Infectious diseases – polio and other viruses: insights from wastewater

Polio, also known as infantile paralysis, spread fear and terror until the first vaccines were developed in the mid-1950s. The disease cannot be treated and can lead to permanent paralysis and, in the worst case, death. In the first half of the 20th century, patients with paralysis of the respiratory system were forced by the disease into the “iron lung,” a ventilator that encircles the body and is no longer used today.

Thanks to vaccination, the disease with the medically correct name poliomyelitis has been almost eradicated worldwide; only in Afghanistan and Pakistan do infections with the wild type of the virus still occur regularly. In other countries, especially in regions with poor health care, polio still occurs sporadically. In the Gaza Strip, despite all the adversities of the war, a childhood vaccination campaign was launched at the end of August under the direction of the World Health Organization. The reason for this was detection of the virus in the sewage from Chan Junis and a baby who tested positive for polio.

In Germany, too, wastewater is regularly tested for polioviruses at some locations as part of a research project. According to a statement from the Robert Koch Institute on December 4th, polioviruses have now been found in wastewater in seven cities (Munich, Bonn, Cologne, Hamburg, Dresden, Düsseldorf and Mainz). However, suspected cases of illness have not yet been reported. The RKI calls on medical staff to close vaccination gaps and to be vigilant about symptoms typical of poliomyelitis. Polio viruses were also recently detected in wastewater in Barcelona and Warsaw. In previous years there had been similar evidence in London and Jerusalem, for example.

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In all of these cases it is a case of weakened viruses from the oral vaccination. Anyone who has been recently vaccinated in this way can excrete the relevant viruses. In Germany, as in most other countries, oral vaccination is no longer used, but an inactivated vaccine is injected into the muscle. Although this is the lower-risk method, it requires a high vaccination rate. Because it only prevents the outbreak of the disease, but not an infection and thus further infections. Therefore, in some regions the oral vaccination is still preferred, which offers sterile vaccination protection a few weeks later. The polioviruses derived from the oral vaccination “are viruses that have regained neurotoxicity through reverse mutation and can therefore, like wild polioviruses, lead to acute flaccid paralysis,” explains Rainer Gosert, who is responsible for molecular diagnostics in clinical virology at the University Hospital of Basel. This means that in individual cases, unvaccinated people can become ill with so-called vaccine polio.

Infection radar shows viral load in wastewater

Without the samples from the wastewater, we would currently know nothing about the circulating viruses from the polio vaccination. In this case, our wastewater can be used as an early warning system to find out which diseases are circulating where in the population. Because pathogens that are excreted in feces, urine or saliva will definitely find their way there. Waves of infection can usually be detected in wastewater samples before more people with these diseases go to the doctor. In Germany, samples are currently being taken regularly from almost 170 sewage treatment plants and tested for Sars-CoV-2, the pathogen that causes Covid-19, as well as the seasonal flu viruses Influenza A and B. In this way, the current infection situation can be mapped, even if only a few people are testing themselves. The viral load in wastewater is also published in the infection radar of the Federal Ministry of Health (BMG).

While the wastewater test for Sars-CoV-2 and influenza can be easily combined, the tests for polio are, according to the RKI, more complex because the viruses – if present at all – only occur in very low concentrations. Therefore, they must first be propagated via cell culture before they can be analyzed using molecular biology methods.

When it came to monitoring wastewater for coronaviruses during the pandemic, other countries were much faster than Germany, such as the Netherlands, Austria, Switzerland and France. In this country, wastewater monitoring was initially tested in pilot operations in 56 sewage treatment plants from February 2022. From May 2023, “Wastewater monitoring for epidemiological situation assessment”, Amelag for short, a cooperation project between the Federal Environment Agency (UBA) and RKI, followed. »Twice a week we take a 24-hour mixed sample from the almost 170 sewage treatment plants, which is brought to the laboratory cooled at four degrees and extracted and processed there. The results of the PCR analysis are then fed into a data platform,” explains Ulrike Braun, head of the department for wastewater analysis and monitoring procedures at the UBA. The RKI is responsible for further evaluation of the data.

It’s not quite as simple as it initially sounds: »The concentration of Sars-CoV-2 in wastewater can be strongly influenced by changes in the wastewater composition, for example due to rain events. This makes trend recognition more difficult,” says the UBA. Therefore, the viral load in the wastewater must be “normalized”. This means that the fluctuations in the amount of wastewater and thus also in the composition of the wastewater components are balanced out.

RSV infection events should also be monitored in the future

In the coming year, monitoring will be expanded to include another common pathogen, the respiratory syncytial virus, or RSV for short. “The methods for monitoring RSV in wastewater have been developed and are currently being tested,” says RKI press spokeswoman Susanne Glasmacher when asked by nd. The virus causes respiratory infections and causes problems primarily in infants, especially premature babies, small children and older adults. In the summer of 2023, two vaccines against RSV were approved in the EU for the first time.

In the event of new epidemics, wastewater testing could also be expanded to include other viruses. And viruses that do not yet play a role in this country could do so in the future, for example due to global warming. In other countries, many different pathogens are monitored, such as measles or dengue, explains Glasmacher. Before new test routines could be established, the corresponding methods would first have to be validated. “We have developed approaches regarding Mpox and bird flu,” says Ulrike Braun from the UBA. But the problem is the practical test: “We need violent waves of infection in order to be able to measure anything at all.”

The wastewater could also provide information about another growing health threat: antibiotic-resistant bacteria. These are also known as “hospital germs” because they often spread in hospitals if adequate hygiene measures are not taken. In a research project, the RKI is working on an early warning system for antibiotic resistance in wastewater. According to the institute, research focuses on resistance in enterobacteria to reserve antibiotics from the group of carbapenems in the model region of the greater Leipzig area. “The detected resistances are compared with data from neighboring medical facilities to ensure that the results have clinical and public health relevance,” says the RKI. This plausibility check is important because bacteria can exchange genes with each other. If resistance genes are found, they could also come from the biofilm in the wastewater, Braun points out.

EU directive requires new wastewater tests

An examination for “antimicrobial resistance” (of which antibiotic-resistant bacteria are a sub-area) is also required by the EU Municipal Wastewater Directive, which was passed at the beginning of November. Procedures for this must be established in settlement areas with more than 100,000 inhabitants within two years at the latest. But the directive should also make determining the viral load of Sars-CoV-2, polio, influenza and emerging pathogens a European standard.

In this context, it seems sensible for the Amelag project to be continued until the end of 2024, even if initially only during the provisional budget management, as the “Ärzteblatt” reports. The regular term ends on December 31st; follow-up financing should actually have been the subject of the parliamentary budget process. Due to the break in the traffic light government, this could no longer take place. Those affected by Long Covid, among others, feared that the government would no longer finance Amelag. A petition was intended to persuade the federal government to extend it.

According to Ärzteblatt, the BMG expects annual costs of around five million euros to continue monitoring Sars-CoV-2, influenza and RSV in wastewater. Further costs were incurred at the municipal and state level for sampling in the sewage treatment plants. The RKI, in turn, says that additional funds are necessary for research, which must be discussed in the budget process. This will be the task of a new federal government next year.

“We need violent waves of infection in order to be able to measure anything at all.”

Ulrike BraunFederal Environment Agency

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