Aedes aegypti suppression in the Americas: historical perspectives.

556 www.thelancet.com Vol 388 August 6, 2016 Today populations in the Americas are under increasing threat from the dengue, chikungunya, and Zika viruses, spread by the Aedes aegypti mosquito. In earlier centuries, the same mosquito spread the deadly haemorrhagic viral infection known as yellow fever. Rigorously organised vector control programmes in the 20th century, however, ended the urban cycle of yellow fever in the Americas. This historic public health success has relevance for the current public health crisis. The A aegypti mosquito arrived in the Americas on the slave ships that transported African captives to the Americas, as did the yellow fever virus. The fi rst epidemic of yellow fever— with its signature symptom of black vomit—exploded in the mid-17th century in the Caribbean. Thereafter, A aegypti sporadically ignited haemorrhagic yellow fever epidemics that ravaged military encampments and coastal cities. In the late 19th century, the Cuban physician Carlos Finlay proposed that a mosquito was the vector for yellow fever, and at the turn of the 20th century, the US Army’s team of medical investigators in Cuba, led by Walter Reed, discovered that A aegypti was indeed the culprit. It was a domesticated mosquito that bred in man-made containers that capture rainwater. In 1901, the US military began rigorous campaigns to destroy its breeding sites in dense urban areas that were thought to be “seedbeds” of infection. The success of the early eff orts was remarkable. Yellow fever was eliminated from Havana and other Cuban port cities and the Panama Canal Zone in the fi rst decade of the 20th century. Others took inspiration. In 1903, Oswaldo Cruz, the Brazilian Director-General of Public Health, began a campaign in Rio de Janeiro that, by 1909, had reduced yellow fever deaths there to zero. In 1916, the Rockefeller Foundation created a Yellow Fever Commission, which determined that Guayaquil in Ecuador was a centre of endemic infection, and eliminated yellow fever deaths there within 2 years. Some gains, however, proved impermanent. In 1928, a yellow fever outbreak in Rio de Janeiro and in a few Brazilian towns and settlements outside of the main urban areas forced a reassessment of vector control strategy. Beginning in 1930, with fi nancial support from the Rockefeller Foundation, the Brazilian dictator Getúlio Vargas authorised a military-style programme of larval source reduction that compelled city and town dwellers to destroy breeding sites on their properties, imposed fi nes for non-compliance, and required the post-mortem extraction of liver tissue samples from individuals whose deaths were suspected to have been caused by yellow fever, in an eff ort to better understand the spatial epidemiology of the outbreaks. Fred Soper, a Rockefeller Foundation health offi cial, spearheaded the Brazilian initiative, which focused on the suppression of A aegypti in urban areas and eliminated the mosquito in several cities. Soper and his colleagues discovered, however, that there was a primate reservoir of the virus in the South American rainforests transmitted by a diff erent genus of mosquito. Although they realised that they could not stop the sylvatic cycle, this did not stem their commitment to vector control. They expanded their eff orts and eliminated A aegypti throughout most of Brazil, and their major challenge became the prevention of the introduction of the mosquito from neighbouring states. Soper and his team reached this milestone before the era of synthetic residual insecticides. They secured the gains by administering the Rockefeller Foundation’s 17D yellow fever vaccine to urban populations. In 1938–39, Soper and his co-workers undertook a separate vector control campaign to suppress a non-domesticated malaria mosquito Anopheles gambiae sensu lato (Anopheles arabiensis) which had been introduced into northeastern Brazil from west Africa. They eliminated it. During World War 2, Soper helped to launch an elimination project in Egypt against an A gambiae sensu lato mosquito introduced from subSaharan Africa and it achieved full success by 1945. In the immediate post-war era, DDT became available for larval suppression. In 1947, Soper was elected Director of the Pan-American Sanitary Bureau, and the member states agreed to eliminate A aegypti—even though there had only been one urban outbreak of yellow fever in the Americas in the preceding 15 years. In 1955, the World Health Assembly ratifi ed a programme for global malaria eradication that was based upon the use of synthetic residual insecticides. By 1964, the malaria programmes had reduced malarial infections to small numbers. In the same year, a full victory against A aegypti and urban yellow fever seemed at hand. Brazil and most other The art of medicine Aedes aegypti suppression in the Americas: historical perspectives