An outbreak of yellow fever in Minas Gerais, a Brazilian state near Sao Paulo, has infected 110 people and killed 30, according to a report released Friday. While a vaccine exists for the disease, this outbreak has taken hold in areas with low rates of vaccination, causing concern that the disease could spread beyond Brazil’s borders to cause a larger epidemic, according to the World Health Organization.
The mosquito that spreads yellow fever can also carry the Zika virus, dengue fever, and chikungunya.
The Brazilian ministry of health has sent teams to investigate the outbreak, kill mosquitos, and vaccinate residents, as part of an attempt to contain the outbreak. The WHO has warned that states neighboring Minas Gerais are at risk for large outbreaks, since they are also home to the Aedes mosquito, and the population is not vaccinated against yellow fever, since the regions were considered low risk for the disease until recently.
Brazil is still recovering from last year’s Zika outbreak, which infected an estimated 214,193 people, leading to 2,366 babies born with congenital Zika syndrome from 2015 to 2017.
An outbreak of yellow fever affected Minas Gerais in 2002 and 2003, with 63 people contracting the disease and 23 people killed. Other parts of Brazil have faced more recent outbreaks, including in 2008 and 2009, when 21 cases of the disease and 9 deaths occurred in Rio Grande do Sul and 28 cases and 11 deaths occurred in Sao Paulo.
The vaccine for yellow fever carries some rare but serious risks, meaning that only those who are living in, or traveling to, high risk areas should get vaccinated. Side effects can include fatal allergic reactions, nervous system disease, and diseases that infect internal organs, according to the U.S. Centers for Disease Control and Prevention. In the 2008/2009 outbreak, Brazil reported six deaths and 45 cases of neurotropic disease, as side effects of the broad vaccination campaign, in which more than 5.5 million people were vaccinated. While these outcomes are rare, it is enough to ensure that the vaccine is not given more universally.
However, yellow fever itself is even more serious. While most people infected will only experience symptoms such as fever, chills, headache, and vomiting, roughly 15 percent of patients will experience more severe symptoms, including high fever, jaundice, and organ failure. Between 20 and 50 percent of those who experience the more severe form of yellow fever are likely to die from the disease. There is no cure for yellow fever, and rest, pain relievers, and increased fluid intake are the only treatments.