History

Patients with West Nile virus (WNV) infection may or may not report a mosquito bite history, although the higher frequency of bites results in a higher probability of encountering the virus. The incubation period is typically 2-6 days but may range up to 14 days and may be longer in immunocompromised patients.^{[22, 23]} West Nile encephalitis (WNE) may start with constitutional symptoms, including the nonspecific symptoms of West Nile fever (eg, fever, headaches, muscle aches, joint pain, vomiting). Clinically, WNE is indistinguishable from other forms of viral aseptic meningitis.^[22]

Neuroinvasive disease manifests as fever and neurologic symptoms. A meningeal-type infection may manifest as typical meningeal symptoms (eg, neck stiffness, photophobia, headache).^{[15, 22]}Encephalitis may be more varied, possibly featuring mental status changes, confusion, lethargy, seizures, local paresthesia, and/or movement disorders.^{[15, 22]}These can manifest as extrapyramidal symptoms—coarse tremor, myoclonus, parkinsonian features such as bradykinesia, rigidity, and postural instability.^{[15, 22]}

In children and adolescents, neuroinvasive WNV disease most commonly manifests as meningitis-type symptoms; however, encephalitis-type symptoms are more common in older adults and elderly individuals.^[24]

Physical Examination

Most patients with symptomatic WNV infection are febrile.

Neurologic examination findings may vary depending on the severity and manifestations of the disease. The presence of Kernig or Brudzinski signs may indicate meningeal irritation in patients with meningitis. Tremor, either fine or coarse, may be encountered. Mental status is likely to be depressed in patients with encephalitis and can manifest as subtle increased sleepiness to frank coma. Confusion or neurocognitive signs may be present. Acute flaccid paralysis results in a poliomyelitis-like loss of tone and strength and may affect one or more extremities.

Examination findings may be remarkable for diffuse maculopapular rash.

Ocular findings may include chorioretinitis featuring “target-like” lesions, retinal hemorrhages, and vitreitis.^{[25, 26, 27]}

Differential Diagnoses

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Chung WM, Buseman CM, Joyner SN, Hughes SM, Fomby TB, Luby JP, et al. The 2012 West Nile encephalitis epidemic in Dallas, Texas. JAMA. 2013 Jul 17. 310 (3):297-307. [QxMD MEDLINE Link].
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Media Gallery

Common encephalitis associations.
Clinical features of arboviral encephalitis.
Differential diagnoses of meningoencephalitis.
The Culex mosquito, common in the eastern United States, is the primary vector responsible for infecting humans with West Nile virus. Prevention of West Nile virus is primarily directed at reducing the mosquito population from May to October and by taking precautions to limit human exposure during these months of high mosquito activity. Image courtesy of the Centers for Disease Control and Prevention.
The geographic distribution of the Japanese encephalitis servocomplex of the family Flaviridae, 2000. Image courtesy of the Centers for Disease Control and Prevention.
States reporting laboratory-positive West Nile virus infection in birds, mosquitoes, animals, or humans between January 1 and August 28, 2002. Image courtesy of the Centers for Disease Control and Prevention.

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Author

David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS Associate Professor of Medicine and Pediatrics, Adult and Pediatric Infectious Diseases, Rutgers New Jersey Medical School

David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS is a member of the following medical societies: American Academy of HIV Medicine, American Academy of Pediatrics, American College of Physicians, American Medical Association, HIV Medicine Association, Infectious Diseases Society of America, Medical Society of New Jersey, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Coauthor(s)

Justin R Hofmann, MD Resident Physician, Departments of Internal Medicine and Pediatrics, Rutgers New Jersey Medical School

Justin R Hofmann, MD is a member of the following medical societies: American Medical Association, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

John L Brusch, MD, FACP Corresponding Faculty Member, Harvard Medical School

John L Brusch, MD, FACP is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America; Fellow of the Royal College of Physicians, London

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Medical Association, Association of Professors of Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, Southern Society for Clinical Investigation

Disclosure: Nothing to disclose.

Additional Contributors

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Acknowledgements

Wesley W Emmons, MD, FACP Assistant Professor, Department of Medicine, Thomas Jefferson University; Consulting Staff, Infectious Diseases Section, Department of Internal Medicine, Christiana Care, Newark, DE

Wesley W Emmons, MD, FACP is a member of the following medical societies: American College of Physicians, American Medical Association, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, and International AIDS Society

Disclosure: Nothing to disclose.