On NPR this morning, the local Northern Colorado affiliate brought us a story about the high numbers of reported and suspected West Nile Virus (WNV) cases in Fort Collins this summer and Larimer County has issued a Health Alert to all area healthcare providers. There have been 35 batches of trapped mosquitos that have tested positive for the virus — most of these in the last two weeks. Northeast Fort Collins has the highest density of infected mosquitos. At Pediatric Associates, we’ve seen one case of WNV.
So, how much should you worry and what can you do to reduce your family’s risk of acquiring WNV infection?
What is West Nile Virus?
This virus showed up in the Western Hemisphere in 1999 and has since caused seasonal epidemics of febrile illness and neurologic disease across the US. It is the leading cause of arboviral encephalitis — tick or mosquito transmitted viruses that cause brain inflammation. The virus is spread by 65 different mosquito species and has been reported in 96% of US counties in the lower 48 states. Some birds (e.g. the American Robin) serve as an amplifier for the virus because it multiplies to high levels in the bird before it passes again to mosquitos who travel widely to spread the disease to humans and other vertebrate animals. Higher incidences are seen where areas of higher population density come close to natural areas with high levels of the the virus. Such a confluence occurs here in the Front Range corridor. (http://www.cdc.gov/westnile/resources/pdfs/wnvguidelines.pdf)
One thing to be very clear on: In most of us, the virus does not cause a particularly severe illness. Studies looking for antibodies to the virus (which indicates a prior infection) show that only 20 – 30% of infected patients develop even a flu-like febrile illness which is characterized by fever, headache, muscle or joint pains and sometimes gastrointestinal symptoms or a transient irregular red rash. 70% of those who are infected show no symptoms at all. (10.1086/503038) Because the rate of severe illness is so low, the incidence of the disease is under reported to medical providers. A CDC study which looked at blood donor WNV antibody prevalence showed there were approximately 750,000 infections with WNV that never came to the attention of physicians in 2003, compared to only about 10,000 that did. (http://wwwnc.cdc.gov/eid/article/12/3/05-1287_article)
But, if you’re one of the unlucky ones, WNV attacks the brain causing encephalitis. Age older than 65, an impaired immune system or the presence of other chronic health conditions increase the risk of developing the encephalitis. Symptoms associated with this manifestation include seizures, mental status changes, focal neurologic deficits (like a facial droop or an arm that won’t work right) and acute flaccid paralysis (like polio). In addition, inflammation of the heart leading to arrhythmias or low blood pressure, inflammation of the structures of the eye causing pain and vision changes and inflammation of the liver and pancreas have also been reported.
Fortunately, less than 1% of infected persons develop these severe manifestations of WNV.
Treatment for WNV is around symptoms. There is not medicine that can be given to cure the virus — it’s up to our immune system to do that. When the severe manifestations of disease occur, hospitalization is required to support breathing and circulation as well as allow close monitoring of cerebral pressure when the brain swells from the encephalitis.
Remove any standing water on your property, or in the case of ponds, treat with the dissolving lozenges that kill the mosquito larvae. Wear long sleeved shirts, long pants and socks that go above the ankle when you can to provide a physical barrier to the biting of mosquitos. A couple of weeks ago I talked about mosquito repellents on our facebook page. Effective ones use picaridin (derived from black pepper), DEET or oil of lemon eucalyptus. Apply one of these before going out a dusk — especially if you’ll be near a swampy spot.
If you’re worried your child may have West Nile Virus, there is a blood test available to check for it. Schedule a visit to discuss any concerning symptoms that sound like those mentioned above.