Health authorities in Hong Kong have launched an investigation into a rare human case of rat hepatitis E virus involving a 61-year-old man who was infected by an undetermined source. The patient, who lives on a public housing estate in Aberdeen, was admitted to Queen Mary Hospital in Pok Fu Lam on April 7 for treatment of his underlying illnesses. Five days later, he was found to have abnormal liver functions. His condition improved and he was transferred to Tung Wah Hospital for rehabilitation on Wednesday. His blood sample tested positive for the rat hepatitis E virus. It was the second infection with the virus this year, after one was recorded in January. There were six cases last year. The Centre for Health Protection’s investigations found neither rodents nor their droppings in the patient’s home on Shek Pai Wan Estate. He also had no travel history during the incubation period. His home contacts remained asymptomatic. “Based on the available epidemiological information, the source and the route of infection could not be determined,” a centre spokesman said on Thursday. The Pest Control Advisory Section would carry out rodent control measures and a survey, the spokesman added. Hong Kong man is world’s first human found with rat hepatitis E virus Typical initial symptoms of acute hepatitis E include fever, reduced appetite, nausea and vomiting. Patients may also experience abdominal pain, itching, skin rash or joint pain. Other signs are jaundice and a slightly enlarged, tender liver. In rare cases, it can result in acute liver failure and death. The exact mode of transmission of rat hepatitis E virus to humans is unknown at the moment. The strain was previously found only in rats and ferrets. Possible routes of transmission include ingestion of food or water contaminated by rats or their droppings, direct contact with rodents or their excreta, and exposure to contaminated environments or objects. The hepatitis E virus that usually causes human infection is transmitted mainly through the faecal-oral route. In September 2018, a 56-year-old Hong Kong man became the first person in the world to be infected with the rat hepatitis E virus. The man, who lived on the Choi Wan public housing estate in east Kowloon, underwent a liver transplant in May 2017 and was tested for the virus after he displayed recurring liver function problems. Help us understand what you are interested in so that we can improve SCMP and provide a better experience for you. We would like to invite you to take this five-minute survey on how you engage with SCMP and the news.