(The conversation is an independent and ideal news source, analysis and commentary from academic experts.) Marisa Eisenberg, University of Michigan;…
(The conversation is an independent and ideal news source, analysis and commentary from academic experts.)
Marisa Eisenberg, University of Michigan; Andrew Brouwer, University of Michigan and Joseph Eisenberg, University of Michigan
(Convergence) The world is at the verge of eradicating polio. Only three countries now have ongoing transfers: Nigeria, Afghanistan and Pakistan. And in 2017, there were only a few dozen cases of paralytic wild polio reported worldwide ̵
1; a massive decrease from the estimated 350,000 cases reported in 125 countries in 1988. Development of the polio vaccine and global vaccination efforts is at the heart of this monumental public health impact.
Epidemiologists typically identify polio transmission based on reported cases of acute lap paralysis (AFP). The World Health Organization declares a country as polio free if there are no AFP reports for three years. But AFP is a difficult result that occurs in a very small part of polio infections. It’s just the tip of the iceberg – a case of AFP indicates significant underlying polio transmission in a population.
That’s why, as the world is approaching the final stage of polio eradication, environmental monitoring becomes important. Looking for poliovirus in sewers is more sensitive than counting cases of AFP. It can detect viral damage in feces from non-paralyzed people who are infected with polio – which epidemiologists call the silence of the polio.
Environmental microbiologists have studied pathogens in wastewater for decades, but its use as a public health tool is relatively new. As epidemiologists who specialize in modeling the spread of disease, we wondered whether we could estimate the intensity of infection in a population by analyzing the number of viruses in its sewage. The discovery of polio transmission in Israel 2013 – the first in the country since 1988 – enabled us to test our model, together with environmental monitoring data from different parts of the world, could be used to assess the amount of silent transmission.
Characterizes a polio outbreak in Israel
In view of all progress made against polio eradication, it was disturbing to realize that polio was actively transferred to Israel in 2013. A sewage monitoring system – established in 1989 by the Israeli Health Department to detect poliovirus – sounded the alarm. The health secretariat worked quickly to vaccinate the public, and fortunately, none of the infections led to paralysis.
To detect polio in human waste in Israel samples are automatically collected from sewers and treatment plants approximately every week. Back to the country’s central virology laboratory, they are checked for poliovirus.
Most of the positive sewage trials in the 2013 outbreak came from the Negev region of Israel, and most of them from the predominant Bedouin community. Based on molecular properties of the virus isolated from the sewage, scientists know that the virus originated from Pakistan, then traveled into the region, diverging to Egypt, Israel and Syria. For a virus, carefully guarded geopolitical boundaries are also floating.
To understand what kept the polio transfer, we needed to better characterize Bedouin’s pipe pattern. Where people travel gives way for them to potentially spread the virus. For example, larger Jewish communities such as Beer Sheva are economic hubs; Bedouiners from communities throughout the region travel there daily. In addition, many communities send children to regional schools, another potential hub for transmission.
Poor hygiene conditions are an important way for poliovirus to be moved from host to host – remember that infected persons secrete viable viruses in stools. Epidemiologists knew surprisingly little about these aquatic and sanitary infrastructure communities, except that they were very variable and often poor compared to neighboring Jewish communities.
Create a model for the spread of polio
The Central Virology Laboratory and the Ministry of Health recognized the potential of their data, but no one had developed a theory for converting environmental monitoring into public health. Due to the ourexperiencein modeling of environmentally transmitted infectious diseases, we met with the Central Virology Laboratory and the Ministry of Health officials on the ground during the later stages of the epidemic and began collaborating on a new solution to the problem.
A mathematical model allows epidemiologists to use what we know about a situation’s underlying biological mechanisms to better interpret or extract more information from data. We knew a number of things in this case: the relative levels of poliovirus in the sewage of different societies over time, the coverage of the vaccination campaigns and the differences in transmission between the wild virus and the weakened vaccine virus. Our goal was to arrive at a model that would explain how the disease was transmitted through the population of Israel that would match the observed changes in sewage levels over time.
Using new analytical methods, we estimated that in Rahat, the largest predominant Bedouin society, which held significant transfer, 56 percent of the risk factors – mainly children under 10 years – were infected.
Positive polio robber from the environment only warns public health professionals as the transfer happens. Our model provides additional information about how many people have been infected. Without a model, researchers could not calculate the extent of the outbreak – the poliovirus in the wastewater could have been collected from many people who did a little or some people throw a lot. But because outbreaks follow recognizable patterns, the dynamic changes in polio concentration can actually tell a lot about how the disease is moving through the population.
Model forecasts are always uncertain, so confirmation of multiple data sources is important. In this outbreak we could compare with rough estimates of infection based on tests on social chairs.
Silent Transfer Surveillance
As we approach the final stages of polio eradication, environmental measures will be the only way to detect polio transmission. And this silent spread of the virus must be stopped to completely eradicate the disease. Waiting until there is a paralytic fall means that there is a lot of polio around and containing it with vaccination efforts becomes more difficult.
Environmental monitoring efforts are growing in all three polio-endemic countries. Since the success of Israel to identify and rapidly contain transmission by administering oral polio vaccine, many countries have begun conducting polio monitoring of the environment. WHO is working to develop organic environmental monitoring standards that are in line with the well-established standards for acute paralysis.
In addition to polio, monitoring and monitoring of other infectious diseases released into sewage can and should be monitored – enterovirus, typhoid and cholera are main candidates. Epidemiologists can then use modeling methods to translate surveillance data to describe population patterns, so that public health professionals can respond quickly to eruptions.
This article is published from the Conversation under Creative Commons License. Read the original article here: http://theconversation.com/sewage-surveillance-is-the-next-frontier-in-the-fight-againstpolio-105012.