The potential impact of a single amino-acid substitution on the efficacy of equine influenza vaccines.
BACKGROUND
The protection induced by an equine influenza (EI) vaccine strain depends on its antigenic relatedness to the challenge virus. Although the World Organisation for Animal Health (OIE) recommend that both Florida sublineage clade 1 (Fc1) and clade 2 (Fc2) viruses should be included in EI vaccines, Japanese EI vaccines have not, thus far, been updated to include a Fc2 virus.


OBJECTIVE
To evaluate the efficacy of antibodies raised against Japanese EI vaccine strains in the neutralisation of recent Fc2 viruses.


METHODS
Antigenic analysis.


METHODS
Virus neutralisation tests were performed using antisera from experimentally infected horses and from horses that had received a primary course of the currently available vaccines.


RESULTS
Antiserum raised against the Japanese EI vaccine strain, A/equine/La Plata/1993, exhibited poor cross-neutralising activity against the Fc2 viruses isolated recently in Ireland and the UK, which have the substitution of alanine to valine at position 144 in antigenic site A of the haemagglutinin gene. In contrast, the antiserum exhibited good cross-neutralising activity against the Fc2 viruses without the substitution. This finding was supported in experiments with antisera collected from vaccinated horses.


CONCLUSIONS
This suggests that the efficacy of the Japanese EI vaccine for some of the recent Fc2 viruses is suboptimal and that vaccines should be updated in accordance with the OIE recommendations.
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
T
T
Yamanaka
Virology Unit, Irish Equine Centre, Johnstown Naas Co., Kildare, Ireland.
A
A
Cullinane
Virology Unit, Irish Equine Centre, Johnstown Naas Co., Kildare, Ireland.
S
S
Gildea
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
H
H
Bannai
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
M
M
Nemoto
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
K
K
Tsujimura
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
T
T
Kondo
Epizootic Research Center, Equine Research Institute, Japan Racing Association, Shimotsuke, Japan.
T
T
Matsumura
D019943:Amino Acid Substitution; D000818:Animals; D006389:Hemagglutinins, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006734:Horse Diseases / Q000517:prevention & control*; D006736:Horses; D007252:Influenza Vaccines / Q000276:immunology*; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D009500:Neutralization Tests / Q000662:veterinary; D009976:Orthomyxoviridae Infections / Q000517:prevention & control*; D010802:Phylogeny
D006389:Hemagglutinins, Viral; D007252:Influenza Vaccines
cross-neutralisation; equine antisera; equine influenza; horse; vaccine update