Neves, M. S. A. S. | bioRxiv Science

bioRxiv2025

Assessing the Sylvatic Yellow Fever Vectors in Southern Brazil

Yellow fever (YF) is an infectious disease caused by the yellow fever virus (YFV), an arbovirus of the Flaviviridae family. It is transmitted through the bite of infected mosquitoes belonging to the Culicidae family and affects both humans and non-human primates (NHPs). This study aimed to investigate the sylvatic Culicidae fauna and the occurrence of natural YFV infection in a microregion of southern Santa Catarina, Brazil, an area recently affected by a sylvatic YF outbreak. Entomological collections were carried out between January and February 2023 in five municipalities with confirmed viral circulation. Natural YFV infection was assessed using RT-LAMP. A total of 4,352 female culicids were collected, representing at least 32 species, including several key sylvatic YFV vectors. Haemagogus leucocelaenus was identified in all sampled municipalities, whereas Haemagogus janthinomys, the primary vector of sylvatic YFV in Brazil, was not detected. Mosquitoes from the genera Aedes, Haemagogus, Psorophora, and Sabethes were tested for YFV. Only one pool, composed of Sabethes albiprivus, tested positive, yielding a minimum infection rate (MIR) of 11.6. This is the first record of natural YFV infection in Sa. albiprivus in southern Brazil, and only the third reported case globally, highlighting its potential role as a secondary vector in maintaining viral circulation in sylvatic environments. Based on species presence and abundance, Hg. leucocelaenus is likely to have acted as the primary YFV vector in the study area. The composition of the culicid fauna, coupled with the detection of YFV in sylvatic vectors, indicates an ongoing epidemiological risk. These findings underscore the need to strengthen entomological surveillance and expand YF vaccination coverage in affected and neighbouring regions. Author SummaryThis study investigated sylvatic mosquito populations in a region of southern Santa Catarina, Brazil, recently affected by a yellow fever outbreak. Yellow fever is a serious mosquito-borne disease that can affect both humans and non-human primates. Nearly 4,400 mosquitoes from various species were collected, and, for the first time in southern Brazil, natural infection with yellow fever virus (YFV) was detected in Sabethes albiprivus. This finding suggests that Sa. albiprivus may play a previously unrecognized role in maintaining YFV in the environment. The known vector Haemagogus leucocelaenus was found in all sampled locations, indicating it may have been the primary vector responsible for virus transmission in the region. These results enhance our understanding of YFVs natural transmission cycles and provide new insights into how the virus persists in sylvatic environments. This research contributes to the fields of biology, ecology, and public health by reinforcing the importance of ongoing entomological surveillance and preventive vaccination, both of which are essential for preventing future outbreaks and protecting vulnerable populations.

microbiology↗

bioRxiv2020

Oviposition in flight: the Sabethes albiprivus incredible egg throwing behavior

Mosquitoes display highly variable oviposition strategies and behavior. By using a high-speed camera, we detailly documented for the first time the egg-throwing strategy of the sylvatic yellow fever vector Sabethes albiprivus Theobald in laboratory. An oviposition trap made with sapucaia nut for field collection of tree-hole mosquitoes and obtaining Sa. albiprivus eggs either in the field or in the laboratory colony is described.

zoology↗

bioRxiv2019

Distinct YFV lineages co-circulated in the Central-Western and Southeastern Brazilian regions from 2015 to 2018

The current outbreak of yellow fever virus (YFV) that is afflicting Brazil since the end of 2016 probably originated from a re-introduction of YFV from endemic areas into the non-endemic Southeastern Brazil. However, the lack of genomic sequences from endemic regions hinders the tracking of YFVs dissemination routes. We assessed the origin and spread of the ongoing YFV Brazilian outbreak analyzing a new set of YFV strains infecting humans, non-human primates (NHP) and mosquitoes sampled across five Brazilian states from endemic and non-endemic regions between 2015 and 2018. We found two YFV sub-clade 1E lineages circulating in NHP from Goias state (GO), resulting from independent viral introductions into the Araguaia tributary river basin: while the strain from 2017 clustered intermingled with Venezuelan YFV strains from 2000, the YFV strain sampled in 2015 clustered with sequences of the current YFV outbreak in the Brazilian Southeastern region (named YFV2015-2018 lineage), displaying the same molecular signature associated to the current YFV outbreak. After its introduction in GO at around mid-2014, the YFV2015-2018 lineage followed two paths of dissemination outside GO, originating two major YFV sub-lineages: 1) the YFVMG/ES/RJ sub-lineage spread sequentially from the eastern area of Minas Gerais state to Espirito Santo and then to Rio de Janeiro states, following the Southeast Atlantic basin; 2) the YFVMG/SP sub-lineage spread from the southwestern area of Minas Gerais to the metropolitan region of Sao Paulo state, following the Parana basin. These results indicate the ongoing YFV outbreak in Southeastern Brazil originated from a dissemination event from GO almost two years before its recognition at the end of 2016. From GO this lineage was introduced in Minas Gerais state at least two times, originating two sub-lineages that followed different routes towards densely populated areas. The spread of YFV outside endemic regions for at least four years stresses the imperative importance of the continuous monitoring of YFV to aid decision-making for effective control policies aiming the increase of vaccination coverage to avoid the YFV transmission in densely populated urban centers.

epidemiology↗