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Doctors say they are confused by what causes a slight rise in cases of polio-like paralysis in children in the United States.
The disease, called acute flaccid myelitis, appears to be on the rise in 2018 after being the cause of a few cases in 2017. Centers for Disease Control and Prevention have investigated 127 reported cases, of which 62 confirmed as MFAs in 22 states. .
"We have not been able to find the cause of the majority of AFM cases," Dr. Nancy Messonnier, CDC told reporters Thursday.
"Despite extensive laboratory testing, we did not determine which pathogen or immune response caused weakness and paralysis of the arm or leg in most patients," added Messonnier.
"We do not know who may be at higher risk of developing AFM or why they may be at higher risk."
Why is it so difficult to understand?
There are not many cases
Since the first wave of MFA cases in 2014, the CDC has confirmed 386 cases of MFA. This is not a big group to study. "Overall, the rate of AFM over the years of diagnosis, that is, since 2014, is less than one in a million. That's why we say that this disease is incredibly rare, "said Messonnier.
The apparent syndrome with polio, which had already swept the country from regular epidemics towards the end of summer, crippling thousands of children. But whatever the cause of AFM, it does not seem to cause paralysis or muscle weakness as much as polio, said Dr. Benjamin Greenberg, a specialist in rare neurological autoimmune diseases at the University's Southwestern Medical Center. from Texas. some AFM patients.
"Back at its peak for 100 to 1,000 people infected with polio, we saw someone paralyzed," Greenberg told NBC News. "We think that with these viruses, it's a fraction of that."
People are not usually tested for viruses
In 2014, the main suspect for causing the AFM was a virus called EV-D68. It was circulating at the same time as MFA cases began to appear and some of the affected children were infected with EV-D68. But others were not there.
EV-D68 is an enterovirus, a distant relative of the poliovirus. However, there are many enteroviruses, which usually cause cold-like symptoms, as do rhinoviruses, adenoviruses, and many other viruses. There are hundreds of virus species that infect people and many cause cold-like symptoms.
Most people do not even go to the doctor with a virus, and doctors rarely test patients to see what virus they have. Thus, unless there are massive epidemics of viruses that cause serious illnesses in the hospital, doctors and public health officials rarely know how "circulating" viruses occur.
But since 2014, according to the CDC, there has been no noticeable increase in the number of EV-D68 cases, even when MFA cases have increased and decreased. However, doctors do not systematically test people for this, so it is possible that cases have been missed.
Because doctors do not know which virus can be responsible – if it is a virus – there is no way to vaccinate people against this virus.
The CDC is open to the possibility that it is not a virus that causes the disease, but that it finds no other plausible cause.
By the time they develop the AFM, patients may have eliminated the virus
It can go away a few days after an infection for a patient to develop what is called a neuroinvasive disease – when a virus attacks the nerves, spinal cord or brain. A child may have a runny nose or a mild fever and, in most cases, parents would have no reason to worry – until the telltale symptoms of a drooping eyelid, an arm low or difficulty standing up. From now on, the body may have eliminated the infection itself and the tests may not reveal any specific viral cause.
Most of the AFM cases studied by the CDC do not indicate any particular infection. This is not to say that there has been no infection, only that the immune system has already eliminated it or that the disease may be caused by an illness that doctors have not considered testing. .
Messonnier said that other viruses that EV-D68 have been found in patients with MFA. "But if you have peaks of illness every late summer or early fall, you'd think we'd find one agent. That's what we do not find, "she said.
The CDC was clear on one point: none of the patients tested positive for polio. In the past, an oral polio vaccine could cause polio-like syndrome in some people, but this vaccine was no longer available in the United States since 2000, and the last known case in the United States involved an infant with other health problems that had been vaccinated. in India, brought to the United States and died in 2013, according to the CDC.
There are many viruses and they can cause many neurological symptoms.
"There are many different viruses that can cause this syndrome," Greenberg said.
Virtually all viruses can cause neuroinvasive disease, but they rarely do. Zika is one of the most notorious recent examples. When it infects pregnant women, the Zika virus can enter the brain of developing fetuses and cause permanent damage.
Last week, the CDC reported viruses transmitted by ticks and mosquitoes that can cause neurological disease. They include West Nile virus, Jamestown Canyon virus, Lacrosse virus, Powassan virus, St. Louis encephalitis and Eastern equine encephalitis. These viruses have caused symptoms, including encephalitis, a life-threatening inflammation of the brain; acute flaccid paralysis, which may include AFM and similar pathologies; and meningitis.
That's why the CDC's advice on preventing an infection that can cause AFM is so general: wash your hands, cover yourself and use an insect repellent to prevent insect and tick bites.
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