Overview

Hepatitis is the inflammation of the liver triggered by different types of infectious viruses and non-infectious agents that result in a wide range of health problems, some of which are fatal. The five common types of the hepatitis virus, are classified as type A, B, C, D, or E. Though they cause liver disease, there are significant differences

In their modes of transmission, severity of the illness, geographical distribution, and prevention methods.¹

Hepatitis E is liver inflammation caused by the hepatitis E virus (HEV).⁸ Hepatitis E (HEV) is similar to hepatitis A and is present worldwide, particularly in areas with poor sanitation practices, such as Asia and Africa. The faecal-oral route can spread it.⁴

Hepatitis E is one of four identified types

• Genotypes 1 and 2: found only in humans and spread mainly through contaminated water
• Genotypes 3 and 4: found in several animals, including wild boars and deers, without causing disease in them but occasionally infecting humans 

Hepatitis E is less common in countries with access to clean drinking water, such as the US and many European nations. A vaccine against hepatitis E virus infection has been developed and licensed in China

but is not yet available elsewhere.⁸ The infection is typically self-limiting, resolving within 2–6 weeks, and is rarely fatal. However, in some cases, it can lead to acute liver failure, particularly in pregnant women and immunocompromised individuals. Hepatitis E is diagnosed by laboratory tests only.²,³

Transmission pathways of HEV

Contaminated water as a primary source of transmission

• Probably the most common source of HEV infections in humans is contaminated water or food. HEV is excreted in the faeces of infected individuals and can enter water sources through inadequate sanitation, leading to outbreaks in communities that rely on untreated water for drinking, bathing, or irrigation
• However, the cases of transfusion-transmitted HEV, in blood donation recipients, are also on the rise
• Transmission of the hepatitis E virus to the foetus during pregnancy has also been documented¹⁰
• Shedding of excreted HEVs into the environment is a reason for much of the transmission of HEV
• human-to-human transmission of HEV genotype 1 and genotype 2 strains in areas without proper drinking water sanitation has been identified as the primary mode of transmission
• In more economically developed nations, the survival of HEVs in water and sewage will have to be studied to support the idea that water-borne transmission can play an important role⁹
• Using untreated river water for bathing, drinking, and disposing of waste products is responsible for the increased rates of human HEV infection in Turkey and some countries in Southeast Asia¹¹
• HEV can be present in shellfish cultivation near land. The isolation of HEV-3 from surface and drinking water shows the potential for risky transmission of HEV-3 through drinking water¹⁰
• Water contamination and sewage may be responsible for HEV infection in both humans and other animals
• Current research suggests that these sources have the potential for transmission but that additional analysis of these sources about all genotypes of HEV better assesses the overall public health risk¹¹
• Coastal waters can be contaminated with HEV, leading to the accumulation of the virus in the digestive tissues of shellfish. This increases the risk of human infection when contaminated shellfish are consumed, particularly if they are raw or undercooked¹¹
• Most of the time, mussels, cockles, or oysters are consumed raw or slightly cooked, and HEV is stable in both acidic and alkaline environments, frozen for more than 10 years, and remains infectious for at up to 60 °C, suggesting that raw, rare-cooked, or slightly steamed, contaminated seafood may transmit HEV to consumers
• There have been case reports of hepatitis E in England, Italy, and France that uncovered shellfish consumption as a common source risk factor for HEV infection
• In addition, Genotype 3 in swine HEV has also been detected in shellfish from Korea and Japan.  
• Travellers who go to high-endemic and endemic regions of the world are exposed to a higher risk of contracting HEV infection through contaminated water and seafood¹¹

Role of contaminated food in HEV transmission

• Zoonotic Transmission of HEV Meat consumption as a source of HEV infection in humans was first described in 2005¹⁰
• Food can be contaminated at any stage, i.e., from farm to table.
• Foodborne viruses are highly resistant to environmental factors, such as heat and low pH (acidity). They can remain infectious for over a month¹⁰
• HEV has been detected in various tissues and organs of deer, swine, and wild boar, and also in bivalves such as cockles, mussels, and oysters
• Commercial pig livers purchased as food from local grocery stores can be contaminated with HEVs, and some of such HEV-contaminated commercial pig livers may contain infectious viruses
• Foodborne transmission of HEV was first identified in clusters of Japanese patients after eating undercooked or raw food⁹
• Cases of hepatitis E presented in Japan were also responsible for the consumption of contaminated wild boar meat
• Wild boar populations in Southeast France and Italy had detectable amounts of HEV RNA in 25% of bile samples and 2.5% of liver samples, respectively
• Cases of acute hepatitis E associated with Genotype 4 HEV have been identified in South Korea, presumably due to the consumption of raw wild boar bile juice¹¹

Sewage water treatment and drinking water sanitation are very important to prevent HEV (genotypes 1 and 2) transmission in developing countries.⁹

Other transmission routes

Blood transfusions

HEV transmission through contaminated blood products has been reported in Europe, particularly among immunocompromised patients. Blood transfusion, dialysis, and other contact with needles are risk factors for HEV.¹²

Mother-to-foetus transmission

Vertical transmission of HEV from infected mothers to their fetuses can occur, leading to severe complications. Pregnant women in HEV-endemic regions are at higher risk of acute liver failure, foetal loss, and death.

Direct human-to-human transmission

This mode is less common but can occur in areas with poor sanitation.

Risk factors and severity of HEV infections

The severity of HEV infections varies based on genotype, host immunity, and pre-existing conditions.

Pregnant women

HEV infection during pregnancy, especially with genotype 1, can lead to acute liver failure, maternal death, and foetal complications.

Immunocompromised individuals

Patients who have undergone organ transplants, those on immunosuppressive therapy, or individuals with chronic liver disease are at risk of developing chronic HEV infections, which can progress to cirrhosis and liver failure.

Elderly and males

In genotype 3 and 4 endemic regions, most HEV-related illnesses occur in men aged 40–60.

Prevention

Water safety measures

• Drink safe water; in HEV-endemic regions, drink only bottled or properly boiled water
• Avoid contaminated water; do not consume water from untreated sources, including rivers and lakes
• Proper sanitation; improved sewage treatment, and sanitation systems can significantly reduce HEV transmission

Food safety measures

• Cook meat thoroughly; pork, venison, and wild boar meat should be cooked to an internal temperature of at least 71°C to inactivate HEV
• Avoid raw or undercooked shellfish; steam or cook seafood properly before consumption.
• Prevent cross-contamination; keep raw and cooked foods separate to reduce the risk of HEV contamination in the kitchen

Hygiene practices

• Wash hands regularly; proper handwashing with soap and water is crucial after using the toilet, handling raw meat, and before eating
• Clean kitchen utensils; wash utensils and surfaces that come into contact with raw meat to prevent foodborne transmission

Travel precautions

• Boil drinking water; when travelling to HEV-endemic areas, always boil water before drinking
• Avoid raw meat and seafood; opt for fully cooked meals and avoid street food that may be contaminated

Summary

Hepatitis E is primarily spread through contaminated water and food. The virus is endemic in regions with poor sanitation, where faecal matter contaminates drinking water and irrigation sources. In developed nations, zoonotic transmission through raw or undercooked meat and shellfish is a significant concern. Proper sanitation, safe food handling, and access to clean drinking water are essential in preventing HEV infections and reducing outbreaks globally.