Marcia Castro: Urban paradise for aedes

In 2019, the highest incidence of dengue was recorded in the Americas, when just over 3.1 million cases were reported, more than half of them in Brazil. Following a cyclical pattern of epidemics every two or three years, the country sees an increase in dengue cases in 2022. By the end of May, more than 1 million cases had been reported. The epidemic curve for this period resembles that of 2019, with a reduction of only 9% of cases, but represents an increase of 191% compared to the same period in 2021.

Critical areas are located in the Midwest and South regions of the country. From November 2021 to January 2022, rainfall was above average in the Midwest, while the South faced severe drought. The climate is important in this analysis, but it is necessary to understand the local context. And this understanding begins with a historical analysis.

the mosquito Aedes aegypti, which transmits dengue, chikungunya, zika and yellow fever, is not native to the Americas. It probably arrived on the mainland on transatlantic slave-trading ships. Upon finding a suitable environment, the mosquito expanded on the continent.

In Brazil, yellow fever was a serious public health problem in the 19th and early 20th centuries. After intense control, urban yellow fever was eliminated in 1942 and the Aedes aegypti it was eliminated in 1958. Control included the use of insecticides, destruction of breeding sites, sanitation of houses, and isolation of sick people. With similar actions promoted by the Pan American Health Organization, the mosquito was eliminated in most countries of the Americas.

After the relaxation of control measures in the late 1960s, the Aedes aegypti was reintroduced in Brazil and the Americas. Dengue outbreaks were reported in the early 1980s in Roraima and Rio de Janeiro. In the last 20 years, epidemics have become more frequent and intense. Two-thirds of dengue cases reported since 1998 occurred between 2010 and 2021, and the disease is progressively spreading in the Amazon region. In addition, zika and chikungunya were introduced in Brazil in the mid-2010s.

The intensification of dengue transmission takes place in a context of disorderly urban sprawl, with precarious infrastructure, such as lack of regular access to water, sewage and garbage collection. According to Mapbiomas data, from 1985 to 2020, this informal growth represented, for example, 52% of urban expansion in Belém, 48% in Manaus, 24% in the city of São Paulo and 10% in the city of Rio de Janeiro. This urban context is a paradise for the Aedes. Water tanks and other reservoirs that are not properly covered, clogged gutters, scrap yards and uncapped junkyards and accumulated garbage are some of the breeding grounds for the Aedes found in abundance.

The daily work of vector control agents is hard and vital. However, the speed with which new breeding sites appear due to the precariousness of cities is faster than the ability to destroy existing breeding sites. Current control actions are extremely important to reduce transmission and save lives. However, they do not solve the problem permanently. The root of the problem lies in the urban context, in social inequalities.

Just as the elimination of malaria demands respect for the forest and forest peoples (as I highlighted last month), dengue control requires a housing and urban infrastructure policy that mitigates the consequences of disorderly expansion. This is not just a matter of public health, but also of human rights and social justice.