Active West Nile virus transmission in Brazil: an epidemiological study
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
Background
West Nile virus (WNV) is a mosquito-borne flavivirus that can cause neurological and fatal disease in animals and humans. Since its introduction into the USA in 1999, WNV has become the leading arbovirus in North America. In contrast, no major WNV outbreak has been reported in South America. Our study investigated active WNV circulation in Brazil.
Methods
We examined WNV epidemiological, molecular, genomic, and serological data from Brazil from January 2014 to December 2024. We also conducted WNV testing in 561 patients with febrile illness, neuroinvasive disease, or death between January 2019 and January 2024 in Ceará State, Brazil. Next, we conducted time series, mapping, ecological niche modeling, age-sex distribution, phylogenetic analyses, and statistical hypothesis tests.
Findings
Between January 2014 and December 2024, 110 West Nile cases were reported from 13 of 27 Brazilian states. In addition, our retrospective study in Ceará State revealed 12.1% (68 of 561 patients) were WNV cases, peaking in 2023, when 42.6% (29 of 68) of cases occurred. Among WNV cases, 7 (10.3%) had detected WNV RNA in serum, cerebrospinal fluid, or both, whereas 62 (89.7%) were IgM-positive, with 29 presenting with neurological complications, 35 with febrile illness, and four fatalities. WNV cases were reported in all months, with the highest numbers between May and August. Most cases were female (female-to-male ratio, 1.1:1), and the median age of patients was 40 years (interquartile range, 20–57). Our phylogenetic analysis showed that WNV lineage 1a circulated in Ceará State and caused a fatal horse case. Our ecological niche models identified several areas, mainly situated in the Northeast region, linked to a potentially higher risk of human exposure to local WNV circulation.
Interpretation
These findings comprehensively described consistent WNV circulation in Brazil and may contribute to informing public health policy, focusing on the strategies to determine the WNV burden in South America.
Funding
Burroughs Wellcome Fund, Wellcome Trust, National Institutes of Health, São Paulo Research Foundation, Brazilian Ministry of Science, and Brazilian National Council for Scientific and Technological Development.
West Nile virus (WNV) is a mosquito-borne flavivirus that can cause neurological and fatal disease in animals and humans. Since its introduction into the USA in 1999, WNV has become the leading arbovirus in North America. In contrast, no major WNV outbreak has been reported in South America. Our study investigated active WNV circulation in Brazil.
Methods
We examined WNV epidemiological, molecular, genomic, and serological data from Brazil from January 2014 to December 2024. We also conducted WNV testing in 561 patients with febrile illness, neuroinvasive disease, or death between January 2019 and January 2024 in Ceará State, Brazil. Next, we conducted time series, mapping, ecological niche modeling, age-sex distribution, phylogenetic analyses, and statistical hypothesis tests.
Findings
Between January 2014 and December 2024, 110 West Nile cases were reported from 13 of 27 Brazilian states. In addition, our retrospective study in Ceará State revealed 12.1% (68 of 561 patients) were WNV cases, peaking in 2023, when 42.6% (29 of 68) of cases occurred. Among WNV cases, 7 (10.3%) had detected WNV RNA in serum, cerebrospinal fluid, or both, whereas 62 (89.7%) were IgM-positive, with 29 presenting with neurological complications, 35 with febrile illness, and four fatalities. WNV cases were reported in all months, with the highest numbers between May and August. Most cases were female (female-to-male ratio, 1.1:1), and the median age of patients was 40 years (interquartile range, 20–57). Our phylogenetic analysis showed that WNV lineage 1a circulated in Ceará State and caused a fatal horse case. Our ecological niche models identified several areas, mainly situated in the Northeast region, linked to a potentially higher risk of human exposure to local WNV circulation.
Interpretation
These findings comprehensively described consistent WNV circulation in Brazil and may contribute to informing public health policy, focusing on the strategies to determine the WNV burden in South America.
Funding
Burroughs Wellcome Fund, Wellcome Trust, National Institutes of Health, São Paulo Research Foundation, Brazilian Ministry of Science, and Brazilian National Council for Scientific and Technological Development.
Date Issued
2025-11-01
Date Acceptance
2025-08-22
Citation
The Lancet Regional Health. Americas, 2025, 51
ISSN
2667-193X
Publisher
Elsevier
Journal / Book Title
The Lancet Regional Health. Americas
Volume
51
Copyright Statement
© 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
License URL
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/40978564
PII: S2667-193X(25)00239-X
Subjects
Arbovirus
Emerging viral diseases
Flavivirus
Health Care Sciences & Services
Life Sciences & Biomedicine
Mosquito-borne flavivirus
NEUROINVASIVE DISEASE
Public, Environmental & Occupational Health
Science & Technology
SURVEILLANCE
UNITED-STATES
Vector-borne viruses
West Nile virus
Publication Status
Published
Coverage Spatial
England
Article Number
101229
Date Publish Online
2025-09-08