Measles virus (MV) is responsible for a childhood infection characterised by a maculopapular rash, dry cough, coryza, conjunctivitis and photophobia. Although mild in developed countries, the infection is associated with significant morbidity in developing countries and still kills more than 200 000 children per annum even though it is a vaccine preventable disease. The virus replication cycle is well understood and the molecular description of the virus has progressed to a stage where the main emphasis of research has reverted towards understanding the pathogenesis and molecular basis of virus attenuation. Such knowledge will assist in the development of new vaccines and serve to increase our understanding of epidemiology and transmission. Our ability to make recombinant viruses that express autofluorescent proteins from additional transcription units within the genome has created a paradigm shift in changing our view of MV from simply a ’respiratory infection‘ causing agent to one that affects the immune system in a serious and potentially dangerous manner. Identification of the early target cells as alveolar macrophages and/or dendritic cells in the deep lung alongside understanding the early events in viral pathogenesis helps shed light on how this highly infectious agent establishes such a profoundly immunosuppressive disease in the host.

Key Concepts:

• Measles is a relatively simple enveloped, negative-sensed RNA virus which contains only six genes.
  
• Measles virus is a highly infectious agent, which causes a profound immunosuppression and a severe disease in susceptible individuals.
  
• The molecular basis of the immunosuppression is unknown.
  
• A highly efficacious vaccine has been developed, although the molecular basis of the attenuation remains an enigma.
  
• It is essential to vaccinate 95% of the birth cohort as the virus is so infectious and when vaccine uptake levels decrease in disease-free regions importations from endemic parts of the world often occur.
  
• The vaccine is exceptionally thermolabile and this is challenging for those involved in delivering the product to remote areas of the developing world and in areas where conflict is rife.
  
• Recombinant measles viruses have helped to define the early steps in the establishment of an infection.
  
• Measles has been considered for eradication although the potential for cross-species infection is being considered due to the cross-protective morbillivirus antibodies which are elicited.