Equine herpesvirus 2 (EHV-2) infection in thoroughbred horses in Argentina

Abstract

Background: Equine herpesvirus 2 is a gamma-herpesvirus that infects horses worldwide. Although EHV-2 has been implicated in immunosuppression in foals, upper respiratory tract disease, conjunctivitis, general malaise and poor performance, its precise role as a pathogen remains uncertain. The purpose of the present study was to analyse the incidence of EHV-2 in an Argentinean horse population and correlate it with age and clinical status of the animals.

Results: A serological study on 153 thoroughbred racing horses confirmed the presence of EHV-2 in the Argentinean equine population. A virus neutralization test showed a total of 79.7 % animals were sero-positive for EHV-2. An increase in antibodies titre with age as well as infection at earlier ages were observed.EHV-2 was isolated from 2 out of 22 nasal swabs from horses showing respiratory symptoms. The virus grew slowly and showed characteristic cytopathic effect after several blind passages on RK13 cells. The identity of the isolates was confirmed by nested PCR and restriction enzyme assay (REA).

Conclusion: This is the first report on the presence of EHV-2 in Argentina and adds new data to the virus distribution map. Though EHV-2 was isolated from foals showing respiratory symptoms, further studies are needed to unequivocally associate this virus with clinical symptoms.

Figure 1

Nested PCR on nasal swab samples from foals with respiratory symptoms. Nested PCR amplification products from two equines (E1 and E2) showing respiratory symptoms were analysed by gel electrophoresis. DNA was extracted from original nasal swabs; DNA from the suspension was used as template in the first round. Genomic DNA from EHV-2 strain LK was used as a PCR positive control (PCR+) and H₂0 as negative control (PCR -). DNA marker φX-174 Hae and λ-RF/Hind III is seen in lane M.

Figure 2

Restriction enzyme assay profile of EHV-2 isolates and reference strains. EHV-2 isolates (E1 and E2), EHV-2 strains H40, T400, and LK4, and EHV-5 strain P48, were amplified in RK-13 cell monolayer. Viral DNA was purified by Genomic-tip 20/G column, digested with Hind III and Eco RI and analysed by gel electrophoresis. DNA marker φX-174 Hae III and λ-RF/Hind III is seen in lane M.