Viral hepatitis has become a major public health problem throughout the world affecting hundreds of millions of people. Currently, the World Health Organization (WHO) has listed hepatitis virus as one of the important threats to global public health. Viral hepatitis is inflammation of the liver caused by a viral infection. According to the data in 2015, 1.43 million people died globally from viral hepatitis, compared with 1.1 million deaths from HIV in that same year, 1.4 million deaths from tuberculosis, and 438,000 deaths from malaria.

The most common causes of viral hepatitis are five unrelated hepatotropic viruses, which include hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV). They share the common host and liver cells they infect, but differ in their genomes, organization, and life cycle. At present, the global situation of viral hepatitis prevention and control is still grim, among which the incidence of hepatitis B and hepatitis C is particularly prominent.

※ Hepatitis A Virus
In 1973, Feinslone first used immunoelectron microscopy to identify Hepatitis A virus (HAV) in the stools of infected persons. It is a small, unenveloped symmetrical RNA virus which shares many of the characteristics of the picornavirus family. Almost everyone can fully recover from hepatitis A and be immune to HAV for life. However, there are a few people infected with hepatitis A who may die from fulminant hepatitis.

※ Hepatitis B Virus
Hepatitis B virus (HBV), a member of the hepadnavirus group, double-stranded DNA viruses which replicate, unusually, by reverse transcription. For some people, hepatitis B is mild and lasts only a few weeks (known as an “acute” infection), but for others, it can become a chronic disease, leading to liver scarring, liver failure, and cancer that can even be life-threatening.

Hepatitis B infection is a worldwide healthcare problem, especially in developing areas. The WHO reports that the Western Pacific Region, which includes 37 countries, has the highest disease burden (prevalence rate of 6.2%), followed by Africa (prevalence rate of 6.1%). In 2015, HBV caused approximately 887,000 deaths, mainly due to complications of cirrhosis and hepatocellular carcinoma. As of 2016, 27 million people (10.5% of all people estimated to be living with hepatitis B) were aware of their infection, while 4.5 million (16.7%) of the people diagnosed were on treatment.

At present, the hepatitis B vaccine is the mainstay of hepatitis B prevention. The implementation of rigorous vaccination programs has led to a decline in the overall prevalence of the disease worldwide, but this has also led to emergence of viral mutations that escape the protection of hepatitis B antibodies.

※ Hepatitis C Virus
Similar to HBV, the hepatitis C virus (HCV) is also a major global health concern, infecting 3% of the world's population. Most infected people will develop chronic HCV infection, which often leads to cirrhosis, liver failure, and hepatocellular carcinoma. However, there is currently no vaccine against HCV. Due to its extremely high sequence variability, HCV can easily evade the immune response. Recent studies demonstrated that neutralizing anti-hepatitis C virus antibodies can be induced by epitope-based, engineered vaccines and provides the basis for further efforts in structure-based design of HCV vaccines.

※ Hepatitis D Virus
Hepatitis D virus (HDV) is an RNA virus that was discovered in 1977. Its infection involves a distinct subgroup of individuals who are simultaneously infected with the hepatitis B virus (HBV) and are usually characterized by severe chronic liver disease. Epidemiological research shows that HDV infection is distributed worldwide, but mainly in southern Italy and the Middle East. The mode of transmission is mainly through blood transfusion or the use of blood products.

※ Hepatitis E Virus
Hepatitis E virus (HEV) has mainly a fecal-oral transmission route that is similar to HAV. HEV is a common cause of hepatitis outbreaks in developing parts of the world, as it is mainly transmitted through the consumption of contaminated water or food. The scientists found that the HEV infection rate in pigs was up to 70%. And HEV is increasingly recognized as an important cause of disease in developed countries, because some cases and small-scale outbreaks of hepatitis E are associated with exposure to pigs and consumption of raw pork.

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