Rising Covid cases in wastewater have led some scientists to wonder whether the virus is now targeting people's intestines.
Traditionally, Covid infects people through the nose and mouth and multiplies in the respiratory tract and sometimes migrates to the lungs.
But some virologists believe the Covid virus has changed its requirements for entering cells, meaning it can do more easily infect the intestines.
Scientists around the world, including in the US, are picking up traces of Covid in much higher quantities in wastewater.
During the pandemic, research into wastewater surveillance was conducted to detect new variants and give officials early warning of flare-ups
Scientists around the world, including in the US, are picking up traces of Covid in much higher quantities in wastewater
Stomach bugs are excreted in large quantities in the fecal waste of infected individuals.
Marc Johnson, molecular virologist and professor of Molecular Microbiology and Immunology at the University of Missouri, told DailyMail.com: 'There were some huge spikes in wastewater in Europe, and many of us wondered what the possible explanations could be – whether it's just a bunch of cases or whether there's some other explanation.”
In Austria, for example, Covid levels in wastewater have risen from almost zero in July this year to around 700 gene copies per person, indicating viral load.
One idea is that the new JN.1 variant has changed its cell entry requirements, possibly to evade vaccine immunity or previous infections.
Professor Johnson said 'it is possible' that the new dominant JN.1 variant of Covid is more focused on the gut – but he said that was not the case. thus far direct evidence for the theory.
But many other coronaviruses infect the gut, Professor Johnson said, “so it wouldn't be that surprising.”
He said: 'Many coronaviruses cause gastrointestinal problems. There are some in cats and pigs, in bats. They're not respiratory infections, they're gastrointestinal infections.'
JN.1, the strain behind the latest spike in cases, is currently the fastest growing variant.
Wastewater monitoring in Austria has shown an increase in the virus
The virus is also becoming increasingly common in waste water in the Netherlands
It now accounts for up to 29 percent of Covid cases, a sharp increase from less than one percent in early November.
The variant is both more contagious and better able to evade the immune system than other strains. But there is no evidence that it causes more severe disease than other variants in circulation.
The latest CDC data shows that almost every state is reporting at least “high” levels of Covid in wastewater.
There has also been a steady increase in virus activity in wastewater over the past six months.
Meanwhile, wastewater detections have increased dramatically in countries such as Austria, Germany, Switzerland and Singapore.
During the pandemic, research into wastewater surveillance was conducted to detect new variants and give officials early warning of flare-ups.
Studying sewage samples was crucial for finding certain variants of Covid, as even someone had no symptoms, the virus would still be present in the sewage.
Anyone infected with a virus excretes small fragments of their DNA in their feces.
Australian virologist Stuart Turville believes JN.1 takes a new route to cells and prefers intestinal cells.
JN.1 shows a greater preference for an uncleaved version of the ACE-2 cell surface protein, which could lead to various tissue infections, such as in the intestines.
Professor Johnson said: 'Dr. Turville has noted that the newer genera prefer a slightly different version of the receptor that is more common in the gastrointestinal tract, which may be supporting evidence.
“But a more likely explanation is that we are currently seeing increasing waves,” he added.”
The World Health Organization this week identified JN.1 as a variant of interest, and the CDC said hospitals and emergency rooms in the US could be forced to ration care.
“Intensive gastrointestinal infections” from Covid “can happen,” Professor Johnson said.
'We find evidence of people who have been infected for years and are excreting crazy amounts of virus, so that we can track them down in sewage sheds with more than 100,000 people.'
However, there has not yet been a corresponding increase in hospital admissions or stomach-related symptoms to support the idea that JN.1 is more stomach-centric.