Yellow Fever
Yellow fever, an acute infectious disease affecting humans, monkeys, and several other small mammals, is found in tropical and subtropical zones in Africa and South America. Caused by a virus transmitted by several species of mosquito, yellow fever is characterized by the abrupt onset of headache, backache, rapidly rising fever, nausea, and vomiting. It also attacks the liver, producing the jaundice which gives it its name. Yellow fever causes death in 2-5% of cases, but survival confers lifelong immunity. Other than reduction of the fever, no specific treatment is available.
Yellow fever had been known on the coast of West Africa for centuries before the first epidemic occurred in the Western Hemisphere. The epidemic, reported in Barbados in 1647, probably resulted from the slave trade. The first epidemic in the United States occurred in New York City in 1668 and, by 1893, 135 major epidemics had occurred in North American port cities, with a death rate of 30-70%.
Yellow fever's scope of influence was wide. In 1802, 29,000 of the 33,000 troops sent by Napoleon to Santo Domingo died in an epidemic. Napoleon changed his plans for an invasion up the Mississippi River, and the following year he negotiated the Louisiana Purchase with Thomas Jefferson. In 1881, construction on the Panama Canal by a company of French engineers was halted when more than 20,000 construction workers died of yellow fever and malaria.
In the mid-1800s, yellow fever became a focus of scientific inquiry. One theory held that humans infected each other, and another held that the disease was caused by bad air, rotting vegetables, or filth. In 1881, Carlos Juan Finlay (1833-1915), a Cuban physician, correctly proposed the Aëdes aegypti species of mosquito as a vector of yellow fever, following up on Alabama physician Josiah Nott's 1848 theory that the mosquito transmitted the disease among humans. But the scientific community was skeptical of Finlay's methodology, and his results were discounted.
In 1900 Walter Reed was appointed head of the United States Army Yellow Fever Board in Havana, Cuba. The commission's task was to determine the bacterial origin of the disease, but instead, with Finlay's assistance, it proved that Aëdes aegypti was indeed the vector and that yellow fever was caused by an unknown microorganism instead of a bacterium. Following carefully controlled experimentation with human volunteers, Reed reported his findings in 1901.
Following this news, in March 1901, William Crawford Gorgas (1854-1920), a member of the United States Army Medical Corps, began a campaign against yellow fever in Havana by protecting infected patients from mosquito bites and eliminating mosquito breeding grounds. A ten dollar fine was instituted for those households not complying with his directions to prevent mosquitoes from breeding. By October 1901, no new cases of yellow fever were reported.
In 1904 the Isthmanian Canal Commission appointed Gorgas chief sanitary officer, and he applied his mosquito eradication measures to the task of eliminating yellow fever and malaria from the Canal Zone. By 1906, no yellow fever remained there, and construction on the canal was completed in 1915. Gorgas continued to implement his mosquito eradication measures in other areas where the disease was endemic, and the Western Hemisphere was almost free from yellow fever within a few years.
In 1927, Reed's microorganism was found to be a virus. Max Theiler (1899-1972), a South African microbiologist, began to study the yellow fever virus at the department of tropical medicine at Harvard. He subsequently accepted a position at the Rockefeller Foundation International Health Division working on a vaccine against yellow fever--a strain of the virus powerful enough to confer immunity but mild enough not to induce severe symptoms.
In 1936 he and his assistant, Hugh Smith, noticed that the 176th subculture of their experimental virus failed to kill the monkeys injected with it, although subsequent subcultures did kill injected monkeys. They concluded that a mutation had occurred, but they could not duplicate it. They announced this subculture as the first safe vaccine against yellow fever in the Journal of Experimental Medicine in June of 1937, and it continues to be the only vaccine used by the World Health Organization in its ongoing efforts to immunize individuals living in areas where yellow fever is endemic. A single dose provides immunity for 10 years. Theiler received the Nobel Prize for physiology or medicine in 1951.
Because mosquito eradication is not possible in large, forested areas, yellow fever is still endemic in parts of South America and Africa. The most severe epidemic ever recorded occurred in Ethiopia from 1960 to 1962, infecting 100,000 people and killing 30,000. Yellow fever is known to have two patterns of transmission. In the classical route, an infected human is bitten by a female Aëdes aegypti mosquito during the first three days of infection. After two weeks, the bite from this mosquito is able to infect another human, and the mosquito remains infectious for up to two months. After an incubation period of three to five days, during which the virus multiplies in the human host, yellow fever's symptoms appear. The second pattern is seen when infected monkeys are bitten by any one of a variety of mosquito species which subsequently bite humans and transmit the virus. Besides the vaccine, the control of yellow fever depends upon the immunization of individuals entering or leaving a zone where the disease is endemic.
This is the complete article, containing 882 words
(approx. 3 pages at 300 words per page).
