Measles, a highly contagious viral disease, is recognized by its characteristic rash and respiratory symptoms. Understanding this illness involves examining its microscopic characteristics.
The Measles Virus Structure
The measles virus is an RNA virus belonging to the Paramyxoviridae family. It is roughly spherical, but can appear irregular. Its size ranges from 150 to 300 nanometers in diameter.
An outer lipid envelope, derived from the host cell membrane, surrounds the virus. Embedded within this envelope are two viral glycoproteins: the hemagglutinin (H) protein, which attaches to host cells, and the fusion (F) protein, which facilitates entry. Inside the envelope, the viral RNA genome is encased by nucleoproteins, forming a helical nucleocapsid.
How Measles Affects Cells
The measles virus initiates infection by attaching to specific receptors on host cells, primarily in the respiratory tract. Once inside, the virus replicates its genetic material and produces new viral proteins within the cell’s cytoplasm. This replication leads to noticeable changes in infected cells, known as cytopathic effects (CPE).
A hallmark of measles infection is cell fusion. Infected cells merge with neighboring cells, forming large, multinucleated giant cells called syncytia. This process allows the virus to spread directly from cell to cell. Viral replication also leads to accumulations of viral components within infected cells, known as inclusion bodies. These bodies represent sites where the virus actively replicates and assembles new particles.
Key Microscopic Features of Measles Infection
Microscopic examination of tissue samples reveals specific features of measles infection. The most distinct feature is the presence of multinucleated giant cells, often called Warthin-Finkeldey giant cells. These multinucleated giant cells, also called syncytia, form when infected cells fuse with surrounding cells.
Inclusion bodies are another indicator, visible as distinct structures under a light microscope. Both eosinophilic intranuclear (within the nucleus) and intracytoplasmic (within the cytoplasm) inclusion bodies appear as pink-staining masses. They represent sites of viral replication and protein accumulation.
Visualizing Measles Through Microscopy
Microscopy uses various techniques to observe the measles virus and its effects. Light microscopy identifies characteristic cellular changes. Stained tissue sections allow visualization of multinucleated giant cells (syncytia) and distinctive inclusion bodies, providing diagnostic information based on cytopathic effects.
Electron microscopy offers higher magnification, necessary for directly visualizing individual measles virus particles. These tiny viral structures, due to their nanometer scale, are not visible with a standard light microscope. Electron microscopy provides detailed images of the virus’s morphology, including its envelope and internal nucleocapsid.
Specialized microscopic techniques like immunofluorescence are used. Antibodies that specifically bind to measles viral proteins are tagged with fluorescent dyes. When tagged antibodies attach to viral components, they glow under a fluorescence microscope, allowing precise localization and identification of the virus.