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Spotting the mutations to find the missing millions infected with Hepatitis B virus

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Rashmi Jha, Asst Product Manager- Immunology, Transasia Bio-Medicals elucidates on how HBV infection affects 325 million people worldwide, claiming 4000 lives a day to spread awareness about this chronic disease this World Hepatitis Day

28th July every year is recognised as World Hepatitis Day, in an effort to create awareness to eradicate the deadly virus by 2030. The second major infectious disease after tuberculosis, hepatitis affects 325 million people worldwide, claiming 4000 lives a day! What is ironical is that 290 of these 325 million people are unaware of their infection!* That’s the story of the missing millions.

Not just globally, hepatitis is a severe health challenge in India as well. According to a 2017 study published in the Journal of Clinical and Translational Hepatology, India has a disease burden of about 50 mn; second only to China; with a prevalence of 2-7 per cent.**

Hepatitis B infection shows no symptoms

Of the five strains A,B,C,D and E of the hepatitis virus, hepatitis B virus (HBV) is 50-100 times more infectious than HIV. HBV infection occurs as acute or a chronic, with chronic HBV infection being the most common presentation of the disease. Without intervention, 15-40 per cent of chronic HBV-infected individuals go on to develop cirrhosis, end-stage liver disease, hepatocellular carcinoma (HCC), or require liver transplantation.

HBV spreads through contact with infected serum, sexual activity, unsafe transfusions and vertical transmission from mother to infant. In endemic areas, most infections occur at birth or during early childhood. Probability of chronic HBV infection in neonates is far more than 90 per cent and in children 2-5 years of age about 30 per cent. But this disease, unlike most others, will remain dormant for several years, before it manifests and show ups as liver cirrhosis or cancer in 20-30 per cent of those suffering from infection.

Why accurate diagnosis is essential?

The lack of symptoms only makes the situation worse. Accurate diagnosis is therefore essential for prevention of transmission and effective treatment. For serodiagnosis, HBsAg (hepatitis B surface antigen) and HBeAg (hepatitis B envelope antigen) are two HBV specific antigens that can be detected directly in the serum of an infected person.
HBsAg is the major viral immunogenic surface protein, produced in all strains of HBV. It can be detected in the serum as a diagnostic marker of active HBV replication. Its presence in the serum for more than six months, indicates a chronic HBV infection.

Diagnostic assays for HBV

Antibody detection, namely detection of anti HBsAg and antiHBe is not useful in diagnosing chronic HBV infection. The presence of anti-HBs (antibody against HBsAg) indicates either a past HBV infection or recent vaccination. Anti-HBe (antibody against HBeAg) indicates lower levels of HBV and low contagiousness.

Mutations pose a challenge in diagnosis

The HBsAg has a single major antigenic determinant, called the ‘a determinant’. Mutations inducing a conformational change within the ‘a determinant’, may result in a variant epitope of HBsAg, that is not recognised by some diagnostic assays. A number of studies have evaluated the available HBsAg diagnostic assays for their ability to detect well-defined HBsAg mutants.

Currently, a majority of the diagnostic assays use monoclonal antibodies directed to the ‘a’ determinant of HBsAg, in order to capture the protein. Mutations within this region, change the ability of the protein to be detected by monoclonal antibodies. Thus, monoclonal antibodies alone may not be sufficient to detect altered HBsAg associated with mutations. A more robust approach is to use a pool of well-characterised polyclonal antibodies directed to HBsAg. Polyclonal antibody based assays appear to detect mutant HBsAg as well.

Advanced test kits that detect mutations

The good news is that a lot of leading diagnostic manufacturers in India have developed ELISA kits with a pool of polyclonal antibodies coated on the microwells to maximise the sensitivity for HBsAg mutations. The conjugate reagent contains monoclonal antibodies specific to HBsAg, thereby ensuring better specificity too. As a result these kits are able to offer an analytical sensitivity of 0.1 ng/ml and <50 pg/ml respectively with a turnaround time (TAT) of only 75 minutes, thereby making them convenient and reliable for use in screening for HBV infection.

Sources:

*https://www.pharmaceutical-technology.com/comment/world-hepatitis-day-2019/
** https://vilabin.com/article/hepatitis-b-causes-symptoms-types-prevention-and-vaccination/

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