Yellow Fever

Overview :

In order to understand how yellow fever is passed, several terms need to be defined. The word "host" refers to an animal that can be infected with a particular disease. The term "vector" refers to an organism which can carry a particular disease-causing agent (such as a virus or bacteria) without actually developing the disease. The vector can then pass the virus or bacterium on to a new host. Many of the common illnesses in the United States (including the common cold, many viral causes of diarrhea, and influenza or "flu") are spread via direct passage of the causative virus between human beings. Yellow fever, however, cannot be passed directly from one infected human being to another. Instead, the virus responsible for yellow fever requires an intermediate vector, a mosquito, which carries the virus from one host to another. WILBUR AUGUSTUS SAWYER (1879–1951) Wilbur Augustus Sawyer was born in Appleton, Wisconsin, on August 7, 1879, to Minnie Edmea (Birge) and Wesley Caleb Sawyer. The Sawyers moved to Oshkosh, Wisconsin and finally to Stockton, California in 1888. Sawyer spent two years at the University of California and then entered Harvard College where he earned his A.B. degree in 1902. In 1906, Sawyer graduated from Harvard Medical School and began a private practice, which lasted until he started his internship at Massachusetts General Hospital. Sawyer returned to California in 1908 in order to obtain a position at the University of California as a medical examiner. He then worked with California State Board of Health from 1910 until 1918. In 1911, Sawyer married Margaret Henderson. The couple had three children. Sawyer's first publication (1913) dealt with his research of poliomyelitis. His discovery, in 1915, that examination of the individual's stool could lead to detection of the disease was later regarded as very significant. In 1918 and 1919, Sawyer worked to control venereal disease while employed by the Army Medical Corps. In 1926 and 1927, while director of the West African Yellow Fever Commission, Sawyer succeeded in isolating the yellow fever virus. He would ultimately return to the United States, where he and Wray Lloyd would devise an immunization against yellow fever (1931). In 1944, Sawyer became director of health for the United Nations Relief and Rehabilitation Administration, a position he held for three years. He retired to Berkeley, California where he died on November 12, 1951. The hosts of yellow fever include both humans and monkeys. The cycle of yellow fever transmission occurs as follows: an infected monkey is bitten by a tree-hole breeding mosquito. This mosquito acquires the virus, and can pass the virus on to any number of other monkeys that it may bite. This form of yellow fever is known as sylvatic yellow fever, and usually affects humans only incidentally. When a human is bitten by an infected mosquito, however, the human may acquire the virus. In the case of South American yellow fever, the infected human may return to the city, where an urban mosquito (Aedes aegypti) serves as a viral vector, spreading the infection rapidly by biting humans. This form of the disease is known as urban yellow fever or epidemic yellow fever. Yellow fever epidemics may also occur after flooding caused by earthquakes and other natural disasters. They result from a combination of new habitats available for the vectors of the disease and changes in human behavior (spending more time outdoors and neglecting sanitation precautions). Cases of yellow fever are uncommon in the United States and Canada as of 2004. The last reported case in an American citizen concerned a man who contracted yellow fever in Brazil in 1996. The last epidemic in the United States occurred in New Orleans in 1905.