Intense campaign was carried out in Minas Gerais. Priority is given to residents in rural areas, now in São Paulo. Photo- Agency Brazil: EBC
Intense campaign was carried out in Minas Gerais. Priority is given to residents in rural areas, now in São Paulo. PHOTO: Agência Brasil/EBC

The monkey found dead in the third week of October 2017, at Horto Forestal in the North Zone of São Paulo, was confirmed to have the yellow fever virus. The State Department of Health closed the Horto Florestal and is administering vaccines to residents of the northern part of the capital.

It is important to point out, however, that the transmission to the monkey was that of the wild yellow fever virus, common in the forest. Monkeys are hosts of the virus, but do not transmit the disease to the population.

Since January of this year, we have warned of this advance.

Read the article published in the Cheers! Brazilians:

According to data released by the Minas Gerais State Health Department on Friday (13), the region faces 20 probable cases of wild yellow fever, with ten probable deaths. In all, there are 133 suspected cases reported and 38 suspected deaths from the disease in 24 municipalities. The return of wild yellow fever is not new. In recent years, isolated cases have been recorded in the Midwest, Southeast and South regions. The number of people affected in Minas Gerais, however, is higher.

An acute febrile infectious disease caused by a virus transmitted by a mosquito, yellow fever has not been reported in urban centers in Brazil since the 1940s. The main symptoms are fever, chills, headache, body aches, fatigue, nausea and vomiting. Clinical manifestations include liver and kidney failure, which may progress to death.

The cases under investigation in Minas Gerais refer to wild yellow fever, present in rural regions. Sylvatic yellow fever and urban yellow fever are caused by the same virus but are transmitted by different mosquitoes.
In wild yellow fever, mosquitoes of the Haemagogus and Sabethes genera transmit the virus and monkeys are the main hosts. In urban yellow fever, the virus is transmitted by the Aedes aegypti mosquito (the same as dengue and Zika) to humans. Experts stress that the virus is never transmitted from human to human.

“Although the affected area is considered an area of ​​potential transmission of yellow fever, without expansion to new areas so far, the number of cases observed is higher than expected, leading to greater concern”, says infectologist André Siqueira, from the Evandro Chagas National Institute of Infectious Diseases (Fiocruz), to Fiocruz Agency.


Even with the wild form being registered, the State of São Paulo, for example, is already publishing a protocol to deal with the disease. The State Health and Environment Secretaries defined joint strategies to strengthen protection against yellow fever in São Paulo, based on guidance to the population and the intensification of preventive measures.

A specific notification flow was established between the two folders to ensure greater agility in identifying possible cases. The Secretary of the Environment will monitor the conservation units, such as parks and environmental protection areas located in risk areas. There are also vaccines available on the public network.

The state of Minas Gerais, in conjunction with the municipalities, will actively search the locations where suspected cases of the disease were recorded in the rural areas of the municipalities. Mobile health centers will be set up in regions where suspected cases of yellow fever are occurring, in addition to extending the opening hours of the units.

According to researcher André Siqueira, from Fiocruz, a combination of factors may be associated with the increase in cases of yellow fever – all related to a greater amount of virus circulating in the region.

He highlights: an increase in the susceptible (non-immune) population of both humans and monkeys; greater proximity between monkeys, mosquitoes and humans which may be due to environmental, climatic and/or demographic factors; and low vaccination coverage.

What is the treatment?

According to Fiocruz, there is no specific treatment for yellow fever. Vaccination remains the main preventive measure against the disease, in addition to vector control. Produced by the Institute of Technology in Immunobiologicals (Bio-Manguinhos/Fiocruz), immunization is offered free of charge in the National Vaccination Calendar of the Unified Health System (SUS).

The yellow fever vaccine, produced by Fiocruz. Photo - Fiocruz Agency
The yellow fever vaccine, produced by Fiocruz. Photo: Fiocruz Agency

How to prevent

“Prevention against yellow fever involves protection against mosquito bites with the use of repellents and protective clothing and the use of the vaccine. The vaccine is highly effective and safe in the indicated groups”, explains André Sigueira, to Agência Fiocruz.

"It is worth remembering that children under 6 months, pregnant women and the elderly over 65 years, as well as individuals undergoing treatment or with conditions that lead to depression of immunity, should not take the vaccine unless there is an explicit recommendation from the doctor", he highlights.

Special attention to travel in risk areas and vaccine

Anyone traveling to wild, rural or forested regions must be vaccinated against yellow fever at least ten days in advance. For residents in risk areas, the Ministry of Health recommends, for children, the administration of one dose at 9 months of age and a booster at 4 years of age.

For people 5 years of age and older who have received a dose of the vaccine, a booster is required; for those who have never been vaccinated or do not have proof of vaccination, it is necessary to administer the first dose of the vaccine and a booster after 10 years. People who have already received two doses of the vaccine in their lifetime are already considered protected.

World Health Organization (WHO) considers that just one dose of the vaccine is enough for lifelong protection. However, as an additional measure of protection, the Ministry of Health defined the maintenance of the two-dose schedule of the vaccine.

Additional information about yellow fever

Sylvatic yellow fever (YF) is an endemic disease in Brazil, particularly in the Amazon region, but also outside of it. In recent years, the Midwest, Southeast and South regions of the country were also affected by AF cases.

The temporal pattern of occurrence is seasonal, with most cases occurring between December and May. There are isolated cases or outbreaks that occur with irregular periodicity, when susceptible individuals come into contact with places where there are mosquitoes that transmit the disease, which usually feed on the blood of monkeys.

This occurs more likely in climatic conditions of high temperature and rainfall, which favor the multiplication of these insects.

In 2015, nine cases of sylvatic yellow fever were recorded throughout Brazil, with five deaths. In 2016, six cases of the disease were confirmed, in the states of Goiás (3), São Paulo (2) and Amazonas (1), with five of them progressing to death. Currently, Brazil only has records of wild yellow fever. The last cases of urban yellow fever (transmitted by Aedes aegypti) were recorded in 1942, in Acre.

*With information from Fiocruz Agency, Ministry of Health, Secretary of Health of the State of São Paulo and Secretary of Health of the State of Minas Gerais. 

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