Here Is How Measles Makes You Sick

, also known as rubeola, is a highly contagious viral disease caused by the measles virus, a member of the . Here's an in-depth look at how the infection happens, the disease process, and how our body fights it off.

How the Infection Happens

When a person infected with measles virus coughs or sneezes, they launch the virus into the air around them. The measles virus is light enough to float in the air for up to two hours, and can survive on surfaces just as long. By “survive,” we mean it can infect and multiply in a host.

Once inhaled or ingested, the virus finds its way into the respiratory tract.

Virus Attachment and Replication

The measles virus attaches to the epithelial (topmost) cells of the nasopharynx (the area in the back of the throat) and respiratory tract. Specifically, it binds to the SLAM (Signaling Lymphocytic Activation Molecule) receptors on cells of the immune system like macrophages and dendritic cells, as well as nectin-4 receptors on epithelial cells. After attaching, the virus enters these cells and starts replicating.

Viruses multiply by hijacking the cells’ machinery for creating proteins. Instead of creating proteins needed for the cells to function properly, proteins for assembling new viruses are created. As the virus particles come out of the cells, they destroy their host cells.

Damage to Cells and Tissues

The virus initially replicates in the respiratory tract, then spreads to local lymphoid tissues. From there, it disseminates throughout the body via the bloodstream in a process called viremia. This systemic spread allows the virus to infect various organs and tissues, including the skin, the lining of the eyelids, and other epithelial surfaces. As those cells are destroyed, the combination of cell destruction and immune response lead to the symptoms of measles.

Measles virus can cause extensive damage to:

Respiratory tract: Inflammation and cell damage can lead to bronchitis, croup, and pneumonia.
Skin: The characteristic maculopapular rash results from immune-mediated responses and viral replication in the skin.
Eyes: Conjunctivitis (pink eye) is common.
Gastrointestinal tract: In some cases, it can cause diarrhea.

Symptoms and Timeline

The time from the initial infection to symptoms (known as the incubation period) for measles is typically 10-14 days. Symptoms develop in stages:

1. Prodromal phase (2-4 days): This phase includes high fever, cough, runny nose (coryza), and conjunctivitis. Koplik's spots—small white spots with a blueish-white center on a red background—may appear on the inside of the cheeks.

2. Exanthem phase (3-5 days): The red, blotchy rash begins on the face and spreads downward to the trunk and limbs. This rash typically lasts about a week.

3. Recovery phase: Symptoms gradually resolve, but the patient may still feel fatigued for several weeks.

Immune System Response

The immune system plays a crucial role in controlling and overcoming measles infection:

- Innate immune response: Macrophages and dendritic cells initially respond to the virus, but measles virus can impair their function, delaying the immune response.

- Adaptive immune response: Cytotoxic T cells attack infected cells, and B cells produce neutralizing antibodies. Memory T and B cells are generated, providing long-term immunity against future infections.

Possible Co-Infections, Complications, and Sequelae

Measles can lead to various complications, especially in malnourished individuals or those with weakened immune systems:

- Bacterial infections: Secondary bacterial infections, such as pneumonia and otitis media (middle ear infection), are common due to the immunosuppressive effects of the virus.

- Encephalitis: About 1 in 1,000 people with measles develop acute encephalitis, which can lead to permanent brain damage.

- Subacute sclerosing panencephalitis (SSPE): A rare but fatal disease of the central nervous system that occurs years after measles infection.

Prevention

Vaccination with the measles-mumps-rubella (MMR) vaccine is the most effective way to prevent measles. High vaccination coverage is essential to achieve herd immunity and prevent outbreaks.

Conclusion

Understanding the measles disease process highlights the importance of vaccination and early diagnosis. Measles not only causes significant morbidity (disease and disability) and mortality (death), but also serious complications. By promoting vaccination and maintaining high immunization rates, we can protect communities and prevent the resurgence of this preventable disease.