Hepatitis B: transmission, prevention and treatment

Hepatitis B is a liver infection caused by the hepatitis B virus (HBV). It spreads through blood, through sexual contact, and from mother to child at birth. Most adults who become infected recover completely, but a proportion are left with lifelong infection (chronic hepatitis B), and it is this form that over the years can lead to cirrhosis and to liver cancer.

The good news is that there is a safe and highly effective vaccine that prevents infection, included in Chile’s immunization program. And when chronic infection requires treatment, we now have once-daily oral antivirals that control the virus and substantially reduce the risk of cirrhosis and cancer.

Electron micrograph of hepatitis B virus particles (reproduced with permission from the CDC, Centers for Disease Control).

How is hepatitis B transmitted?

The virus is present in the blood and other body fluids of infected people. The main routes of transmission are:

• Mother-to-child (vertical) transmission: it usually occurs around the time of birth. It is a very important route because a newborn who becomes infected has an extremely high risk of developing chronic infection. It is prevented with vaccine and immunoglobulin given at birth.
• Contact with blood: through sharing needles or syringes, and also personal items that may carry traces of blood (razors, nail clippers, toothbrushes). Tattoos and piercings with non-disposable equipment are also a risk.
• Sexual contact: the virus is transmitted through unprotected sex, whether heterosexual or homosexual.

Transmission through blood transfusions is now practically nonexistent in Chile, because all donated blood is tested. The virus is not spread by shaking hands, hugging, sharing utensils, or by breastfeeding when the child is properly vaccinated.

Acute and chronic hepatitis B: why age matters

When a person is infected, the course depends above all on the age at which the virus is acquired:

• Acute hepatitis B: the infection during the first six months. In adults, more than 95% clear the virus on their own and are immune for life. Only a very small minority (under 1%) develop a severe form with liver failure (fulminant hepatitis).
• Chronic hepatitis B: defined when the virus persists beyond six months. The risk of becoming chronic depends decisively on age: about 90% of infected newborns become chronic, compared with fewer than 5% of adults. This is why prevention in the newborn is so important.

Chronic hepatitis B is often silent for years. Many people feel well and have no symptoms, which does not mean the virus is inactive. Over time, and in some patients more than others, sustained inflammation can produce fibrosis, cirrhosis, and liver cancer.

Symptoms of hepatitis B

In the acute phase, when symptoms appear, they do so one to four months after infection. They may include:

• Fatigue and a general feeling of being unwell.
• Loss of appetite and nausea.
• Jaundice (yellowing of the skin and eyes).
• Dark urine.
• Discomfort in the upper right side of the abdomen.
• Joint pain.

These symptoms usually resolve within a few weeks. Chronic hepatitis B, by contrast, is almost always symptom-free until advanced stages, when signs of cirrhosis may already be present. For this reason it is often diagnosed through a blood test ordered for another reason.

How is it diagnosed?

The diagnosis is made with blood tests. The most important is the surface antigen (HBsAg): if it is present, there is HBV infection. If it persists for more than six months, it defines chronic hepatitis B. Other tests the physician uses:

• Anti-HBc IgM: marks recent acute infection.
• HBeAg and anti-HBe: report on the activity of the virus.
• Viral load (HBV DNA): measures how much the virus is replicating and is key to deciding on and monitoring treatment.
• Liver enzymes (ALT and AST): estimate liver inflammation.
• Fibrosis assessment: by elastography (for example FibroScan) or, in selected cases, liver biopsy, to determine how much damage there is and define the prognosis.

In everyone with chronic hepatitis B it is also worth checking for coinfection with hepatitis D, hepatitis C, and HIV (see hepatitis B and HIV coinfection).

The vaccine: the best prevention tool

The hepatitis B vaccine is safe and highly effective: it achieves protection in more than 95% of people and prevents, in addition to infection, the liver cancer associated with the virus. It was the first vaccine shown to prevent a human cancer.

In Chile the vaccine is included in the National Immunization Program (PNI) and is given universally in childhood. Vaccination is also recommended for at-risk adults who are not immune (health care workers, partners and household contacts of infected people, people with multiple sexual partners, patients on dialysis).

Two prevention measures deserve special attention:

• Screening in pregnancy: every pregnant woman should be tested for HBsAg, to identify mothers who carry the virus and protect the newborn.
• Newborn prophylaxis: babies born to mothers with hepatitis B should receive, within the first hours of life, the vaccine together with hepatitis B immunoglobulin. This combination prevents the great majority of mother-to-child transmissions.

Treatment of chronic hepatitis B

The first thing to understand is that not everyone with chronic hepatitis B needs treatment. The decision is made by a specialist (gastroenterologist or hepatologist) based on the viral load, the level of liver enzymes, and the degree of liver fibrosis. Many people only require regular monitoring.

When treatment is indicated, the drugs of choice are the oral nucleos(t)ide analogues, taken once daily:

• Entecavir.
• Tenofovir disoproxil (TDF).
• Tenofovir alafenamide (TAF), a newer formulation with a better kidney and bone profile.

These are potent, very well tolerated drugs with a very low chance of the virus becoming resistant. The goal of treatment is to suppress the virus in order to curb inflammation, prevent cirrhosis, and reduce the risk of liver cancer. In selected cases pegylated interferon may be used for a defined period.

It is important to be honest on two points. First, there is currently no cure that fully eliminates the virus; the antivirals keep it under control, and that is why treatment is usually long-term, often for years or for life, with excellent adherence. Second, there are research efforts seeking a “functional cure” (the body controlling the virus without the need for medication), but these are still under study.

General measures: people with chronic hepatitis B should be vaccinated against hepatitis A if they are not immune, avoid alcohol, and maintain a healthy weight, because fatty liver worsens the damage. Patients with cirrhosis are advised to have an abdominal ultrasound every six months to detect liver cancer early. When cirrhosis is advanced, liver transplant is an option.

Screening before chemotherapy or immunosuppression

There is one point that is sometimes overlooked and that can be serious. In a person who has had contact with the B virus, even if they seem “cured,” the virus can reactivate when they receive chemotherapy or treatments that lower the defenses (for example high-dose corticosteroids, biologics such as rituximab, or immunosuppressants for transplants). This reactivation can cause severe hepatitis.

For this reason, before starting chemotherapy or immunosuppression, screening for hepatitis B (HBsAg and anti-HBc) is recommended. In at-risk patients, a preventive oral antiviral is prescribed for the duration of the immunosuppressive treatment.

Hepatitis B in Chile

Chile is a country of low hepatitis B prevalence, thanks in large part to the universal vaccination incorporated into the PNI. This contrasts with high-prevalence regions such as East Asia and sub-Saharan Africa. Even with low prevalence, screening in pregnant women, protection of the newborn, and timely diagnosis of people living with the virus remain essential, so they can be treated when appropriate and their complications avoided.

See also

• Hepatitis C
• Cirrhosis
• Liver cancer (hepatocellular carcinoma)
• Hepatitis B and HIV coinfection