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What does it take to eradicate a deadly disease?

August 25, 2015 by Tracy Romoser

A woman holds an infant while a nurse administers an oral vaccine.

Over the last two decades, the number of polio cases has fallen by 99 percent, thanks to global immunization campaigns. Photo: PATH/Wendy Stone.

Africa is on the cusp of being polio-free after news that Nigeria has gone one year without recording a single case of polio. How did they do it?

On an October night in 1977, Ali Maow Maalin didn’t feel well. He soon developed a fever that wouldn’t go away and a few days later his skin broke out in a rash. Concerned, Ali went to the hospital only to be sent home, misdiagnosed with a case of chickenpox.

At the time, Ali didn’t know that he was the last person on Earth to catch naturally occurring smallpox. He survived, but here’s the truly good news: after he was properly diagnosed, a search revealed no smallpox cases in Somalia on the local and city levels. A subsequent regional and country-level search confirmed that the virus stopped at Ali. In 1980, after the World Health Organization certified that smallpox had been eradicated, routine vaccination was discontinued around the world.

Smallpox showed us we could win the fight against a global disease.

It’s only a matter of time before a “last person on Earth” story can be told about polio.

A river runs through a village.

The poliovirus lurks in sewage and can be passed onto populations for years. Photo: PATH/Robyn Wilmouth.

Environmental surveillance: a game of hide and seek

Over the last two decades, the number of polio cases has fallen by 99 percent worldwide, thanks to global immunization campaigns. Africa is on the cusp of being polio-free after news that Nigeria—a country that has persistently battled the poliovirus—has gone one year without recording a single case.

And yet, despite worldwide vaccination efforts, there are still pockets of the disease. The virus is incredibly contagious, it’s not always easy to spot, and small outbreaks can quickly spread across geographies with no consideration for borders. A dangerous proposition when international conflicts interfere with routine vaccination.

Monitoring the presence of polio is still measured by cases of paralysis (acute flaccid paralysis). But many cases are “silent,” meaning people carry the virus asymptomatically without exhibiting clinical signs of polio. Because the virus is shed through feces, the infection can pass onto populations for years, potentially sparking a resurgence.

“Because resurgence is a risk,” says David Boyle, senior research scientist in PATH’s Diagnostics Program, “we’re always asking: ‘Is the virus no longer there or are we just not seeing it?’”

Instead of waiting for cases to appear, there is an alternative approach—an early warning signal that tells us if the virus is present in the environment. And in the environment, that means looking for poliovirus in sewage.

Two men scoop water out of a river with a bag.

Surveillance and testing are important tools used to identify where diseases like polio might make a resurgence. Photo: University of Washington/Scott Meschke.

It’s a dirty business but someone had to make it more manageable

For years, environmental surveillance teams have used an aggressive strategy to identify the poliovirus before it has a chance to sicken a population. They do this by hand collecting samples of waste water that likely include sewage, which are then shipped to labs that can search for the virus.

Transporting waste water is difficult and limits how much material is used for sampling. An alternative approach is to use a tool called a “bag-mediated filtration system,” developed by Scott Meschke, a professor of environmental and occupational health sciences in the University of Washington (UW) School of Public Health, and his laboratory staff. It works by capturing polio and other viruses onto a filter, which is then shipped for testing. This allows the sampling of larger volumes, yet greatly reduces the size and weight of material shipped to the labs.

A prototype of the “bag-mediated filtration system.”

This prototype of the “bag-mediated filtration system” works by capturing polio and other viruses onto a filter, which is then shipped to a lab for testing. Photo: PATH/Robyn Wilmouth.

PATH and the UW School of Public Health have developed an all-in-one sampling kit and a processing tool to streamline testing. This team is working with polio laboratories in Kenya and Pakistan to validate the performance of the new sewage-sampling kit.

A second tool, a rapid and instrument-free polio diagnostic, can help surveillance officers test people who have symptoms that indicate potential poliovirus infection. It doesn’t require expensive equipment and has the potential to complement existing, more complex tests that are used only at regional laboratories. It may also be used as backup in areas where political unrest makes it difficult to ship samples to the regional laboratories for testing.

A man in a lab coat holds a test tube.

A fast, inexpensive polio diagnostic test can help surveillance officers test people who have symptoms of poliovirus infection. Photo: University of Washington/Scott Meschke.

The PATH and UW team recently met with global surveillance experts in South Africa and presented the project data and hands-on training of both tools. Their feedback, as well as comments from the field, are helping to refine the design and operation of these tools to optimize their performance.

“Good surveillance is crucial to monitor this approach and push the eradication strategy forward.” adds David Boyle, “It’s also important for us to know when immunization is working.”

The only way to fight polio is with immunization and vigilance

If we’re ever to tell that story about the last person on Earth who contracted polio, we need a multifaceted approach. Along with immunization, we need to continue global surveillance long after it looks as if the battle has been won. Effective tools will help confirm that the poliovirus has been eradicated at the global scale. Then, and only then, will polio be history.

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