Excretion of infectious hepatitis E virus into milk in cows imposes high risks of zoonosis

Abstract

Hepatitis E virus (HEV) represents the main cause of acute hepatitis worldwide. HEV infection in immunocompromised patients involves a high risk for the development of chronic hepatitis. Because HEV is recognized as a zoonotic pathogen, it is currently believed that swine is the primary reservoir. However, this is not sufficient to justify the strikingly high seroprevalence of HEV in both developing and Western countries. Thus, this study aimed to identify new zoonotic sources that bear a high risk of transmission to humans. We collected fecal, blood, and milk samples of cows in a typical rural region of Yunnan Province in southwest China, where mixed farming of domestic animals is a common practice. HEV RNA was quantified by quantitative real-time polymerase chain reaction, and the whole genome was sequenced. HEV infectivity was assessed in rhesus macaques. We found a high prevalence of active HEV infection in cows as determined by viral RNA positivity in fecal samples. Surprisingly, we discovered that HEV is excreted into milk that is produced by infected cows. Phylogenetic analysis revealed that all HEV isolates from cow/ milk belong to genotype 4 and subtype 4h. Gavage with HEV-contaminated raw and even pasteurized milk resulted in active infection in rhesus macaques. Importantly, a short period of boiling, but not pasteurization, could completely inactivate HEV. Conclusion: Infectious HEV-contaminated cow milk is recognized as a new zoonotic source that bears a high risk of transmission to humans; these results call attention to understanding and establishing proper measurement and control of HEV zoonotic transmission, particularly in the setting of mixed farming of domestic animals. (HEPATOLOGY 2016;64:350-359) H epatitis E virus (HEV) is a positive singlestranded RNA virus with four defined genotypes and other newly discovered strains that have not been assigned to these known genotypes. (1) It is the most common cause of acute hepatitis globally. (2) In the Western world, chronic hepatitis has been frequently described in immunocompromised patients. (3) Thus, HEV infection has emerged as a global public health issue with a particularly high mortality rate in pregnant women. (4) Seroprevalence is rather high in the developing world, ranging 30%-80%. Strikingly, it is also very high in Western countries. In the United States, population-based surveys have indicated a seroprevalence of 21% from 1988 to 1994 and 6% from 2009 to 2010. (5) An overall seroprevalence of 22.4% and 27% was found in French (6) and Dutch (7) blood donors, respectively.In the developing world, epidemics of hepatitis E occur periodically and are mainly attributed to genotypes 1 and 2. They account for annually 20 million infections, over 3 million cases with symptomatic diseases, and 70,000 deaths. (8) Fecal contamination of drinking water is a major route of transmission of these two genotypes. (8) In contrast, in developed countries, HEV genotype 3 is predominant and spread by zoonotic transmission.

Zoonotic Hepatitis E Virus: Classification, Animal Reservoirs and Transmission Routes

“…It is divided into nine subtypes (a–i) mainly isolated from pig, wild boar and human. HEV-4 was also detected in other animals such as sheep, cow and goat in China [52,53]. Nevertheless, more investigations are necessary to determine if these species are reservoirs of HEV-4 or accidental hosts.…”

Review article: hepatitis E—a concise review of virology, epidemiology, clinical presentation and therapy

“…In China, where mixed farming is common practice, a high prevalence of active HEV infection in cows was identified, and Huang demonstrated that HEV is excreted into milk that is produced by infected cows. 96 Therefore, HEV-contaminated cows' milk is another …”

Acute Hepatitis E: Two Sides of the Same Coin

“…A recent report from China discovered that HEV GT 4 is also excreted into milk and demonstrated that HEV-contaminated raw and even pasteurized milk resulted in active infection in rhesus macaques, while short time boiling inactivates the virus [28]. Thus, milk products may be an important source of HEV GT 4 infection in China, but the relevance of milk products as a source of HEV GT 3 infections in Europe remains to be assessed.…”