Mt. Vernon Register-News

Community News Network

March 11, 2014

How virus sleuths and public health officials track the cause of a mysterious illness

Ident: X7376

Selector: tm--a

Priority: r

Slug: bc-paralysis

bc-paralysis 03-11 1172

ATTN: National, Science editors



When a mysterious disease fells people - as happened in California recently, with as many as 20 children experiencing unexplained paralysis - teams of physicians and epidemiologists quickly mobilize. Perhaps you saw the movie "Contagion"? The idea is to find the culprit before it spreads but also to prevent public panic.

The investigation typically begins with a doctor reporting a sudden increase in patients with a particular disease or symptom to a state health department. It then falls to the government to determine whether the report is a false perception, a statistical quirk or a genuine surge.

The paralysis cases are a classic example: The symptoms are well known but their incidence appears to have spiked. Acute flaccid paralysis, the technical term for the symptoms observed in California, is something that many pediatricians have seen, and it has myriad causes. "I probably see one case like this every five years," says Keith Van Haren, the Stanford neurologist who is leading the hunt for an explanation for the paralysis reports. "Five cases in one year seems like an abnormality."

It's much harder to prove an abnormality than to perceive one, though. Surveys by the World Health Organization suggest that approximately one of every 100,000 children each year develops acute flaccid paralysis. It's not clear whether the rate is the same within the United States, but, since approximately 7.7 million kids younger than 15 live in California, 20 cases in a year might be within a normal range. A final determination on that question, however, will depend on whether the cases are related and whether they are clustered within a small geographic range. There is also a risk that clusters of cases can generate more such reports, especially once the media get involved.

"What you start looking for, you see," says Daniel Firkin, epidemiology branch chief in the division of viral diseases at the Centers for Disease Control and Prevention. Physicians usually don't report childhood paralysis, he explains, because the CDC doesn't require it.Now that they're on notice, however, more cases are going to be reported. It can be difficult to distinguish a surge in cases from a mere surge in reports.

Another challenge is determining which cases to include in the count. Establishing a case definition - a concise statement of what the patients have in common - prevents unrelated cases from leading investigators astray. According to Stanford's Van Haren, the working definition for the California cases is "paralysis with evidence of injury to the motor neurons in the anterior horn of the spinal cord."

That definition explains why the disease is being described as "polio-like." It's not simply that the children have become paralyzed. Several medical conditions can lead to paralysis. The autoimmune disease Guillain-Barre syndrome and the inflammatory disease transverse myelitis, for example, can paralyze children. Poliovirus, however, has a specific profile, ending in paralysis, that sets it apart from most other illnesses.

Polio is a classic fecal-oral disease. The virus usually spreads from one person's stool to another person's mouth, often through contaminated water or unclean hands. Since 95 percent of people who are infected with the pathogen never experience symptoms, polio victims rarely have reason to suspect they have come into contact with the disease; this is one reason that the eventual paralysis seems sudden.

In some patients, polio progresses to a brief bout of flulike symptoms, which has been observed in a few of the California patients. In a small minority of cases, the virus reaches the central nervous system. Poliovirus has proteins on its surface that match proteins on certain human nerve cells, as a key fits into a lock. Because the fit must be precise, poliovirus typically unlocks only the cells responsible for controlling muscles in the arms and legs - the motor neurons - in the front part of the spinal cord. Sensation usually remains intact in the paralyzed limbs, because polio can't enter the sensory nerves.

This clinical observation - paralysis of the limbs with little or no loss of sensation - probably rules out a large number of possible causes for the California cases, according to John Modlin, a physician working to eradicate polio at the Bill and Melinda Gates Foundation. Herpes simplex and varicella zoster, the pathogen responsible for chickenpox, are known to paralyze children in rare cases, but they usually affect sensation as well. The same is true for Guillain-Barre.

Since polio has been eradicated in the United States and the patients in California were vaccinated against it, the suspicion has fallen on other members of the enterovirus family, to which poliovirus belongs. Based on symptoms, doctors can probably rule out many of those viruses as well. Many enteroviruses have protein "keys" to other parts of the central nervous system. Some enteroviruses, such as the worrisome Enterovirus 71, which has caused outbreaks in Asia and other parts of the world, can inhibit breathing or heart rhythm by attacking respiratory or cardiac nerves. Those symptoms have not occurred in the California cases.

Despite all of these clinical clues, doctors can't know for certain what caused the paralyses until they catch the virus in the central nervous system. That's difficult, because enteroviruses typically remain in the spinal fluid for only a few days, or sometimes just hours. If the patient doesn't appear at the hospital immediately after the first signs of weakness, physicians have to sample other areas of the body to find the disease. Enteroviruses remain in nasal and oral secretions for up to 10 days and can be found in the stool for several weeks. Two of the victims in California had Enterovirus 68, another relative of poliovirus, in their nasal secretions.

That doesn't prove anything, because enterovirus can be present without causing paralysis. The probability is significant, though. Modlin, a globally recognized expert on enteroviruses, sets the odds that Enterovirus 68 caused the paralyses in the children where it was found at "well in excess of 80 percent." Of course, it's entirely possible that one virus caused some of the paralyses while other pathogens were responsible for other cases.

There's one important question remaining to be answered: If an infectious agent is responsible for the paralyses in California, is this an outbreak that puts other children in danger? The question has even reached Washington, where Sen. Barbara Boxer, D-Calif., is urging the CDC to open an investigation.

At this point, there appears to be little likelihood of an epidemic, according to doctors investigating the cases in California. The children had no apparent contact with each other, and physicians are still attempting to determine whether they have anything else in common, such as travel or contact with certain animals. If an enterovirus is the cause, the disease is unlikely to spread.

Aside from polio and Enterovirus 71, few of the pathogens in that family have shown any ability to cause epidemics. The California cluster may just be a tragic and infrequent consequence of a fairly rare infection.

 

1
Text Only
Community News Network
  • Darth Vader is polling higher than all potential 2016 presidential candidates

    On the other hand, with a net favorability of -8, Jar Jar is considerably more popular than the U.S. Congress, which currently enjoys a net favorability rating of -65.

    July 23, 2014

  • 072214 Diamond Llama 1.jpg Llama on the loose corralled in Missouri town

    A llama on the lam cruised Main Street Tuesday before it mistook a resident’s fenced backyard for a place to grab a meal and freshen up.

    July 22, 2014 2 Photos

  • Screen Shot 2014-07-22 at 2.00.42 PM.png VIDEO: Train collides with semi truck carrying lighter fluid

    A truck driver from Washington is fortunate to be alive after driving his semi onto a set of tracks near Somerset, Ky., and being struck by a locomotive, which ignited his load of charcoal lighter fluid.

    July 22, 2014 1 Photo

  • mama.jpg What we get wrong about millennials living at home

    If the media is to be believed, America is facing a major crisis. "Kids," some age 25, 26, or even 30 years old, are living out of their childhood bedrooms and basements at alarmingly high numbers. The hand-wringing overlooks one problem: It's all overblown.

    July 22, 2014 1 Photo

  • Malaysians wonder 'Why us?' after second loss of airline jet

    It was all too familiar. Grieving families rushing to airport. The flashing television graphics of a plane's last radar appearance. The uncomfortable officials before a heavy thicket of microphones.
    For many Malaysians, the disappearance of Flight 370 in March has been a long trauma from which the nation has not yet recovered.

    July 18, 2014

  • The terrible history of passenger planes getting shot out of the sky

    What is more clear is that, if initial reports are true, this would be the deadliest incident of a civilian passenger plane being shot down in modern memory. In some instances, the causes of the disaster are still shrouded in mystery. Here are some of the worst events.

    July 17, 2014

  • 130408_NT_BEA_good kids We're raising a generation of timid kids

    A week ago, a woman was charged with leaving her child in the car while she went into a store. Her 11-year-old child. This week, a woman was arrested for allowing her 9-year-old daughter to go to the park alone. Which raises just one question: America, what the heck is wrong with you?

    July 17, 2014 1 Photo

  • Screen Shot 2014-07-16 at 2.12.33 PM.png Gunshots narrowly miss TV reporter

    A reporter for a West Virginia television station narrowly escaped injury or worse Monday while covering a fatal weekend shooting in Beckley.

    July 16, 2014 1 Photo

  • 25 hidden secrets in "Weird Al's" "Word Crimes" video

    Yankovic's 14th album was released this week, and it warms my heart containers that he's kept up his geeky brand of humor for so long. While he has written so many incredible songs, none have spoken to my love of proper grammar.
    Until "Word Crimes."

    July 16, 2014

  • State lawmakers tweak gun regulations

    Obtaining a concealed carry weapons license within the Commonwealth of Kentucky is not a simple task.

    July 16, 2014

Twitter Updates
Facebook
Stocks