Parasitic worm may be cause of mysterious seizure disorder in children
The parasitic worm Onchocerca volvulus may be the cause of a childhood seizure disorder called Nodding Syndrome. (Avindra Nath, M.D., NIH/NINDS)
Published Wednesday, February 15, 2017 2:01PM EST
A parasitic worm may trigger the onset of a mysterious and incurable seizure disorder affecting children in parts of Africa, according to a new study.
The study’s lead author Dr. Tory Johnson, from Johns Hopkins University, led experiments for the U.S. National Institute of Neurological Disorders and Stroke in a multinational effort to understand what was causing a progressive and often fatal type of epilepsy known as Nodding Syndrome (NS).
“What happens is that previously healthy children develop what are called atonic seizures, so they lose muscle tone, and we see that in the neck and the head sort of tips forward,” Johnson explained in a phone interview with CTVNews.ca from Baltimore, Md. on Tuesday.
According to the World Health Organization (WHO), NS typically affects children between the ages of five and 15 years old, although there have been a few cases reported in children as young as two years old and in adults up to 32 years old.
NS can lead to progressive cognitive dysfunction, neurological deterioration, stunted growth and the nodding of the head during seizures, according to the WHO website.
Johnson said there’s no cure for NS and that it’s currently being treated with valproic acid and other anti-seizure medicines to help with the symptoms.
She said cases of NS has been restricted to South Sudan, northern Uganda and regions in Tanzania and that access to medication is a real concern in some of these areas. According to WHO, the disease was first documented in Tanzania in the late 1960s.
Finding a link:
Johnson explained that the African Ministry of Health and the U.S. Centers for Disease Control and Prevention (CDC) showed there was a consistent association with the parasite Onchocerca volvulus, which can cause blindness, and NS.
Johnson said her group of researchers wanted to figure out if the body’s immune system was inappropriately reacting to the parasite and causing inflammation or an autoimmune process causing NS because the parasite itself can’t enter the brain. The parasitic worm is transmitted into the body through black flies’ bites.
Through experiments comparing children with NS to other children without the disorder in the same villages, they discovered that children with NS had increased levels of an antibody that recognized a protein called leiomodin-1, found naturally in the brain. The parasitic worm Onchocerca volvulus has several proteins that resemble leiomodin-1, which tricked the children’s immune system into attacking their brains’ healthy proteins.
“These kids are getting infected with the parasite Onchocerca and their immune systems are doing a great job and attacking it, but several of the proteins that this worm makes really resemble proteins that are being expressed in the human brain,” Johnson explained.
Johnson said this process known as “molecular mimicry” doesn’t happen all that often and that every child infected with the parasitic worm won’t necessarily develop NS.
Dr. Avindra Nath, the Chief of the Section of Infections of the Nervous System at the National Institutes of Health (NIH) and National Institute of Neurological Disorders and Stroke (NINDS) called the findings an “important breakthrough” in understanding NS.
“We think that our observations for the first time really provide a testable hypothesis that can be explored in the field,” Nath said.
Where the parasite is found:
The parasitic worm connected with NS has been found in other areas without NS cases, such as sub-Saharan Africa but it is also prevalent in Yemen and Latin America, according to WHO.
The researcher said there are a few possible explanations as to why NS hasn’t been a problem in other areas where the parasite is found. One of them is that other places may have more access to anti-parasitic medicines and the parasitic worm is better controlled in those places. Another reason may be that children in the affected areas have a different genetic background that makes them more predisposed to the disorder. She also added that the worm itself may be a little different in the affected regions.
Prevention is key:
Johnson said the most meaningful takeaway from the study is to focus on preventing infection with the parasite to avoid further cases of NS.
“An ounce of prevention is worth a pound of cure,” she said.
Johnson cited a general deworming medication called ivermectin as a cheap and easy defence against parasites that has been useful in preventing NS. She said limiting black fly populations through aerial spraying is a much more difficult undertaking in some of the affected regions, especially in remote villages.
Johnson acknowledged that preventative measures don’t help the families with children already suffering from NS and that further research into treatment options will still need to be conducted.