In 2012, there have been more cases of West Nile virus thus far leading up to September than in any year since the disease was first detected in the US in 1999, the Centers for Disease Control and Prevention (CDC) reported on their website. No continental US state has been left unscathed by the infection (in people, birds, or mosquitoes).
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“We are on course to have one of the worst years ever with respect to West Nile virus infections and that's not only in Mississippi — that's across the nation,” A. Arturo Leis, MD, a senior scientist at the Center for Neuroscience and Neurological Recovery and clinical professor of neurology at the Methodist Rehabilitation Center in Jackson, told Neurology Today.
At press time, a total of 3,142 cases of West Nile virus (WNV) disease in people, including 134 deaths, have been reported this year to the CDC. Of these, 52 percent were classified as neuroinvasive disease (such as meningitis or encephalitis) and 48 percent were classified as non-neuroinvasive disease. Two thirds of the cases have been reported from six states (Texas, South Dakota, Mississippi, Oklahoma, Louisiana, and Michigan) and 40 percent of all cases have been reported from Texas.
“Over the last few years we've had relatively few cases [of WNV] nationwide and in Mississippi,” Dr. Leis said. “Because of that, I think we got a little complacent in terms of the public and in terms of doctors — and this, coupled with a relatively warm winter, which allowed mosquitoes to survive, likely combined to contribute to the season of infections that we're having now.”
The exact reason for this increased incidence of the virus this year is not known, though speculations abound. Robert W. Haley, MD, professor of internal medicine and director of the Division of Epidemiology in the internal medicine department at the University of Texas (UT) Southwestern Medical Center at Dallas, said that given prior epidemiology, “we typically see big West Nile years after a mild winter because you have more mosquitoes surviving the winter — so they start out with an advantage.”
Dallas and Fort Worth, among the areas hardest hit by the virus, are right at the edge of a weather zone, Dr. Haley said, and this has also likely had an effect. “The last several years, we've had almost no cases of West Nile, which means that our bird populations are much more susceptible to getting infections.” However, next year, we may see a slowing again because many of our birds will have been infected once already and will be immune, he added.
About 80 percent of individuals who are infected with WNV are asymptomatic, Dr. Haley said, while the other 20 percent may develop West Nile fever (symptoms include fever, headache, tiredness, body aches, skin rash, and/or swollen lymph glands), which lasts from days to weeks. According to the CDC, an estimated 1 in 150 persons infected with the WNV will develop neuroinvasive disease.
“Although you can see WNV throughout the country and throughout the calendar year, the most common time is July to September. Patients with neurologic symptoms can present with either encephalitis, meningitis, or they can present with a flaccid paralysis of the extremities. These patients can often be mistaken for having other kinds of diseases,” said Avindra Nath, MD, chief of the Section of Infections of the Nervous System and clinical director of NINDS. He added that neurologists should be “highly suspicious” of the possibility of WN encephalitis if a patient presents with encephalitis during these months. “Multi-organ involvements with neurological complications should also raise a level of suspicion,” Dr. Nath said. Those most at risk for neuroinvasive disease include the very young, very old, and those with pre-existing conditions or taking immunosuppressive medications — in essence, individuals with an immune system that is already compromised in some way.
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Here in Mississippi, Dr. Leis told Neurology Today, “We're seeing a lot of cases of neuroinvasive disease with profound muscular weakness and this is attributed to the virus attacking the gray matter of the spinal cord, giving rise to a poliomyelitis syndrome that is indistinguishable from the polio epidemic of the 1940s and the 1950s.
“WNV is indeed a neurotropic virus, meaning it targets the gray matter of the spinal cord and the motor neurons within the brain stem and some of the deep nuclei of the brain — and this is where it does most of its damage.”
Dr. Haley said that the cases of WNV he is seeing in Texas are similarly distributed to those that have been present in the US since1999. “We're seeing the full spectrum — we're seeing a lot of sero-conversions in asymptomatic blood donors, meaning they've just recently developed the infection but didn't get sick. We're also seeing a relatively large number of people who had only the WN fever.”
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Dr. Leis said that since 2002, his work with the Mississippi State Department of Health to facilitate regular support group meetings for individuals with WNV has been immensely helpful in understanding the virus as well as the affected patients. The distinct advantage “of having a group of patients who have the same diagnosis, with a spectrum of problems, who are asking different questions; it's invaluable,” he told Neurology Today. “I would encourage all states that have high numbers of WNV to create their own support group meetings.”
Joseph Kass, MD, an associate professor of neurology and medical ethics and director of the neurology residency program at Baylor College of Medicine, in Houston, TX, stressed that neurologists must not become complacent just because a disease is on the wane. For example, he said, one of the grand rounds last year at Baylor was on WNV. “We saw a spike a few years ago, but it's really been on the decline. So, when we did those grand rounds, no one was predicting that this [increase] was going to occur.”
At this point, Dr. Kass, who is also chief of the neurology service at Ben Taub General Hospital, said, “if I'm doing a lumbar puncture on somebody to rule out a CNS infection, I always check for WNV. If the person has encephalitis, that's going to be on my differential [diagnosis list].” The only difference is that in the past, “I wouldn't have expected it to be positive. At least for us here at Baylor, looking for WNV has become routine.”
Dr. Haley said that neurologists and physicians should be aware of anybody with an unexplained fever from late June to the end of September — particularly with headache, rash, diarrhea, lymphadenopathy, and/or neurological signs. WNV should be considered and ruled out in these instances, he said.
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Additionally, anyone with resulting neuroinvasive disease needs to be hospitalized, he continued, both for diagnosis and also observation because “neurological deficits can continue progressing long after the infection begins — even weeks later because the virus stays and proliferates in the body and in the brain.”
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There is no specific treatment or cure for WNV. We continue to learn about the pathophysiology of the disease with animal models that have been developed, Dr. Nath said, and there are several groups that are studying ways of making antibodies and pharmacological agents for treatment, but these are all in pre-clinical stages of development.
Really, Dr. Kass, told Neurology Today, treatment is currently comprised of excellent supportive care — often in the intensive care unit.
Neurologists play an important role, he said, because “if a patient is intubated and they're not moving, the primary care team may not recognize that as being due to neurological injury, but a neurologist can look for any subtle neurological sequelae.”
Although we can't modify the course of the disease by curing it, Dr. Kass said, “we can help deal with potential complications from spasticity or contractures or mobility issues. Some of the patients may have cognitive sequelae, or some may have movement disorders that develop.
“I think there's a role for the neurologist in identifying the disease initially, helping control some of the complications, and then also following these patients to see if they do have any neurological sequelae and seeing if we can improve their quality of life.”
Avindra Nath, MD, chief of the Section of Infections of the Nervous System and clinical director of NINDS, discusses West Nile virus in humans, as well as research and treatments in the pipeline: http://bit.ly/rCBryX.
RESOURCES ON WEST NILE VIRUS:
* AAN's Neuro-infectious Disease Section: aan.com/go/about/sections/disease.
* CDC, Division of Vector-Borne Diseases: cdc.gov/ncezid/dvbd.
* Neuro-ID Interest Group from the NIH: sigs.nih.gov/NeuroID/Pages/default.aspx.
* Archive of Neurology Today coverage of West Nile virus: http://bit.ly/TYkw11.