Morbilli is an exanthematic disease caused by the measles virus, genus Morbillivirus, a member of the Paramyxoviridae, a family of enveloped, negative, single-stranded RNA viruses.
In most populations, the majority of adults and children are immune due to exposure to the measles virus or vaccination. However, in resource-poor countries with low vaccination coverage, measles remains a significant cause of morbidity and mortality. In countries where measles vaccination is part of the pediatric vaccination program, measles has become a rare disease and is often diagnosed as an imported disease brought by nonimmune individuals from endemic countries. Sporadic epidemics may also occur in religious communities where vaccination is not accepted. Humans are the only known reservoir of measles.
The infection is highly contagious and spreads through airborne droplets. The virus replicates in the respiratory mucosa and spreads (primary viremia) in leukocytes to endothelial and epithelial cells, monocytes, and macrophages. These cells release large amounts of the virus during the secondary viremia, several days after the first viremia.
The asymptomatic incubation period of measles lasts 10โ14 days. During the secondary viremia, symptoms such as malaise, fever, anorexia, conjunctivitis, coryza, and cough appear. This prodromal phase lasts 2โ3 days, sometimes up to 8 days. Contagion begins 5 days before the rash appears and lasts until 4 days after. The maximum contagion likely occurs in the late prodromal phase when fever and respiratory symptoms are present.
Dr. William Schaffner, Infectious Disease Expert:“Measles is one of the most contagious diseases known to humanity, and vaccination remains our most effective tool in preventing its spread and protecting vulnerable populations.”
Clinical Features
During the late prodromal phase, patients may develop an enanthem known as Koplikโs spots. These are 1โ3 mm grayish or bluish elevations with an erythematous base, found on the buccal mucosa opposite the molars or on the labial mucosa. Described as “salt grains on a red background,” these spots appear approximately 48 hours before the measles exanthem and disappear by the second day of the rash.
The characteristic maculopapular rash of measles begins on the face and spreads to the neck, upper trunk, lower trunk, and extremities. Lesions may become confluent, particularly on the face. The palms and soles are rarely involved. The cranial-to-caudal progression of the rash is characteristic. The rash is non-pathognomonic, begins to fade 3โ4 days after appearing, and may change to a purplish-brownish color followed by fine desquamation.
Clinical improvement usually occurs within 48 hours of rash onset.
The differential diagnosis includes HHV-6 infection, rubella, infectious mononucleosis, scarlet fever, Kawasaki disease, toxic shock syndrome, dengue, Rocky Mountain spotted fever, drug allergies, erythema infectiosum (parvovirus B19), roseola, and enteroviral infections. The intensity and brownish coloration of the rash, combined with other findings like coryza and conjunctivitis, help differentiate measles from these conditions.
Dr. Natasha Crowcroft, Measles Immunization Specialist:“The global fight against measles requires a collective effort to improve vaccination coverage, especially in resource-poor settings where the disease continues to cause unnecessary deaths.”
Complications
In conditions of poor hygiene, crowding, or malnutrition, severe infections of macerated perioral or perinasal skin (cancrum oris) may occur, caused by pyogenic organisms often accompanied by Herpes simplex or anaerobic mouth flora. Rare complications include postinfectious encephalitis and subacute sclerosing panencephalitis.
Management
The introduction of the live attenuated measles vaccine in the 1960s led to rapid control of this epidemic disease. In areas with poor health care and nutrition, oral vitamin A is recommended at diagnosis due to its inverse relationship with measles mortality.
There is no specific treatment for measles.
