The viruses that cause measles, mumps, rubella, roseola, and slapped cheek syndrome 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 measles, mumps, and rubella (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 and is caused by parvovirus B19. Roseola infantum is a childhood disease characterized by high fever and a rash. It is caused by human herpesvirus-6 (HHV-6). Coxsackievirus which causes hand, foot, and mouth disease in children is discussed in Chapter 40.
Additional information regarding the clinical aspects of infections caused by the viruses in this chapter is provided in Part IX, entitled Infectious Diseases.
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, non-segmented 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 ||Download (.pdf) TABLE 39–1 Properties of Important Childhood Viruses
|Property ||Measles Virus ||Mumps Virus ||Rubella Virus ||Parvovirus B19 ||Human Herpesvirus-6 |
|Virus family ||Paramyxoviruses ||Paramyxoviruses ||Togavirus ||Parvovirus ||Herpesvirus |
|Genome ||Single-stranded RNA; negative polarity ||Single-stranded RNA; negative polarity ||Single-stranded RNA; positive polarity ||Single-stranded DNA ||Double-stranded DNA |
|Virion RNA polymerase ||Yes ||Yes ||No ||No ||No |
|Nucleocapsid ||Helical ||Helical ||Icosahedral ||Icosahedral ||Icosahedral |
|Envelope ||Yes ||Yes ||Yes ||No ||Yes |
|Number of serotypes ||One ||One ||One ||One ||Two |
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 prodromal period and for a few days after the rash appears. Measles occurs worldwide, usually in outbreaks every 2 to 3 years, when the number of susceptible children reaches a high level. The World Health Organization (WHO) estimates there are 7 million cases of measles each year worldwide.