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What you need to know about the neuroinvasive form of West Nile virus

West Nile Virus is transmitted to humans through mosquitoes
West Nile Virus is transmitted to humans through mosquitoes

Most people who get infected by a mosquito bite won’t know it. Some may experience a flu-like illness. But as in six recent cases in Dallas, Denton and Tarrant counties, about 1% of all people infected with West Nile virus will develop something far more serious.

Dr. John Beckham, an internal medicine professor and chief of infectious diseases at UT Southwestern Medical Center, spoke with KERA’s Sam Baker.

What is West Nile neuroinvasive disease?

What that means is the virus has actually gotten into the central nervous system or into the brain or the lining of the tissues around the brain.

And that can cause various different types of complications and symptoms from severe headache, light sensitivity, a mild kind of stiff neck all the way to confusion, and loss of consciousness.

And in some cases, for example, it can attack the spinal cord as well and can cause a paralysis called poliomyelitis. So it has a number of different areas where the virus can kind of attack in the central nervous system.

Then there aren't different strains of West Nile virus. It just depends on who's infected and the condition of that person.

The people that get neuroinvasive West Nile virus infection have specific kinds of profiles or risks. The biggest risk is age over 65. And anyone on immune-suppressing medications, especially people in our transplant kind of groups.

There's really nothing different about the virus in one person who's asymptomatic and one person who has neuroinvasive disease. The main difference is the host.

Are there symptoms that would let you know which one you likely have or do you need a lab test to tell if you have neuroinvasive versus West Nile fever?

If we are concerned that someone has symptoms that the virus has gotten into the nervous system, the main diagnosis or way to diagnose that is with a spinal fluid analysis through a lumbar puncture.

So it's a matter of getting a sample of the spinal fluid and we send it for specific tests, looking for the virus again, looking for antibodies in the spinal fluid to the what, to West Nile virus, or looking for the genetic material or the genome of the virus itself.

And then a lot of times, if someone has what we think is a more severe disease, meaning they've lost consciousness or they're having some type of paralysis, we'll typically get an MRI of the brain and or the spinal cord. And that can show kind of characteristic patterns of injury. In some patients, probably about 40% are kind of indicative of a neuroinvasive kind of infection from West Nile virus.

That sounds very uncomfortable, if not scary.

You know, it's scary for the patients and for the physicians as well.

Sometimes we'll have patients come in, they'll have a headache, they'll have a high fever. We diagnosed them with West Nile virus, and then they can kind of progress before our eyes and we try to support their breathing, their kidneys and give them fluids and help relieve their pain.

But we don't have a specific kind of antiviral treatment. We don't have an FDA-approved vaccine for this virus. So it's actually quite scary for both the physicians and the patients because we kind of have a limited number of tools when people start to get really sick with this virus.

Has there been any progress made, though, on treatments for West Nile virus?

There are probably a couple of really good vaccine candidates for West Nile virus.

The problem has been the clinical trials process, meaning the cases tend to pop up in different areas. How do you set up the trials so that you can kind of predict where the cases are going to be, capture those cases, and actually do a trial to make sure your vaccine or your treatment or whatever you're testing is going to be safe and effective for our patients?

Within the last month or so of when we're talking, there have been at least six confirmed cases of West Nile neuroinvasive disease in Dallas, Denton and Tarrant counties. Is that number a cause for concern?

You know, it's always a cause for concern when we start seeing a spike in cases.

The mosquitoes are most active in the summer. And that's when the birds are around to help develop the cycle. And then when we start seeing a spike in cases, we do get concerned, especially for our high-risk patients, the older populations, and immune-compromised patients, that we could have a busy year. The mosquitoes could have kind of an increased carriage rate, if you will, of West Nile virus and put people at risk.

And so what we recommend for everyone in Dallas and in surrounding areas where there's ongoing West Nile virus transmission is our best mechanism to prevent these cases is avoidance of the mosquitoes:

  • Mosquitoes tend to bite more in the kind of early morning or evening kind of hours. And if you do go outside, wear long sleeves and long pants, which is hard during this kind of heat in Texas.
  • If you are outside for a period of time, use the DEET-containing insect sprays, typically around 7 to 10% or above. That's a good way to repel these biting mosquitoes that carry West Nile virus.

    Regarding these recommendations for prevention, most people will say wear long- sleeved and light-colored clothing. What does that have to do with it?

The light-colored clothing is cooler and so mosquitoes are attracted made them.
One of the many things that attracts a mosquito to bite, is a heat signature. If you're wearing light-colored clothing and your body temperature is cooler, then it's actually more difficult for the mosquitoes to find you.

You know, the way they spread the virus itself is before mosquitoes take what we call a blood meal, they actually insert their mouthparts into the skin. And they have salivary glands that allow them to take a blood meal. And those salivary glands kind of spit, for lack of a better word, into the skin to kind of make it easier for them to take a blood meal. And that's actually when the transmission occurs.

So if you can, prevent that initial bite by using long sleeves or DEET-containing sprays, and that prevents that whole transmission process from happening.


West Nile virus (CDC)

West Vile virus (Texas)

Sam Baker is KERA's senior editor and local host for Morning Edition. The native of Beaumont, Texas, also edits and produces radio commentaries and Vital Signs, a series that's part of the station's Breakthroughs initiative. He also was the longtime host of KERA 13’s Emmy Award-winning public affairs program On the Record. He also won an Emmy in 2008 for KERA’s Sharing the Power: A Voter’s Voice Special, and has earned honors from the Associated Press and the Public Radio News Directors Inc.