West Nile virus (WNV) is a zoonotic pathogen that affects birds, horses, and humans, as well as other vertebrates worldwide. Maintained in a mosquito-bird-mosquito transmission cycle, WNV infection in birds may lead to death within 24 h of symptom onset. In humans and horses, WNV is responsible for causing fever, meningitis, and encephalitis, with long-term sequelae, or death a possibility. Due to its nonspecic clinical presentations, it is vital that specic and sensitive laboratory methods are available and applied for differential diagnosis of West Nile disease. This will help prevent the further spread of this emerging disease.