Wastewater monitoring is the next frontier in the fight against polio

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Marisa Eisenberg, University of Michigan; Andrew Brouwer, University of Michigan and Joseph Eisenberg, University of Michigan

(THE CONVERSATION) The world is about to eradicate polio. At present, only three countries have an ongoing transmission: Nigeria, Afghanistan and Pakistan. And in 2017, only about 20 cases of wild paralytic poliomyelitis have been reported worldwide, a significant decrease from the 350,000 cases reported in 1988 countries in 125 countries. Poliomyelitis vaccine development and global immunization efforts are at the heart of this huge public health achievement.

Epidemiologists generally detect poliomyelitis transmission based on reported cases of acute flaccid paralysis (AFP). The World Health Organization certifies that a country is polio-free if there has been no AFP declaration for three years. But PFA is a serious outcome that occurs in a very small fraction of polio infections. This is just the tip of the iceberg: a case of AFP indicates a significant underlying transmission of polio in a population.

Therefore, as the world approaches the final stages of polio eradication, environmental monitoring becomes essential. The search for poliovirus in wastewater is more difficult than counting AFP cases. It can detect the virus excreted in the feces of non-paralyzed people infected with poliomyelitis – what epidemiologists call the silent circulation of poliomyelitis.

Environmental microbiologists have been studying pathogens in wastewater for decades, but its use as a public health surveillance tool is relatively new. As epidemiologists specialized in modeling the spread of disease, we wondered if we could estimate the intensity of infection in a population by analyzing the number of viruses in its wastewater. The discovery of polio transmission in Israel in 2013 – the first in this country since 1988 – allowed us to test whether our model, combined with environmental monitoring data from different parts of the world, could be used to assess the degree of Silent transmission is always happening on a global scale.

Characterize a polio outbreak in Israel

Given all the progress made in the eradication of polio, it was disturbing to realize that polio was being actively transmitted to Israel in 2013. A wastewater monitoring system – set up in 1989 by the Israeli health service to detect poliovirus – sounded the alarm. The Ministry of Health worked quickly to vaccinate the public and, fortunately, none of the infections resulted in paralysis.

To track polio in human waste in Israel, samples are taken automatically weekly from the sewer lines and treatment plants. Back at the country's central virology laboratory, they are checked for poliovirus.

Most of the positive wastewater samples during the 2013 outbreak came from the Israel region in the Negev, and most of them came mainly from Bedouin communities. On the basis of the molecular characteristics of the virus isolated from wastewater, scientists know that the virus originated in Pakistan, then traveled to the region, then to Egypt, Israel and Syria. For a virus, even well-guarded geopolitical boundaries are fluid.

To understand what was driving the transmission of polio, we needed to better characterize Bedouin circulation patterns. The places where people travel provide them with routes for the potential spread of the virus. For example, large Jewish communities such as Be'er Sheva are economic centers; Bedouins from communities throughout the region go there every day. In addition, many communities send children to regional schools, another potential center of transmission.

Poor sanitation is an important way for poliovirus to move from one host to another. Remember that infected people excrete a viable virus in their stool. Epidemiologists knew very little about the water supply and sanitation infrastructure of these Bedouin communities, apart from that, they were very variable and often poor compared to neighboring Jewish communities.

Create a model on the spread of polio

The Central Laboratory for Virology and the Ministry of Health have recognized the potential of their data, but no one has developed a theory to convert environmental monitoring into public health parameters. Based on our experience in modeling infectious diseases that are transmissible to the environment, we met with representatives of the Central Virology Laboratory and the Ministry of Health in the latter stages of the epidemic and began collaborating on a new initiative. approach to the problem.

A mathematical model allows epidemiologists to use what we know about the underlying biological mechanisms of a situation 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 wastewater of various communities over time, the coverage of vaccination campaigns and the differences in transmission between the wild virus and the attenuated vaccine virus. Our goal was to propose a model that would explain how the disease was transmitted by the Israeli population and that would correspond to observed changes in polio levels of wastewater over time.

Using new analytical methods, we estimated that in Rahat, the largest predominantly Bedouin-dominated community, 56% of the population at risk, mainly children under 10, were infected.

Positive polio specimens taken from the environment only alert public health officials that transmission occurs. Our model provides additional information on the number of people infected. Without a model, researchers would have no way of estimating the extent of the epidemic – poliovirus in wastewater could have been collected from many people who shed little or no. But because epidemics follow identifiable patterns, the dynamic changes in polio concentration can tell a lot about the progression of the disease in the population.

There is still uncertainty in model predictions, so it is important to corroborate multiple data sources. In this outbreak, we were able to compare crude estimates of infection based on stool samples from the community.

Monitoring environment for silent transmission

As the final stages of polio eradication approach, environmental measures will become the only feasible way to detect polio transmission. And this silent spread of the virus must be stopped to completely eradicate the disease. Waiting for a case of paralysis means that there is a lot of polio and that containing it with vaccination efforts becomes more difficult.

Environmental monitoring efforts are increasing in the three endemic countries. Indeed, since the success in Israel in identifying and rapidly limiting transmission by administering the oral polio vaccine, many countries have begun implementing environmental surveillance for polio. WHO is working to develop organized environmental monitoring standards similar to well-established standards for acute flaccid paralysis.

Beyond poliomyelitis, environmental monitoring can and should be extended to other infectious diseases prevalent in wastewater – enterovirus, typhoid and cholera are the first candidates. Epidemiologists can then use modeling approaches to translate surveillance data by describing population trends, allowing public health officials to respond quickly to outbreaks.

This article is republished from The Conversation under a Creative Commons license. Read the original article here: http://theconversation.com/sewage-surveillance-is-the-next-frontier-in-the-fight-against-polio-105012.