An unusual strain of hepatitis that can pass from rats to humans is continuing to spread in Hong Kong, where it was first discovered in 2018. Known as rat hepatitis E virus (HEV), scientists are baffled as to how it spreads and what can be done to prevent future infections.
The world-first discovery of hepatitis E spreading from rats to humans was made in 2018 when infectious disease experts at the University of Hong Kong examined a liver transplant patient with continuing liver function issues. Tests for human strains of hepatitis E came back negative but when researchers used a different diagnostic test, it was confirmed the man had rat HEV.
Since the first study, 10 more Hong Kong residents have tested positive with rat HEV with the most recent case presenting in a 61-year-old man with abnormal liver function at the end of April. While it’s known that human-to-human hepatitis E can spread from infected water sources, there hasn’t yet been any concrete evidence as to how these patients are catching rat HEV. The question becomes all the more complex as while some cases could be linked to rat-infested accommodations, others showed no clear route of exposure to rats or their excretions.
Hong Kong is taking steps to begin testing rat populations citywide in an effort to identify clusters of the illness before it jumps to humans, but without understanding how humans can catch the illness there is little that can be done to prevent further infections. "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," Dr Siddharth Sridhar, a microbiologist and one of the HKU researchers who made the discovery, told CNN. "That's the missing link."
Eliminating rat populations in Hong Kong could be one solution, but rat eradication is a long, complex, and expensive process that isn’t terribly realistic in a city so rich in food and shelter for rats. For now, all authorities can do is urge people to continue to be vigilant with hygiene practices such as hand washing and storing food properly.
Hong Kong is the first city on Earth to have confirmed cases of rat HEV (bar one patient in Canada) and is also the first city on Earth to test for the illness. It’s quite possible therefore that cases exist elsewhere but the available diagnostic tools haven’t been able to detect it. Hepatitis E can cause mild symptoms in humans, meaning those infected might never present to the hospital in the first place. The condition isn’t mild for everyone, however, and can have a devastating impact on the health of those infected, especially for those with weakened immunity, including long-term liver damage and tissue scarring.
"We need ongoing vigilance in the public to control this unusual infection,” Sridhar told CNN. “I really hope that public health authorities take the first step and look at how much their populations are actually being exposed to rat hepatitis E."