Molecular Evolution of Hepatitis B Virus in India: Insights into Genotype Diversity and Recombination

Hepatitis B is a virus that hides inside the human liver, capable of causing long-term damage that can lead to cirrhosis or cancer. While vaccines have existed for decades, the virus remains a stubborn global challenge, particularly in regions where access to care is limited. The virus is not a single, uniform entity; it exists in different genetic versions called genotypes, which behave differently in the body. Some versions respond better to treatment, while others are more likely to cause severe disease. Furthermore, the virus is constantly changing. It can swap pieces of its genetic code with other versions of itself, creating new hybrid strains. Understanding exactly which versions are circulating in a specific population, and whether new hybrids are emerging, is essential for doctors to choose the right treatments and for public health officials to design effective vaccines. Without this genetic map, efforts to eliminate the disease can miss their target.

In India, a country with a large population of people carrying the virus, scientists recently took a closer look at the genetic makeup of Hepatitis B to see what was actually circulating across the nation. Researchers from the ICMR-National Institute of Virology, working with a network of laboratories across the country, analyzed blood samples collected over nearly two decades. They started with nearly two thousand samples that had tested positive for the virus, but to get a clear picture of the virus's full genetic code, they focused on thirty-two samples with high amounts of virus in the blood. These samples came from nine different states, representing a wide geographic spread from the north to the northeast and the south. Using a portable sequencing device that can read genetic material directly from the blood, the team pieced together the complete genomes of these viruses. This approach allowed them to see not just which version of the virus was present, but also if any of them were genetic mixtures.

The results revealed a clear pattern of dominance. In the samples they studied, one specific version, known as genotype D, was by far the most common, appearing in more than seventy percent of the cases. This version was found throughout the northern, western, and central parts of the country. A different version, genotype A, was rare, showing up in only a few samples from the central and southern regions. Another version, genotype C, was found almost exclusively in the northeast, specifically in Assam, likely due to the region's proximity to Southeast Asia where this version is widespread. This geographic split confirms that the virus does not spread evenly across India; instead, it follows distinct regional patterns, with the dominant strain in the north and west being different from the one found in the northeast.

Perhaps the most significant discovery was the presence of hybrid viruses. The researchers found five samples that were not pure versions of a single genotype but were instead mosaics, containing genetic material from two different types. These recombinant strains were found in West Bengal, Chhattisgarh, Maharashtra, and Assam. In some cases, the virus had swapped parts of its code between genotype A and genotype D, while in others, it mixed genotype C and D. The scientists were able to pinpoint exactly where the switch happened in the genetic code. For instance, one sample from West Bengal started as genotype A, switched to genotype D in the middle, and then switched back to genotype A. Another sample from Chhattisgarh showed a more complex pattern, flipping between the two types three times. These findings suggest that in areas where different versions of the virus circulate together, people can be infected with more than one type at the same time, allowing the viruses to mix and create these new hybrids.

The study also looked at specific mutations, or small errors in the genetic code, that are known to affect how the virus behaves. Some of these changes can make the virus harder to detect or less responsive to treatment. The researchers found that certain mutations were common among the dominant genotype D strains and also appeared in the hybrid viruses. However, because the study used leftover blood samples from a quality control program, the team did not have access to the patients' medical histories. This means they could not link these genetic findings to how sick the patients were or how well they responded to medication. They could confirm the genetic changes existed, but they could not say for certain how those changes impacted the patients' health outcomes.

Despite this limitation, the work provides a crucial foundation for future efforts. The successful use of a portable sequencing device to analyze the virus directly from blood samples demonstrates that it is possible to conduct large-scale genetic surveillance even in settings with limited laboratory infrastructure. The study highlights that India's Hepatitis B landscape is genetically diverse and dynamic, with recombination acting as a key driver of new viral variants. As the country moves toward its goal of eliminating Hepatitis B as a public health threat by 2030, these genetic insights will be vital. They will help health officials track emerging variants, ensure that vaccines remain effective against the circulating strains, and guide treatment strategies for the millions of people living with the virus. The next step, as the authors suggest, is to expand this sequencing effort nationwide and link the genetic data with clinical information to fully understand how these viral changes affect human health.