West Nile Virus (WNV) is a fairly rare infection, yet it has been on the rise in North America since the turn of the century, subsiding occasionally and then going through an outbreak. Between 1999 and 2003, US states including California, Arizona, Colorado, Texas, Illinois, New York, Nebraska, North Dakota, South Dakota, and Louisiana, reported increases in the number of cases. In 1999, there was a sharp increase in the new number of WNV cases in New York City.
Most outbreaks, on the other hand, have occurred in the great plains region. As of November 2017, the US Centers for Disease Control and Prevention reported 1,832 cases of WNV in the United States. Of these, 1,210 (66%) have been neuroinvasive disease, meaning that the cases including inflammation of the brain (encephalitis), or inflammation of the layers of connective tissue surrounding the brain (meningitis). The remaining 622 cases were less severe.
WNV is one of many viruses that can make humans sick and is spread by mosquitoes. In the case of WNV, the mosquito that spreads the virus is part of the genus Culex, usually the species Culex pipiens. 80 percent of people who become infected with WNV do not get sick. Most of the remaining 20 percent develop flu-like symptoms such as fever, headache, and fatigue, plus rash. In some of these cases, fatigue can persist for many months. 1 in 150 people infected with WNV develop not only the flu-like symptoms and rash, but also meningitis (inflammation of the layers surrounding the brain) and/or encephalitis (inflammation of the brain). Pregnancy is not thought to increase the risk of you getting sick from WNV following a bite from C. pipiens, but there have been cases of WNV infection in pregnant women.
If you or your doctor suspect that you might be infected with WNV, your doctor will draw a sample of cerebrospinal fluid (CSF). To make this test possible, a computed tomography scan (CT) of the head is performed to assure that the pressure of CSF around the brain and spinal cord is not elevated. Then, a procedure called “lumbar puncture” is performed, in which a needle is inserted through the back of the lower spine in a very safe way to draw a sample of the fluid that surrounds the spinal cord. The lumbar puncture is performed 3-8 days after the start of symptoms and the resulting CSF sample then is tested to see if it contains antibodies against the WNV. Because there are different classes of antibodies, there are different ways that the test could come out. Some results can demonstrate an infection in the past, while others can demonstrate the possibility of either an old or a new WNV infection. If testing of the CSF sample shows high levels of a type of antibody called IgM against WNV, and if it does not show a type of antibody called IgG against the same virus, then it is likely that you has been infected recently with WNV. If the test comes out a different way, however, more testing will be needed on CSF samples, blood samples, or both. This testing may involve examination of body cells for changes that are caused by WNV living inside and tests to determine whether particular genes of the virus are turned on, and thus creating a molecule called RNA.
It is possible for WNV to enter the fetus from the mother, but the risk of this happening appears to be extremely low. A handful of WNV cases have been reported in newborns, and pregnant women certainly should reduce their risk of getting WNV virus in the first place. This means avoiding mosquitoes, applying insect repellent, and wearing protective clothing.
There is no specific treatment for WNV. Treatment, thus, is supportive, meaning that the doctor will give you fluids as well as medications to combat pain and fever (acetaminophen in the United States and paracetamol in several other countries). These drugs are considered safe during pregnancy. Acetaminophen and paracetamol are also safe to be used during breastfeeding. In the past, some mothers have been concerned about insect repellent possibly affecting a nursing infant. However, the risk of insect repellent entering breast milk is less than the risk of the virus itself entering breast milk, although both scenarios are unlikely. Therefore, the take-home message is to take your medication and to use insect repellent.