(CNN) – In 2018, infectious disease experts at the University of Hong Kong came across an unusual patient. The 56-year-old man, who had undergone a liver transplant, was showing abnormal liver functions with no obvious cause. Tests found that his immune system was responding to hepatitis E — but they couldn’t actually find the human strain of the hepatitis E virus (HEV) in his blood.

Hepatitis E is a liver disease that can also cause fever, jaundice, and an enlarged liver. The virus comes in four species, which circulate in different animals; at the time, only one of these four was known to infect humans. With tests for that human strain of HEV negative, the researchers redesigned the diagnostic test, ran it again — and found, for the first time in history, rat hepatitis E in a human.

“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. It was such an unusual and unprecedented infection that the team wondered if it was a “one-off incident, one patient who was in the wrong place at the wrong time.” But then it happened again. And again. READ MORE


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