He is also credited for using the first type of medical consent form during his experiments in Cuba, an attempt to ensure that participants knew they were taking a risk by being part of testing.Like Cuba and Panama, Brazil also led a highly successful sanitation campaign against mosquitoes and yellow fever. Beginning in 1903, the campaign led by Oswaldo Cruz, then director general of public health, resulted not only in eradicating the disease but also in reshaping the physical landscape of Brazilian cities such as Rio de Janeiro. During rainy seasons, Rio de Janeiro had regularly suffered floods, as water from the bay surrounding the city overflowed into Rios narrow streets. Coupled with the poor drainage systems found throughout Rio, this created swampy conditions in the citys neighborhoods. Pools of stagnant water stood year-long in city streets and proved to be a fertile ground for disease-carrying mosquitoes. Thus, under Cruzs direction, public health units known as "mosquito inspectors" fiercely worked to combat yellow fever throughout Rio by spraying, exterminating rats, improving drainage, and destroying unsanitary housing. Ultimately, the citys sanitation and renovation campaigns reshaped Rio de Janeiros neighborhoods. Its poor residents were pushed from city centers to Rios suburbs, or to towns found in the outskirts of the city. In later years, Rios most impoverished inhabitants would come to reside in favelas. During 1920–1923, the Rockefeller Foundations International Health Board  undertook an expensive and successful yellow fever eradication campaign in Mexico. The IHB gained the respect of Mexicos federal government because of the success.
This infection of vectors without a previous blood meal seems to play a role in single, sudden breakouts of the disease.Three epidemiologically different infectious cycles occur in which the virus is transmitted from mosquitoes to humans or other primates. In the "urban cycle", only the yellow fever mosquito A. aegypti is involved. It is well adapted to urban areas, and can also transmit other diseases, including Zika fever, dengue fever, and chikungunya. The urban cycle is responsible for the major outbreaks of yellow fever that occur in Africa. Except for an outbreak in Bolivia in 1999, this urban cycle no longer exists in South America.Besides the urban cycle, both in Africa and South America, a sylvatic cycle (forest or jungle cycle) is present, where Aedes africanus (in Africa) or mosquitoes of the genus Haemagogus and Sabethes (in South America) serve as vectors. In the jungle, the mosquitoes infect mainly nonhuman primates; the disease is mostly asymptomatic in African primates. In South America, the sylvatic cycle is currently the only way humans can become infected, which explains the low incidence of yellow fever cases on the continent. People who become infected in the jungle can carry the virus to urban areas, where A. aegypti acts as a vector. Because of this sylvatic cycle, yellow fever cannot be eradicated except by eradicating the mosquitoes that serve as vectors.In Africa, a third infectious cycle known as "savannah cycle" or intermediate cycle, occurs between the jungle and urban cycles. Different mosquitoes of the genus Aedes are involved.