Myxoviruses are a group of RNA viruses responsible for several well-known diseases in humans and other animals. Their genetic blueprint is composed of ribonucleic acid rather than DNA. These pathogens primarily target the respiratory system, leading to illnesses from mild colds to more severe conditions. The term ‘myxovirus’ points to the interaction these viruses have with components of mucus.
The Two Families of Myxoviruses
Myxoviruses are scientifically divided into two families: Orthomyxoviridae and Paramyxoviridae. This classification reflects differences in their genetic organization and structure. Although both are RNA viruses, their genomes are arranged differently, which has implications for how they replicate and behave within a host.
The Orthomyxoviridae family is defined by its segmented genome, meaning the virus’s genetic information is broken into separate RNA segments. This segmentation is a feature of influenza viruses, the most prominent members of this family. The fragmented nature of their genome allows for genetic reassortment, where segments from different viral strains can mix if they infect the same cell, leading to new virus variants.
In contrast, the Paramyxoviridae family possesses a non-segmented genome, with its genetic information contained within a single, continuous strand of RNA. This structural difference makes genetic reassortment much less common. This family includes the viruses responsible for measles and mumps, which are more genetically stable than the constantly shifting influenza viruses.
Associated Human Diseases
The two myxovirus families are responsible for several human diseases that primarily affect the respiratory tract. The illnesses they cause vary in severity, from seasonal flu to childhood diseases now largely controlled by vaccination.
Orthomyxoviridae
This family contains the influenza viruses, which cause the seasonal flu. There are three main types that infect humans: Influenza A, B, and C. Influenza A viruses are known for causing widespread epidemics and pandemics due to their high rate of genetic change and their ability to infect animals like birds and pigs. Influenza B causes less severe, localized outbreaks, while Influenza C results in mild, cold-like symptoms.
Paramyxoviridae
The Paramyxoviridae family includes the viruses that cause measles and mumps. Measles is a highly contagious respiratory infection characterized by a distinctive rash, high fever, and cough. Mumps is recognized by painful swelling of the salivary glands. This family also includes respiratory syncytial virus (RSV), a cause of lower respiratory tract infections like pneumonia in infants and young children.
Core Biological Characteristics
These viruses share core biological features related to their physical structure and interaction with host cells. Their name, myxovirus, is derived from the Greek ‘myxo’ for mucin, a protein found in mucus. This name was chosen because of the viruses’ affinity for mucin on the surface of red blood cells and respiratory tract cells.
All myxoviruses are enveloped viruses, meaning the core RNA is enclosed within a protective lipid membrane. The surface of this envelope has spikelike protein projections that allow the virus to attach to and enter host cells. One of these proteins, hemagglutinin, is responsible for binding to host cell receptors to initiate the infection process.
A defining laboratory characteristic of myxoviruses is their ability to cause hemagglutination, the clumping of red blood cells. The hemagglutinin spikes on the viral envelope bind to receptors on red blood cells, causing them to stick together. This reaction was a foundational tool in virology for detecting and quantifying these viruses before the advent of modern molecular techniques.
Transmission and Prevention
Myxoviruses primarily spread from person to person through the air. When an infected individual coughs or sneezes, they release respiratory droplets containing the virus that can be inhaled by a nearby person. The viruses can also be transmitted through contact with contaminated surfaces, known as fomites.
Vaccination is the most effective method for preventing diseases caused by many myxoviruses. The annual flu shot is designed to protect against the Influenza A and B strains predicted to be most common during the upcoming season. The MMR vaccine provides robust protection against measles and mumps.
Practicing good hygiene is a fundamental step in reducing the spread of these viruses. Regular handwashing with soap and water can remove or inactivate viruses picked up from contaminated surfaces. Avoiding touching the face, particularly the eyes, nose, and mouth, helps prevent the transfer of the virus from hands into the body.