Hepatitis B

Hepatitis A virus, HAV, is an envelope-less RNA virus classified as picornavirus. It was first isolated in 1979. Humans are its only natural host, although several nonhuman primates have been infected under laboratory conditions.

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). Development of chronic infection is most common in infants infected by the mother, or before the age of five years.
Hepatitis B is also spread by exposure to infected blood. In addition, infection can occur during medical, surgical and dental procedures, through tattoos or the use of razors and similar objects contaminated with infected blood and not properly sterilized.
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.
The hepatitis B virus can survive outside the body for at least 7 days. During this period, the virus maintains its ability to infect.

Hepatitis B infection is considered endemic worldwide. WHO estimates that globally a total of 257 million are infected with hepatitis B. The prevalence of hepatitis B is highest in the Western Pacific region and the African continent, where 6.2 percent and 6.1 percent of the adult population is infected, respectively. In the Eastern Mediterranean region, the Southeast Asian region, and the European region, an estimated 3.3 percent, 2.0 percent, and 1.6 percent of the general population is infected, respectively.

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The incubation period of hepatitis B virus averages 75 days, but can range from 30 to 180 days. The virus can be detected within 30 to 60 days of infection and can persist and develop into chronic hepatitis B. Most people have no symptoms at the time of infection. However, some people develop an acute illness with symptoms lasting 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. The infection, when acquired in adulthood, evolves to chronic hepatitis in less than 5 percent of cases, while infection acquired in childhood chronizes in 95 percent of cases. In some people, hepatitis B virus can also cause chronic liver infection that can later develop into cirrhosis (a 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 a person is infected. Children younger than 6 years of age who become infected with hepatitis B virus are more likely to develop chronic infections.

In infants and children:

• 80-90% of children infected during the first year of life develop chronic infections; and
• 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; and
• 20-30% of chronically infected adults will develop cirrhosis and/or liver cancer.

HBV-HIV co-infection

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

It is not possible on a clinical basis to differentiate hepatitis B from hepatitis caused by other viral agents; therefore, laboratory confirmation of the diagnosis is essential.
Laboratory diagnosis is based on the detection of hepatitis B surface antigen HBsAg. The WHO recommends that all blood donations be tested for hepatitis B to ensure the safety of blood and excipients and to avoid accidental transmission to people receiving blood products.
Acute HBV infection is characterized by the presence of HBsAg and immunoglobulin M (IgM) antibodies to the HBcAg antigen. During the early stage of infection, patients are also seropositive for hepatitis B e antigen (HBeAg). HBeAg is usually a marker of high levels of virus replication.
Chronic infection is characterized by persistence of HBsAg for at least 6 months (with or without concomitant HBeAg). HBsAg persistence is the major risk marker for the development of chronic liver disease and liver cancer (hepatocellular carcinoma).

To date, there is no specific treatment for acute hepatitis B. Therefore, treatment is aimed at restoring health status and adequate nutritional balance, including replacement of fluids lost due to vomiting and diarrhea.
Chronic hepatitis B infection can be treated with medications, including oral antiviral agents. Treatment can slow the progression of cirrhosis, reduce the 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 control hepatitis B virus.
In most people, however, the treatment does not cure hepatitis B infection, but only suppresses virus replication. Therefore, most 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 many resource-limited settings. In 2016, of the more than 250 million people living with HBV infection, 10.5 percent (27 million) were aware of their infection. Of those diagnosed, overall treatment coverage is 16.7 percent (4.5 million). Many people are diagnosed only when they already have advanced liver disease.

Prevention of Hepatitis B transmission begins with meticulous attention to certain behaviors, such as the use of mechanical protective devices during sexual intercourse, or avoiding sharing and using contaminated syringes and needles.
The only safe and effective weapon to counter the spread of the virus is the Hepatitis B vaccine, administered preventively.
The Hepatitis B vaccine is the cornerstone of prevention. WHO recommends that all children receive the Hepatitis B vaccine as soon as possible after birth, followed by the doses needed to complete the vaccine cycle.
In 2019, 3-dose coverage of the vaccine reached 85 percent worldwide compared with about 30 percent in 2000. However, birth dose coverage of the hepatitis B vaccine remains uneven, reaching only 6% in some low-resource countries.