Hepatitis B is a DNA virus. It is transmitted by direct contact with blood or bodily fluids. This may occur during sexual intercourse or sharing needles, for example amongst IV drug users or tattoos. It can also be passed through sharing contaminated household products such as toothbrushes or contact between minor cuts or abrasions. It can also be passed from mother to child during pregnancy and delivery. This is known as vertical transmission.
Most children fully recover from the infection within 2 months, however a portion go on to become chronic hepatitis B carriers. In these patients the virus DNA has integrated into their own DNA and they continue to produce the viral proteins. The risk of developing chronic hepatitis B after exposure is:
- 90% for neonates
- 30% for children under 5
- Under 10% for adolescents
Most children with chronic hepatitis B are asymptomatic, with normal growth and development and normal liver function tests. Less than 5% will develop liver cirrhosis and less than 0.05% will develop hepatocellular carcinoma before adulthood. These risks increase once they enter adulthood.
Remember that antibodies are produced by the immune system against pathogen proteins. Antigens are proteins that are targeted by the antibodies, in this scenario they are part of the virus. The different antigens and antibodies can be difficult to understand. There is a video on the Zero to Finals YouTube channel that may be helpful for understanding this topic.
- Surface antigen (HBsAg) – active infection
- E antigen (HBeAg) – marker of viral replication and implies high infectivity
- Core antibodies (HBcAb) – implies past or current infection
- Surface antibody (HBsAb) – implies vaccination or past or current infection
- Hepatitis B virus DNA (HBV DNA) – this is a direct count of the viral load
When screening for hepatitis B, test HBcAb (for previous infection) and HBsAg (for active infection). If these are positive do further testing for HBeAg and viral load (HBV DNA).
HBsAb demonstrates an immune response to HBsAg. The HBsAg is given in the vaccine, so having a positive HBsAb may simply indicate they have been vaccinated and created an immune response to the vaccine. The HBsAb may also be present in response to an infection. The other viral markers are necessary to distinguish between previous vaccination and infection.
HBcAb can help distinguish between acute, chronic and past infection. We can measure IgM and IgG versions of the HBcAb. IgM implies an active infection and will give a high titre with an acute infection and a low titre with a chronic infection. IgG indicates a past infection where the HBsAg is negative.
HBeAg is important. Where the HBeAg is present it implies the patient is in an acute phase of the infection where the virus is actively replicating. The level of HBeAg correlates with their infectivity. If the HBeAg is higher, they are highly infectious to others. When they HBeAg is negative but the HBeAb is positive, this implies they have been through a phase where the virus was replicating but the virus has now stopped replicating and they are less infectious.
Which Children to Test
- Children of hepatitis B positive mums (screen at 12 months of age or any time after that)
- Migrants from endemic areas
- Close contacts of patients with hepatitis B
Hepatitis B Positive Mothers
To reduce the risk of the baby contracting hepatitis B, at birth (within 24 hours) neonates with hepatitis B positive mothers should be given both:
- Hepatitis B vaccine
- Hepatitis B immunoglobulin infusion
Infants are given an additional hepatitis B vaccine at 1 and 12 months of age. They will also receive the hepatitis B vaccine as part of the normal 6 in 1 vaccine given to all infants aged 8, 12 and 16 weeks. They are tested for the HBsAg at 1 year to see if they have contracted hepatitis B.
The hepatitis B virus can be found in the breast milk of mothers with hepatitis B. Babies of these mothers have already been exposed to the virus during pregnancy and birth. They should also receive the hepatitis B vaccine and hepatitis B immunoglobulin infusion. Therefore, the general advice is that it is safe for hepatitis B positive mother to breastfeed provided their babies are properly vaccinated.
Vaccination involves injecting the hepatitis B surface antigen. The vaccine requires 3 doses at different intervals. Vaccination to hepatitis B is now included as part of the UK routine vaccination schedule as part of the 6 in 1 vaccine.
Most children with chronic hepatitis B are asymptomatic and do not require treatment. They require regular specialist follow up to assess monitor their serum ALT, HbeAg, HBV DNA, physical examination and liver ultrasound.
Where there is evidence of hepatitis or cirrhosis, treatment with antiviral medications may be considered.
Last updated January 2020