West Nile fever is an acute febrile disease caused by West Nile virus and transmitted by mosquitoes. West Nile virus can invade central nervous system and cause encephalitis, and is endemic in Africa, southern Europe, the Middle East, Central Asia, West Asia, and Oceania. The main clinical manifestations are fever, eruption, and lymphadenopathy.


Causes

West Nile fever virus is located in the salivary gland of mosquitoes. Mosquitoes transmit the virus to humans or animals while biting, leading to diseases or recessive infections. The virus enters brain parenchyma through blood-brain barrier, causing fever or encephalitis.

West Nile fever virus is sensitive to diethyl ether and sodium deoxycholate and is resistant to low temperature and dryness, and can be stored for several years at 4 °C by freezing and drying lyophilization.


Signs and Symptoms

The incubation period is 1 to 6 days, sometimes up to 20 days. Clinical manifestations are fever and encephalitis, with sudden onset and suddenly rising to 40 °C of body temperature, sometimes with chills.

Sudden fever is present. West Nile fever is manifested by diphasic fever, headache, eye pain, systemic muscle aches, sometimes accompanied by pharyngitis and nausea, vomiting, abdominal pain, diarrhea, loss of appetite, and other gastrointestinal symptoms. High fever can cause facial flushing and conjunctival congestion. The axillary and inguinal lymph node enlargements are present, but obvious tenderness is absent. About half of patients can erupt during or after fever. Light red roseola or maculopapular rash occurs in the back, neck, trunk, and limbs, persisting for about 1 week, spontaneously subsiding. Mild patients have only cold-like symptoms, and most patients can be spontaneously healed in 3 to 6 days.

A small number of patients, especially older adults, children, and adolescents, can develop encephalitis and meningitis after infection, which is characterized by sharply rising and persistent body temperature, severe headache, nausea, vomiting, drowsiness, as well as obnubilation, nuchal rigidity, abnormal nerve reflex, trembling limbs, spasm, convulsions, coma, difficulty breathing, and even respiratory circulatory failure.

Occasionally, skin blisters, acute anterior poliomyelitis, myocarditis, pancreatitis, and hepatitis can occur. Lymph node enlargement often lasts for several months.


Diagnosis

On the basis of medical history, clinical presentations, antibodies detected in serology, and virus isolated from blood or cerebrospinal fluid, a diagnosis can be provided.


Treatment

There are currently no specific treatments for West Nile virus. Symptomatic and supportive treatments can be applied to mild patients. Intensive treatment may be necessary for patients with encephalitis.