To fill gaps in knowledge of yellow fever (YF), a group of researchers in Brazil affiliated with the Department of Pathology at the University of São Paulo’s Medical School (FM-USP), Hospital das Clínicas (HC, the hospital complex run by FM-USP), the Heart Institute (InCor, linked to HC) and Emílio Ribas Institute of Infectious Diseases (IIER) decided to study the pathogenesis of YF-associated heart injury.
The team was led by Fernando Rabioglio Giugni, a cardiologist, and Amaro Nunes Duarte-Neto, an infectious disease specialist and pathologist; both work at FM-USP.
“There’s still no specific treatment for yellow fever. Patients receive support in intensive care, including blood transfusions, mechanical ventilation and treatment of seizures, but the death rate in severe cases is high, above 35%,” Giugni said.
A total of 696 cases of YF were notified in São Paulo state between 2017 and 2019, with 232 deaths (33.3%). The main factors that contributed to establishment of the epidemic were environmental alterations, expansion of urban areas into Atlantic Rainforest remnants where circulation of the virus was increasing, and unvaccinated people going into the forest.
YF is now considered a re-emerging disease in Brazil (and Latin America generally). Vaccination is recommended throughout the country, but a substantial number of susceptible people have not received the vaccine, especially in densely populated non-endemic urban areas, which could suffer from outbreaks if the virus spreads quickly as it did in São Paulo, and indeed throughout the Southeast of Brazil, in the late 2010s.
The disease has two main forms of transmission. In the sylvatic (wild) transmission cycle, humans are infected by the bite of Haemagogus and Sabethes mosquitoes. In the urban transmission cycle, the virus is transmitted by the mosquito Aedes aegypti. The 2017-19 outbreak in São Paulo was considered an epidemic due to sylvatic transmission.
Rare cases in which complications follow vaccination are termed yellow fever vaccine-associated viscerotropic disease (YEL-AVD), typically associated with 17DD substrains of the vaccine used in South America.
IMAGE CREDIT: Duarte-Neto & Giugni.
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