A 70-year old woman from the Wong Tai Sin district of Hong Kong was diagnosed with the disease earlier this month, according to Hong Kong's Department of Health. She does not recall having direct contact with rodents or their excreta (feces and bodily fluids) and didn't notice any rodents in her residence, the Department of Health said in a statement.
The woman was admitted to a public hospital on May 4, 2017 for headache, anorexia, malaise, abdominal pain and palpitations which she had developed since May 1, 2017.
She soon recovered and was discharged four days later, on May 8, 2017. The woman had underlying illnesses, according to the Department of Health.
In September the first case was reported, involving a 56-year old man. Before this, it was not known the disease could be passed from rats to humans.
Following that case, the Centre for Health Protection (CHP) of the Department of Health provided blood samples from patients that had tested positive for immune protein called anti-HEV immunoglobulin -- a sign someone is infected with hepatitus E, known as HEV. Further investigations by Hong Kong University detected elements of DNA evident of rat HEV.
This is how the new case of the 70-year old woman was identified.
Genetic sequencing results show the viruses in both cases to be highly similar, wrote Dr. Yh Leung, senior Medical and Health Officer from the CHP, in the Department of Health's newsletter Thursday.
"Rat hepatitis E virus now joins this list of infections as an important pathogen that may be transmitted from rats to humans," Dr. Siddharth Sridhar, clinical assistant professor at the University of Hong Kong, previously told CNN, adding that the risk of rat hepatitis E affecting humans has been underestimated.
The CHP's investigation showed the two people with hepatitis E infections caused by rats had no travel history during the usual incubation period -- of two to ten weeks -- of the virus. Both the 56-year old man and 70-year old woman resided in Hong Kong's Wong Tai Sin District -- just over a mile apart. There are no other findings hinting at epidemiological links between the two cases, said Yh Leung in the newsletter.
The apparent clustering of the two cases is of concern and CHP will continue to closely monitor the situation, wrote Leung, adding that the sources and routes of the infections could not be determined.
"It is likely that the virus can be found commonly in rats, with one study in Vietnam suggesting that more than 10% of them may have been infected," wrote Martin Hibberd, professor of emerging infectious diseases at the London School of Hygiene & Tropical Medicine, in an email to CNN. Hibberd added, "infection can be acquired by close contact with rats, or perhaps more likely through rat contaminated food or water."
Hong Kong's Public Health Laboratory Services Branch has implemented a molecular test targeting different hepatitis E viruses and will use this to test cases testing positive for anti-HEV immunoglobulins.
To prevent future infections, the public are advised to practice food safety when handling food -- such as keeping hands and utensils clean, cooking thoroughly and keeping food at safe temperature -- the letter adds.
Specific food safety suggestions include choosing safe raw materials, keeping hands and utensils clean, separating raw and cooked food, keeping food at safe temperature and cooking thoroughly.
The increasing number of case observations in Hong Kong are, according to Hibberd "likely at this stage to be due to improved diagnostic tools and increased surveillance, as the clinical presentation can be confused with other diseases."
Hibberd said that "the recommendation by the Hong Kong team for increased surveillance in immune compromised patients seems sensible, given the observations of disease in them. Luckily the disease can be treated, so diagnosis therapy can play an important role in disease prevention."
Hepatitis causes inflammation of the liver, with various viruses that cause it. Most commonly, hepatitis A, B and C spread through either contaminated food and water or blood and other body fluids, depending on the virus.
The human form of hepatitis E is typically transmitted through contaminated water, and is estimated to infect 20 million people worldwide, resulting in 3.3 million people showing symptoms each year, according to the World Health Organization. It caused approximately 44,000 deaths in 2015, making up 3.3% of all deaths from viral hepatitis.
The animal form of the disease is thought to infect wild boars, domestic pigs and deer, as well as rats and other rodents.
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