Symptoms:

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

• Abdominal pain
• Diarrhea
• Fever
• Headache
• Lack of appetite
• Muscle aches
• Nausea
• Rash
• Sore throat
• Swollen lymph nodes
• Vomiting

These symptoms usually last for 3 - 6 days.

More severe forms of disease, which can be life threatening, may be called West Nile encephalitis or West Nile meningitis, depending on what part of the body is affected. The following symptoms can occur, and need prompt attention:

• Confusion or change in ability to think clearly
• Loss of consciousness or coma
• Muscle weakness
• Stiff neck
• Weakness of one arm or leg

Signs and tests:

Signs of West Nile virus infection are similar to those of other viral infections. There may be no specific findings on a physical examination. However, up to half of patients with West Nile virus infection may have a rash.

Tests to diagnose West Nile virus include:

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

The most accurate way to diagnose this infection is with a serology test, which checks a blood or CSF sample for antibodies against the virus. More rapid techniques using polymerase chain reaction (PCR) may be used.