Infectious Diseases A to Z – West Nile Virus

With this column, Elite Healthcare will compile an index of various infectious diseases, with occasional highlights of emerging conditions. 

West Nile Virus

General definition and information:

A viral infection that is transmitted by mosquitoes to humans and other animals, West Nile virus is the leading cause of mosquito-borne diseases in the continental United States, according to the Centers for Disease Control and Prevention (CDC). Although most people who are infected will not feel sick, fever and other symptoms can occur and can be fatal. 

Most symptomatic patients experience an acute systemic illness that includes headache, weakness, myalgia, or arthralgia, according to the CDC. Gastrointestinal symptoms and a transient maculopapular rash also are commonly reported. 

Most women known to have been infected with the condition during pregnancy have delivered infants without evidence of infection or clinical abnormalities, according to the CDC. A nationally notifiable condition, all cases of West Nile virus should be reported to local public health authorities in a timely manner, as reporting can assist local, state, and national authorities in recognizing outbreaks and implementing control measures to reduce future infections. Most patients are expected to completely recover, but fatigue, malaise, and weakness can last for months, and chronic neurologic deficits may arise. 

Causes & Modes of Transmission: 

Cases of West Nile virus occur during mosquito season, which starts in the summer and continues through fall. Mosquitoes that feed on infected birds become infected and then spread the virus by humans and other animals. Although rare, the condition can also be spread through exposure in a laboratory setting; blood transfusion or organ donation; and during pregnancy, delivery, or breastfeeding, according to CDC officials, who also remind healthcare providers that the virus is not spread through coughing, sneezing, or touching; through contact with live animals, from handling infected birds, or through eating infected birds or animals. Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.

As of late July, 34 states had reported a presence of West Nile virus infections among people, birds, or mosquitoes in 2019. Overall, 76 cases of West Nile virus disease in people have been reported to CDC. Of these patients, 70% were classified as having a neuroinvasive disease (such as meningitis or encephalitis) and 30% were classified as a non-neuroinvasive disease. In addition to other more common causes of encephalitis and aseptic meningitis, such as herpes simplex virus and enteroviruses, other arboviruses should also be considered in the differential etiology of suspected West Nile illness.

Treatment Strategies:

With no vaccine or specific antiviral treatments for West Nile virus available, patients can turn to over-the-counter pain relievers to reduce fever and relieve some symptoms. In severe cases, patients may require hospitalized to receive supportive treatment, such as IV fluids, pain medication, and nursing care. Drugs have been evaluated or empirically used for the disease, the CDC reports.1 The CDC also offers guidance on the condition as it relates to pregnancy and breastfeeding.2 Recent studies have additionally examined the possibility of West Nile virus infection and subsequent renal disease.3

Prevention Parameters: 

Trying to prevent West Nile virus means preventing mosquito bites. Patients should be reminded to use insect repellent and wear long-sleeved shirts. Environmental Protection Agency-registered insect repellents that have been proven safe are available online.3 Healthcare providers are also reminded that insect repellent should not be used on babies younger than 2 months old (or products containing oil of lemon eucalyptus or para-menthane-diol on children younger than 3 years old. Children should wear clothing that covers arms and legs as appropriate and strollers and carriers should be covered with mosquito netting. When sunscreen is also being used, patients should be instructed to apply the sunscreen first. Permethrin, an insecticide that kills or repels mosquitoes, can be used to treat clothing and gear (such as boots, pants, socks, and tents), or permethrin-treated clothing and gear can be purchased.

Screens, windows, and doors should be monitored in the home and repaired/replaced as necessary. Trash cans and other objects that can collect water should be emptied and cleaned on a regular basis. When traveling, patients should be encouraged to choose a hotel or lodging with air conditioning or screens on windows and doors and to sleep under a mosquito bed net if possible.4

Avoiding barehanded contact when handling any dead animal is also encouraged by the CDC, though the disease does not spread in this fashion. When disposing of a dead bird, gloves or double plastic bags should be use to place the carcass in a garbage can. And patients should be reminded to always follow instructions for cooking meat from either birds or mammals.


  1. West Nile virus disease therapeutics. CDC. 2018. Accessed online:
  2. Mother to baby during pregnancy, delivery, or breast feeding. CDC. 2018. Accessed online:
  3. Possible persistence of west nile virus infection. CDC. 2018. Accessed online:

  1. Insecticide-treated bed nets. CDC. 2019. Accessed online:

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