A second case of rat hepatitis E has been reported in a human in Hong Kong, making it also the second recorded globally.
A 70-year-old woman from the Wong Tai Sin district of Hong Kong was diagnosed with the disease 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.
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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. 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 that the disease could be passed from rats to humans.
After that case, the Centre for Health Protection of the Department of Health provided blood samples from patients who had tested positive for immune protein called anti-HEV immunoglobulin -- a sign someone is infected with hepatitis 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 Centre for Health Protection, 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 said, adding that the risk of rat hepatitis E affecting humans has been underestimated.
The Centre for Health Protection's investigation showed that the two people with hepatitis E infections caused by rats had no travel history during the virus' usual incubation period of two to 10 weeks. Both the 56-year-old man and the 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, Leung wrote.
The apparent clustering of the two cases is of concern, and the Centre for Health Protection will continue to closely monitor the situation, Leung wrote, 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," Martin Hibberd, professor of emerging infectious diseases at the London School of Hygiene & Tropical Medicine, wrote in an email. "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 is advised to practice food safety, 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 is, 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 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.