Measles: Videos & Practice Problems

Measles is caused by the measles virus, a single-stranded RNA virus belonging to the genus Morbillivirus. The virus initially infects the upper respiratory tract, where it replicates. From there, it spreads systemically throughout the body via the lymphatic system and bloodstream. This systemic spread allows the virus to affect multiple organs and tissues, leading to the characteristic symptoms of measles. The virus is highly contagious and can be transmitted through respiratory droplets when an infected person coughs, sneezes, or talks. Importantly, individuals can spread the virus even before symptoms appear, making containment challenging.

Measles presents with flu-like symptoms such as fever, dry cough, and sore throat. A hallmark diagnostic feature is the presence of Koplik spots—small white or gray lesions with a red halo found inside the mouth. As the disease progresses, a maculopapular rash develops, starting on the face and spreading to the trunk and limbs. This rash consists of red, raised lesions. The virus also destroys memory B and T cells, weakening the immune system and increasing susceptibility to secondary infections. These symptoms and signs are critical for clinical diagnosis, which can be confirmed by serological tests detecting measles-specific antibodies.

Measles is transmitted primarily through respiratory droplets released when an infected person coughs, sneezes, or talks. It can spread via both direct contact and indirect transmission through contaminated surfaces. The virus is one of the most contagious infectious agents known because it can infect others even before symptoms appear in the infected individual. This pre-symptomatic infectious period allows the virus to spread widely and rapidly, making quarantine alone insufficient to control outbreaks. The high contagion rate underscores the importance of vaccination and herd immunity to prevent epidemics.

Measles can lead to serious health complications, especially in infants, older adults, and immunocompromised individuals. The virus destroys memory B and T cells, weakening the immune system and increasing vulnerability to secondary infections. Common complications include pneumonia, diarrhea, dehydration, and encephalitis (inflammation of the brain). In severe cases, measles can be fatal. These complications highlight the importance of early diagnosis, supportive care, and preventive vaccination to reduce morbidity and mortality associated with the disease.

Measles diagnosis begins with clinical observation of characteristic symptoms such as Koplik spots and the maculopapular rash. To confirm infection, serological testing is performed to detect measles-specific antibodies or viral components in the blood. These tests provide definitive evidence of measles infection. Early and accurate diagnosis is essential for managing the disease, preventing complications, and controlling outbreaks through timely public health interventions.

There is no specific antiviral treatment for measles. Management is primarily supportive, focusing on relieving symptoms and preventing complications such as pneumonia and encephalitis. Supportive care may include hydration, fever control, and treatment of secondary infections if they occur. Because the virus impairs immune memory cells, patients are more susceptible to other infections, so close monitoring is important. Prevention through vaccination remains the most effective strategy to control measles.

The MMR vaccine provides long-term immunity against measles, mumps, and rubella by stimulating the immune system to produce antibodies and memory cells without causing disease. This vaccine is highly effective and is the primary method of preventing measles infection. Herd immunity occurs when a high percentage of the population is vaccinated, reducing the overall amount of virus circulating and protecting those who cannot be vaccinated, such as infants or immunocompromised individuals. Maintaining high vaccination coverage is crucial to prevent outbreaks and epidemics of measles.