Nav: Home

How to wipe out polio and prevent its reemergence

June 19, 2015

Public health officials stand poised to eliminate polio from the planet. But a new study shows that the job won't be over when the last case of the horrible paralytic disease is recorded.

In an article publishing June 19 in the Open Access journal PLOS Biology, graduate research fellow Micaela Martinez-Bakker and professors Aaron A. King and Pejman Rohani of the University of Michigan Department of Ecology and Evolutionary Biology use disease-transmission models to show that silent transmission of poliovirus could continue for more than three years with no reported cases.

To ensure that the disease is truly eradicated, aggressive surveillance programs and vaccination campaigns must continue in endemic countries for years after the last reported case, they conclude.

"Using transmission models, we demonstrate that you can have sustained chains of silent transmission in populations for more than three years, without a single person ever showing up as a reported polio case," said Martinez-Bakker, who completed the six-year polio study as part of her doctoral dissertation.

"Once we've eradicated polio--or think we've eradicated polio--we probably should intensify the environmental surveillance to make sure the virus is not just lurking under the hood at very low levels," she said. "Polio eradication is about eradicating the virus. It's not about eradicating the disease paralytic polio."

Pakistan, Afghanistan and Nigeria are the only countries where polio remains endemic - down from more than 125 countries in 1988. The disease mainly affects children under 5, and one in 200 infections leads to irreversible paralysis, according to the World Health Organization, which reported 416 cases of polio worldwide in 2013.

Martinez-Bakker analyzed polio case reports from large-scale U.S. epidemics in the pre-vaccine era, along with birth statistics and census numbers from every state. This enormous data set provided a unique glimpse into the ecology of polio infection in the relative absence of human intervention.

And it led her to conclude that the leading explanation for the marked increase in U.S. polio incidence from the 1930s to the 1950s--an idea known as the hygiene hypothesis or the disease of development hypothesis--is likely wrong.

In particular, the sharp increase in cases that occurred after the mid-1940s appears to be a straightforward consequence of a surging birth rate during the post-war "baby boom," not the result of improvements in sanitation and hygiene, as textbooks currently suggest.

"If you have more kindling, you can have a much larger forest fire," Martinez-Bakker said. "The baby boom provided more kindling for polio epidemics--young children and infants over 6 months of age--so much more explosive outbreaks were now possible."

Disease transmission models allowed her to track the movement of poliovirus and reconstruct the millions of unobserved, symptomless infections that spread the disease in the first half of the 20th century.

The number of U.S. polio cases peaked in 1952 at 57,000. Three years later, mass inoculations with Jonas Salk's vaccine began after it was declared "safe, effective and potent" during an April 1955 scientific meeting at the University of Michigan.

The new U-M research shows for the first time that more than 3 million Americans were likely infected with poliovirus during that peak year of 1952. The study also explains why U.S. polio epidemics in the pre-vaccine era were explosive, seasonal and varied geographically.

"Reaching eradication and preventing reemergence of polio requires intimate knowledge of how the virus persists," Martinez-Bakker said.

"Historical epidemics that predate the use of vaccines can be used to disentangle the epidemiology of disease from vaccine effects," she said. "They allow us to establish a baseline by studying the system in the absence of intervention."
-end-
Please mention PLOS Biology as the source for this article and include the links below in your coverage to take readers to the online, open access articles.

All works published in PLOS Biology are open access, which means that everything is immediately and freely available. Use this URL in your coverage to provide readers access to the paper upon publication: http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002172

Contact:

James Erickson
University of Michigan News Office
ericksn@umich.edu
734-647-1842

Ms. Micaela Martinez-Bakker (Author)
Department of Ecology & Evolution
University of Michigan
bakkerma@umich.edu

Citation:

Martinez-Bakker M, King AA, Rohani P (2015) Unraveling the Transmission Ecology of Polio. PLoS Biol 13(6): e1002172. doi:10.1371/journal.pbio.1002172

Funding:

MMB is supported by the NSF Graduate Research Fellowship Program and the University of Michigan Rackham Merit Fellowship. PR and AAK are supported by the Research and Policy in Infectious Disease Dynamics program of the Science and Technology Directorate, Department of Homeland Security, the Fogarty International Center, National Institutes of Health and by MIDAS, National Institute of General Medical Sciences U54-GM111274 and U01-GM110744. This research was supported in part through computational resources and services provided by Advanced Research Computing at the University of Michigan, Ann Arbor; and by UAF Life Science Informatics. UAF Life Science Informatics as a core research resource is supported by Grant Number RR016466 from the National Center for Research Resources, a component of the National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests:

The authors have declared that no competing interests exist.

PLOS

Related Infants Articles:

Deaf infants' gaze behavior more advanced than that of hearing infants
Deaf infants who have been exposed to American Sign Language are better at following an adult's gaze than their hearing peers, supporting the idea that social-cognitive development is sensitive to different kinds of life experiences.
Initiating breastfeeding in vulnerable infants
The benefits of breastfeeding for both mother and child are well-recognized, including for late preterm infants (LPI).
Young infants with fever may be more likely to develop infections
Infants with a high fever may be at increased risk for infections, according to research from Penn State College of Medicine.
Early term infants less likely to breastfeed
A new, prospective study provides evidence that 'early term' infants (those born at 37-38 weeks) are less likely than full-term infants to be breastfeed within the first hour and at one month after birth.
Infants are more likely to learn when with a peer
Researchers at the University of Connecticut and University of Washington looked at the mechanisms involved in language learning among nine-month-olds, the youngest population known to be studied in relation to on-screen learning.
Allergic reactions to foods are milder in infants
Majority of infants with food-induced anaphylaxis present with hives and vomiting, suggesting there is less concern for life-threatening response to early food introduction.
Non-dairy drinks can be dangerous for infants
A brief report published in Acta Paediatrica points to the dangers of replacing breast milk or infant formula with a non-dairy drink before one year of age.
Infants can't talk, but they know how to reason
A new study reveals that preverbal infants are able to make rational deductions, showing surprise when an outcome does not occur as expected.
Infants are able to learn abstract rules visually
Three-month-old babies cannot sit up or roll over, yet they are already capable of learning patterns from simply looking at the world around them, according to a recent Northwestern University study published in PLOS One.
Baby brains help infants figure it out before they try it out
Researchers at Penn State are using new statistical analysis methods to compare how we observe infants develop new skills with the unseen changes in electrical activity in the brain, or electroencephalography (EEG) power.
More Infants News and Infants Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Risk
Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#540 Specialize? Or Generalize?
Ever been called a "jack of all trades, master of none"? The world loves to elevate specialists, people who drill deep into a single topic. Those people are great. But there's a place for generalists too, argues David Epstein. Jacks of all trades are often more successful than specialists. And he's got science to back it up. We talk with Epstein about his latest book, "Range: Why Generalists Triumph in a Specialized World".
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.