How should equine herpesvirus myeloencephalopathy be tested?

Equine herpesvirus myeloencephalopathy (EHM) is a serious neurological condition caused by equine herpesvirus type 1 (EHV-1). The diagnosis of EHM can be complex, as clinical signs may mimic other conditions. Testing for EHM typically involves culturing samples, particularly from the nasal cavity or blood, to confirm the presence of the virus.

Culturing samples allows for the direct detection of the virus, which is crucial for an accurate diagnosis. This method enables veterinary professionals to isolate the virus from the horse’s respiratory secretions or from tissues, providing definitive evidence of infection. While serological testing can indicate exposure to the virus, it won't confirm active disease, as it detects antibodies rather than the virus itself.

Clinical observation provides important information about the horse's health status, but it does not definitively diagnose EHM. Similarly, comparative blood tests can help assess various health parameters but are not specific enough to confirm EHV-1 infection.

Thus, culturing samples is the most effective method for testing for equine herpesvirus myeloencephalopathy, making it the correct answer for the question.