The West Nile virus (WNV) is a single-stranded RNA flavivirus first isolated in Uganda in 1937. The virus first appeared in the United States in 1999 and, to date, has been documented in almost every state. The routes of transmission include the mosquito, which serves as the vector, and birds (e.g., crows, sparrows, jays), which are the reservoir hosts. The infected mosquito can then carry the virus particles in its salivary glands and infect susceptible bird species as well as humans. Transmission can also occur during blood transfusions, organ transplants, exposure in a laboratory setting, or from mother to baby. There is no evidence that the virus can be spread by human-to-human casual contact or from handling infected birds.
Symptoms of WNV include fever, headache, neck stiffness, and skin rash. West Nile fever is the mild form of the infection, characterized by flu-like symptoms lasting only a few days with no long-term effects. West Nile encephalitis is the more severe form of the infection, characterized by encephalitis, meningitis, or both, which can lead to stupor, disorientation, coma, convulsions, and occasionally death.
Enzyme immunoassay is used to measure the antibodies IgM, which are produced early in the course of the infection, and IgG, which may not, however, be detectable for 4–5 days into the illness.
Collect either a blood or CSF sample. Not all laboratories are equipped to measure the antibody, and the sample may have to be forwarded to a commercial or public health laboratory.
Procedural Alert
The ELISA test can cross-react with other flaviviruses, such as yellow fever; therefore, additional serologic testing may be necessary to confirm a positive sample.
The CDC has made recommendations for both the employer and the employee (healthcare worker) when handling potentially infectious materials. The employer should provide training that addresses and reinforces how WNV is transmitted and the potential risks of exposure as well as personal protective equipment (PPE). The healthcare worker should use the PPE provided, minimize aerosol generation when handling specimens, and report any needlestick or sharps-related injury.
Pretest Patient Care
Explain purpose of and procedure for test.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Monitor and counsel the patient appropriately.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
Clinical Alert
Currently, there is no vaccination against WNV. Treatment is aimed at prevention of secondary infections (e.g., pneumonia and urinary tract infection), airway management, and supportive care.
Exposure to the St. Louis encephalitis virus may result in a false-positive test result for WNV.
Clinical Alert
In 2003, the CDC reported that 1000 blood donors tested positive for WNV, and as a result, about 24 people were infected from transfusions. All donated blood is now tested for WNV to detect and remove infected donations from the blood supply.
Normal
Negative for the WNV IgM antibody by ELISA
Negative for the WNV IgG antibody by ELISA
Clinical Alert
The blood test may be negative early in the course of the infection; however, within 8 days of the onset of symptoms, 90% of infected people will become positive.