Results on 1.5% agarose gel of reverse tranferase–polymerase chain reaction (RT-PCR) products stained with ethidium bromide and imaged under UV light. M: 100-bp marker; H1–4, H10: horses 1–4 and 10; (+): positive control viral RNA, 1.8 x 102 PFU amplified; (N-): negative control for nested PCR (-); negative control from single round RT-PCR. All horse samples and the positive control show a band at the expected size (134 bp), and negative controls show only the primers (below 100 bp).