Hepatitis B

Hepatitis B is a viral infectious disease, caused by the HBV virus, a member of the Hepadnaviridae family.

Today, the disease represents a major global public health challenge. HBV can cause chronic infection and expose people to a high risk of cirrhosis and liver cancer.

A safe and effective vaccine is available that offers 98-100% protection against hepatitis B.

CAUSES

The Hepatitis A virus (HAV), is a nonenveloped RNA virus classified as picornavirus. The virus was first isolated in 1979. Humans are its only natural host, although several nonhuman primates have been infected under laboratory conditions.

TRANSMISSION

In highly endemic areas, hepatitis B is most commonly spread from mother to child at birth (perinatal transmission) or by horizontal transmission (exposure to infected blood). The development of chronic infections is very common in infants infected by the mother, or before the age of five years.

Hepatitis B can also be spread by exposure to infected blood. In addition, infection can occur during medical, surgical and dental procedures, tattoos, or the use of razors and similar objects contaminated with infected blood that have not been adequately sterilised.

Transmission can also occur through contact with body fluids, such as saliva and vaginal and seminal fluids. Sexual transmission of hepatitis B can occur, particularly in unvaccinated men who have sex with men.

Hepatitis B virus can survive outside the body for at least 7 days. During this time, the virus is still infectious.

GEOGRAPHICAL DISTRIBUTION

Hepatitis B infection is considered endemic worldwide. WHO estimates that a total of 257 million people are infected with hepatitis B worldwide.

The prevalence of hepatitis B is higher in the Western Pacific region and the African continent, where 6.2% and 6.1% of the adult population is infected, respectively. In the Eastern Mediterranean region, the Southeast Asian region, and the European region, an estimated 3.3%, 2.0%, and 1.6%, respectively, of the general population is estimated to be infected.

SYMPTOMS

The incubation period of the hepatitis B virus averages 75 days, but can range from 30 to 180 days. The virus can be detected within 30-60 days of infection and can persist and develop into chronic hepatitis B.

Most people show no symptoms when newly infected. However, some people have acute illness with symptoms that last several weeks, including yellowing of the skin and eyes (jaundice), dark urine, extreme fatigue, nausea, vomiting and abdominal pain. A small subgroup of people with acute hepatitis may develop acute liver failure, which can lead to death. When acquired in adulthood, the disease evolves into chronic hepatitis in less than 5% of cases, while infection acquired during childhood leads to chronic disease in 95% of cases.

In some people, the hepatitis B virus can also cause chronic liver infection, which can later develop into cirrhosis (scarring of the liver) or liver cancer.

Who is at risk of chronic disease?

The likelihood of the infection becoming chronic depends on the age at which the person is infected. Children under 6 years of age who become infected with the hepatitis B virus are more likely to develop chronic infections.

New-born babies and children:

• 80-90% of children infected during the first year of life develop chronic infections;
• 30-50% of children infected before age 6 develop chronic infections.

In adults:

• Less than 5% of otherwise healthy people who are infected as adults will develop chronic infections;
• 20-30% of adults with chronic infection will develop cirrhosis and/or liver cancer.

HBV-HIV co-infection

About 1 percent of people living with HBV infection (2.7 million people) also have HIV.  Tenofovir, which is included in the treatment combinations recommended as first-line therapy for HIV infection, is also active against HBV.

DIAGNOSIS

It is not possible on clinical grounds to differentiate hepatitis B from hepatitis caused by other viral agents, hence laboratory confirmation of the diagnosis is essential.

Laboratory diagnosis is based on the detection of hepatitis B surface antigen HBsAg. WHO recommends that all blood donations be tested for hepatitis B to ensure blood safety and avoid accidental transmission to people receiving blood transfusions.

Acute HBV infection is characterised by the presence of HBsAg and immunoglobulin M (IgM) antibodies against the HBcAg antigen. During the early stage of infection, patients are also seropositive for the hepatitis B e antigen (HBeAg). HBeAg is usually a marker of a high level of virus replication.

Chronic infection is characterised by the persistence of HBsAg beyond 6 months (with or without concomitant HBeAg). HBsAg persistence is a major risk marker for the development of chronic liver disease and liver cancer (hepatocellular carcinoma).

TREATMENT

To date, there is no specific treatment for acute hepatitis B. Therefore, care is aimed at maintaining comfort and adequate nutritional balance, including replacement of fluids lost from vomiting and diarrhoea.

Chronic hepatitis B infection can be treated with medicines, including oral antiviral agents. Treatment can slow the progression of cirrhosis, reduce incidence of liver cancer, and improve long-term survival.

WHO recommends the use of oral treatments (tenofovir or entecavir) as the most potent drugs to suppress hepatitis B virus.

However, treatment does not cure hepatitis B infection, it only suppresses virus replication. This means that the majority of people who start hepatitis B treatment must continue it for life.

To date, there is still limited access to hepatitis B diagnosis and treatment in low-income settings. In 2016, out of over 250 million people living with HBV infection, only 10.5 percent (27 million) were aware of their infection. While for patients with a confirmed diagnosis, overall treatment coverage is 16.7 percent (4.5 million). Many people are only diagnosed only when they already have advanced liver disease.

PREVENTION

Prevention of Hepatitis B transmission begins with meticulous attention to certain behaviours, such as the adoption of barrier protective measures (condoms) during intercourse, or avoiding sharing and using contaminated syringes and needles.

The Hepatitis B vaccine is the cornerstone of prevention and the only safe and effective weapon to counter the spread of the virus.

 WHO recommends that all infants receive the hepatitis B vaccine as soon as possible after birth, followed by the recommended booster shots to complete the vaccination series.

In 2019, 3-dose coverage of the vaccine reached 85% worldwide, compared to approximately 30% in 2000. However, administration of the hepatitis B vaccine at birth is still variable, reaching only 6% in some low-income countries.

Source:

epicentro.iss.it/epatite/epatite-b

cdc.gov/hepatitis/hbv/index.htm

WHO