WEST NILE VIRUS (WNV) is an RNA arbovirus of the Flaviviridae family.1,2 Transmitted to humans by mosquitoes, the virus first hit the United States in Queens, New York, in 1999. WNV is now the leading cause of domestically acquired arboviral disease in the country.2 An understanding of WNV, its signs and symptoms, prevention, and treatment options remains important for nurses.
WNV was first identified in Uganda in 1937 and has since spread across the world with large outbreaks occurring in Eastern Europe, Northern Africa, Russia, and the United States.3,4 It's now been identified in 47 states with the CDC reporting 2,038 cases within the United States.5 Of these cases, 1,140 (56%) were classified as neuroinvasive (meningitis, encephalitis), while the remaining 44% were classified as nonneuroinvasive. The highest incidence occurs in the west, central, and mountain regions of the United States. Between 1999 and 2015, the states with the highest incidence of WNV infection were California (5,589), Colorado (5,213), Texas (4,907), Nebraska (3,558), Illinois (2,214), and South Dakota (2,208).6
WNV is primarily transmitted through the bite of mosquitoes that have fed on infected birds; 65 mosquito species have been positively identified as carriers.7 Although cases have been identified throughout the year, most transmissions occur during the summer and fall.2
Mosquito bites are the primary method of infection, though some infections have been transmitted through blood transfusions, organ transplants, percutaneous or conjunctival exposure, unidentified exposure within a dialysis center, and from mother to baby in utero or via breast milk.8-13 While birds are the primary reservoir for WNV, people are unlikely to acquire the disease through handling sick or dead birds.
Since 2003, the blood supply within the United States has been screened for WNV.14 In 2016, blood donation centers identified approximately 271 cases of infected donations that were effectively screened and removed from the blood supply.15 A small risk remains within donated blood pools because donations with low viremia levels may not be detected by the nucleic acid testing used by blood centers.13 No case of tick-borne transmission of WNV within the United States has been documented, though ticks have been identified as carriers in Africa and Asia.8
Signs and symptoms
WNV infection has a typical incubation period of 2 to 14 days (though longer periods have been documented), with an estimated 60% to 80% of all infections being asymptomatic.16 For symptomatic cases, WNV infections are generally divided into nonneuroinvasive and neuroinvasive.
- Patients with nonneuroinvasive infections will experience an acute febrile illness characterized by headache, myalgia, arthralgia, nausea, and vomiting.2,17 Patients may complain of anorexia, eye pain, lymphadenopathy, and, in more severe cases, a maculopapular rash. Most patients recover completely in these cases, though fatigue and weakness can last for months after recovery.18
- Neuroinvasive infection, which is thought to affect less than 1% of all those who contract it, presents as meningitis, encephalitis, or acute flaccid paralysis.2 Besides the signs and symptoms described above, patients experience severe muscle weakness; maculopapular rash to the neck, trunk, arms, and legs; seizures; mental status changes; ataxia; and focal neurologic deficits.2,8,19 Meningitis associated with WNV resembles aseptic meningitis caused by other viruses; WNV-related flaccid paralysis is clinically identical to poliovirus-associated poliomyelitis.2,19 Mortality for patients with neuroinvasive WNV infection is 10%.12
As with Zika virus, WNV has also been associated with Guillain-Barré syndrome.1,2,19 Rare complications associated with WNV infection include myocarditis, cardiac dysrhythmias, rhabdomyolysis, optic neuritis, uveitis, orchitis, pancreatitis, and hepatitis.2,8,20 The more serious forms of WNV infection can present in patients of any age, but the risk is higher in older adults; those who are immunocompromised or have medical disorders such as cancer, diabetes, hypertension, or kidney disease; and those with organ transplants.2,8
Diagnosing WNV infection can be difficult due to its similarities to other arboviral/viral infections. Currently, the immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay from the CDC or one of the four FDA-approved commercially available tests is used to identify WNV IgM antibodies.2 These assays should be used in conjunction with specific data collected regarding the patient and his or her recent history, including location of residence and recent travel, onset of signs and symptoms, and vaccination history.2 Additionally, the plaque reduction neutralization test and reverse transcription-polymerase chain reaction tests can help diagnose WNV infection.16 This information can also help rule out similar diseases such as dengue and yellow fever.
Treatment and surveillance
No cure or specific treatments are available for WNV infection; patient care is supportive.21 For mild cases, supportive care includes over-the-counter medications for fever control and pain relief. In severe cases, patients may require hospitalization for I.V. fluid administration, medication to control fever and pain, and possibly respiratory support.8 For patients with meningitis, encephalitis, or flaccid paralysis secondary to infection, treatment is based on guidelines for managing those disorders. After recovery, patients are conferred immunity that gradually decreases over time.9
WNV infection is a nationally notifiable disease that requires reporting by state and local health departments to the CDC through an electronic system called ArboNET. This passive system assists in the tracking, identification, and response to potential outbreaks throughout the country and allows researchers to gain a better understanding of related disease data. Originally developed to track WNV, this network now provides surveillance for all arboviral diseases, including chikungunya, Powassan, and Zika viruses.22
Prevention centers around mosquito control and prevention of bites. Personal mosquito control involves eliminating potential breeding sites by removing standing water in and around the home and the use of screens over doors and windows.23 Additionally, community health departments in areas with a history of WNV conduct vector assessment and testing during the warmer months of the year.
Prevention of bites begins with proper clothing choice, including wearing light-colored cotton clothing that's loose-fitting and fully covers the limbs.1 Limiting the time outdoors during dawn and dusk, when mosquitos are most active, is helpful, as is the use of synthetic or plant-derived oil repellents on skin and clothing. Those useful for application to the skin include DEET (20%-30%) (N,N-diethyl-m-toluamide/N,N-diethyl-3-methylbenzamide), Picaridin (1-piperidinecarboxylic acid, 2-(2-hydroxyethyl)-1-methylpropylester), and IR3535 (3-[N-butyl-N-acetyl]-amino-propionic acid ethyl ester).1
Permethrin, when applied to clothing or tents, has been found to reduce the incidence of bites by 36%.1,24 Other plant-based repellents include oil of eucalyptus and citronella. The effectiveness of these products diminishes over time, on contact with water, or if used in conjunction with sunscreen. Periodic reapplication is recommended.1 At this time, no human vaccine is available for WNV, though numerous preclinical studies and eight clinical trials have been conducted.25
1. Simon RB, Carpenetti TL. Zika virus: facing a new threat. Nursing
2. Centers for Disease Control and Prevention: Division of Vector-Borne Diseases. West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control (4th revision). U.S. Department of Health and Human Services. 2013. http://www.cdc.gov
3. McMullen AR, May FJ, Li L, et al Evolution of new genotype of West Nile virus in North America. Emerg Infect Dis
4. Marcantonio M, Rizzoli A, Metz M, et al Identifying the environmental conditions favouring West Nile virus outbreaks in Europe. PLoS One
5. Centers for Disease Control and Prevention. West Nile virus home. Preliminary maps & data for 2016. 2017. https://http://www.cdc.gov
6. Centers for Disease Control and Prevention. West Nile virus disease cases and deaths reported to CDC by year and clinical presentation, 1999-2015. http://www.cdc.gov
7. Centers for Disease Control and Prevention. West Nile virus disease and other arboviral diseases—United States, 2011. MMWR Morb Mortal Wkly Rep
8. McKinney M, ed. West Nile virus infection. In: Lippincott's Guide to Infectious Diseases
. Philadelphia, PA: Wolters Kluwer Lippincott Williams & Wilkins; 2011:107-108, 348–349.
9. Centers for Disease Control and Prevention. West Nile virus: general questions about West Nile virus. 2015. http://www.cdc.gov
10. Iwamoto M, Jernigan DB, Guasch A, et al Transmission of West Nile virus from an organ donor to four transplant recipients. N Engl J Med
11. Hinckley AF, O'Leary DR, Hayes EB. Transmission of West Nile virus through human breast milk seems to be rare. Pediatrics
12. Practice Committees of the American Society for Reproductive Medicine; Society for Assisted Reproductive Technology. Position statement on West Nile virus: a committee opinion. Fertil Steril
13. Petersen LR. Epidemiology and pathogenesis of West Nile virus infection. 2015. UpToDate.com.
14. Centers for Disease Control and Prevention. Detection of West Nile virus in blood donations—United States, 2003. MMWR Morb Mortal Wkly Rep
15. Advancing Transfusion and Cellular Therapies Worldwide. West Nile Virus Biovigilance Network. 2016. http://www.aabb.org
16. Petersen LR. Clinical manifestations and diagnosis of West Nile virus infection. 2017. UpToDate.com.
17. Zou S, Foster GA, Dodd RY, Petersen LR, Stramer SL. West Nile fever characteristics among viremic persons identified through blood donor screening. J Infect Dis
18. Centers for Disease Control and Prevention. West Nile virus: Symptoms and Treatment. 2015. https://http://www.cdc.gov
19. Sejvar JJ, Marfin AA. Manifestations of West Nile neuroinvasive disease. Rev Med Virol
20. Hayes EB, Sejvar JJ, Zaki SR, Lanciotti RS, Bode AV, Campbell GL. Virology, pathology, and clinical manifestations of West Nile virus disease. Emerg Infect Dis
21. Asadi L, Bunce PE. West Nile virus infection. CMAJ
22. Hadler JL, Patel D, Nasci RS, et al Assessment of arbovirus surveillance 13 years after introduction of West Nile virus, United States. Emerg Infect Dis
23. Ostroff SM. West Nile virus: too important to forget. JAMA
24. Boulware DR, Beisang AA 3rd. Passive prophylaxis with permethrin-treated tents reduces mosquito bites among North American summer campers. Wilderness Environ Med
25. Amanna IJ, Slifka MK. Current trends in West Nile virus vaccine development. Expert Rev Vaccines