Epidemiological update: Yellow fever outbreak in Brazil, 30 March 2017

Yellow fever is a mosquito-borne viral infection present in some tropical areas of Africa and South America.

In South America, there are two transmission cycles of yellow fever: 

• A sylvatic cycle, involving transmission of the virus between Haemagogus or Sabethes mosquitoes and primates. The virus is transmitted by mosquitoes from primates to humans when humans are visiting or working in the forest.
• An urban cycle, involving transmission of the virus between Aedes aegypti mosquitoes and humans. The virus is usually introduced in an urban area by a viraemic human who was infected in the forest.

Brazil has been experiencing an outbreak of yellow fever since December 2016. The outbreak was notified on 6 January 2017. From the beginning of the year to 29 March 2017, WHO PAHO has reported cases in Brazil, Colombia, Ecuador, Peru, Bolivia and Suriname.

Weekly Summary 

Between 16 and 29 March 2017, national public health authorities in Brazil have reported 232 additional cases of yellow fever, 72 of which were confirmed.

On 29 March, the state of Pará reported four confirmed cases of yellow fever, all fatal.

Epidemiological summary

Two transmission cycles of yellow fever are taking place in South America: - A sylvatic cycle, involving transmission of the virus between Haemagogus or Sabethes mosquitoes and primates. The virus is transmitted by mosquitoes from primates to humans when humans are visiting or working in the forest. - An urban cycle, involving transmission of the virus between Aedes aegypti mosquitoes and humans. The virus is usually introduced in an urban area by a viraemic human who was infected in the forest.

 
Brazil:

Between 6 January and 29 March 2017, Brazil has reported 1 589 cases (1 093 suspected and 496 confirmed).

 

States reporting suspected and confirmed autochthonous cases:

• Minas Gerais has reported 1203 cases (828 suspected and 375 confirmed)
• Espírito Santo has reported 249 cases (140 suspected and 109 confirmed)
• São Paulo has reported 49 cases (44 suspected and five confirmed)
• Rio de Janeiro has reported 23 cases (20 suspected and three confirmed)
• Pará has reported four confirmed cases, all fatal

The following eleven states have reported suspected cases: Maranhão (12), Bahia (11), Goiás (10), Paraná (9), Santa Catarina (6), Tocantins (5), Rio Grande do Sul (4), Amapá (1), Ceará (1), Distrito Federal (1), Mato Grosso (1).

In addition, investigations are ongoing to determine the probable infection site of four further suspected cases.

Other countries in South America:

From week 1 to 13 of 2017, five other countries reported suspected and/or confirmed cases of yellow fever: Bolivia (1), Colombia (1), Ecuador (1), Peru (8) and Suriname (1).

Sources: Brazil MoH | PAHO | WHO vaccination recommendations

ECDC assessment

The ongoing outbreak should be carefully monitored, as the establishment of an urban cycle of yellow fever would have the potential to quickly affect a large number of people. EU/EEA citizens who travel to, or live in, areas where there is evidence of yellow fever virus transmission should check their vaccination status and obtain medical advice about being vaccinated against yellow fever. In Europe, Aedes aegypti , the primary vector of yellow fever in urban settings, is present in Madeira. Recent studies have shown that Aedes albopictus can potentially transmit the yellow fever virus. However, the risk of the virus being introduced into local competent vector populations in the EU through viraemic travellers from Brazil is considered to be very low, as the current weather conditions in Europe are not favourable for vector activity.

Actions

ECDC closely monitors this event in collaboration with the World Health Organization. ECDC published a rapid risk assessment on the outbreak of yellow fever in Brazil on 26 January 2017 and a rapid risk assessment on yellow fever among travellers returning from South America on 15 March 2017. ECDC is also producing a map for travel advice.