Yellow fever was the first human disease to have a licensed vaccine and has long been considered important to an understanding of how epidemics happen and should be combated.  Centuries after the disease was first reported in the Americas, an international team of researchers will embark on a groundbreaking study to develop models that predict epidemics of yellow fever and other diseases caused by mosquito-borne arboviruses such as dengue, zika, and chikungunya.

Knowledge of these diseases, their cycles ,and the possibilities of new outbreaks is very well-established, but we still lack a systematic understanding of how to predict when outbreaks will occur. Our goal is to create predictive models to help monitor and combat outbreaks, protect the public, and develop a deeper understanding of the combination of factors that leads to epidemics.
Maurício Lacerda Nogueira, a professor at the São José do Rio Preto Medical School (FAMERP) in the state of São Paulo, Brazil, and a member of the CREATE-NEO project funded by the US National Institutes of Health (NIH).

The new study is part of a Thematic Project supported by FAPESP to monitor the mosquito population in the urban area of São José do Rio Preto and the monkey and mosquito populations in the transition zone between rural and urban Manaus, the Amazonas state capital.

In addition to FAMERP, the Brazilian research centers that are participating in the initiative include the National Institute for Research on the Amazon (INPA), the Federal University of Mato Grosso (UFMT), the Federal University of Amazonas (UF AM), and the Heitor Vieira Dourado Foundation for Tropical Medicine (FMT-HVD). Participants located elsewhere include the University of Texas Medical Branch (UTMB), New Mexico State University (NMSU), the Massachusetts Institute of Technology (MIT), and Cary Institute of Ecosystem Studies in the US, and the Gorgas Memorial Institute for Health Studies (ICGES) in Panama, among others.

An article written by the researchers to mark the project’s inception is published in Emerging Topics in Life Science, reviewing the factors that influence the potential re-emergence of yellow fever in the Neotropics.

The project also aims to find out more about spillovers and, if possible, anticipate these outbreaks in which arboviruses jump from humans to animals or vice-versa. Dengue, zika, and chikungunya are transmitted to humans and non-human primates by infected Aedes aegypti mosquitoes. In the case of yellow fever, A. aegypti is the urban vector but mosquitoes of a different genus (Haemagogus) are responsible for transmission in the countryside (sylvatic cycle).

Despite the existence of a highly effective vaccine since 1937, and no reported cases caused by urban transmission since 1942, sylvatic outbreaks of yellow fever frequently spill over into cities.

Many people and monkeys die of yellow fever in Brazil and other parts of the Americas, as well as in Africa. Despite the vaccine and progress in controlling transmission of the disease, we continue to see cases emerging from the sylvatic cycle. The virus is endemic in part of Brazil, with persistent circulation between mosquitoes and non-human primates, which are its primary hosts.
Livia Sacchetto


This enzootic cycle is far from easy to control.

Once established, the enzootic cycle ensures that the virus stays in forests or other rural areas, but it can spread to a city via accidental infection of a human. Hence the importance of epidemiological surveillance studies and maintenance of large-scale vaccine coverage to control outbreaks.
Livia Sacchetto


Predictive models for arboviruses also take into account climate change and urbanization destroying native vegetation.

We have active cases of yellow fever in both non-human primates and humans in the Southern states of Paraná and Santa Catarina. This hasn’t happened for several decades.
Maurício Lacerda Nogueira


The article “Re-emergence of yellow fever in the Neotropics - quo vadis?” (doi: 10.1042/ETLS20200187) by Livia Sacchetto, Betania P. Drumond, Barbara A. Han, Mauricio L. Nogueira and Nikos Vasilakis can be read at: portlandpress.com/emergtoplifesci/article/4/4/411/227095/Re-emergence-of-yellow-fever-in-the-neotropics-quo.

 

 

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