Clinical and Public Health Microbiology

Brazil’s Yellow Fever Outbreak is Over

On August 4, the Pan American Health Organization said that no new cases of yellow fever had been reported in Brazil in July and the epidemic is considered over. In the neighboring countries to which the epidemic had spread, only Bolivia reported activity and it was only one case.

The outbreak began in January (midsummer for the southern hemisphere) when Brazil reported 712 suspected cases of yellow fever, which is five times the normal incidence at that time of year. Most were in Minas Gerais, a rural state, and around 40 residents of the state died. The outbreak spread over the next few months, reaching states that are home to Brazil’s biggest cities of Rio de Janeiro and Sao Paulo. Looking back, Brazilian health officials say total cases peaked in January, fell substantially by March, and were close to zero by June.

Yellow Fever Endemic Zone in the Americas

In Brazil, yellow fever normally circulates in forest monkeys and forest mosquitoes, and occasionally kills people who live or work in the forest, such as loggers, miners, and small farmers. Although the government distributed 20 million doses of yellow fever vaccine, three million of which were from the World Health Organization’s emergency stockpile, panicked residents started killing monkeys because they blamed them for spreading the disease.

Health officials were worried that infected human beings would carry the virus into cities, where it could be picked up by Aedes aegypti mosquitoes that thrive in urban slums and bite people aggressively. If that had occurred, there was a serious risk that the disease could have spread to the northern hemisphere, where yellow fever vaccine is in short supply, or to Asia, where hundreds of millions of people with no natural immunity or history of vaccination live in the tropical climates favored by Aedes aegypti.

For more information, go to