Measles

• Measles is an infection of the respiratory system.
• Maximum incidence in 6m-3 year age group
• Also sometimes known as English Measle
• An alternative name for measles in English-speaking countries is rubeola
  • Confused with rubella (German measles); the diseases are unrelated

• A paramyxovirus
• Genus Morbillivirus.
• Only one strain causes infection
• Enveloped, single-stranded, negative-sense RNA viruses.
• Nucleocapsid proteins
• Protect the genome RNA from nuclease digestion
• Recognize the location in the cell membrane for budding

Immunity 

• The receptor for measles virus is CD46 (membrane cofactor protein), a regulator of complement activation.
• T and B lymphocytes are infected by measles virus.

Transmission

• Spread through respiration
  • Contact with fluids from an infected person’s nose and mouth
  • Either directly or through aerosol transmission
• Highly contagious
  • 90% of people without immunity sharing living space with an infected person will catch it.

SAR 

• Approximately 80%.
• Formula to Calculate SAR
• No. of exposed persons developing the disease within the range of incubation period/Total number of exposed/”susceptible” contacts*100

Incubation period

• An asymptomatic incubation period occurs nine to fourteen days from initial exposure

• Infectivity lasts from two to four days prior
• Until two to five days following the onset of the rash (i.e. four to nine days infectivity in total).

Clinical Manifestations 

Prodromal/Pre-eruptive stage

• Koplik’s spot

• A day or two before the appearance of rash
• Bluish white with erythematous halo
• Appear on the buccal mucosa opposite the first and second upper molars.
• Pathognomonic enanthem of measles.
• Disappears after the onset of rash
• Cough coryza conjunctivitis and increasing fever.

Eruptive Stage

• Rash appears on the 4th day from fever.
• It begins at hairline and behind the ear,and spreads downward rapidly.
• Characteristically it is erythematous, non-pruritic and. maculopapular.
• Fever usually resolves by 4th day after the onset

Post measles stage

Complications

• Complications relatively common
• Mild and less serious
• Pneumonia is the most common life-threatening complication
• Mortality in developing countries may be as high as 10 to 15% 
• Diarrhea
• Otitis media
  • Most common complication
• Acute encephalitis (and rarely subacute sclerosing panencephalitis)
  • The mortality rate in encephalitis associated with measles is about 10-20 %
  • Rare complication
  • Most serious complication
• Corneal ulceration leading to corneal scarring.
• Complications are usually more severe in adults who catch the virus.

Diagnosis

Microscopy

Warthin–Finkeldey cell :

• Giant multinucleate cell found in hyperplastic lymph nodes
• Seen early in the course of measels
• Under the light microscope, these cells consist of a large, grape-like cluster of nuclei.
• Rapid diagnosis is possible by immunofluorescence or PCR.