Rocio virus sustained circulation in Brazil: first infection case in a horse highlights the need for enhanced arbovirus surveillance.
Abstract: Rocio virus (ROCV), a neurotropic arbovirus of the genus, caused Brazil’s largest encephalitis outbreak in the 1970s but has since been rarely detected. We report the first ROCV encephalitis clinical case after nearly 40 years and isolated and sequenced the virus from CNS tissue of a horse. Metatranscriptomics enabled full-genome sequencing, revealing divergence from the reference sequence at an evolutionary rate of 5.8–7.0 × 10⁻⁴, consistent with . Thirty-one non-synonymous substitutions were identified, with the envelope protein most affected. Findings indicate ROCV cryptic circulation and ongoing evolution. Horses may act as sentinels, underscoring the need for strengthened ROCV genomic surveillance. The online version contains supplementary material available at 10.1007/s00705-026-06574-9.
Publication Date: 2026-02-28 PubMed ID: 41760960PubMed Central: PMC12948843DOI: 10.1007/s00705-026-06574-9Google Scholar: Lookup
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Summary
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Overview
- This research article reports the first confirmed case of Rocio virus infection in a horse in Brazil after nearly 40 years, highlighting that the virus is still circulating and evolving in the region.
- The study demonstrates the importance of enhanced genomic surveillance for Rocio virus to monitor and understand its activity and evolution.
Introduction to Rocio Virus and Historical Context
- Rocio virus (ROCV) is an arbovirus, meaning it is transmitted by arthropods such as mosquitoes.
- It belongs to a genus known for neurotropic viruses, which have an affinity for the nervous system.
- ROCV caused a significant encephalitis (brain inflammation) outbreak in Brazil during the 1970s, representing the largest such outbreak recorded in the country at the time.
- Since the 1970s outbreak, ROCV infections have been rarely detected, leading to assumptions that its circulation might have diminished or ceased.
Significance of the Recent Case and Study Details
- The article reports the first identified clinical case of ROCV encephalitis in nearly four decades, this time observed in a horse, representing a new species for clinical detection of the virus.
- The research team isolated the virus directly from the central nervous system (CNS) tissue of the infected horse, confirming a neurotropic infection.
- Advanced metatranscriptomic techniques were employed to sequence the full genome of the virus from the infected tissue, allowing for a detailed genetic analysis.
Findings on Virus Evolution
- Genomic sequencing showed that the isolated ROCV strain has genetic divergence from the historical reference strain.
- The evolutionary rate was calculated as 5.8–7.0 × 10⁻⁴ substitutions per site per year, a rate consistent with other RNA viruses indicating ongoing virus evolution.
- Thirty-one non-synonymous mutations were identified, which are changes in the virus’s genome that alter amino acids in the resultant proteins and can affect virus properties such as infectivity or immune evasion.
- The envelope protein of the virus, critical for virus entry into host cells and a major target of host immune responses, showed the highest number of these amino acid changes.
Implications for Surveillance and Public Health
- The identification of ROCV in a horse suggests that animals may serve as sentinel species, offering an early warning system for detection of virus circulation before human cases emerge.
- Cryptic circulation means the virus has been present and evolving undetected for years, posing a hidden risk for outbreaks.
- The findings underscore the necessity to enhance genomic surveillance of ROCV, including sampling in animals and humans, to better track its evolution and spread.
- Improved surveillance can inform public health strategies to prevent or control potential encephalitis outbreaks caused by ROCV.
Additional Information
- The paper mentions supplementary material available online, which likely contains detailed data and methods that support the findings.
- This study contributes important new knowledge to the understanding of ROCV ecology and evolution, emphasizing that long-dormant viruses can re-emerge and evolve unexpectedly.
Cite This Article
APA
Gräf T, Rodriguez MC, de Oliveira Brandão Y, Royer CA, do Nascimento Ferreira C, Confortin C, Zanluca C, Strottmann DM, Duarte Dos Santos CN, Joineau MEG.
(2026).
Rocio virus sustained circulation in Brazil: first infection case in a horse highlights the need for enhanced arbovirus surveillance.
Arch Virol, 171(4), 106.
https://doi.org/10.1007/s00705-026-06574-9 Publication
Researcher Affiliations
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil. tiago.graf@fiocruz.br.
- Marcos Enrietti Diagnostic Center, Paraná Agricultural Defense Agency, Rua Jaime Balão, 575, 80040-340, Curitiba, Paraná, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Laboratório de Virologia Molecular, Instituto Carlos Chagas, Fundação Oswaldo Cruz, Curitiba, Brazil.
- Marcos Enrietti Diagnostic Center, Paraná Agricultural Defense Agency, Rua Jaime Balão, 575, 80040-340, Curitiba, Paraná, Brazil.
Conflict of Interest Statement
Declarations. Competing interests: We declare no competing interests.
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