Time to call the Pied Piper?

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It seems like Hong Kong’s rising rodent population may have given rise to a new mysterious outbreak in the region. In 2018, Hong Kong reported the world’s first-ever case of rat hepatitis in a human.

The 56-year-old liver transplant patient was diagnosed with Hepatitis E after presenting with abnormal liver function tests. Despite evidence of immune response to Hepatitis E virus (HEV), the human strain of HEV was nowhere to be found in the patient. Doctors then redesigned the diagnostic test and were able to discover the rat HEV in the patient. 

HEV is responsible for Hepatitis E, a liver infection. It is mainly transmitted by coming in contact with contaminated food and water. In most cases, it causes a mild self-limiting disease whereas, in immunocompromised individuals, it is known to cause fulminant hepatitis which can lead to acute liver failure. The common signs and symptoms of Hepatitis E are fever, yellowing of the skin, abdominal pain, and nausea. HEV variants that can infect humans belong to the HEV-A family. HEV-C, a variant found in rats and ferrets, was believed to be incapable of infecting humans. That is, up till now.

It is believed that the patient’s immunosuppressed state allowed the virus to cross the species barrier. There was also evidence of a rat infestation near the patient’s residence. Thus, leading researchers to suggest that contamination of food by infected rat droppings may have played a role in the transmission of the virus. Transmission due to an infected donor was ruled out as there was no serologic or virologic evidence of HEV-C infection in both the donor’s and recipient’s serum pre-transplant. 

Since the study, 10 more people, the majority of whom are immunocompetent, have tested positive for rat HEV in Hong Kong with the latest case being reported on 30th April 2020. However, it looks like the region’s rat infestation problem cannot be blamed for the rising number of cases as more patients have presented from areas of low rat numbers, contrary to popular belief.

While studies have found evidence that rats in Hong Kong do carry the virus HEV-C, it is still unclear as to how the virus is able to jump from rats to humans. Whether there is an intermediate animal involved, or whether its due to the ingestion of food or water contaminated with rat droppings, the mystery is yet to be solved. 

For now, the best measure to control the spread of the virus remains to be educating the public on proper hygiene practices and other preventative measures. 

Outside of Hong Kong only one case of rat HEV in a human has been discovered, a 49-year-old immunocompetent man in Canada. The man had a history of travel to Africa however, he denied contact with rats, or rat’s droppings, or any other live animal exposure while there.

It is important to remember that all these cases were only discovered due to the broad Polymerase chain reaction (PCR) test available in these regions, that were able to detect variants of HEV. The risk remains that there might be several more cases worldwide as most countries aren’t testing for rat HEV. 

References:

Sridhar S, Yip CC, Wu S, et al. Transmission of rat hepatitis E virus infection to humans in Hong Kong: a clinical and epidemiological analysis [published online ahead of print, 2020 Jan 20]. Hepatology. 2020;10.1002/hep.31138. doi:10.1002/hep.31138

Sridhar S, Yip C, Wu S, et al. Rat Hepatitis E Virus as Cause of Persistent Hepatitis after Liver Transplant. Emerging Infectious Diseases. 2018;24(12):2241-2250. doi:10.3201/eid2412.180937.

Andonov A, Robbins M, Borlang J, et al. Rat Hepatitis E Virus Linked to Severe Acute Hepatitis in an Immunocompetent Patient. J Infect Dis. 2019;220(6):951‐955. doi:10.1093/infdis/jiz025

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