University of Virginia Historical Collections at the Claude Moore Health Sciences Library

Yellow Fever Research & Mosquito Control

Mosquito Control by Pesticides, Reduction of Breeding Areas, and Larva-eating Fish

Aedes aegypti

“Aedes (Stegonyia) aegypti” mosquito. Courtesy of the National Library of Medicine.[1] (Translation: aëdes (place of refuge or rest / house) aegypti (of Egypt / Aegyptus, the mythical king of Egypt whose fifty sons married the fifty daughters of his twin brother Danaus.)[2]

The following overview of the state of medical knowledge on yellow fever and its control and prevention during the 1920s and 30s was compiled from Dr. Henry Hanson’s A Study of Sanitary Conditions in Peru with Special Reference to the Incidence of Malaria, published in 1921; The Pied Piper of Peru: Dr. Henry Hanson’s Fight against “Yellow Jack” and Bubonic Plague in South America, 1919-1922, written about 1935 and published posthumously in 1961; and other source materials mentioned in the footnotes. Once the Reed Commission made the monumental breakthrough in discovering the yellow fever vector, the Aedes aegypti mosquito, scientists sought to “control” the mosquito. Its elimination was seen as a crucial component in sanitary measures, and various methods were used, including:
Spraying in Ecuador

“1918: Anti-Mosquito Methods Control Yellow Fever in Ecuador.” Courtesy of The College of Physicians of Philadelphia.[3]

Pesticides: Mosquito squads were employed to spray chemicals on rooftops and other surfaces as shown in this picture taken in Guayaquil, Ecuador which features one of 25 mosquito squads assigned to the work.

Cheesecloth over cisterns

Cheesecloth over water cisterns in New Orleans, 1905 from Yellow Fever Prophylaxis in New Orleans 1905 by Robert Boyce, published in 1906.”[4]

Eliminate mosquito breeding: Community water tanks, household water containers, and any other object that would potentially hold standing water (a prime environment for the mosquito to lay eggs) were sealed. Various materials were utilized, such as the cheesecloth over the cisterns in this image taken during the 1905 New Orleans outbreak.


Larva as depicted in the West African Pocket Book, 1920.[5]

Weekly house inspections: As a field inspector in West Africa, Dr. Hanson used this method to detect and destroy mosquito larvae. Hanson made frequent references to the “household index,” which is the percentage of houses that were found to have Aedes aegypti mosquitoes. The goal was to achieve a percentage under two percent.[6]

Larva-eating fish

One of the fish species used in Colombia’s fight against yellow fever, 1924.[7]

 Larva-eating fish: Dr. Hanson implemented this method in large water containers with significant success in Peru. Over “three hundred thousand fish” were distributed as larvae consumers in the campaign.[8] Hanson documented his results in the report, A Study of Sanitary Conditions in Peru with Special Reference to the Incidence of Malaria, published in 1921 by Panama Canal Press.[9]


It’s Up to You: Dengue-Yellow Fever Control.[10]

 Public health campaigns continued to employ the same methods of mosquito control for many decades after the campaigns in South America and West Africa, as demonstrated in this 1945 U.S. Public Health Service film, It’s Up to You: Dengue-Yellow Fever Control.

Transmission of the Yellow Fever Virus.

Transmission of the Yellow Fever Virus.[13]

Additional studies showed that mosquitoes other than Aedes aegypti contained the yellow fever virus: Haemagogus, Sabethine, and Aedes lencocelaenus in South America and Aedes africanus and Aedes simpsoni in Africa.[11]

Today researchers describe three transmission cycles for the yellow fever virus: jungle (sylvatic), inter­mediate (savannah), and urban as depicted in the graph created by the Centers for Disease Control and Prevention. The disease is transmitted in the jungle by mosquitoes between nonhuman primates; humans can get the virus when they visit the jungle. The infected person can then take the disease back to an urban area where the virus is generally transmitted from human to human by means of the Aedes aegypti. In Africa, the intermediate cycle involves yellow fever transmission from mosquitoes to humans who live or work in areas near the jungle border. The mosquitoes can be the disease vector from monkeys to humans or from humans to humans.[12]

Although, these discoveries led to the realization that total elimination of yellow fever vectors was not possible, fever fighters today still focus on the control of mosquito populations, as in the Florida Keys where the three basic methods are source reduction or reducing the number of habitat areas for larvae, larval control which targets the immature mosquitoes before they mature into biting adults, and the adult surveillance program which aims to count, collect, and control the adult mosquitoes. The technique of larvae-eating fish espoused by Dr. Hanson is still used.[14]

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