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West Nile Virus Infection


West Nile Virus infection, also known as West Nile fever, occurs after being bitten by a mosquito that carries the virus. The virus belongs to the same family of viruses that cause dengue fever and yellow fever. The majority of the people infected by this virus do not develop any symptoms. If they do, the symptoms are mild in nature and recover in a few days. Rare cases of these infections can lead to severe complications of the brain and spinal cord. 


West Nile infection is caused by the West Nile virus, which is transferred to human beings via culex mosquito bites. The mosquitoes carry this virus after biting infected birds and then spread it to human beings. If this virus enters into your blood, you can spread this infection to others by blood transfusion or sharing contaminated syringes or needles.

There is also evidence of transmission of this virus from a pregnant woman to her baby during pregnancy or breastfeeding. However, the reported cases are not strong enough to support this evidence.

Risk Factors And Epidemiology

West Nile virus infection can develop in any person, but older people are at a higher risk. This is because they have a weakened immune system compared to adults. Those with a weakened immune system due to diseases or medical treatment may also develop this infection.

People living in the regions of active infection are also at risk. This virus has been reposted across the majority of the states of the United States. The rate of infection is higher from July to September. Apart from the US, this virus has also been reposted in Asia, Africa, the Middle East, and Europe.

Among all cases of West Nile virus infection, only 1% of patients develop a serious infection. Women are more likely to be infected by this virus. 

Signs And Symptoms

After being bitten by a carrier mosquito, it can take from 3 to 14 days for symptoms to appear. Around 80% of people remain asymptomatic. The symptoms of this infection are mild, which include fever, rash, vomiting, headache, body ache, diarrhea, and fatigue.

In very rare cases, a serious infection develops, which presents with neurological signs and symptoms. These include high-grade fever, severe headache, neck stiffness, disorientation, tremors, seizures, numbness, vision loss, partial paralysis, or coma


It is difficult to diagnose West Nile virus infection on the basis of symptoms alone. This is because a mild infection caused by this virus can resemble the symptoms of influenza or the common cold. Your doctor will require a brief medical and traveling history. This is followed by a blood test. If you have been infected, antibodies against this virus will appear in your blood after a few days.

In case of a serious infection, more invasive tests may become necessary. This includes lumbar puncture to screen cerebrospinal fluid for indicators of infection. A brain MRI or electroencephalography (EEG) may be done to visualize any damage to the brain and spinal cord. 

Differential Diagnosis

West Nile virus infection needs to be differentiated from other illnesses that cause similar symptoms. These include infections caused by influenza, rhinovirus, enterovirus, coxsackievirus, echovirus, and herpes virus. Other diseases that cause severe headaches or neck stiffness must be differentiated from this infection. 


Treatment of West Nile virus infection is focused on symptomatic care. Although some drugs are being studied, there are no medicines to cure the West Nile virus yet. If you have been infected with this virus, the best thing to do is to rest well and drink plenty of fluids to keep your body replenished. It can take one to two weeks to fully recover from this infection.

Medicines are generally not prescribed for West Nile virus infection unless you have a high fever or pain. Antipyretics such as acetaminophen can be taken for fever. Over-the-counter analgesics such as ibuprofen or diclofenac can be taken to reduce pain. Precaution must be taken while taking aspirin because aspirin can cause complications if you have been infected with another virus with resembling symptoms. 


The prognosis of West Nile virus infection is really good. Majority of the patients achieve complete recovery after one to two weeks without developing any complications. People with serious infections need to be kept on a close check for any neurological abnormalities. Fatality due to the West Nile virus is very rare and occurs if the virus has caused severe damage to the brain, spinal cord, and other vital organs. 


The most common neurologic complications caused by West Nile virus infection are meningitis and encephalitis. These complications are rare to develop, but they can cause inflammation of the brain and its associated tissues if they do. Other rare complications include West Nile poliomyelitis, cerebellar dysfunction, Parkinson’s disease, cranial nerve palsy, deep vein thrombosis, hearing loss, hepatitis, and other organ dysfunctions. 


There is no vaccine available yet against the West Nile virus. Preventive measures should be taken to reduce the chances of being bitten by a carrier mosquito. Wear clothes covering maximum skin regions and use a mosquito repellant cream or spray. Since these mosquitos breed in tropical areas, avoid areas with standing water or unsanitary collection of water. Limit your outdoor time during dawn or dusk. If you require a blood transfusion, make sure that the blood you’re receiving is free of infections.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on June 03, 2023.



West Nile virus (who.int)


West Nile Virus Infection | Microbiology Spectrum (asm.org)


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