Measles is caused due to a single stranded RNA virus from Paramyxoviridea family of genus Morbillivirus.
Man is the only reservoir of infection. Infection is usually transmitted when droplets spray into the air from nose, throat and mouth secretions of infected people and other people inhales them. The infected droplets can even remain active for several hours on surfaces and person can get infected by putting fingers in his mouth or nose or rubbing his/her eyes after touching the infected surface.
The measles virus gains its entry mainly through respiratory tract or conjunctivae when it comes in contact with droplets aerosols where the virus is released. A patient becomes infectious from 3 days before the rash up to 4-6 days after its onset.Pathogenesis-
Incubation period- The incubation period varies from 7 to 21 days from exposure to onset of fever and rash appears about 14 days after exposure. During this measles virus migrates to regional lymph nodes and produces a primary viraemia (where virus goes to bloodstream and spreads to rest of body) that spreads the virus to respiratory tract. The secondary vireamia spread the virus to reticuloendothelial system.
Prodromal illness- It is followed by secondary vireamia with the formation of necrosis of respiratory tract and formation of giant cells in the body tissues by 7-11 days. Two types of giant cells are seen- Warthin- Finkeldy cells and Epithelial giant cells.
Recovery phase- During this period, CD4 AND CD8 cells gets activated and viral replication occurs with the development of rash followed by recovery phase.