One Health Resource Center

One Health Resource Center

March 10, 2017
2 min read

Epizootic transmission fuels yellow fever outbreak in Brazil

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Health officials investigating an outbreak of yellow fever in Brazil have identified 1,500 suspected patients as of March 6, according to the country’s ministry of health.

The outbreak was first detected in December and has since spread to several states. Among the suspected patients, 371 (24.73%) were confirmed to have yellow fever and 241 had died. Based on available information, the mortality rate is estimated to be 34.2%, health officials said.

Thomas Yuill

So far, all of the cases have been linked to an outbreak of yellow fever among monkeys in the Amazon basin and other tropical forests in Brazil, and not to person-to-person transmission involving Aedes aegypti mosquitoes, Thomas M. Yuill, PhD, ProMED virus diseases moderator and professor emeritus of the departments of pathobiological sciences and forest and wildlife ecology at the University of Wisconsin-Madison, told Infectious Disease News. The ministry of health identified 968 epizootic cases in monkeys, 386 of which were confirmed. WHO reported that epizootic cases were detected in rural areas bordering Argentina, Paraguay and Bolivia, which officials said is a “cause of concern.”

“There have been annual scattered cases affected by this jungle cycle of yellow fever throughout the Amazon basin and other tropical forests in South America; however, having this many cases in such a short amount of time is unusual,” Yuill said. “These jungle cycles of transmission can spillover to urban cycles with A. aegypti spread that are the really dangerous, involving hundreds — sometimes thousands — of people if the population hasn’t been immunized. The big concern now in Brazil is that an infected person might initiate an outbreak in urban settings where there are a lot of A. aegypti mosquitoes”

According to the Pan American Health Organization, suspected and confirmed cases of yellow fever in humans were identified in Minas Gerais, Espírito Santo, São Paulo, Bahia, Rio Grande do Norte, Tocantins and Goiás. In response to the outbreak, the ministry of health distributed approximately 14.85 million doses of the yellow fever vaccine in the country. WHO recommends that individuals who plan on visiting areas with ongoing transmission receive a vaccine 10 days before travel. Those with contraindications for the vaccine, including children under 9 months of age, women who are pregnant or breastfeeding and people who are immunocompromised or have severe hypersensitivity to egg antigens, should consult their health care professionals for advice, WHO said.


“My impression is that the Brazilians are really trying hard to stay on top of this through their immunization programs,” Yuill said. “That is in contrast to what happened in Angola during a yellow fever outbreak that occurred last year, which took a while to get organized. As a result, the outbreak was pretty widespread in the country and officials had trouble keeping up with vaccine availability. That does not appear to be a problem in Brazil.”

Yuill added that although vaccination efforts will help mitigate the outbreak among people, not much can be done to halt transmission among monkeys.

“That raises another issue of concern, and that is some of these monkey species that are affected are ones that are endangered,” he said. “So, this is not only a human public health issue — it’s also a wildlife conservation issue of concern.” – by Stephanie Viguers

Disclosure: Yuill reports no relevant financial disclosures.