Experimental infection with equid herpesvirus 3 in seronegative and seropositive mares.

Equine coital exanthema (ECE), caused by equid herpesvirus 3 (EHV-3), has been recognized as an economically significant venereal disease for years. However, no infection models on the natural host have been established. In order to set up an experimental infection protocol, seronegative and seropositive mares were topically inoculated in the perineal region with 4 × 10(6)TCID(50)/ml of EHV-3. Clinical signs were then evaluated by means of a designed scoring system, and body temperature was recorded daily. Virological, and serological studies were also performed. Typical ECE lesions, with clinical scores of 90, 92, 160 and 172, were observed in the four seronegative animals. Only mild ECE lesions were observed in the two seropositive mares, being the clinical scores 53 and 41. Both groups of mares shed the virus, but the duration of virus shedding was shorter and its intensity was lower in seropositive mares than in seronegative ones. Moreover, EHV-3 antibody response was detected in both seronegative and seropositive mares after experimental infection and re-infection, being more moderate in seropositive ones. As a conclusion, EHV-3 infection of mares was experimentally achieved in a reproducible manner. The typical lesions of ECE were observed after topical EHV-3 infection in seronegative mares, in association with virus excretion and neutralizing antibody kinetics.

Subclinical infection and periodic shedding of equid herpesvirus 3.

The temporary disruption of reproductive activities due to equine coital exanthema (ECE), caused by equid herpesvirus 3 (EHV-3), at thoroughbred breeding facilities and embryo transfer centres, has an appreciable economic impact. The aim of the present study was to estimate the prevalence of excretion of EHV-3 in mares without clinical symptoms under field conditions and the re-excretion patterns of the virus in two seropositive (presumably latently infected) mares maintained in isolation for 11 mo. The EHV-3 virus was detected in perineal-vaginal swabs by real time PCR in 14 (6%) of 220 thoroughbred mares without clinical symptoms at the time of breeding. In the two isolated mares, re-excretion of EHV-3 was demonstrated on two occasions, 3 mo apart (each for a 3 d interval) in one mare, and on only 1 d in the other mare. Antibodies against EHV-3 were identified by seroneutralization in 105 (48%) of the thoroughbred mares, and during the entire period in the two isolated mares. Therefore, the present study provided evidence of EHV-3 shedders in a healthy mare population under both field and isolation conditions. Furthermore, at least two periods of spontaneous EHV-3 reactivation and re-excretion in the presence of serum antibodies occurred in one mare in an 11 mo interval. These findings could assist in the design and implementation of measures to minimize the spread of EHV-3 and control ECE outbreaks.

Experimental reactivation of equine herpesvirus-3 following corticosteroid treatment.

State of latency, well known for several herpesviruses, has been proposed for equine herpesvirus-3 (EHV-3) and supported by epidemiological observations. No detailed assessment about reactivation, patterns of excretion and reexcretion has been formally reported. An experimental reactivation study by corticosteroid treatment in previously naturally infected horses was therefore carried out. Two polo mares with clinical and virologically confirmed history of equine coital exanthema were injected with dexamethasone and prednisolone on 3 successive days. Clinical signs, body temperature and clinical samples for virological and serological studies were obtained daily. Mares did not show any systemic clinical signs or hyperthermia. EHV-3 shedding, seroconversion and the presence of a small lesion were observed in one of the mares under study 2 weeks after corticosteroid treatment. The results demonstrate that this virus exhibits a latency-reactivation behaviour similar to that of other alpha herpesviruses. Reactivation of latency may have an important bearing on the appearance of clinical signs in mares and/or stallions during the breeding season without the actual evidence of transfer from mare to stallion or vice versa.

Standardization and validation of an agar gel immunodiffusion test for the diagnosis of equine infectious anemia using a recombinant p26 antigen.

We developed and validated an agar gel immunodiffusion test (AGID) test for the diagnosis of equine infectious anemia (EIA) using as antigen the p26 protein of equine infectious anemia virus (EIAV) produced in the Escherichia coli expression system. The developed rp26-AGID test showed an excellent diagnostic relative sensitivity (100%) and specificity (100%) compared to a commercial AGID assay when 1855 field serum samples were analyzed. In addition, the rp26-AGID demonstrated to be a precise assay with excellent repeatability and reproducibility. In the analytical sensitivity trial, positive sera showed nearly the same endpoint dilutions for both compared tests. No positive-reactions were observed with 35 serum samples with antibodies related to other endemic agents and also with severely hemolysed samples, demonstrating that the rp26-AGID has an excellent analytical specificity. Complete concordance with blind previous results from five proficiency test panels confirmed the capability of the assay of accurate detection of EIAV antibodies. This is the first time that a recombinant AGID assay able to identify EIAV infections has been standardized and validated in Argentina according to international guidelines. Taking into account the results obtained, the p26-AGID could be adopted as an official test method for the diagnosis and control of EIA in this country.