Sunday, December 6, 2015

Measles (excerpted)

By Intisar K. Hamidullah

In 1762 a French Physician, Tissost pointed out that measles rarely killed and when death occurred it was due to complications. However, at the end of the century it was concluded that this disease is more common, more dangerous and more widespread than most people believed. Although, in North America epidemics were less frequent they tended to be severe when they occurred, attacking people of all ages. Measles was also called the Covered Wagon Disease because it traveled with human communities. As a result of accessible travel and a growing population, measles became an endemic disease of North America never absent and reaching epidemic proportions at intervals.

Measles was thought to be a disease of large cities. Urbanization brings close contact between large groups of people which allows viruses and diseases to spread easily. Although a source for the infection was not found in humans it was suggested that large groups of animals living closely with humans passed the disease. The disease was identified as a virus in 1911. Scientists had started to study measles infections, and realized that development of a vaccine would prevent the spread by causing lifelong immunity. John Enders, a Harvard graduate student, successfully grew the virus in brain tissue, as well as cells from the skin, muscles, and intestines. The virus was tested in human kidneys, human amniotic fluid, fertile hen eggs, and it ended up that chick embryo cell cultures became most useful in producing the measles vaccines, similar to methods still used today. The first demonstration was done in monkeys injected with virus and observed to develop protective antibodies against the virus. After that success a clinical trial was done using American children. Consequently, in 1961 Enders and colleagues reported that measles infection could be prevented through vaccination. Widespread vaccination of children caused the incidence of measles to reduce drastically. Accordingly the World Health Organization reported that during the 1980's and 1990's over 2.5 million children died from measles due to lack of vaccination given to susceptible individuals. From the records during the Civil War, we know that two thirds of the soldiers died from infectious diseases. In the Union army over 67,000 men had measles and more than 4,000 died. During the first year of the war alone, there were 21,676 reported cases of measles and 551 deaths of Union soldiers mainly from respiratory and cerebral brain involvement.

Measles is transmitted between humans through the air, such as by coughing, talking and sneezing. Infected individuals contract the virus through the lining of the mouth, throat, nose and eyes. Once infected it takes the virus two to four days to replicate inside of respiratory cells and to spread to lymph nodes. Then the second round of viral production occurs when it enters the blood stream within the white blood cells. Next, the virus circulating in blood carries infection to many parts of the body. During the final eight to twelve day incubation period, fever, weakness and loss of appetite is followed by hours of coughing and runny nose and eyes. At this point the infection spreads through tissue and the virus replicates throughout the body causing signs and symptoms of disease. Finally, cells in the capillaries become infected and interact with the body's natural immune system and a rash develops and spreads on the face, arms, legs and rest of your body.

From: teachers.yale.edu


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