Measles

Measles is a highly contagious infectious disease characterized by fever, cough, conjunctivitis, and a distinctive spreading rash. It is caused by an RNA virus of the genus Morbillivirus and the family paramyxovirdae. Documented as early as the 7th Century, measles remains an important human pathogen today. Prior to widespread immunization, measles infected nearly 100 percent of North American children. In under or un-immunized populations in the developing world, measles continue to cause widespread morbidity and mortality.

Humans are the only known host for the measles virus. Transmission occurs mainly through direct contact with infected droplets and less commonly through airborn spread.

The primary site of infection is the epithelial cells of the nasopharynx. Immediately after infection, the virus replicates within the respiratory epithelial cells and local lymph nodes. The incubation period of measles is between 8 to 12 days from exposure to onset of clinical symptoms. During this period, the virus spreads from the primary site of infection, systemic viremia ensues, and the infected individual becomes symptomatic.

The classic rash of measles begins several days after the fever, starts at the head and spreads to cover the body, and is described as red and patchy. Measles is generally self-limited and a full recovery is expected. However, high levels of morbidity and mortality may result. Measles infection may also be complicated by bacterial superinfection of the lower respiratory tract.

In the developing world, the diagnosis of measles is generally made on a clinical basis. Diagnosis may also be made through the use of serum serology. There is [Page 1076]no percentage of cases may result in measles pneumonia or encephalitis. In both these cases, specific antiviral therapy that is routinely used against measles and treatment is generally supportive. The WHO and UNICEF recommend the use of Vitamin A for all children infected with measles in regions known to have Vitamin A deficiency or measles case fatality rate exceeding 1 percent. Measles immune globulin can be given to exposed individuals within six days of exposure to prevent or decrease severity of infection. Concurrent bacterial infection should be treated with appropriate antibiotics.

The measles vaccine is the single most important public health tool for the prevention of measles infection. In North America, the measles vaccine is generally given as a trivalent combination formulation with mumps and rubella (MMR vaccine) at 12 to 15 months of age with a booster dose between 4 to 6 years of age. In the developing world, the WHO and UNICEF Expanded Program of Immunization (EPI) recommends a monovalent (measles only) vaccine at 9 months followed by the trivalent vaccine at 15 months of age.

Important gains have been made in reducing the global burden of measles. The measles vaccine was first licensed in the United States in 1963, and since that time, the routine use of the vaccine has contributed to a greater than 99 percent decrease in the incidence of disease. Only a decade ago, measles was responsible for over a million childhood deaths in the developing world each year. The WHO estimates that worldwide, mass vaccination campaigns resulted in a near 40 percent decrease in measles related deaths between 1999 and 2003. The largest reduction was seen in Africa, where deaths due to measles decreased by over 45 percent.

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