Paramyxoviruses are from the family Paramyxoviridae, consisting of related viruses that cause such familiar diseases as measles, mumps, parainfluenza, and some respiratory diseases. These viruses all possess an ss-RNA and a helical symmetry. The helical capsid is wound in a lose sphere that is somewhat irregular in shape. The virus possesses an envelope with hemagglutination (clumping of blood cells) and neuraminidase (an enzyme) activities.
Parainfluenza viruses do not survive long outside the host. Four serotypes (designated 1-4) primarily affect infants and young children. Illnesses range from subclinical, to mild upper respiratoy infections, to croup or pneumonia, but they rarely spread to the blood. These viruses cause about 30% of the respiratory diseases seen in children. Treatment is symptomatic.
The respiratory syncytial viruses (RSV) cause about half of all bronchiolitis cases and about ¼ of all the pneumonia occurring in infants under two months of age. Death can result. Infections are mild in older children, and usually limited to the upper respiratoy tract. The RSV virions vary in size. The envelope contains neither hemagglutinin nor neuraminidase activity. Two types exist, A and B.
Mumps virus is one of the most communicable diseases of children and young adults, but not as contagious as measles or chickenpox. The mumps virus is a typical paramyxovirus, and is inactivated within hours once expelled from the body. Only one serotype is known, and humans are the only natural host. Mumps is transmitted by the airborne route and by direct contact with the saliva of an infected person. The incubation time is twelve to thirty-five days. During this time, the virus passes from the site of entry in the respiratory tract into the lymphatic system, and then into the blood. From there it travels into the meninges and such various organs as the the following: salivary glands, ovaries, testes, mammary glands, and pancreas. Several days to a week before the onset of symptoms and for about a week after symptoms, the virus can be found in the saliva, urine, stool, and blood. In about 1/3 of the cases, the infected person will have no symptoms and will unknowingly spread the disease, as will those who initially develop generalized symptoms since they, too, are contagious before they realize they have the disease.
Swelling occurs on one side only in about 25% of the cases. Several days to a week or more following the onset in the parotid gland, involvement of other glands may become apparent. Inflammation of the testes (orchitis) is rare in prepuberty males, whereas about 30% of older males do experience this inflammation. Inflammation of the ovaries and mammary glands occurs in a small percentage of the female population. The most serious complication from mumps results from infection of the central nervous system.
Mumps is one of the most common causes of aseptic (nonbacterial) meningitis and encephalitis, but most recover without permanent damage. Deafness may result in a small percentage of the population. There is a live attenuated vaccine that has been used since 1968, and is part of the combination known as MMR (measles, mumps, and rubella).
Measles (rubeola) is one of the most contagious diseases known. Before the development of an effective vaccine in the mid-1960s, 98% of the population of the US would have contracted the disease by age eighteen. Only one serotype of the measles virus exists, and the morphology is much like other paramyxoviruses. The virus is transmitted via inhalation of the particles. An infected person can spew over 5,000 of the microbes into the air in one hour just through normal breathing. These particles can remain in the room for as long as two hours thereafter. The measles virus enters the respiratory tract and is taken up by the draining lymph ducts. It then passes into the blood to be deposited throughout the body. The incubation period is nine to twelve days before the onset of fever, cough, runny nose, and conjunctivitis. Lesions, called ‘Koplik spots,’ begin to appear on the inside of the cheek. After three more days, a rash appears on the skin, and intensifies, over the next day or two. General symptoms can be severe, and secondary infections are common. The CNS is infected in about one out of every 1,000 cases, causing encephalitis and death about 15% of the time. Others may have such permanent damage as epileptic seizures, hearing loss, and personality changes. Measles infection makes a huge demand on the body’s Vitamin A store; and those deficient before the disease will certainly be dangerously deficient afterwards, to the point where vision can be seriously affected.
A rare degenerative neurological disease with the formidable name of subacute sclerosing panencephalitis (SSPE) develops in a few children or adolescents several years after a measles infection. It is thought that it is caused by measles viruses that have remained latent in the central nervous system. In the mid-1970s, a new dimension in the clinical picture of the measles disease appeared. The immunity of some children who had been vaccinated waned or their vaccinations were not sufficiently potency enough to produce full immunity. Consequently, a significant number of cases of atypical measles resembling various other diseases occurred. It was then necessary to use serologic tests to confirm a diagnosis of measles. The measles vaccine is usually given as part of the MMR (measles, mumps, and rubella) vaccination.