Measles is a highly contagious infectious disease that was once a common childhood illness but can affect individuals of all ages. It is characterized by a distinctive rash, fever, cough, runny nose, and red, watery eyes. While often thought of as a mild childhood ailment, measles can lead to severe complications, including pneumonia, brain swelling, and even death, particularly in young children and those with weakened immune systems.
The Measles Virus: Identity and Key Features
Measles is caused by the measles virus (MeV), also known as Morbillivirus hominis. This pathogen belongs to the Morbillivirus genus, which is part of the Paramyxoviridae family of viruses. The measles virus is a single-stranded, negative-sense RNA virus, meaning its genetic material is composed of RNA and requires a specific enzyme to be translated into proteins. It is an enveloped virus, containing two surface glycoproteins: hemagglutinin (H) and fusion (F) proteins.
The hemagglutinin protein is responsible for attaching the virus to host cells, specifically binding to receptors like the signaling lymphocyte activation molecule (SLAMF1 or CD150) found on immune cells, and nectin-4 on epithelial cells. Following attachment, the fusion protein facilitates the merging of the viral envelope with the host cell membrane, allowing the virus to enter the cell and begin replication. There is only one serotype of the measles virus, meaning antibodies developed against one strain provide protection against all other known strains.
How Measles Spreads and Develops
The measles virus is highly contagious, spreading primarily through airborne droplets. These infectious droplets can remain suspended in the air for up to two hours. The virus can also survive on surfaces for a similar duration, allowing for indirect transmission, such as touching contaminated surfaces.
Upon inhalation, the virus initially infects cells in the respiratory tract. Within two to four days, the measles virus spreads to local lymphatic tissues, often carried by pulmonary macrophages. The virus then amplifies in regional lymph nodes before disseminating throughout the body via the bloodstream, a process known as viremia. This systemic spread allows the virus to infect various organs and tissues, including the skin, conjunctivae, and other epithelial surfaces, leading to the characteristic symptoms such as the maculopapular rash. The incubation period, from exposure to the appearance of initial symptoms, typically ranges from 10 to 12 days, but can be between 7 and 21 days.
Protection Against Measles
The most effective public health intervention for preventing measles is vaccination. The measles vaccine is typically administered as part of the measles, mumps, and rubella (MMR) vaccine, or the MMRV vaccine which also includes protection against varicella (chickenpox). This vaccine contains live-attenuated (weakened) versions of the measles virus, capable of stimulating an immune response.
When vaccinated, the body’s immune system is exposed to these weakened antigens, prompting it to produce antibodies and develop memory cells. These antibodies are specifically targeted at the hemagglutinin protein, thereby providing long-term immunity against future infections. One dose of the MMR vaccine is approximately 93% effective at preventing measles, with two doses increasing effectiveness to about 97%. High vaccination rates within a population contribute to “herd immunity,” which protects individuals who cannot be vaccinated, such as infants or those with compromised immune systems, by making it difficult for the virus to spread.