What Does Hepatitis A Look Like Under a Microscope?
Explore the visual evidence of Hepatitis A, from the distinct structure of the virus particle to the cellular changes it causes within the liver.
Hepatitis A is an infection of the liver caused by the Hepatitis A virus (HAV). The condition is characterized by liver inflammation, which can lead to various symptoms, though some individuals may not experience any. Transmission occurs through the ingestion of contaminated food or water or through direct contact with an infectious person. Unlike some other forms of hepatitis, Hepatitis A does not cause chronic liver disease and is a self-limiting illness from which people recover completely. Understanding this virus involves looking at the individual viral particle and its effects within the liver tissue.
The Hepatitis A Virus Particle
The Hepatitis A virus (HAV) particle, or virion, is incredibly small, measuring 27 to 30 nanometers in diameter. The virus is classified as a non-enveloped virus, meaning it lacks an outer lipid membrane that surrounds many other types of viruses. This structural characteristic contributes to its unusual stability in the environment, allowing it to survive for extended periods outside a host.
The virion’s structure is defined by its protein shell, known as a capsid. This capsid has a symmetrical shape called an icosahedron, a geometric form with 20 triangular faces. This icosahedral shell is constructed from four different viral proteins that assemble themselves into a protective coat.
The primary function of this protein capsid is to safeguard the virus’s genetic material. Encased within the shell is a single strand of ribonucleic acid (RNA), which carries all the instructions the virus needs to replicate once it infects a host cell. The faceted, angular surface of the HAV particle is a feature that distinguishes it from other viruses that may have smoother, more spherical shapes.
How Scientists View the Virus
Visualizing an object as small as the Hepatitis A virus requires technology far more powerful than a conventional light microscope. Scientists rely on electron microscopes, specifically a technique called transmission electron microscopy (TEM), to directly observe individual virions. A standard light microscope’s resolution is limited by the wavelength of light, making viruses invisible.
Transmission electron microscopy overcomes this limitation by using a focused beam of electrons instead of light. Since electrons have a much shorter wavelength, they can resolve much smaller objects. To prepare a sample for viewing, purified virus particles are treated with a method called negative staining. Applying a solution containing heavy metal atoms, such as tungsten or uranium, to the sample.
The heavy metal solution surrounds the virus particles but does not penetrate them, creating a “negative” image. When the electron beam passes through the sample, it is blocked by the dense metal stain but passes through the less dense virus particles. This generates a high-contrast silhouette, outlining the virion’s size and its icosahedral shape against a dark background.
Microscopic View of an Infected Liver
Examining a tissue sample from an infected liver under a microscope reveals the virus’s impact on the body. Pathologists study thin, stained slices of liver tissue, often from a biopsy, to observe the histopathology, or the changes in tissue caused by disease. In a case of acute Hepatitis A, the liver tissue shows clear signs of widespread inflammation, a condition known as acute hepatitis.
A hallmark of Hepatitis A infection is a significant inflammatory response within the portal tracts—small regions in the liver that contain branches of the portal vein, hepatic artery, and bile duct. Under the microscope, these areas are seen to be heavily infiltrated by the body’s own immune cells. This cellular infiltration disrupts the normal, orderly arrangement of liver cells, or hepatocytes, creating lobular disarray.
Beyond the portal inflammation, direct damage to the hepatocytes is also visible throughout the liver lobule. Some liver cells become swollen and pale, a change referred to as ballooning degeneration. Other liver cells die off in a process called apoptosis, shrinking and forming dense structures known as acidophilic bodies. This scattered necrosis, combined with the immune cell presence, provides the microscopic evidence of the liver’s battle against the Hepatitis A virus.