Wastewater monitoring offers new tool for cervical cancer prevention

Scientists in Uruguay have found genotypes of the Human Papillomavirus (HPV) linked to cervical cancer in urban wastewater, saying it could help inform disease prevention efforts.

They believe their findings, published in the journal Food and Environmental Virology, position wastewater monitoring as a useful tool for finding information about diseases in low- and middle-income countries, where epidemiological data is scarce.

HPV is the main cause of cervical cancer, detected in 99 per cent of cases. Low- and middle-income countries have the highest prevalence of this type of cancer — and the highest mortality rate from it.

Many of our working groups are seeing this environmental monitoring of such diverse viruses … as a way to understand what’s happening in the population even before observing cases.”

Fernando Spilki, virologist, Feevale University, Brazil

The researchers hope their results can spur more epidemiological studies and prevention strategies for cervical cancer and other cancers linked to the HPV virus.

Wastewater, which is discharged through the sanitation system after domestic or commercial use, has been the subject of many studies to determine the health of a population because it contains traces of disease-causing organisms that are naturally eliminated through bodily fluids.

In the case of HPV, the presence of the virus in wastewater can come from skin washing, urine, or faeces.

HPV is a virus spread through sexual contact with an infected person and can cause problems ranging from genital warts to various types of cancer, especially cervical cancer in women. Worldwide, this cancer is the fourth most common cancer among women.

Of the 200 known HPV genotypes, only a few are related to cervical cancer, such as genotypes 16 and 18.

Clinical detection through tests such as the Pap smear is key to identifying the disease in time.

DNA analysis

The wastewater study was conducted in Salto, a city of 114,000 inhabitants in the north of Uruguay, led by researchers from the University of the Republic’s Molecular Virology Laboratory, the city’s public hospital, and the local headquarters of OSE, Uruguay’s national water supply and sanitation company.

Between September 2022 and August 2023 scientists took monthly samples from the sewage system, which covers 86 per cent of the city.

Genetic analysis detected the presence of the virus in 75 per cent of the samples, and DNA sequencing identified 28 genotypes. Of these, eight were high-risk for cervical cancer, such as genotypes 16 and 18. Six were low-risk, such as six and 11 — associated with genital warts — and the remaining 14 were other general genotypes.

The study also analysed 140 clinical Pap smear samples taken from patients in the city. Of these, 63 (45 per cent) were positive for HPV, and 21 genotypes were detected: nine high-risk, five low-risk, and seven general.

When comparing the frequent genotypes in both sample types, researchers observed that the four most prevalent in the clinical samples (six, 16, 31 and 66) were also present in the wastewater samples.

Overall, 88 per cent of the detected genotypes were present in both samples.

Matías Victoria, a researcher at the Molecular Virology Laboratory and one of the study’s authors, told SciDev.Net: “[These findings] would indicate that this wastewater-based epidemiology approach is useful for HPV surveillance.” 

Explaining why 13 per cent of genotypes were recorded only in clinical samples, Victoria suggested that this may be due to “sampling limitations”, which could perhaps be reduced by increasing sampling frequency.

For him, the variety of genotypes detected was expected “given the low HPV vaccination coverage in the country”.

HPV vaccines

In Uruguay, the HPV vaccine is offered free of charge to all people between the ages of 11 and 26, regardless of gender, but is not part of the mandatory vaccination plan.

In 2023, the country achieved 65 per cent vaccination coverage for girls aged under 15 and 55 per cent for boys, with the first dose.

The HPV vaccine requires two or three doses, depending on age and other factors.

Victoria stressed that, due to the vaccination campaigns implemented in Uruguay in recent years, the number of high-risk genotypes will likely decrease in frequency and quantity.

Fernando Spilki, a virologist at Feevale University in Brazil and coordinator of the country’s National Institute of Science and Technology for Virus Genomic Surveillance and One Health, says the development of this type of study is “a legacy of the pandemic”.

“Before COVID-19, we practically only monitored faecal-oral viruses — like noroviruses — in wastewater and sewage,” he told SciDev.Net.

“Today, many of our working groups are seeing this environmental monitoring of such diverse viruses, such as arboviruses and others, as a way to understand what’s happening in the population even before observing cases.”

Spilki agreed that this type of work is also important for vaccine management and other forms of disease prevention.