Paramyxoviruses are a family of enveloped, single-stranded RNA viruses. They are responsible for a variety of respiratory illnesses that affect both humans and other vertebrates. Their structure includes a core of genetic material enclosed within a lipid envelope. This diverse family is divided into groups that contain well-known infectious agents like those causing measles and mumps.
Common Paramyxovirus Infections in Humans
Measles (Morbillivirus)
Measles, caused by the Morbillivirus, is an infection known for its distinct symptoms. The illness begins 7 to 14 days after exposure with a high fever, often over 104°F, accompanied by a cough, runny nose, and red, watery eyes. Two to three days after these initial symptoms, small white spots known as Koplik spots may appear inside the mouth. A characteristic rash then emerges, starting as flat red spots on the face at the hairline and spreading down the body. This rash can become bumpy and the spots may merge as they spread.
Mumps (Rubulavirus)
Mumps is caused by a Rubulavirus and is recognized for causing painful swelling of the salivary glands. This condition, known as parotitis, leads to the puffy cheeks and swollen jawline characteristic of the infection. Before the swelling appears, a person might experience a few days of symptoms like fever, headache, muscle aches, and fatigue. While parotitis is the most common sign, the mumps virus can also affect other parts of the body.
Respiratory Syncytial Virus (RSV)
Respiratory Syncytial Virus (RSV) is a widespread virus that causes respiratory tract infections. It often results in mild, cold-like symptoms in adults and older children but can be more serious for infants and the elderly. In these vulnerable populations, RSV is a cause of bronchiolitis, an inflammation of the small airways in the lungs, and pneumonia. Nearly all children are infected with RSV by age two, but the immunity that develops is not long-lasting, allowing for reinfections.
Human Parainfluenza Viruses (HPIVs)
Human parainfluenza viruses (HPIVs) are a group of four viruses that are a frequent cause of respiratory illness in infants and young children. HPIV-1 and HPIV-2 are most often associated with croup, an infection of the upper airway that causes a characteristic barking cough. HPIV-3 is more commonly linked to bronchiolitis and pneumonia. HPIV-4 is less common but can still cause a range of respiratory illnesses.
How Paramyxoviruses Spread
Paramyxoviruses are highly contagious and primarily spread from person to person through the air. When an infected individual coughs or sneezes, they release respiratory droplets containing the virus. These droplets can then be inhaled by others, leading to a new infection by infecting cells within the respiratory tract.
Transmission can also occur through direct contact with an infected person’s saliva or nasal mucus. Another route is through contact with contaminated surfaces or objects, known as fomites. Some paramyxoviruses can survive on surfaces for several hours, and a person can become infected by touching a contaminated object and then their eyes, nose, or mouth.
Preventing and Managing Infections
Vaccination is a primary method for preventing several common paramyxovirus infections. The MMR vaccine protects against measles and mumps, with two doses being about 97% effective at preventing measles and 88% effective at preventing mumps. This vaccine uses weakened live viruses to stimulate the immune system to build long-term protection without causing the disease.
For most paramyxovirus infections, there are no specific antiviral treatments, so management focuses on supportive care to alleviate symptoms. This includes getting adequate rest, staying hydrated, and using over-the-counter fever reducers to manage discomfort. Good hygiene practices, such as frequent handwashing and covering coughs and sneezes, also help reduce the spread.
Paramyxoviruses in Animals
The Paramyxoviridae family also includes viruses that infect a wide range of animal species. Some of these, known as zoonotic viruses, can be transmitted from animals to humans. Nipah virus and Hendra virus are examples, with fruit bats acting as their natural reservoirs. Hendra virus emerged in Australia, causing severe disease in horses, which then spread to humans. Nipah virus was identified after an outbreak in pigs in Malaysia led to encephalitis in humans.
Other paramyxoviruses primarily affect animals without posing a significant threat to human health. Canine distemper virus is a morbillivirus that causes a serious systemic disease in dogs and other carnivores like ferrets and raccoons. Newcastle disease virus is another example, which impacts birds. These animal-specific viruses show the broad host range of the paramyxovirus family.