Simposio: Enferemedades transmitidas por mosquitos y otros dípteros

Epizootic outbreak of WEE virus in Uruguay: Strengths of inter-institutional collaboration.

FRABASILE, Sandra¹, MOREL, Noelia², PÉREZ, Ramiro³, MOREIRA MARRERO, Lucía¹, BURGUEÑO, Analía², CORTINAS, Ma. Noel⁴, BASSETTI, Lucía³, NEGRO, Raúl³, RODRÍGUEZ, Sirley³, BÓRMIDA, Victoria⁴, GAYO, Valeria³, COSTA DE SOUZA, Víctor⁵, GOMES NAVECA, Felipe^5,6, MARTÍNEZ GÓMEZ, Mariela⁷, GRESH, Lionel⁷, MENDEZ-RICO, Jairo⁷, CHIPARELLI, Héctor², DELFRARO, Adriana¹.

¹ Sección Virología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.
² Unidad de Virología, Departamento de Laboratorios de Salud Pública (DLSP), Ministerio de Salud Pública, Montevideo, Uruguay.
³ División de Laboratorios Veterinarios (DILAVE), Dirección General de Servicios Ganaderos (DGSG), Ministerio de Ganadería Agricultura y Pesca, Montevideo (MGAP), Uruguay.
⁴ Laboratorio de Genómica, Departamento de Laboratorios de Salud Pública (DLSP), Ministerio de Salud Pública, Montevideo, Uruguay
⁵ Núcleo de Vigilância de Vírus Emergentes, Reemergentes ou Negligenciados – ViVER/EDTA. Instituto Leônidas e Maria Deane, Fiocruz, Manaus, AM, Brazil.
⁶ Laboratório de Arbovírus e Vírus Hemorrágicos, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, RJ, Brazil.
⁷Infectious Hazards Management Unit, Health Emergencies Department, Pan-American Health Organization, Washington D.C., USA
E-mail address: adriana@fcien.edu.uy

In November 2023 an outbreak of equine encephalomyelitis in horses was reported in Western Uruguay, concomitantly with an outbreak initiated in the Argentinean provinces of Corrientes and Santa Fe. On 5th December, Western Equine encephalitis virus (WEEV) was laboratory confirmed as the causative agent, in a dead horse from Salto Department. Up to March 2024 the outbreak extended all along the country. The most recent reports of WEEV in the region were a PRNT-seropositive horse collected in 2007, and a fatal human case reported in 2009, both in Uruguay. In North America, there are no reports of equine or human WEEV cases since 1998. 
The rapid identification of the virus was achieved thanks to an interinstitutional collaboration between the health authorities and the academia. Homogenates of brain tissue samples and cerebrospinal fluid were subjected to nucleic acid extraction. Diagnosis was done using a RT-nested PCR targeted on the nsp4 gene, followed by Sanger sequencing and phylogeny. Complete genomes from six samples were obtained by hybrid–capture enrichment Miseq Illumina NGS using the Viral Surveillance Panel from Illumina®. 
Maximum likelihood phylogenetic analysis showed that Uruguayan sequences form a monophyletic group in the WEEV clade, together with Brazilian genomes from the outbreak and group independently from the North American sequences. The outbreak sequences were closely related to an old Argentinean virus isolated from a sick horse in 1950. Two additional Argentinean sequences isolated from a Culex spp mosquito (1980) and a horse (1933) were related to the epizootic clade. The old Uruguayan sequence retrieved from the 2009 case was unrelated to the outbreak and clusters together with USA sequences. The origin and spreading of this outbreak are intriguing but are probably influenced by a highly rainy season and extensive floodings occurred in the previous months, followed by intense mosquito proliferation, specially of the “flooding mosquito” Aedes albifasciatus. Field work is undergoing to identify the amplifying vertebrate hosts and the mosquito species acting as vectors.

Keywords: WEEV, equine, genomics