A British man has been shedding live poliovirus in his stool for the past 28 years, researchers say. The man has an autoimmune disorder that appears to have kept him from clearing the weakened virus contained in the oral polio vaccine he received as a child from his system.
Javier Martin from the UK's National Institute for Biological Standards and Control and his colleagues report in PLOS Pathogens that they collected stool samples from the man for some 20 years, for a total of 185 samples. The viruses in the first sample, they say, differed from those in the Sabin OPV VP1 sequence at about 10 percent of the nucleotides, but viruses obtained from the most recent sample from March of this year exhibited a 17.7 percent VP1 sequence drift from the Sabin 2 poliovirus.
In mice, the virus shed from the man caused paralysis, though it could be neutralized in human blood.
Martin and his colleagues further reported that the man has been excreting this highly virulent and antigenically modified type 2 poliovirus at high titers, likely since his last OPV vaccine 28 years ago.
"This virus is no different from any other polio virus," Martin tells NPR. "If people are properly immunized, there is no reason for infection."
The Guardian notes that this finding could mean that it might be slightly more difficult to eradicate polio — it's currently only found in Afghanistan, Nigeria, and Pakistan — if it's being shed from more people than currently suspected.
"We are at the end stage of polio eradication," Martin tells NPR. "But we still need to continue high immunization coverage and surveillance."