August 11, 2017
Mosquito-Borne West Nile Virus Hits Home
West Nile virus (WNV) is an infection that is commonly spread by a mosquito bite. This infection is found worldwide and, in the United States, it tends to occur between June and September. In rare cases, WNV can lead to serious complications, or death.
Mosquitoes with WNV have been sighted in all of the 48 contiguous states (not Alaska and Hawaii), including a recent discovery near the border of Henrico County and Richmond, Virginia. To best protect yourself, it is important to understand how WNV is transmitted and the steps you can take to prevent getting infected.
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How is West Nile virus transmitted?
In nature, West Nile virus cycles between mosquitoes (especially the Culex species) and birds. Some infected birds develop high levels of the virus in their bloodstream and mosquitoes become infected by biting these infected birds. After about a week, infected mosquitoes can pass the virus to more birds when they bite.
Mosquitoes with West Nile virus also bite and infect people, horses and other mammals. These are “dead end” hosts, meaning that they do not develop high levels of virus in their bloodstream and cannot pass the virus on to other biting mosquitoes.
It is possible for blood infected with WNV to pass the infection from human to human via blood transfusions or from a pregnant mother to her baby, but this is very rare. The Centers for Disease Control and Prevention (CDC) state that “The weather, numbers of birds that maintain the virus, numbers of mosquitoes that spread the virus, and human behavior are all factors that can influence when and where outbreaks occur.”
The greatest risk factors for WNV are spending time in areas where mosquitoes are present and not using insect repellent. The risk of complications with WNV is highest in people:
- Over 60 years old
- With a weakened immune system
West Nile Virus Transmission Cycle
In nature, West Nile virus cycles between mosquitoes (especially Culex species) and birds. Some infected birds, can develop high levels of the virus in their bloodstream and mosquitoes can be infected by biting these infected birds. After about a week, infected mosquitoes can pass the virus to more birds when they bite.
Mosquitoes with West Nile virus also bite and infect people, horses and other mammals. However, humans, horses and other mammals are 'dead end' hosts. That means they do not develop high levels of the virus in their bloodstream, and cannot pass the virus on to other biting mosquitoes.
Fortunately, most people with WNV have no symptoms. According to the CDC, about 20% of people who become infected will develop flu-like symptoms such as:
- Fever and chills
- Muscle pain
- Nausea and vomiting
- Swollen lymph nodes
- Eye inflammation—conjunctivitis
Symptoms may appear within 2-6 days and can last from a few days to several weeks, but these individuals usually recover completely. A small number of people with WNV, about 1 in 150, will develop serious and potentially fatal neurological symptoms, which can last weeks or months. These symptoms may include:
- High fever
- Stiff neck
- Vision loss
- Severe muscle weakness
About 1 in 10 people who develop severe neurological issues related to WNV will die. Anyone experiencing any of these symptoms should seek emergency care immediately.
In addition to taking your medical history and doing a physical exam, your doctor will ask you:
- What kind of symptoms you are experiencing
- Where you have been living or traveling
- Whether you have been exposed to mosquitoes
A blood test is commonly used to confirm the diagnosis of WNV. Depending on your symptoms, your doctor may order other tests, such as:
- MRI scan
- Cerebrospinal fluid testing to evaluate the fluid that surrounds the brain and spinal cord
Currently, there is no vaccine available to protect against WNV, so treatment focuses on supportive care. Depending on your symptoms your doctor may recommend:
- Pain relievers
- Antiemetic medication to reduce nausea and vomiting
If you are dehydrated, you may need to drink an oral rehydration solution or have fluid delivered through an IV. Treatment for severe symptoms may include:
- Breathing support—mechanical ventilation
- Medication to control seizures
- Medication to decrease brain swelling
The best preventive measure is to avoid mosquito bites. Prevention steps include:
- Avoid outdoor activities at dawn or dusk.
- Wear lightly-colored long pants and long-sleeve shirts when outdoors.
- Apply insect repellent that contains 20 percent or more DEET, picaridin, or IR3535 on exposed skin and clothing for protection that lasts several hours. Parents should apply the product to their children, avoiding hands, eyes, and mouth. The Environmental Protection Agency (EPA) website can help determine the insect repellent that is right for you or your family.
- Repair screens to prevent mosquitoes from entering the house.
- Use proper mosquito netting at night. Look for netting treated with insecticide.
- Remove standing water to prevent mosquito breeding. Empty items like bird baths, flower pots, children’s toys, trash containers, and planters around your house.
- Treat larger water areas or puddles with larvicide pellets that stop mosquito larvae from maturing.
Mosquitoes pick up WNV by biting infected birds. If you see a dead bird, call the public health department. Do not touch the dead bird unless you are wearing disposable gloves.
For further questions about mosquito bites, West Nile virus, general health and wellness, or to schedule an appointment for a consultation, contact Karen Galichon, MD, of Primary Health Group – Henrico, at (804) 282-2580.