Structure of Measles Virus

• Structure of Measles Virus-
• 
  
• Measles virus is a member of the genus Morbillivirus of the family Paramyxoviridae
• Measles) virus is a typical paramyxovirus (spherical enveloped particles that contain a non segmented negative strand RNA genome)
• Measles virus have two types of envelope spikes that shows:

    Hemagglutinating activity

Cell fusion and hemolytic activity

• Single serotype i.e. Life long immunity occurs in individuals who have had the disease.
• Hemagglutinin is the antigen against which neutralizing antibody is formed.
• Infants are protected during the first six months of life ( they get maternal antibody as it passes the placenta)

Replication cycle of Measles Virus

• Adsoprtion to the cell surface: via Hemagglutinin. Cellular receptor of measles virus is CD46 molecule.
• Penetrates the cell surface and uncoats
• Virion RNA polymerase transcribes the negative-strand genome to mRNA
• Specific viral proteins are formed
• Assembly to helical nucleocapsid
• Release of virus by budding

Transmission and Epidemiology of Measles

• Worldwide distribution, outbreaks in 2-3 years
• Transmitted via respiratory droplets produced by sneeze or cough during prodromal period which continues up to few days after rash appears
• Measles virus is extremely infectious, most children contract clinical disease on exposure
• More serious outcomes in Malnurished children, people with deficient cell mediated immunity.

Pathogenesis

• Measles virus infects the cells lining the upper respiratory tracts
• Enters blood and infects reticuloendothelial cells and replicates again.
• Spread to skins
• Appearances of rash: (because of cytotoxic T cells attacks measles virus infected vascular endothelial cells in the skin).
• Formation of Multinucleated giant cells.

Clinical features of Measles

• Incubation period: 10-14 days
• Prodromal phase: Characterized by fever, conjunctivitis (causing photophobia), running nose, and coughing
• Appearance of Koplik’s spot (bright red lesions with the white, central dot) # Diagnostic feature
• Appearance  of Maculopapular rashes, common features of which includes:
  
  

  Child infected with Measles
  Source:: CDC
• Occurs 5‐7 days after symptoms    
• Lasts 3 or more days
• Brownish hue
• Progresses from face to body to extremities
• Rash becomes confluent as it progresses
• Rash affects palms and soles
• Soon after the rash appears, the patient is no longer infectious.

Complications  because of Measles infections

• Encephalitis: 1 per 1000 cases
• Subacute sclerosing panencephalitis (SSPE): Fatal disease of nervous system can develop after several years after measles.
• Giant cell pneumonia
• Co-infections:

–     Secondary bacterial pneumonia –     Bacterial otitis media

• Increased risk of still birth in pregnant women infected with measles.
• Measles virus infection of fetus causes fetal death
• Atypical measles develops in some people who were given killed vaccine and subsequently infected with measles virus.