Scientists from Adolfo Lutz Institute (IAL) and the University of São Paulo (USP) have found the virus origin of yellow fever epidemic in Brazil in howler monkeys.

The study in Scientific Reports was able to retrace the spread of the yellow fever pathogen  from the state of Pará by analysing tissue samples from dead howler monkeys. The current ongoing yellow fever epidemic is the worst in forty years.

Establishing the source of yellow fever

Using a molecular study of yellow fever viruses found in dead monkeys, including howler monkeys, and in mosquitoes, the research group discovered that the origin of the strain behind the current epidemic originated in Pará State in North Brazil in 1980.

The chain of events they identified is as follows:

  • The virus infected monkeys in Pará;
  • It spread throughout the Amazon region until it reached Venezuela and Suriname;
  • From 2000 on, the disease migrated to the Center-West and Southeast of Brazil via infection of monkeys;
  • The virus reached São Paulo State in 2013; and
  • The first deaths of humans in São Paulo occurred in 2016.

The deaths of the howler monkeys from yellow fever

“More than 90% of the dead monkeys are believed to be Alouatta guariba. The species is extremely susceptible to yellow fever,” said Ester Sabino, Director of IMT-USP.

Speaking about the deaths of howler monkeys from yellow fever in Horto Florestal, a nature reserve in the north of São Paulo City in late 2017, Mariana Sequetin Cunha, the lead of this investigation and a researcher from IAL’s Vector-Borne Disease Group, added: “Troops of more than 80 monkeys were entirely destroyed.”

The potential applications for the epidemic in São Paulo State

According to the researchers, the results of the forthcoming studies may enable the determination of whether or not the current epidemic in São Paulo State is on the wane or whether there could be fresh outbreaks due to the virus still spreading in monkeys despite mass vaccination.

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