West Nile Virus: Origin, Variations And Difficulty Of Treatment

Jun 25, 2012

Dallas, Tarrant and Denton counties recently confirmed their first human cases of West Nile Virus. Dr. Cedric Spak says most people bitten by a mosquito carrying West Nile will never know it. But in this KERA Health Checkup, the infectious disease specialist said West Nile is a potentially serious disease of two variations.

Dr. Spak: There are two variants. One is going to be called West Nile fever. It is a febrile episode – it is a period of fever, you kind of feel like you’ve got the flu, and then you get over it. Less than, estimates are between two and five percent, of those people develop West Nile encephalitis, which is an infection of the lining and the inside of the brain, that causes the person to have neurologic symptoms. Coma, seizures, confusion with very high fever. And those are the individuals that actually end up presenting to the hospitals. And those are the individuals that we want to try and help. But the frustration is that we cannot identify who’s going to get that level of illness.

Baker: What is it that separates one group from the other?

Dr. Spak: That’s what we don’t know. We think it has to do with individuals with multiple medical co-morbidities, that’s doctor talk for a lot of other medical conditions – they have kidney failure, they have liver failure, they have diabetes –

Baker: Because as I’m listening to you, I’m thinking, in past years, when we’ve heard reports of those who’ve died during the disease, it’s usually elderly people. And they had some other condition in addition to West Nile.

Dr. Spak: Correct. That’s what’s usually seen in the hospital setting. It does seem to have a predilection for those that are already sick and of advanced age. This is very different than a lot of the other encephalitis syndromes. Before West Nile came to Texas, the most common mosquito-borne encephalitis was St. Louis encephalitis. It differs in a lot of ways. One, St. Louis encephalitis, is what we refer to as an epidemic virus. So you’ll have a sporadic outbreak, typically it’s preceded by a large rainstorm, and then you get an explosion in the mosquito population. And then individuals get exposed and so back in the nineties, that was the most common mosquito-borne viral encephalitis, within the state of Texas. And you can swap war stories with other doctors, Oh yeah, this big rainstorm, and then you knew, say, seven to 15 days after the rainstorm, individuals could potentially show up. And then you think, wait a minute, big rainstorm, St. Louis, etc.

So from a public health standpoint, our public health infrastructure knows that. And so that’s why the trucks come out after the rainstorm to spray the mosquitoes and that’s why we always educate the population – dump the standing water, you want to try and prevent that so you don’t have mosquito growth.

Baker: So are we saying that recent rains here have led to West Nile virus cases coming out earlier than normal?

Dr. Spak: That would be a reasonable supposition. Because the thing is, you have to have surveillance to know that West Nile’s there. And you have to first get the mosquitoes. So if you identify the virus in the mosquitoes well then the next step is, well, the mosquitoes could potentially transmit it. The interesting difference between St. Louis and West Nile is West Nile is actually a virus that has several reservoirs within the ecosystem. So the mosquitoes actually will infect birds with the virus and the birds will be symptomatic and actually can die. And then the mosquitoes can actually get it from the bird and then fly across the park and then give it to the human. And this kind of infection, when it crosses species, we can also call it a zoonotic infection, so there are many infections that are specific for one species, and in fact this is another way to do the surveillance. If you have a population where there’s a die-off of crows or other fowl then that is an important clue that something’s wrong.

And that was actually how it was discovered n New York City back in 1999. In New Jersey and in New York City there were observations of hundreds or thousands of dead birds which is almost Biblical. So they didn’t have an answer. So public health is not just the health of the human population but also the animal population and there are veterinarians that work with them. They actually conducted investigations on those birds, found the West Nile, and they thought that was interesting and that was a report.

They didn’t have the sufficient experience to realize what was going to happen next. But what happened next with West Nile when it went to humans was that there were these hospitals in the boroughs of New York where people were showing up with encephalitis, the doctors were seeing them, they were diagnosing them and trying to figure out what it was.

One of the doctors, around 1990 to 2000, actually was on one of those mail-ins where you get the letter from the health department, and he was like, ‘Oh, there are all these birds that are dying from West Nile, holy cow!’ And then he was like, what about this patient? Could this patient have west Nile? And it was an elderly woman, and so he sent the test, and the test came back positive. So that was the first West Nile case in the United States.

Baker: While we’re on the subject of origin, in a nutshell, where does West Nile come from to begin with?

Dr. Spak: The original virus was actually described in the West Nile region. So the waters of the Nile, they finish in Egypt but they start in East Africa, in sort of the Uganda, Kenya, sort of region. It’s adjacent to a part of Africa called the Rift Valley. There’s a lot of viral illnesses borne by mosquitoes that come from that part of the world. And West Nile slowly migrated up the Nile, so that it was present in the mosquitoes within that area. And then actually slowly because of trade, trucking, etc. and migration, slowly disseminated across the Middle East. A lot of our cutting-edge, first World medicine investigations on West Nile had actually come from Israel. Israel has a lot more experience with West Nile than the U.S. had had. And so when it came in 1999, the CDC then started working closely with the health ministry in Israel to figure out what needed to be done.

Baker: Back to today. If a person is bitten by a mosquito carrying West Nile, does that mean they’re going to develop the fever or even the encephalitis later on?

Dr.     Spak: Probably not. The other interesting thing about West Nile is that it appears that it’s gone from an epidemic infection to what we refer to as an endemic infection. An endemic infection is actually present all the time, and we’ve probably all been exposed. When the epidemic came in the nineties, and you can look on the CDC and other health department web sites, you can follow the wave of the infection as it follows from state to state sort of contiguously and it looks like a quilt work, almost like an election map where the stares are progressing from New York all the way up until the last one, the state of Washington. It took almost ten years to cross the continent. Within individual hospitals, officials saw spikes in cases, and then the cases seem to have subsided. So I can tell you at Baylor University Medical Center, we haven’t had a case of West Nile encephalitis in a couple of years. The last case I saw of West Nile was 2008. We certainly test for it all the time, but we haven’t had a confirmed case in years.

Baker: Should you develop West Nile fever, how is it treated?

Dr. Spak: It’s not. It’s kind of like a cold. You have a fever, you feel bad; it usually lasts a few days. And in fact most physicians wouldn’t even be able to diagnose it. I don’t want people to be too concerned and go seek immediate medical attention after a rainstorm, they got a mosquito bite, and got a temperature. That really wouldn’t help them.

Baker: But at one point should you become concerned and maybe seek medical attention?

Dr. Spak: That’s a good question, because the real uncertainty is who’s going to develop an encephalitis and if they do, what could be done to prevent it from happening or to reduce its symptoms so the person wasn’t so sick and the answer to all of that is, we don’t know. There is no treatment for West Nile, there is no antiviral for it. There have been studies for vaccines. They are not ready for prime time, there really is no vaccine that’s available to prevent it from occurring. So if an individual gets symptomatic West Nile encephalitis – I don’t want to sound like a nihilist but there’s not a whole lot you can do.

Baker: So what is done currently?

Dr. Spak: Well, “supportive” measures is the way doctors refer to it. So let’s say you have this 75-year-old woman, she’s got diabetes, she shows up in the emergency room, she’s confused, she’s got a temperature of 103.5. Well, she’s sick, and then the doctors need to figure out why. There are a lot of other things that could cause the patient to be sick. So clearly she needs medical attention. The way I approach it when I see a patient is, first things first, you’ve got to figure out if there’s anything reversible. Do they have a bacterial infection? Maybe it’s an atypical manifestation. Maybe they have a urinary tract infection, etc. Maybe they have meningitis which can be treatable. There are one or two kinds of encephalitis that are potentially treatable with antivirals, that are less common than West Nile but still important to know. And so as the physicians evaluate that individual patient, that’s the way they think about it. If it turns out to be West Nile, you can tell the family, there’s nothing we can do, we know what it is, and you’ve got to let it ride its course.

Baker: So in the meantime, the word for the public is be careful, don’t take chances.

Dr. Spak: Be careful don’t take chances in the sense that everything you were taught about avoiding mosquitoes is the most important, but also recognizing this consequence of a mosquito bite is rare because probably what’s happened since Texas got West Nile is that most of us have been exposed to West Nile in kind of the same way that a lot of us when we were kids were exposed to chicken pox, or whatever. So now, we’re protected. We’re immune, we can’t get it again.

Baker: Once you’ve had it, you don’t get it again?

Dr. Spak: Correct. We have most of that information and it’s funny how we get these data. But one of the ways we get that info is from blood donors. Back in 2008, there were a couple of cases of West Nile being transmitted accidentally through blood transfusions and these were not in healthy patients, these were in the sickest patients. Patients with leaukemia or trasplants or whatever. And this was another call for alert. So the blood banks are extremely vigilant, very safe in the U.S., so they started screening all the blood. They actually found that in counties across the eastern U.S., in some areas up to fifty percent of us have already been exposed to West Nile, without us even knowing,. When you compare it to the research done in East Africa, that’s the same thing. We all get bitten by mosquitoes, we’re not all dropping dead from getting bitten by mosquitoes. And if you think about it from a virus perspective, that makes sense. The virus doesn’t want to commit genocide and kill all the people. It just wants to be transmitted so that it can continue its life cycle. It may actually make some individuals sick. Those are the unlucky ones.

Baker: For those who may not know, what should you do to protect yourself against mosquitoes?

Dr. Spak: So the best thing is to not go outside, which is not practical. The second best thing is to wear clothes that protect your skin. Also using insect repellants. Kids are not going to want to wear pants and a long-sleeved shirt when they’re running outside. Funny thing is, the kids themselves are probably at lower risk. Older individuals could be done as well. Other things to protect us from mosquitoes is to use the different repellants, there is a tremendous variety you can find at stores. If you really want to maximize your protection from mosquitoes, is to have it with DEET. There’s a variety of products that can have DEET at ust about any grocery store or pharmacy.

Baker: You mentioned how West Nile virus had spread across the united states. As recently as last year the CDC was saying that, except in Alaska, Hawaii and Washington. Why not those three states?

Dr. Spak: Once again it has to do with the mosquito. So for example in Washington, that was one of the last ones, and the joke there was because its God’s favorite state. I know, silly. You have to be able to get the mosquitoes there and they have to be able to reproduce successfully and there were certain barriers. It was difficult to get to western Washington just because of the mountains and everything else. I think last year they finally had their first human case. In 2007 they did have animal cases already. As far as Alaska and Hawaii, it goes along with that as well. Think about it, how do you get those mosquitoes to that next location? Or alternatively, get those birds that would carry those mosquitoes, or that virus? Those birds don’t migrate that direction.

Dr. Cedric Spak is with North Texas Infectious Diseases Consultants and Baylor Medical Center Dallas.

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