While rare, fatal West Nile virus has been reported in children

Reprinted with permission of AAP News

Ned Hayes, M.D., FAAP
AAP News - June, 2004


More than 9,000 patients with West Nile virus (WNV) illness were reported in the United States in 2003. Nearly 30% of these patients had neuroinvasive disease, such as encephalitis, meningitis or acute paralysis, and more than 250 deaths were reported.

While the risk of neuroinvasive and fatal WNV disease increases with age and is most common in adults over 50 years old, fatal encephalitis has been described in children. In 2002, 105 children with WNV neuroinvasive illness were reported, and more than 140 were reported in 2003. In 2003, one child who was born with lissencephaly died following a superimposed WNV infection, and a 14-year-old boy died following WNV encephalitis.

WNV is antigenically related to St. Louis encephalitis and Japanese encephalitis viruses and is transmitted to humans primarily through the bite of infected Culex mosquitoes.

Most WNV infections are asymptomatic, but about 20% of infected people will develop an acute fever accompanied by headache, malaise, fatigue, abdominal pain, and sometimes nausea and diarrhea. Less than 1% of infected people develop meningitis, encephalitis or acute paralysis, which resembles poliomyelitis.

WNV infection should be considered in the differential diagnosis of children who present with aseptic meningitis, encephalitis or acute paralysis during times of the year when mosquitoes are active. Transmission of WNV through blood transfusion and organ donation were first documented in 2002. Also in 2002, the first case of transplacental transmission was reported, as well as possible transmission through breast milk.

WNV infection can be diagnosed by detecting specific IgM antibody to WNV in patient serum and, if the patient has signs of neuroinvasive disease, in cerebrospinal fluid (CSF).

While IgM antibody may persist in some patients for more than a year, the presence of IgM in serum or CSF from a patient with compatible symptoms provides good evidence that the patient’s illness is caused by WNV infection. A second serum sample obtained two to three weeks after the first may help in diagnosing acute infection by showing at least a fourfold change in neutralizing antibody titer. Currently, no specific treatment has been shown to be effective against WNV infection.

In an initiative by blood collection and government agencies to protect the blood supply, more than 6.2 million units of blood were screened for presence of WNV by nucleic acid amplification tests in 2003. More than 1,000 possible WNV infections were prevented through this screening, but six transfusion-associated WNV infections were identified in 2003, indicating that a small risk of transfusion-associated transmission remains.

Spreading from east to west

Following the initial detection of WNV in New York City in 1999, the virus spread across the United States as well as into Canada, Latin America and the Caribbean.

The North American WNV epidemic in 2002 was the largest epidemic of arboviral encephalitis ever recorded in the Western Hemisphere, with 2,942 cases of WNV neuroinvasive disease reported. Approximately 9% of these patients died.

During 2003, more than 2,700 cases of WNV neuroinvasive disease and more than 250 deaths were reported. The focus of most intense WNV transmission moved farther westward in 2003, with the largest number of cases reported from states in the western plains and eastern edge of the Rocky Mountains.

Mother-to-child transmission

In 2002, a pregnant woman who developed WNV encephalitis transmitted the virus to her baby. At birth, the infant had a normal physical exam but on further investigation was found to have cystic destruction of cerebral tissue noted on cranial imaging studies, and chorioretinitis.

Three other infants born to women infected with WNV during pregnancy had no evidence of WNV infection and appeared to be normal at birth and at their 6-month health evaluations. One other infant was born prematurely following maternal WNV infection and preeclampsia, but the infant was not tested for evidence of WNV infection.

The Centers for Disease Control and Prevention (CDC) is following more than 70 women infected with WNV during their pregnancies in 2003. At press time, many of these women had not yet delivered, but more than 40 have delivered apparently normal infants without any evidence of congenital infection.

To better evaluate the implications of WNV infection during pregnancy, CDC is seeking the help of clinicians throughout the country to identify and evaluate mothers who become infected with WNV during pregnancy and infants born to such mothers. Clinicians are encouraged to report these cases to their state health departments or the CDC by calling (970) 221-6400.

CDC recently published guidelines for the clinical evaluation of infants born to mothers who were infected with WNV during pregnancy (www.cdc.gov/ncidod/dvbid/westnile/congenitalinterimguidelines.htm). These guidelines recommend careful evaluation for any dysmorphologic or neurologic abnormalities as well as hearing evaluations for all such infants. Infants who have abnormalities or laboratory evidence of WNV infection should be examined more intensively, including looking for cerebral lesions by CT scan, and for chorioretinitis by ophthalmologic exam.

CDC also is trying to gather more information on the risks of WNV transmission through breast milk. Clinicians who are aware of breastfeeding mothers who have WNV infection also are encouraged to report such cases. Until more data are available, and because the benefits of breastfeeding are well-documented, mothers should be encouraged to breastfeed even in areas of ongoing WNV transmission.

Preventing WNV infection

Pediatricians and other pediatric health care providers should help their patients understand the risk of WNV infection and methods to prevent infection. Children and pregnant women should be encouraged to apply insect repellent to skin and clothing when exposed to mosquitoes. The most effective repellents contain DEET, which can be used by children and pregnant women without adverse effects.

The Academy recommends using formulations containing no more than 30% DEET on infants older than 2 months of age and children. DEET should not be used on infants younger than 2 months old.

Vaccines against WNV are under development, but none are available yet for use in humans.

Dr. Hayes is a medical epidemiologist in the Division of Vector-Borne Infectious Diseases at the Centers for Disease Control and Prevention.