Detection of equid alphaherpesvirus 1 in serum samples collected from infected horses

Equid alphaherpesvirus 1 (EqAHV1; <i>Orthoherpesviridae</i>, <i>Varicellovirus equidalpha1</i>) spreads by viremia to susceptible organs. Because EqAHV1 circulates in the bloodstream in a cell-associated manner, serum samples are not considered valuable for detecting EqAHV1 and have therefore not been tested by highly sensitive detection methods such as real-time PCR (rtPCR). We investigated whether EqAHV1 could be detected by this method in equine serum samples. We performed rtPCR on archived sera and peripheral blood mononuclear cells (PBMCs) collected from 3 horses experimentally inoculated with EqAHV1. Acute-phase field sera from 40 febrile horses, including 11 positive for EqAHV1 on antibody ELISA, were also tested by both standard rtPCR and direct rtPCR without nucleic acid purification. EqAHV1 was detected by standard rtPCR in the PBMCs of the experimentally infected horses for 3-6 d and in the serum of these horses for 5-7 d. Six of the 11 ELISA-positive acute-phase field sera were positive on standard rtPCR, whereas the remaining were negative. All 6 of these samples were positive on direct rtPCR without nucleic acid purification. These results suggest that serum samples can be used to detect EqAHV1; however, false-negatives may result from low viral gene copy numbers.