West Nile Fever – risk factors, transmission, prevention and more

West Nile infection is a viral infection that primarily affect birds. Humans get affected after getting bitten by mosquitos that carry the virus from an infected bird.

West Nile virus was first identified in 1937 in Uganda. This term became popular as it was reported in United States and is now a seasonal epidemic with peak activity during the months August – September.  Huge outbreaks were reported in Canada, Europe, Russia, Greece and Israel.

Risk factors

  • Mosquito bite – as it is spread by the vector mosquito
  • Summer season – cases are more reported during this season
  • Age above 50
  • Blood transfusions
  • Organ transplantation


The transmission is commonly called as bird – mosquito – human cycle.  A bird infected with this virus carries it and the virus can circulate in its bloodstream. A mosquito that bits the bird, now becomes the carrier. When this mosquito bites a human it is then transmitted to him from the salivary gland into the bloodstream. The mosquito can spread the virus to other birds or a nimals through bites. Mosquitos that transmit West Nile virus is usually of Culex species.

west nile
west nile transmission cycle

The virus is not transmitted through kissing, touching or sharing utensils with the infected person.

Symptoms of West Nile virus infection

The symptoms usually develops within 15 days of mosquito bite and is progressed into West Nile fever.

  • Fever
  • Muscle aches
  • Body pain
  • Headache
  • Decreased appetite
  • Rash

Severe disease: in certain condition the virus travels through the blood and affect the brain and spinal cord and develop severe neuroinvasive disease. Immunocompromised patients are at high risk of developing severe disease. Symptoms of severe disease include – convulsions, coma, paralysis and disorientations. Long lasting neurological abnormalities can also develop.


The diagnosis is made based on the possible symptoms and the patient’s history to get infected with the WN infection. Antibody testing is also done to determine the presence of antibodies that are produced in response to foreign substances. The blood test is also done to detect the presence of virus.

In cases with central nervous system involvement the CSF usually presents an elevated protein (<150 mg/dL). MRI shows abnormal findings.

A positive MAC-ELISA test also confirms diagnosis.


WN virus infection generally resolve on its own. Severe cases require hospitalizations.


The best way to prevent WN virus infection is to prevent and resist mosquito bites. Mosquito is most active at dawn and dusk, so be more cautious during these time. While in outdoors use mosquito repellents that contain DEET, oil of lemon eucalyptus, IR3535 and picardine. Long sleeves shirts and pants can also help in preventing bites.

Community mosquito/vector control programs should be initiated. Endemic areas should be sprayed with mosquito repellent chemicals. Proper drainage of stagnant water should be ensure.

There is no human vaccine for West Nile virus.

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