Symptoms:

Mild disease, generally called West Nile fever, has some or all of the following symptoms:

• Fever
• Headache
• Back pain
• Muscle aches
• Lack of appetite
• Sore throat
• Nausea
• Vomiting
• Abdominal pain
• Diarrhea

These symptoms usually last for 3 to 6 days.

With more severe disease, the following symptoms can also be seen and require prompt attention:

• Muscle weakness
• Stiff neck
• Confusion or change in clarity of thinking
• Loss of consciousness

Signs and tests:

Signs of West Nile virus infection are similar to those of other viral infections. There is nothing that can be found on physical examination to diagnose West Nile virus infection.

A rash is present in 20-50% of patients. True muscle weakness in the presence of other related symptoms is suggestive of West Nile virus infection.

Tests to diagnose West Nile virus include:

• CBC
• Lumbar puncture and cerebrospinal fluid (CSF) testing
• Head CT scan
• Head MRI scan

However, the most accurate way to diagnose this infection is a serology test, which checks a blood or CSF sample for antibodies against the virus.

Rarely, a sample of blood or CSF may be sent to a lab to be cultured to look for the presence of West Nile virus. The virus can also be identified in body fluids using a technique called polymerase chain reaction (PCR). However, these methods can provide false negative results.