Worldwide diversity of hepatitis A and E viruses in urban wastewater
This study utilized wastewater metagenomics across 62 cities in 38 countries to map the global diversity of hepatitis A and E viruses, revealing widespread zoonotic rat HEV transmission and demonstrating the value of sewage surveillance for monitoring both human and animal hepatitis strains.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Imagine the world's cities as giant, bustling beehives. Inside these hives, millions of people, pets, and pests live, eat, and leave behind a constant stream of waste. If you could take a tiny sip of the sewage flowing out of a city, it wouldn't just smell bad; it would be a glowing, chaotic library of genetic secrets. This is the world of wastewater-based epidemiology. Instead of waiting for people to get sick and visit a doctor, scientists treat the city's sewer system like a giant, continuous blood test for the entire population.
In this library, two specific "villains" are always looking for trouble: the Hepatitis A virus (HAV) and the Hepatitis E virus (HEV). Think of these viruses as invisible spies that travel through contaminated food, water, or close contact. While Hepatitis A is a classic human-to-human spy, Hepatitis E is a bit more tricky; it has a "zoonotic" side, meaning it can jump from animals (like pigs) to humans. But there's a third, sneaky character in this story: the rat. For a long time, scientists thought a specific type of Hepatitis E virus lived only in rats and never bothered humans. However, recent whispers suggest these rat spies might be trying to cross over. The big question is: How widespread are these spies, and are they hiding in our sewers more than we thought?
The Great Sewage Spy Hunt
A team of scientists from around the globe decided to play detective. They didn't just look at one city; they cast a massive net, collecting sewage samples from 62 cities across 38 countries on six different continents. They used a high-tech method called "hybrid-capture metagenomics," which is like using a super-powerful magnet to pull out tiny genetic fragments of viruses from the messy soup of wastewater, even if they are hiding in the background noise. They looked at samples collected between 2017 and 2019, and then dug deeper into five European cities with samples from 2020 to 2021.
Here is what they found in the city's "genetic library":
The Rat Spy is Everywhere
The biggest surprise was the Rat Hepatitis E virus (scientifically known as Rocahepevirus ratti). The team found this virus in 70% of the cities they tested. Before this study, we only knew about it in a few places; now, the map has expanded by 12 countries, including Australia, India, and parts of Africa.
But here is the crucial twist: the scientists used a clever trick to figure out where the virus was coming from. They looked for astroviruses (another type of virus) in the same sewage. Since different animals have their own specific astroviruses, the mix of astroviruses acts like a fingerprint for the poop in the pipe. When they found Rat Hep E, they also found a huge amount of rat astroviruses and very few human ones. This strongly suggests that the Rat Hep E in the sewage is coming from rats living in the sewers, not from humans getting infected. It's like finding a pile of rat droppings next to a rat's toy; the rat is the source, not the human.
The Human Spy: Hepatitis E
The "human" version of Hepatitis E (Paslahepevirus balayani) was found in 42% of the cities. In Europe, the most common version was Genotype 3, specifically a sub-type called 3c. This makes sense because Europe has a lot of pig farming, and pigs are the main reservoir for this virus. The study found that in cities like Budapest and Vienna, there was a wild mix of different Hep E subtypes, likely because of how pigs are traded and moved around. Interestingly, they found the "human-only" Genotype 1 in places like Togo and Malaysia, which fits with known waterborne outbreaks in those regions.
The Classic Spy: Hepatitis A
Hepatitis A was detected in 37% of the samples. The types of Hep A found matched what we usually see in those regions. For example, in Africa, they found Genotype IB, which is common there. In Europe, they found Genotype IA, which was linked to a known outbreak among men who have sex with men (MSM) that happened around 2016–2017. This shows that sewage can catch viruses that clinical doctors might miss because the infected people didn't go to the hospital.
The "What If" and the "What We Know"
The study suggests that while Rat Hep E is everywhere in the sewers, it is likely staying with the rats. However, the authors are careful to say that we don't know the full picture yet. We know that rats live in sewers and that their poop is in the water. We know that a few human cases of Rat Hep E have been reported in hospitals, but the sewage data suggests that for now, the rat virus is mostly a "rat problem" in the pipes, not a widespread human infection.
The researchers also noted that their method is a bit less sensitive than a standard lab test. For instance, in one city (Yaoundé), they didn't find Rat Hep E, even though other tests had found it before. This means they might have missed some viruses, and the true diversity could be even higher.
The Bottom Line
This paper paints a vivid picture of the invisible world in our sewers. It confirms that Rat Hep E is a global resident of our urban rat populations, spreading through the sewer systems of 70% of the cities studied. It also shows that sewage surveillance is a powerful tool that can see the "silent" circulation of viruses—catching outbreaks and animal viruses that clinical testing often misses. While the rat virus is currently hanging out with its rodent hosts, its presence in our water systems is a reminder that the line between animal and human health is thinner than we thought, and keeping an eye on the sewage is one of the best ways to stay one step ahead of the spies.
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