EQUINE HERPESVIRUS TYPE-2 - PREVALENCE AND SEROEPIDEMIOLOGY IN FOALS

Whole blood and serum were collected from foals to determine the preva lence of Equine herpesvirus type 3 (EHV2) infection in foals, age at w hich infection ran first be identified and serological responses to in fection. Equine herpesvirus type 2 was isolated from peripheral blood mononuclear cells (PBMC) from 68 of 69 foals, 1-8-months-old, sampled once. Virus isolation was performed twice at intervals of 2-7 months o n PBMCs from 33 foals and EHV2 was isolated on both occasions in all b ut one foal (negative, then positive). Regression analysis of log(2)-t ransformed reciprocal serum EHV2 virus neutralising (VN) titres reveal ed that in foals age 1-7 months, EHV2 VN antibody titre was positively correlated with age (r = 0.94). Paired serum samples were obtained fr om 58 foals, with the first samples collected age 1-6 months and the s econd samples collected 2-4 months later, There were significant (P<0. 05) increases in mean VN titres to EHV2 in foals sampled initially at age 1-4. Eight foals had blood sampled prior to sucking and at age 7, 20, 30 and 45 days. Each foal was negative for EHV2 in PBMC and each f oal had a negative serum EHV2 VN titre immediately after birth. Each f oal was positive for EHV2 in PBMC by age 45 days, with the earliest is olation at 25 days. Tracheal aspirate fluid and peripheral blood were collected from 20 foals without clinical signs of respiratory disease and from 30 foals with clinical signs of lower respiratory disease. In 20 foals rrithout clinical signs of respiratory disease, EHV2 was iso lated from tracheal aspirates (1/20 foals) and PBMC (20/20 foals) and in 30 foals with such clinical signs, from trachea aspirates (20/30 fo als: P<0.01) and from PBMC (30/30 foals). In one 6-month-old foal, EHV 1, but not EHV2, was isolated from the tracheal aspirate, 3 months aft er EHV2 had been isolated from a tracheal aspirate. These results demo nstrate a greater prevalence of EHV2 in lower respiratory secretions i n foals with clinically apparent lower respiratory disease, but a caus e and effect relationship between the virus and lower respiratory dise ase remains to be elucidated, It is noteworthy, however, that of virus isolations performed on 50 tracheal aspirates, a virus (EHV1) other t han EHV2 was isolated only once.