The viruses that cause measles, mumps, rubella, and slapped cheek syndrome (parvovirus B19) are typically thought of as childhood diseases, although they can cause disease in adults as well. Measles, mumps, and rubella viruses are united as components of the widely used, very successful MMR vaccine. Note that measles and rubella are characterized by a rash, whereas mumps is not. The prominent feature of mumps is parotid gland swelling. Slapped cheek syndrome, as the name implies, is characterized by a rash on the face.
Rabies virus and Ebola virus are considered together as they both have an animal reservoir. This implies that these viruses can replicate within both the cells of the host animal and within human cells. Most viruses that cause human disease are limited to replicating in human cells as the attachment proteins on the viral surface interact only with receptors on the surface of human cells. Note that in addition to rabies virus and Ebola virus, most arboviruses have an animal reservoir. Arboviruses are described in Chapter 43.
Many mammals serve as a reservoir for rabies virus. In the United States, bats, skunks, and raccoons are common reservoirs, whereas worldwide, dogs are the most common. The animal reservoir for Ebola virus is uncertain, but bats are suspected.
IMPORTANT CHILDHOOD VIRUSES
This virus causes measles, a disease characterized by a maculopapular rash. It occurs primarily in childhood.
The genome of measles virus consists of single-stranded RNA with a negative polarity (Table 39–1). It is an enveloped virus with a helical nucleocapsid. The virus has a single serotype. Humans are the natural host.
TABLE 39–1Properties of Important Childhood Viruses |Favorite Table|Download (.pdf) TABLE 39–1 Properties of Important Childhood Viruses
|Property ||Measles Virus ||Mumps Virus ||Rubella Virus ||Parvovirus B19 |
|Virus family ||Paramyxoviruses ||Paramyxoviruses ||Togavirus ||Parvovirus |
|Genome ||Single-stranded RNA; negative polarity ||Single-stranded RNA; negative polarity ||Single-stranded RNA; positive polarity ||Single-stranded DNA |
|Virion RNA polymerase ||Yes ||Yes ||No ||No |
|Nucleocapsid ||Helical ||Helical ||Icosahedral ||Icosahedral |
|Envelope ||Yes ||Yes ||Yes ||No |
|Number of serotypes ||One ||One ||One ||One |
Summary of Replicative Cycle
After adsorption to the cell surface via its hemagglutinin, the virus penetrates and uncoats and the virion RNA polymerase transcribes the negative-strand genome into mRNA. Multiple mRNAs are synthesized, each of which is translated into the specific viral proteins; no polyprotein analogous to that synthesized by poliovirus is made. The helical nucleocapsid is assembled, the matrix protein mediates the interaction with the envelope, and the virus is released by budding from the cell membrane.
Transmission & Epidemiology
Measles virus is transmitted via respiratory droplets produced by coughing and sneezing both during the ...