First isolation of West Nile virus in Brazil

Lívia Caricio Martins, Eliana Vieira Pinto da Silva, Livia Medeiros Neves Casseb, Sandro Patroca da Silva, Ana Cecília Ribeiro Cruz, Jamilla Augusta de Sousa Pantoja, Daniele Barbosa de Almeida Medeiros, Arnaldo Jorge Martins, Ermelinda do Rosário Moutinho da Cruz, Marialva Tereza Ferreira de Araújo, Jedson Ferreira Cardoso, Marcos Antônio Correia Rodrigues da Cunha, Gilton Luiz Almada, Alessandro Pecego Martins Romano, Maria Guadalupe Dias Pestana Santos, Gilsa Aparecida Pimenta Rodrigues, Jannifer Oliveira Chiang, Juarez Antonio Simões Quaresma, Valéria Lima Carvalho, Pedro Fernando da Costa Vasconcelos

Serological evidence of West Nile virus (WNV) infection has been reported in different regions of Brazil from equine and human hosts but the virus had never been isolated in the country. We sought to identify the viral etiology of equine encephalitis in Espírito Santo state. We performed viral culture in C6/36 cells, molecular detection of WNV genome, histopathology and immunohistochemistry from horse cerebral tissue. We also carried out sequencing, phylogenetic analysis and molecular clock. Histopathologic analysis from horse cerebral tissue showed injury related to encephalitis and WNV infection was confirmed by immunohistochemistry. The virus was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) from brain tissue and subsequently isolated in C6/36 cells. WNV full-length genome was sequenced showing the isolated strain belongs to lineage 1a. The molecular clock indicated that Brazilian WNV strain share the same common ancestor that were circulating in US during 2002-2005. Here we report the first isolation of WNV in Brazil from a horse with neurologic disease, which was clustered into lineage 1a with others US WNV strains isolated in beginning of 2000's decade.