Equine herpesvirus type 2: prevalence and seroepidemiology in foals

Abstract

Summary Whole blood and serum were collected from foals to determine the prevalence of Equine herpesvirus type 2 (EHV2) infection in foals, age at which infection can first be identified and serological responses to infection. 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 on PBMCs from 33 foals and EHV2 was isolated on both occasions in all but one foal (negative, then positive). Regression analysis of log2‐transformed reciprocal serum EHV2 virus neutralising (VN) titres revealed that in foals age 1–7 months, EHV2 VN antibody titre was positively correlated with age (r = 0.94). Paired serum samples were obtained from 58 foals, with the first samples collected age 1–6 months and the second 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 foal had a negative serum EHV2 VN titre immediately after birth. Each foal was positive for EHV2 in PBMC by age 45 days, with the earliest isolation 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 without clinical signs of respiratory disease, EHV2 was isolated from tracheal aspirates (1/20 foals) and PBMC (20/20 foals) and in 30 foals with such clinical signs, from trachea aspirates (20/30 foals: P<0.01) and from PBMC (30/30 foals). In one 6‐month‐old foal, EHV1, but not EHV2, was isolated from the tracheal aspirate, 3 months after EHV2 had been isolated from a tracheal aspirate. These results demonstrate a greater prevalence of EHV2 in lower respiratory secretions in foals with clinically apparent lower respiratory disease, but a cause and effect relationship between the virus and lower respiratory disease remains to be elucidated. It is noteworthy, however, that of virus isolations performed on 50 tracheal aspirates, a virus (EHV1) other than EHV2 was isolated only once.

Equine herpesvirus infections in yearlings in South-East Queensland

“…This observation warrant further investigations to establish the pathogenicity role of these EHV-5 strains. EHV-2, a member of the Gammaherpesvirinae closely-related to EHV-5, has been isolated in conjunction with other herpesviruses, in particular EHV-1 [30,44,46]. These authors reported cases of combined infection with members of the Alphaherpesvirinae (EHV-1) and Gammaherpesvirinae (EHV-2).…”

The Use of a Neutralizing Monoclonal Antibody to Detect Infections of Equine Herpesvirus Type 2 (EHV-2)

“…EHV-2 infection in young foals has been reported by others. 10,19 In the present study, samples were obtained from 11 foals from stable 1 3 times over a period of 6 months. All foals went through an active infection of EHV-2 (Fig.…”

Equid Herpesvirus 2-Associated Oral and Esophageal Ulceration in a Foal

“…13 Most EHV-2 infections are either not associated with clinical signs or with signs of nonspecific illness, such as upper respiratory difficulty, poor performance, malaise, pyrexia, lymphadenopathy, granulomatous dermatitis, and immune suppression. 15,17,20 Despite its uncertain pathogenicity, EHV-2 has been proposed to be associated with keratoconjunctivitis and respiratory disease in foals. 4,7,15,17,20 Equid herpesvirus 2 has also been proposed to play a role in transactivation and possibly reactivation of EHV-1 and EHV-4, 23 as well as modulation of foal immune responses, predisposing them to Rhodococcus equi pneumonia.…”

“…15,17,20 Despite its uncertain pathogenicity, EHV-2 has been proposed to be associated with keratoconjunctivitis and respiratory disease in foals. 4,7,15,17,20 Equid herpesvirus 2 has also been proposed to play a role in transactivation and possibly reactivation of EHV-1 and EHV-4, 23 as well as modulation of foal immune responses, predisposing them to Rhodococcus equi pneumonia. 16 As a cytopathogenic gammaherpesvirus, 21 EHV-2 is related to Human herpesvirus 4 (commonly known as Epstein-Barr virus).…”