Weakened polio borrows genes to gain strength for outbreak
Genetic sleuthing has revealed how a dose of oral polio vaccine (OPV) can revert to the deadly poliovirus and cause an outbreak. The research highlights problems that global health organizations face completing their eradication of polio, and the urgency of that effort1.
"It reminds us that we need to be very careful in our development of a post-eradication policy," says Bruce Aylward, leader of the World Health Organization’s polio eradication program.
No wall of immunity
The Americas were declared free of wild poliovirus in 1999. Around this time a polio outbreak began on Hispaniola, a Caribbean island shared by the Dominican Republic and Haiti. The disease killed two children and paralysed a further 19.
From the genetic sequence of virus samples from each of these children, virologist Olen Kew at the US Centers for Disease Control and Prevention in Atlanta, Georgia, and his team have now deduced the origin of the deadly virus. "It came from a single dose of OPV given to a single [probably Haitian] child," says Kew.
Genes crucial to polio’s virulence are switched off in OPV. They had switched back on in the Hispaniola virus, the researchers found, probably through random mutation. This is hardly surprising because poliovirus "is one of the most rapidly evolving viruses we know", says Kew.
The researchers found other genes that didn’t belong to polio at all. The offending virus had borrowed genetic information from related gut pathogens called enteroviruses in the children it infected. This cut’n’paste trick may have enabled it to regain strength more quickly than it could by random mutation. "It is a great shortcut," says Mark Pallanch, a member of the CDC team.
Fortunately this kind of reversion can only happen in certain situations, says Pallanch. The situation in Hispaniola, it turns out, was perfect.
As many as 20% of children in some parts of Hispaniola had not been fully vaccinated with OPV. And wild poliovirus, which also causes immunity, had been absent from the island for many years. So there were sufficient children on the island who were susceptible enough to polio to carry and spread the virus
In Hispaniola "the process of reversion was not blocked by a wall of immunity", says Kew. OPV passed from child to child, replicating as it went. It reverted to a virulent form in about a year, the researchers estimate.
Time running out
Good vaccine coverage in most areas means that such outbreaks are rare. But two others recently in Egypt2 and the Philippines3 have raised concerns that the clock is ticking on efforts to eradicate polio globally4.
The big fear is a vaccine-derived outbreak devastating a completely susceptible child population, in the United States or Europe, which have been free of polio and OPV for decades, for instance.
To prevent this, OPV must be given to children in unvaccinated areas as quickly as possible and in a synchronized manner. The vaccine must then be withdrawn from use immediately. "The ongoing use of OPV poses a risk in itself," says Kew.
"It confirms something we already knew," says Aylward, who is concentrating on plans to phase out OPV. The recent OPV-related outbreaks have provided an idea of what to watch out for, he says. "We’ve now heightened our surveillance worldwide to catch this," he adds.
TOM CLARKE | Nature
Biofilm discovery suggests new way to prevent dangerous infections
23.05.2017 | University of Texas at Austin
Another reason to exercise: Burning bone fat -- a key to better bone health
19.05.2017 | University of North Carolina Health Care
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy