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West Nile Virus Symptoms and Transmission

West Nile Virus Symptoms and Transmission

October 28, 2020

West Nile Virus is Not Just a Foreign-Country Disease

Recent news reports state that north Texas is currently seeing an increase in mosquitoes positive for West Nile Virus. The symptoms of West Nile infection in humans resemble some of those associated with COVID-19. So, while a test for COVID-19 might be negative, the possibility of infection with West Nile Virus should not be overlooked.

According to the Centers for Disease Control and Prevention (CDC), only about one in five people infected will experience noticeable West Nile virus symptoms. A small percentage of people infected with the virus (about one in 150) develop serious diseases affecting the central nervous system, like inflammation of the brain (encephalitis) or inflammation of the membranes around the brain and spinal cord (meningitis).

How is West Nile Virus Transmitted?

The CDC states that West Nile Virus is the most frequent cause of mosquito-borne illness in the continental United States. A member of the family Flaviviridae, specifically the Flavivirus genus, the West Nile virus is accompanied in this category by other viruses that cause Zika virus disease, dengue fever and yellow fever. West Nile virus is primarily spread through mosquitoes in the Culex species, with birds serving as an amplifier host.

In nature, when some birds are infected with West Nile virus through the bite of an infected mosquito, they develop high levels of the virus in their bloodstream. The virus is then transferred to other mosquitoes that bite these birds. The infected mosquitoes pass the virus along to other birds as well as to humans, horses and other mammals that they bite. Humans, horses and other animals are called “dead-end hosts,” because they do not develop high levels of the virus in their bloodstream and therefore don’t pass the virus along to other biting mosquitoes.

In a very small number of cases, West Nile virus can be transmitted through laboratory exposure, blood transfusions and organ donation, or passage from mother to child during pregnancy, delivery or breastfeeding.

west nile chart

What are the Symptoms of West Nile Virus Infection?

As stated earlier, only about 20% of people infected with West Nile virus develop symptoms, which can include fever, headache, body aches, joint pains, vomiting, diarrhea and rash. In the milder form of the illness, most people recover completely. However, fatigue and weakness can persist for weeks or months.

The more serious form of West Nile Virus that affects peoples’ central nervous system can manifest in high fever, headache, neck stiffness, confusion/disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. About one person in 10 with this severe infection will die.

Individuals who are over 60 and have certain other concurrent medical conditions (e.g. cancer, diabetes, hypertension, kidney disease) or who have received organ donations are at greater risk for the severe form of West Nile Virus infection. Recovery can take weeks to months, with some types of damage to the central nervous system being permanent.

Importance of Prevention

In terms of prevention, the CDC recommends using insect repellents registered with the Environmental Protection Agency that contain DEET, Picaridin (known as KBR 3023 and icaridin outside the U.S.), IR3535, Oil of lemon eucalyptus (OLE), Para-menthane-diol (PMD) and 2-undecanone.

They also recommend wearing long, loose, light-colored clothing when outside; limiting the time you spend outdoors; and eliminating areas of standing water around your home, where mosquitoes could lay eggs.



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