect on the formation of VEE antibodies. Despite this, the research found that the number of horses which developed VEE antibodies still exceeded the level generally thought necessary to suppress a VEE outbreak in a horse population.

Hemagglutination-Inhibition Tests and Neutralisation Tests

The relationship between the Hemagglutination-Inhibition (HI) tests and the Neutralization (Nt) tests for VEE antibodies was also examined, with an 88% correlation found between the two. This high correlation suggests a strong relationship between these two types of VEE antibodies.