Call for active surveillance of West Nile Virus in Brazil

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A mosquito, at right, dwarfs a tiny biting midge.
A mosquito, at right, dwarfs a tiny biting midge. Photo: Dunpharlain CC BY-SA via Wikimedia Commons

Scientists in Brazil suggest that the country adopts active surveillance of West Nile Virus, which is capable of infecting horses and humans.

The virus was first genetically sequenced in Brazil in 2019, when it was isolated from a horse in the state of Espírito Santo.

Despite multiple studies reporting serological evidence suggestive of past circulation of the virus since 2004, West Nile remains a low priority for surveillance and public health in the country, Professor Érica Azevedo Costa and her fellow researchers noted in the journal Pathogens.

Because of this, much is still unknown about its genomic diversity, evolution, and transmission in the country.

West Nile transmission is maintained in a mosquito–bird cycle. Humans, equines, and other mammals are considered “dead-end” hosts, given their weak potential to pass on the infection.

About 80% of infections in humans are symptom-free, while the rest may develop mild or severe disease. Mild disease includes fever, headache, tiredness, and vomiting, while severe cases can involve neurological problems, a high fever, coma, convulsions, and paralysis.

Equine infections can occasionally cause neurological disease and death.

The study team described a series of diagnostic tests, molecular-based sequencing and epidemiological modeling to provide a holistic overview of what is known about the virus in Brazil.

The researchers reported new genetic evidence of the circulation of the virus in the southern states of Minas Gerais and São Paulo, and the northeastern state of Piauí, based on equine blood testing.

They said their analysis work indicates that more information is required to better identify routes of West Nile importation both into and within Brazil, and to more generally understand the local transmission dynamics.

“Interestingly, our data suggest that the circulation of the virus may have resulted from multiple independent introductions, since the new isolates did not group with the previously sequenced genome in 2019 from the Espirito Santo state.”

This, they said, suggests that introduction events stemming from the mobility of infected birds or mosquitoes across the continent might be a more plausible mechanism for the multiple introductions of the virus in South American countries, including Brazil.

This scenario is consistent with previous studies that showed that multiple independent introductions into Latin America occurred following the introduction of the virus in the US in 1999.

“While migrating birds are a convenient explanation of West Nile Virus dispersal, other possible ways of dispersion exist, such as infected mosquitoes that are accidentally transported via aeroplane or by road transport.

“Another likely scenario is commercial legal or illegal human transportation of birds and/or mosquitoes, which could be transported on aeroplanes.”

Important questions remain unanswered around case numbers and seasonality, they said.

“Our output demonstrates the scarceness of existing data, and that although there is sufficient evidence for the circulation and persistence of the virus, much is still unknown on its local evolution, epidemiology, and activity.

“The occurrence of a West Nile Virus outbreak affecting humans in Brazil may simply be a matter of time,” the study team cautioned.

“Shifting from passive to active West Nile Virus screening and sequencing in animal reservoirs (e.g., equines, birds, vectors) in Brazil must be implemented to better understand the virus’s local epidemiology and to be able to act accordingly in preventing and controlling any future epidemics with spill-over to humans.”

The large study team is affiliated with a range of Brazilian institutions.

Costa, É.A.; Giovanetti, M.; Silva Catenacci, L.; Fonseca, V.; Aburjaile, F.F.; Chalhoub, F.L.L.; Xavier, J.; Campos de Melo Iani, F.; da Cunha e Silva Vieira, M.A.; Freitas Henriques, D.; Medeiros, D.B.d.A.; Guedes, M.I.M.C.; Senra Álvares da Silva Santos, B.; Gonçalves Silva, A.S.; de Pino Albuquerque Maranhão, R.; da Costa Faria, N.R.; Farinelli de Siqueira, R.; de Oliveira, T.; Ribeiro Leite Jardim Cavalcante, K.; Oliveira de Moura, N.F.; Pecego Martins Romano, A.; Campelo de Albuquerque, C.F.; Soares Feitosa, L.C.; Martins Bayeux, J.J.; Bertoni Cavalcanti Teixeira, R.; Lisboa Lobato, O.; da Costa Silva, S.; Bispo de Filippis, A.M.; Venâncio da Cunha, R.; Lourenço, J.; Alcantara, L.C.J. West Nile Virus in Brazil. Pathogens 2021, 10, 896. https://doi.org/10.3390/pathogens10070896

The study, published under a Creative Commons License, can be read here

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