Summer can bring the West Nile Virus
Sunday, June 23, 2013 10:00 PM
Now that we've officially entered summer, news reports of West Nile virus will probably start to pick up in the next couple of weeks. West Nile is a virus that is spread to humans by mosquitoes.
Dr. John Roberts is a Crawfordsville physician and one of the owners of The Paper. In addition to his weekly column, he writes a daily health tip that can be found on page A1.
Many people wonder what a disease named "West Nile" is doing in Indiana. Shouldn't it be called "West Sugar Creek," "West Wabash" or "West White?" The name is derived from the first description of the disease in 1937 in a woman living in the West Nile District of Uganda.
The virus first appeared in non-human mammals in the Western hemisphere in 1999. Shortly thereafter, it was found in humans around New York City, and then rapidly spread across the U.S. There were 5674 reported cases of West Nile infection and 286 deaths in the U.S. in 2012. Indiana had 77 infections and eight deaths.
The virus has an interesting life cycle. Its primary reservoir is in birds where it reproduces in large numbers. The sentinel appearance of dead birds often precedes an outbreak of West Nile in other mammals and humans. Mosquitoes feed on the birds and then may eventually bite humans and transmit the virus. The virus survives over the winter in mosquitoes that live in warmer underground locations.
West Nile has also been found to spread through blood transfusions, organ transplants, from mother to fetus, and through breastfeeding. Blood banks now routinely screen for the virus in donated blood. Certain populations are more susceptible to infection with the virus. These include the elderly, organ transplant recipients and diabetics.
West Nile causes three types of infections in humans in roughly a 110:30:1 ratio. The first type is called an "asymptomatic" infection. The patient is infected with the virus but shows no symptoms. The second is called "West Nile Fever." These people develop fever, headache, chills, sweating, fatigue, and swollen lymph nodes. They may also exhibit a rash. The symptoms start anywhere from 2-15 days after the mosquito bite and may last for 7-10 days or sometimes longer. The fatigue can last a number of weeks.
The third, and most serious manifestation is "neuroinvasive" West Nile disease which causes meningitis or encephalitis. Meningitis is an infection of the tissues surrounding the brain and spinal cord whereas encephalitis is an infection of the brain itself. These patients initially have symptoms of West Nile Fever but then progress to a decreased level of consciousness and even coma. It can also cause many other nervous system problems.
There is no treatment that kills West Nile virus. Since it is a virus, we need to depend on our immune systems to clear it from the body. Those who have severe disease are treated supportively until they recover. There is a vaccine that is used in horses, but one has not been developed for humans. As the virus becomes more widespread, humans have become more immune and the number of infected individuals has been in decline, a pattern that has been seen in Africa and elsewhere.
The best way to avoid infection is to avoid the mosquitoes in the first place. Since mosquitoes prefer to feed at dawn and dusk, stay indoors during those times. If you have to be outdoors, cover up with long clothing. Clothing brands such as Insect Shield® and BuzzOff®, impregnated with permethrin, are very effective as is mosquito repellant containing the chemical DEET.
In addition to prevention with chemicals and barrier clothing, it is important to reduce the breeding areas for mosquitoes. Standing water has to be present for the mosquitoes to lay eggs in and for the larvae to develop into adult mosquitoes. Areas with standing water should be drained or emptied if possible.