It was at the very beginning of the 20th century that science and public health began to look more closely at insects, mosquitoes and the diseases they transmit.

In the Amazon, the Swiss zoologist Emílio Goeldi (1859-1917) was the researcher who led the movement, acted as a director of Pará Museum of Natural History and Ethnography in Belém, and published several works on Amazonian mosquitoes.

Goeldi began studying mosquitoes in the Amazon in 1901, when the subject was experiencing a certain effervescence thanks to the confirmation, in Cuba, that yellow fever was transmitted by mosquitoes. This is how the so-called "mosquito theory" began to gain strength.

A mere hypothesis at the moment began to arouse worldwide curiosity from then on. In the case of yellow fever, in 1881, mosquitoes were already suspected by the Cuban Carlos Juan Finlay, who argued that the "mysterious" disease originated from an agent that did not depend on the patient or on the morbigenic element: the mosquito.

This theory was in line with researches conducted mainly by English and German physicians and bacteriologists since the 1860s.

Both the United States and the Liverpool School of Tropical Medicine decided to set up commissions to investigate the causes of the disease in depth.

British researchers Walter Myers and Herbert Durham packed their bags and headed to Belém, the capital of Pará, with a stop in Cuba, where they became impressed with Finlay's research, which was already being followed by the North Americans.

They landed in the capital of Pará in August 1900 and were installed in a laboratory established by the state government at Domingos Freire Isolation Hospital, in the vicinity of the current João de Barros Barreto University Hospital.

"The British, however, did not have, in Pará, the same data volume, experiences and previous studies that the North Americans found in Cuba, which can be attributed to Finlay and his collaborators. For this reason, they had to start their investigations by mapping the culicidae in the region and trying to define their geographical distribution.

The collection of mosquitoes they compiled in Belém became notorious, attracting the attention of physicians who lived in the neighboring state of Amazonas", says researcher Nelson Sanjad, in his article On the ‘abominable profession’ of being a vampire: Emílio Goeldi and Mosquitoes in Pará.

Furthermore, according to Sajad, the British expedition faced a problem in Pará that did not exist in Cuba: the low rate of morbidity and mortality due to yellow fever in Belém (at the time, Belém was the only focus of the disease in the entire Amazon region). This factor, according to Durham, prevented him from continuing with his experiments and influenced his decision to transfer, in May 1901, the expedition to Cuba.

Goeldi comes on the scene

Emílio Goeldi was not always interested in mosquitoes or in the diseases they carry. Prior to 1901, the zoologist's work was more focused on the taxonomy of mammals and birds. He had been invited in 1893, to take over the direction of Museu Paraense, which today bears his name. By inviting him to the mission, the idea of the governor of Pará at the time, Lauro Sodré, was to convert the abandoned institution into a major research center in the Amazon region.

Nelson Sanjad supposes that advances in research on malaria and yellow fever made Goeldi realize that he was in a privileged location for this type of study. Furthermore, in the 1890s and 1900s, at the height of gum production in the Amazon, yellow fever emerged as one of the main obstacles to commercialize the product with Europe, especially with England. The flow of immigrants increased considerably in this period, rising the number of yellow fever cases.

"In 1895, for example, less than 100 people were infected; however, in 1899 there were almost 400 cases. The Municipal Intendency of Belém and the state government decided to design a broad sanitation program for the capital. Goeldi started working with mosquitoes, having received unrestricted support from public authorities to carry out his research", points out Sanjad, who holds a doctorate in the history of science and health.

So, Goeldi began to describe the main mosquitoes associated with diseases in the region and to list all the countries where these mosquitoes had already been observed, in order to cross-reference data from the geographic distribution map of mosquitoes with the disease distribution map. The zoologist compared the biology of each species studied, aided by several authors and by his own scientific observations, describing the processes of: laying eggs, development of the larvae, formation of pupae and their rupture, feeding, digestion, mating, humming, choice of the place to lay the eggs and, finally, their death.

AEDES AEGYPTI

Sanjad recalls that during this period, Goeldi manipulated over 220 adult individuals of Stegomyia fasciata, which was later renamed Aedes aegypti, the famous dengue mosquito. Additionally, he handled more than 260 individuals of Culex fatigans, along with thousands of eggs and larvae. The study resulted in the book "Os Mosquitos do Pará", which includes four articles by Goeldi on diseases transmitted by mosquitoes, becoming a milestone in the history of scientific research in the Amazon.

Goeldi's conclusions elevated the Museum to international prestige, inspiring public leaders to commit to the development of sanitation in Belém. Moreover, his findings challenged a skeptical portion of the medical community that questioned the role of mosquitoes in disease transmission, as highlighted by Sanjad.

"Simultaneously, Goeldi established a research program encompassing the observation of mosquitoes’ biological cycle, experiments involving feeding and reproduction, inventory and descriptions of species found in the Amazon. The value of Goeldi's work is evident not only in the enduring recognition of the species he described and the genus he established, or in his contributions to the study of mosquito biology and physiology, but also in the impact of his ideas and in his scientific network", points out Sanjad.

In 1907, following 13 years of engagement in Belém, Emílio Goeldi, already unwell, departed for Switzerland. At the age of 58, he passed away in the city of Bern due to a heart attack.

The region remains a reference for mosquito research.

The tropical setting of the Amazon, surrounded by forests and rivers, plays a significant role in upholding the longstanding tradition of scientific research on mosquitoes in the region. In early May 2023, the Oswaldo Cruz Foundation (Fiocruz) published a warning regarding the recent resurgence of serotype 3 of the dengue virus in Brazil. This particular serotype had not caused any epidemics in the country for over 15 years.

"The serotypes serve as a classification system for the dengue virus based on the antibody response. This means that being infected with one serotype provides protection against that specific serotype, but not against the others. Consequently, individuals can experience dengue infection up to four times, as there are four serotypes of the virus. Serotype 3 was initially identified by the 'Laboratório Central de Roraima' and in Paraná. Notably, the cases in Roraima are among individuals who have not traveled, raising concerns for the coming year," explains Felipe Naveca, the head of the Emerging, Reemerging, and Neglected Virus Surveillance Nucleus at Fiocruz Amazônia.

The study is important as it unveils that the recent cases are not attributed to the existing serotype 3 of dengue, already present in the Americas. Rather, it involves the introduction of a new virus from Asia, which is now circulating in various Latin American regions, including Cuba, Suriname, and Puerto Rico. The US state of Florida has already reported over 50 cases, while Puerto Rico has recorded six infection cases. Additionally, three cases were reported in Roraima, and one case in the state of Paraná, which was imported from Suriname.

"The actual number of cases is probably higher than what has been identified. It is natural for serotypes to replace each other. Currently, dengue 1 and dengue 2 are predominant, but it is anticipated that cases of dengue 3 will increase next year. Preventing the entry of these viruses into the country is challenging, since individuals travel constantly. Sometimes, a person may return to their home country without displaying any symptoms, as they can take some time to manifest. When multiple kinds of serotypes are circulating, the risk of severe illness increases. In the case of a second dengue infection, there is a scientifically higher probability of a more severe disease. Therefore, it is crucial to strengthen monitoring", he explains.

Research discovers new yellow fever vector

Biologist Rossela Damasceno Caldeira joins the new generation of researchers in the Amazon who are devoted to investigating the impacts that mosquitoes in the region may have on human health.

Rossela’s doctoral research, conducted under the guidance of Dr. Ana Cecília Cruz, has recently been published in the scientific journal Viruses. The study highlights the identification of a new potential vector for the transmission of the yellow fever virus, known as Aedes albopictus. This mosquito species is found in both wild and urban environments. This discovery raises concerns, since cases of yellow fever have not been reported in urban regions of Brazil for several decades. The comprehensive four-year study indicates a risk of urban reemergence of yellow fever through this vector.

The detection of the yellow fever virus in the saliva, head, thorax, and legs of Aedes albopictus mosquitoes, as well as in the blood of the monkeys involved in the study, serves as confirmation that this species is capable of becoming infected and transmitting the yellow fever virus. This finding underscores the significance of entomological surveillance and emphasizes the need for further studies on this species. According to the researcher, in addition to the necessity of receiving more investment in this area, another challenge is to improve vaccination coverage.

"We used monkeys and mosquitoes. In the laboratory, we were able to transmit the virus to both the mosquito and the monkey. The mosquitoes were raised in the laboratory, from egg to adult stage. The monkeys were donated by the National Primate Center. The mosquitoes fed on the monkey blood. It was a significant process to prove our hypothesis. It was a major project by the Instituto Evandro Chagas (IEC) coordinated by Dr. Lívia Carício, because in 2017 and 2018 there was an outbreak of sylvatic yellow fever in southeastern Brazil, then many questions emerged. It was a very important confirmation for science, since this mosquito has been studied all over the world, and it is relevant to know the agents that it can transmit", she says.