Mild disease, generally called West Nile fever, has some or all of the following symptoms:
These symptoms usually last for 3 - 6 days.
With more severe disease, the following symptoms can also occur, and need prompt attention:
Signs of West Nile virus infection are similar to those of other viral infections. There may be no specific findings on a physical examination to diagnose West Nile virus infection.
About 20 - 50% of patients may have a rash. Muscle weakness with other related symptoms are signs of a West Nile virus infection.
Tests to diagnose West Nile virus include:
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.
Rarely, a sample of blood or CSF may be sent to a lab to be cultured 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 and are not commonly used.
Tsai TF, Vaughn DW, Solomon T. Flaviviruses (Yellow fever, Dengue, Dengue hemorrhagic fever, Japanese encephalitis, West Nile encephalitis, St. Louis encephalitis, Tick-borne encephalitis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2005: chap 149.
Naides SJ. Arthropod-borne viruses causing fever and rash syndromes. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 405.
Bleck TP. Arthropod-borne viruses affecting the central nervous system. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 406.