Researchers are urging strengthened efforts against mosquito-borne pathogens in Brazil, amid evidence that West Nile Virus may be circulating nationally.
Hegger Fritsch and her fellow researchers, writing in the journal Viruses, noted that several studies have provided serological evidence of the circulation of West Nile virus in Brazil.
West Nile Virus was first detected in the Americas in 1999 in New York City. In 10 years, it had spread across the United States mainland. Wild birds serve as a reservoir for the virus, which can infect both horses and humans, causing potentially fatal brain inflammation in the most severe cases.
Much is still unknown regarding the genomic diversity and transmission dynamics of West Nile in Brazil, Fritsch and her colleagues wrote. Recently, testing has shown the virus is circulating in several Brazilian regions.
They said the general lack of gene-based data reinforce the need for prompt investigation of West Nile infection in horses, which may precede human cases of encephalitis (brain inflammation) in Brazil.
In their study, they retrospectively screened 54 samples from suspected West Niles cases, collected between 2017 and 2020 from the spinal cords and brains of horses with encephalitis. In doing so, they generated three new West Nile Virus genomes from the Ceará and Bahia states, in northeast Brazil.
Analysis revealed at least two independent introduction events, they said. The first was likely related to the North American outbreak, and was estimated to have occurred in March 2013.
The second introduction appears to have occurred in September 2017 and is likely related to the circulation of West Nile in South America (potentially in Colombia).
However, the authors noted that, since 2004, several studies have provided serological evidence of the circulation of West Nile Virus in mammal and bird reservoirs in the country. The short period of infection, followed by low virus levels in the blood and the difficulty of accessing the possible infected animals, reduced the possibility of molecular confirmation and sequencing, they said.
They said the lack of genomic data and viral surveillance decreases the possibility of reconstructing the dispersal routes of West Nile, and monitoring sources of new introductions.
The information to date reinforces the idea that multiple independent introduction events of West Nile Virus have occurred in the country.
Despite the molecular-based data suggesting the earliest introduction may have occurred in 2013, the reporting of its circulation in mammals and birds since 2004 in several serological studies might reflect a possible cryptic transmission of the virus in the region – essentially, the virus might have been spreading undetected.
The authors noted that, between 2017 and 2019, 715 cases of neurological problems in humans arising from infections with mosquito-borne viruses were reported in Brazil. “Although the incidence of severe complications remains low when compared to the number of arboviruses cases, neurological disorders are increasing.”
To date, the Brazilian Ministry of Health notified 165 cases of West Nile Virus infection between 2017 and 2021.
The monitoring of wild birds and equines with neurological problems has been adopted as a strategy for detecting the presence of the virus in Brazil.
Despite the scarcity of data, it can be assumed that West Nile Virus might be circulating unnoticed throughout the national territory, the researchers said.
“Together, our results reinforce the importance of strengthening epidemiological and genomics investigations towards zoonotic arbovirus in Brazil, increasing the priority of West Nile Virus genomic surveillance in equines with encephalitis in order to follow the dispersion of this emerging pathogen through the country.”
The study team came together from a range of laboratories and tertiary institutions across Brazil, including the Laboratory of Research in Animal Virology, part of the veterinary school at the Federal University of Minas.
Fritsch, H.; Pereira, F.M.; Costa, E.A.; Fonseca, V.; Tosta, S.; Xavier, J.; Levy, F.; Oliveira, C.d.; Menezes, G.; Lima, J.; Santos, L.; Silva, L.; Nardy, V.; Astete, M.K.G.; Santos, B.S.Á.d.S.; Aguiar, N.R.; Guedes, M.I.M.C.; Faria, G.C.d.; Furtini, R.; Drumond, S.R.M.; Cunha, G.M.; Souza, M.S.P.L.; Jesus, R.d.; Guimarães, S.A.F.; Nuno, I.C.; Santana, I.C.B.d.; Sá, J.E.U.d.; Santos, G.R.; Silva, W.S.; Guedes, T.F.; Araújo, E.L.L.; Said, R.F.d.C.; Albuquerque, C.F.C.d.; Peterka, C.R.L.; Romano, A.P.M.; Cunha, R.V.d.; Filippis, A.M.B.d.; Leal e Silva de Mello, A.; Giovanetti, M.; Alcantara, L.C.J. Retrospective Investigation in Horses with Encephalitis Reveals Unnoticed Circulation of West Nile Virus in Brazil. Viruses 2022, 14, 1540. https://doi.org/10.3390/v14071540