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Could an Oral Measles Drug Help the Unvaccinated?

A medication designed to inhibit measleslike virus in infected ferrets shows promise



Image: CDC/Dr. Edwin P. Ewing, Jr.

It all begins with a cough or a simple rash. Then a note from school may be sent home with students that says someone in the fifth grade class has been diagnosed with measles, a highly infectious disease that could have been prevented with a vaccine. If another child in class has not been vaccinated, by that point it’s too late—there is nothing to do but wait and see what happens.
 
Like the flu, measles can spread through the air via droplets carried by sneezes, coughs and breathing. When an unvaccinated person is exposed to the virus there is about a 90 percent chance that he, too, will soon have measles, according to the U.S. Centers for Disease Control and Prevention. A new medication geared toward staving off sickness among the unvaccinated but measles-exposed, however, is showing some early promise. New work indicates an oral medication is effective at preventing measleslike disease in ferrets.
 
A research team reports in the April 16 Science Translational Medicine that after a small group of ferrets were exposed to the canine distemper virus—a close cousin of measles—and then three days later treated with a newly developed antiviral medication, the disease was completely suppressed. “This is a phenomenal first step forward,” says Pritish Tosh, an infectious disease physician and researcher at Mayo Clinic who was not involved in this study. All three of the exposed animals not only survived the virus but developed high amounts of protective antibodies against it, likely protecting them against future exposures (although the research team has not yet explored how long that immunity lasts). “We strongly support vaccination,” says study author Richard Plemper of the Institute for Biomedical Sciences at Georgia State University. “This drug was not developed as an alternative to vaccination but rather as an additional weapon in our arsenal against the virus that may enable us to improve disease management and rapidly silence outbreaks,” he says. The researchers hope that a therapeutic drug will be particularly useful for combating outbreaks in unvaccinated hotspots.
 
Although most people in the U.S. receive measles vaccinations, the small number of people who refuse the vaccine are fueling outbreaks. In 2014 alone there have been 125 cases of measles across 13 states. Many of those cases were among unvaccinated individuals, according to the CDC.
 
After exposure to measles a person typically does not develop symptoms for two weeks. But during this incubation window the virus silently replicates in the body. A future iteration of this medication would ideally be used during this interval. Before they begin clinical trials in humans, however, the team says they plan to explore how the medication may work in monkeys infected with the measles virus. Moreover, Plemper adds, his team believes this drug could have additional applications in veterinary medicine to treat other morbilliviruses in animals other than humans.
 
The medication is not structured like a vaccine, however, which would have either a weakened or dead version of the virus that would help the body mount a strong defense against the virus in the future. (Indeed, nine ferrets exposed first to the drug and then to the virus died.) Instead, the medication is an inhibitor drug that blocks the viral RNA polymerase—an enzyme that would otherwise help measles replicate.
 
Plemper and colleagues also studied if administering a drug like this could help promote the rise of a formidable “superbug” of measles that would be resistant to this new drug and potentially fuel even more lethal strains of disease. They created several different drug-resistant versions of the measles virus and infected lab animals. Yet the researchers found that most strains caused milder versions of the disease than the original virus. One strain, however, killed all the animals that it infected (although the subjects took longer to die than those infected with the normal strain). Fortunately that drug-resistant strain did not travel as easily among the ferrets as typical canine distemper virus, so Plemper says that the strain would likely be “clinically insignificant.”

The researchers have not yet calculated how expensive an oral measles medication would be if it clears clinical trials in humans.
 

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