Brazil has had a disheartening start to 2017, with 555 suspected cases of yellow fever and 107 deaths reported. Thus far, 87 of the suspected cases have been confirmed, 26 have been discarded, and the remaining 442 remain under investigation. Among the deaths, 42 of the 107 are confirmed to have been a direct result of yellow fever infection .
Yellow fever is a virus transmitted by mosquito, and is typically found in tropical and subtropical areas across Africa and South America. Most of those infected only have mild symptoms for a short period of time, which may include fever, chills, vomiting, fatigue, and general body aches. However, approximately 15% of cases will develop into more serious symptoms, which can result in severe fever, jaundice, and/or hemorrhage. Approximately 20-50% of severe yellow fever cases result in death .
There are three different transmission cycles of yellow fever. The first, sylvatic (jungle) yellow fever, occurs when a monkey with yellow fever is bitten by infected mosquitos in a rainforest, who then bite and infect other monkeys. Monkeys are the primary reservoir of yellow fever. The intermediate transmission cycle involves the infection of both humans and monkeys by semi-domestic mosquitoes, who breed both in the wild and around households . The urban yellow fever transmission cycle occurs when the disease is introduced into heavily populated urban areas, and is spread by the aedes aegypti mosquito, which is also a vector for the Zika virus .
It can be difficult to diagnose yellow fever during the beginning stages due to its similar presentation to other mosquito-borne illnesses such as dengue fever and malaria . This presents an added challenge to identifying cases quickly in order to more effectively control the outbreak.
The suspected cases have been reported in the following Brazilian states: Minas Gerais, Espírito Santo, Bahia, São Paulo, Mato Grosso do Sul, Goiás, and the Federal District. The Brazilian Ministry of Health reported that, to date, there have only been records of wild yellow fever. Despite the fears of many that it will spread to urban areas, the last cases of urban yellow fever were recorded in 1942. 
This outbreak is startling, given that there were only seven total number of confirmed cases in Brazil last year, of which five died. Last year’s affected areas include Goiás, São Paolo, and Amazonas. At this point, it is still unclear what factors have caused the rise in cases .
In response to the outbreak, the governor of Minas Gerais has declared a 180-day state of emergency. In January, the Brazilian Ministry of Health distributed 650,000 doses of the yellow fever vaccine as standard monthly routine, and has since distributed an extra 5.4 million doses to the affected states . The Ministry of Health has created designated Yellow Fever Vaccine Recommendation Areas, and is encouraging everyone residing in, as well as anyone traveling to rural or forested regions within those areas, to get vaccinated.
The last two years have posed unexpected health threats to the residents of Brazil. The Ministry of Health must keep vigilant, and both the communities in Brazil and surrounding countries must engage in public health efforts to reduce the amount of disease inflicted upon the population.