West Nile Outbreak: What You Should Know

Northwestern Medicine
Infectious Disease August 29, 2012

Rahul Khare, MDWith more than 1,100 cases and 41 deaths, the recent West Nile virus outbreak is the largest ever in the United States. Below are my answers to some of the most frequently asked questions about the disease and my tips for how to keep you and your family safe.

What is West Nile Virus?
It is a virus that is transmitted to people through mosquitoes. Mosquitoes get it from feeding on infected birds.

How common is it and what are the symptoms?
When a person is bitten by an infected mosquito, only about 20 percent of the time will that person actually get the virus. Typically, you experience body aches, fever, headaches and sometimes a rash and swollen lymph nodes. Of those cases, about one person will go on to get neuro-invasive or West Nile Encephalitis. That means the virus passes the blood brain barrier and people experience neck pain, high fever and severe overall pain. Those cases are more dangerous because about 20 percent of the severe cases can result in brain damage or death. But, keep in mind that chances are good that you won’t get West Niles and even better that you won’t get the full blown Encephalitis.

How long does the season last?
It usually starts here later in the summer as it gets hotter and dies out in the fall when it gets colder.

Why are there so many more cases this year?
Last year we had about 700 cases total. This year so far we have 1,100. The season started earlier this year and I have a feeling it has to do with the type of summer we’ve had. With a mild winter and early warmth, mosquitoes have increased in numbers more than in the past. The virus itself hasn’t changed, it’s just being transferred more because there are more mosquitos.

How many cases have we seen at Northwestern Memorial?
None this year.

Why do you think Cook County has the most cases in Illinois?
We do a very good job of getting and reporting numbers. If someone comes in with symptoms that are typical of West Nile Virus and they’ve been in a place, like a wooded area where it makes sense that they could have it, we’ll test because, even though it can’t be treated, we want to know if it’s here and if it’s on the rise. Funding for preventive measures like the spraying they’re doing in Texas can come based on these numbers.

How long does it take for symptoms to appear and how long do they last?
After you are bitten, it takes three days to two weeks to incubate. Symptoms usually last three to 10 days. 80 percent of the people who get the virus don’t ever exhibit any symptoms.

How do I know if I’m at risk?
The people we worry about the most are people who are immune compromised, such as those getting cancer treatment, kids younger than 2 and the elderly. Those are the people we want to make sure get mosquito repellent and wear long sleeves and long pants when going to mosquito infested areas.

How are cases diagnosed?
Usually a patient will experience body aches, headache and a high fever. They often come to the ED, or they go to their primary care physician who will refer them to the ED. It can be diagnosed with a blood test. But, usually when you have a headache and high fever, we have to rule out meningitis and encephalitis, so we often do lumbar puncture (spinal tap).

How can I prevent it?
If you’re outside, I would put on insect repellent spray or lotion containing DEET. That’s the only kind that is scientifically proven to repel mosquitos. It’s important that everyone who goes outside in a wooded area in the evening puts it on.

Do citronella candles work?
Cintronella is fine, but I wouldn’t stop there. If you’re outside where you know you will be bitten, you should put on spray or lotion.

How important is prevention for the average, healthy person?
You should do what you usually do. If you’re going into the states that have a lot of cases, like Texas, Florida and South Dakota, you should definitely use some kind of insect repellent. If you know you’re going to be in a place where you’re going to be bitten up, put on repellent, wear long sleeves and long pants when possible and stay inside during dusk and dawn, which are the hours mosquitos feed on people. I am not an alarmist about this and I don’t think you should worry too much about it.

West Nile virus mosquitoAre more people coming into the ED suspecting West Nile virus because it is in the news?
We’ve seen a few. We ask if they were in an area where they got insect bites or if they remember having a bite. If they say no, we tell them it’s unlikely that’s what it is. Most people just want reassurance and a professional opinion. They don’t even always want to be tested. The bottom line is, use insect repellent if you’re going to be in an area where there are a lot of mosquitos. And, if you do develop headache, a fever and chills, it’s best to see your doctor or come to the ED to get checked out.

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