By Greg Basky for SHRF
In 2012, hundreds of young children in the US started developing a mysterious condition that left them unable to move their hands or legs and -- in some extreme cases -- incapable of breathing without mechanical assistance. The medical community and parents feared they were witnessing the return of polio. Testing, however, revealed that while this new condition caused symptoms similar to a disease that -- at its peak in 1953 claimed the lives of 500 children worldwide -- it was not in fact polio. Equally perplexing, as quickly as this new menace emerged, it seemed to disappear just as fast.
North America saw outbreaks again in 2014 and 2016, with hundreds of infected children going on to develop full-blown polio-like symptoms. Researchers eventually determined the viral disease was a member of the polio family called acute flaccid myelitis. In 2018 the scientific community discovered that the illness was caused by Enterovirus-D68 (EV-D68), a virus originally identified in the 1960s. However, until recently little research was done on the virus because it previously caused only minor, short-lived respiratory illness in children.
With the support of a SHRF Establishment Grant, USask virologist Anil Kumar is working to solve the mystery of how what started out as mild-mannered virus has turned into such a serious health threat. “There are around 20 mutations which this virus acquired between the original 1960s strain and the recent strains which can cause acute flaccid myelitis,” says Kumar. “We know these genetic changes are there, but we don't know which ones are the most critical changes that actually made this virus attack the nerves and cause such harm to kids.”
Kumar and his research team at the U of S will be drawing on several techniques to better understand the mechanisms behind this virus’s evolution. They will trace back from the new form to its earlier iteration, to identify what genetic changes took place as it mutated. By manipulating the genetic sequence, changing genes one at a time or in groups, they hope to identify the point at which EV-D68 gained the ability to multiply in a particular tissue type or organ. Kumar will systematically “knock out” cellular genes using cutting-edge CRISPR gene editing technology to identify the receptors on cells that enable the virus to enter the body’s neuronal cells.
He and his team plan to use an approach called single cell-based transcriptomics to examine which cell types serve as viral reservoirs in the central nervous system, enabling EV-D68 to kill off motor neurons. These motor neuron deaths are what cause paralysis in the muscles that control a person’s limbs, faces, and ability to breathe.
The group wants to know which mutations equipped the virus to replicate efficiently at higher temperatures; at some point, the virus moved its home base out of the upper respiratory tract, which has a lower temperature than our body’s core. Kumar says that somewhere along the line of genetic changes, EV-D68 developed the ability to cross the blood-brain barrier or efficiently replicate in muscle cells to reach the motor neurons.
Two things attracted Kumar to study the virus. First, plain old curiosity. “As a scientist, I want to know what’s going on,” says Kumar, who -- during his postdoc at the University of Alberta -- was part of one of the first labs to study the Zika virus. “It’s a scientific mystery. This was a benign respiratory virus that wasn’t causing any serious illness, then all of a sudden it becomes a neurotropic virus that causes a lot of harm in children.”
Limiting -- or better still, preventing -- that harm is perhaps the bigger driver for Kumar. “It’s a terrible disease,” he says. “These kids who contract it suffer from long-term sequelae. Their movement and muscle problems extend for years. And even if they receive rehabilitation therapy, not every kid eventually becomes fine. It’s just like polio. Some people end up having to just live with it.” If the long-term effects of acute flaccid myelitis are anything like those of polio -- which Kumar believes they will be -- children who are infected will over time develop complications similar to post-polio syndrome including progressive muscle weakness, muscle and joint pain and chronic fatigue.
Figuring out how EV-D68 enters neurons is a critical first step in preventing the virus from causing acute flaccid myelitis, according to Kumar. “Viral entry into cells is a lock and key type mechanism,” he says. “If we can design a drug that can prevent the virus from attaching to cells, then it will not be able to infect the cell and cause the damage.”
The work he and his team will be doing over the next three years could pave the way for prophylactic drug therapy. By blocking the interaction with the motor neurons, medication could eventually reduce the number of children who develop the serious form of this disease. “If we could screen for EV-D68 in children who come down with the respiratory illness, then we could provide drug treatment that would prevent it from advancing to the serious polio-like disease.”