02.25.14 7:40 PM ET
Relax, There’s No Polio Epidemic—Yet
The American Academy of Neurology (AAN) chilled the hearts of parents across California and beyond with their announcement. Sunday that five children there had developed polio-like paralysis over the last year. The AAN press release is derived from a presentation researchers are to give at the annual meeting this May.
Among the five, an illness that began like every other infection—fever, some respiratory symptoms, standard-issue kid stuff, i.e., no-big-deal in any way—ended up causing limb paralysis that has not improved over several months. In addition to these five, the group also is looking into reports on roughly another 20 kids who may have developed a similar disease.
Scientists have long known that polio is not the only virus that can cause "polio-like" paralysis. Indeed, as polio has slowly been eradicated—currently Pakistan (where several polio workers have been killed) is the last hotbed globally—public health workers have reported persistence of cases of polio-like paralysis in children. These cases are thoroughly examined to determine the cause, which generally sorts out one of three ways. First, there can be a failure of vaccination for polio, either because the vaccine was not given (see Pakistan issue above) or because there was a problem with the vaccine itself. Maintenance of a “cold chain” for the live attenuated oral polio vaccine can be a challenge in countries where electricity is a luxury.
Second, there is the possibility that the disease was caused by the polio vaccine itself, called vaccine-associated paralytic polio (VAPP). Jenna Bush’s father-in-law, John Hager, former Lieutenant Governor of Virginia, developed a polio-like paralyzing disease as a young man, possibly after exposure to a son who had received the live oral vaccine. This set of polio-related illnesses, called vaccine-derived polioviruses has led to a gradual shift away from the slightly dangerous oral live vaccine (the “Sabin”) to the safe but less potent injected, inactivated (“Salk”) vaccine, first in the resource-rich countries but increasingly in poorer nations as well.
The third possibility, which appears operative in California, is that a distinct non-polio virus is causing the disease. Polio is one of many viruses belonging to the "enterovirus" family. The "entero" prefix denotes the fact that many have been found to cause intestinal problems—often a 24-hour "stomach flu." Others in the vast genus of viruses—at least 100—cause human disease. Included in this list are rhinoviruses (the nose-virus causing the common cold) and Coxsackie virus (named after the New York town where an outbreak of hand-foot-mouth blisters and fever occurred in kids). Enterovirus itself, with dozens of different types that affect humans, is another, as is—most famously—poliovirus.
When cases of polio-like illness are seen, as has happened in California, investigators comb through the situation looking for these other viruses, called non-polio enterovirus, or NPEV, to determine whether one might be the cause. The medical literature publishes regular reports of these investigations, both from the Americas and Europe. Each of these related viruses can cause a polio-like syndrome by attacking the same specific area of the spinal cord that polio destroys, an area that is required for movement, while leaving the rest of the spinal cord untouched. And even in 2014, polio, as well as the other enteroviral causes of sudden flaccid paralysis, has no treatment. A patient’s outcome is determined by time and luck.
In the report from the American Academy of Neurology, the same systematic search for a non-polio viral cause led to discovery of the closely-related enterovirus 68, which was isolated from two of the five cases. The other 3 cases did not have specimens submitted for study but may well be related to the same strain. The investigation of the 20 other possible cases is ongoing but many may be found to have the same enterovirus 68. Indeed, it is likely that the researchers will find a few more alarming cases beyond the 20. California (and the U.S. in general) does not have a central reporting program for such syndromes; therefore, energetic investigators calling colleagues are likely to find an additional case here and a case there.
It is very unlikely though that there is an epidemic underfoot in California. Rather it is likeliest that interested investigators are pulling back the curtain on a chronic but stable, low rate of these devastating infections.
As more information is gathered, it is important to note that the cases are confined to small children and not spreading to their parents. Enteroviruses are common and likely the parents are immune from new infection because of a previous infection with an enterovirus that, in them, did not provoke a severe paralytic disease but rather was simply a mild forgettable illness.
In other words, immunity works. That the disease should be seen in California, home of perhaps the most intense anti-vaccine movement in the US, raises the possibility that the current California tragedy may help public health experts convey the message of the benefits of vaccination against polio and other diseases. Because they have been nearly eradicated, the devastation caused by diseases such as polio and measles and whooping cough is unknown to the current generation that hears only of the side effects, real and imagined, of vaccines. No, there is no vaccine—yet—against enterovirus 68, but to see flaccid paralysis in a young kid is to understand the ardency of vaccine enthusiasts. One can only hope that the current California tragedy will serve to inform parents of the value of vaccines and thereby prevent future cases of vaccine-preventable diseases, including poliomyelitis.