The name measles is derived from the Latin, misellus, meaning miserable. Measles (also called Rubeola-(from rubeolus, Latin for reddish) ) is usually a disease of childhood (aged 3-10 years) and is followed by life-long immunity. Measles is a highly contagious and sometimes deadly disease that spreads through coughing and sneezing. It can spread like wildfire in naive populations. Measles is an important cause of childhood mortality in developing countries. Human is the natural host of this pathogen.
Structure of Measles Virus
- Measles virus is a member of the genus Morbillivirus of the family Paramyxoviridae. Paramyxoviruses are so called because they have an affinity for mucous membranes (Greek: myxa = mucus).
- Measles virus is a typical paramyxovirus (spherical enveloped particles that contain a non segmented negative strand RNA genome with a linear arrangement of genes)
- Measles virus have two glycoproteins spikes that are important in pathogenesis:
- F (fusion) protein, which is responsible for fusion of virus and host cell membranes, viral penetration, and haemolysis, and the
- H (haemagglutinin) protein, which is responsible for binding of virus to cells
- Measles virus has only one 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
- Measles virus is extremely infectious, most children contract the clinical disease on exposure
- Transmitted via respiratory droplets produced by sneeze or cough during prodromal period or direct contact with nasal or throat secretions from an infected person, which continues up to few days after the rash appears.
- Less commonly, it is spread by airborne aerosolised droplet nuclei or by indirect contact with freshly contaminated articles.
- More serious outcomes in malnurished children, people with deficient cell-mediated immunity.
- Measles virus invades the cells lining the upper respiratory tracts i.e respiratory epithelium of the nasopharynx and spreads to the regional lymph nodes
- After 2-3 days of replication in these sites, a primary viraemia widens the infection to the reticuloendothelial system where further replication takes place.
- Secondary viraemia occurs and the virus enters skin, conjunctivae, respiratory tract and other organs, including the spleen, thymus, lung, liver, and kidney and further replication occurs.
- Appearances of rash (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:
- 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
– 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.
- Most diagnoses are made on clinical grounds; presence of koplik’s spot provides a definitive diagnosis.
- If laboratory diagnosis is necessary, it can be done by
- Isolation of virus in a cell culture
- a positive serologic test for measles IgM
- Demonstrating rise in antiviral antibody titer of greater than four-fold.
- Identification of measles virus RNA from a clinical specimen by PCR
Prevention of Measles
Measles can be prevented with MMR vaccine. The vaccine protects against three diseases: measles, mumps, and rubella.
The MMR vaccine is very safe and effective. Two doses of MMR vaccine are about 97% effective at preventing measles; one dose is about 93% effective.
CDC recommends children get two doses of MMR vaccine,
- the first dose at 12 through 15 months of age, and
- the second dose at 4 through 6 years of age.
Teens and adults should also be up to date on their MMR vaccination.