In 2018, experts at the University of Hong Kong discovered an unusual patient. This patient had an infectious disease that was incredibly uncommon—actually, virtually unheard of at the time.
Researchers discovered that the patient had responded to hepatitis E, but they couldn’t find any human strain of the virus in his blood.
A Man Walks into the Hospital…
The 56-year-old man, who had undergone a liver transplant, was showing abnormal liver functions with no obvious cause.
While the patient tested positive for hepatitis E, which is a liver disease that can cause fever, jaundice, and an enlarged liver–the researchers redesigned the diagnostic test to discover what virus the patient really had.
Patient Zero
When the researchers ran the redesigned diagnostic test, they found rat hepatitis E in a human for the first time.
“Suddenly, we have a virus that can jump from street rats to humans,” said Dr. Siddharth Sridhar, a microbiologist and one of the HKU researchers who made the discovery, told CNN Health.
The Increasing Number of Cases
This was such an unprecedented infection that the team asked themselves if this patient was a “one-off incident, one patient who was in the wrong place at the wrong time.”
Then, another patient came in with the same virus, then another and another. Pretty soon, the number of patients caused concern among the researchers.
Rat HEV Infections Are on the Rise
Since 2018, 10 more Hong Kong residents have tested positive for rat hepatitis E (also known as rat HEV). The most recent case happened in April 2024 when a 61-year-old man with abnormal liver function tested positive.
Sridhar says to CNN Health that this rise in rat hepatitis E cases could suggest that there are hundreds of more undiagnosed cases in the world.
How the Virus Is Spreading
The human strain of hepatitis E can be transmitted through fecal contamination of drinking water, according to the World Health Organization, but researchers are unsure how the rat strain is infecting people.
Since the discovery, researchers have not identified the exact route of transmission from rats to humans.
Other Symptoms
There are some theories as to why more and more humans are getting infected with rat hepatitis E. One way of transmission could be through drinking contaminated water like the usual human strain.
Another suggestion is that humans who do become infected with the virus could have handled contaminated objects. However, nothing has been proven as of now.
What Officials Can Do
The research team and authorities in the city have been working to figure out why this threat has been on the rise since 2018. So far, the team has spread awareness among the healthcare sector for doctors to be on the lookout for signs of hepatitis E.
By knowing that cases are on the rise, doctors can test for rat HEV. Patients also know the risks through several public awareness campaigns.
Testing Popular Areas
Scientists are testing rat populations throughout the city to help identify clusters of infected rats before the virus jumps to humans. This hunt for more clusters has also provided data on how many rodents in the city carry the diseases and which areas have the most rats.
While scientists and researchers are working hard to find the causes of increased cases, there is still so much that we don’t know.
The Challenges of the Unknown
Researchers do not know how long this virus’ incubation period is, which means how long it takes for patients to show noticeable symptoms of illness after exposure.
The teams behind this study are also working to find a treatment for the virus. Right now, medication used to treat the human variant of the virus has had mixed results on patients with rat HEV.
The Numbers Don’t Add Up
Because we don’t know how the virus jumps from human to human, it is tough to prevent further infections.
With the current data provided to the team, the number of rat-infested areas is getting the same number of infections as those in communities with low rat numbers.
The Future of the Study
“What we know is the rats in Hong Kong carry the virus, and we test the humans and find the virus. But how exactly it jumps between them – whether the rats contaminate our food, or there’s another animal involved, we don’t know,” said Sridhar. “That’s the missing link.”
While getting rid of all the rats in Hong Kong would be a long and tough process, Authorities are urging people to take preventative measures to limit the spread of rat HEV.
