West Nile Virus and Chikungunya

Posted on: July 10th, 2014
by Dr. Mobley

West Nile Virus




How common is West Nile Virus?


For the most part, mosquito bites are harmless and more nuisance than threat. There are numerous viruses spread by mosquitos in the United States, but about half of these viruses cause, on average, fewer than 10 reported cases per year; and most of the other half cause, on average, fewer than 100 reported cases per year. West Nile Virus is the exception, normally causing more illnesses than all the other viruses combined. The number of reported cases of West Nile Virus from 2004-2013 averaged 2500 per year, ranging from 712 in 2011 to 5674 in 2012. Of course, only the severe cases get reported, so there would have been at least 4 times that many total cases in the US during these years.


How serious is infection?


West Nile Virus was first isolated in Uganda, Africa in 1937 and first appeared in the United States in 1999 in New York. Although it can make us pretty sick and even cause death, most West Nile Virus infections cause no symptoms whatsoever. Only 20% of infected persons get any symptoms at all. That means that 80% of the time West Nile Virus infections go entirely unnoticed!   Only 1% of infected persons develop neuroinvasive disease, such as meningitis, encephalitis, and paralysis. Of that 1% who develop neuroinvasive disease, 10% of adult cases are fatal (mostly in adults over 60), and fewer than 1% of childhood cases are fatal. That means that fewer than 1 in 10,000 children infected with West Nile Virus will die from it. Another way of looking at it is that more than 99% of children who develop serious neuroinvasive disease will survive and most will have no long-term sequelae.  This does not minimize the catastrophic event of a childhood death, but it does give some perspective. For information on how to protect your children, see my blog post on Mosquito Control.


What are the symptoms?


West Nile Virus is transmitted to humans through the bite of infected Culex mosquitos, which tend to feed most avidly from dusk to dawn (when it’s dark). Mosquitos acquire the virus by feeding on infected birds and then transmit the virus to humans. The symptoms of West Nile include fever, headaches, muscle aches, weakness, and frequently abdominal pain, nausea, vomiting, or diarrhea.  The viral illness usually lasts fewer than 7 days. The incubation period is normally 2 to 6 days but ranges from 2 to 14 days.


How do I know if I have West Nile infection?


Since 80% of persons infected with West Nile have no symptoms at all, most people never know they were infected.  And for those who are infected, the symptoms are similar to those of many other viruses.  Realistically, in most cases it doesn’t matter whether a summertime febrile illness is caused by West Nile or some other virus — the virus cannot be spread from one person to another, and most people have no serious sequelae from the infection.  Blood tests for West Nile Virus are rarely done, since most patients do not get very sick and even fewer get neuroinvasive disease.  Additionally, testing in the first 8 days of the illness might not show infection even when present.  There is no specific treatment for West Nile Virus infection; however, there are many supportive measures that can be taken in a hospital setting that greatly improve the chances of survival.



Chikungunya (Chicken WHAT?!?…..say “chick en goon ya”)



What is Chikungunya?


In July, 2014 the Texas Department of State Health Services confirmed the first human case of Chikungunya, a viral disease that can cause high fever and severe joint pain. The patient testing positive for Chikungunya became infected on a recent trip to the Caribbean, where chikungunya has been causing human disease since late 2013. The patient lives in Williamson County, north of Austin.  The virus is spread to people by Aedes mosquitos, which are active and bite during the day. It is not yet commonly acquired in the United States. I only discuss it because you may hear reports in the news. Over the coming years it remains to be seen how common and widespread this illness will become.


Who is at risk of getting infected?


With recent outbreaks in the Caribbean and the Pacific, the number of chikungunya cases among travelers visiting or retuning to the United States from affected areas will likely increase. Cases have also occurred in Africa, Southern Europe, Southeast Asia, and islands in the Indian and Pacific Oceans.


What are the symptoms?


Infections are rarely fatal but can cause severe joint pain, high fever, head and muscle aches, joint swelling, and rash. Symptoms usually begin 3 to 7 days after being bitten by a mosquito. There is no vaccine or treatment for the virus. Most people feel better within a week, though some people may develop longer-term joint pain. The rash occurs in 40-50% of all cases and usually appears 3 to 5 days after the onset of fever and subsides in 3 to 4 days. It is sometimes mildly itchy. The rash most often starts on the arms and can spread to the neck, earlobes and trunk. Skin pigmentation may occur after the rash has resolved and may last for months.


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