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Reviewer 1: "Dynamics and Ecology of a Multi-stage Expansion of Oropouche Virus in Brazil"

Reviewers recommend a more rigorous methodological framework, including integrated phylogeographic analysis, improved spatial resolution, and explicit justification for key assumptions.

Published onJan 21, 2025
Reviewer 1: "Dynamics and Ecology of a Multi-stage Expansion of Oropouche Virus in Brazil"
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Dynamics and ecology of a multi-stage expansion of Oropouche virus in Brazil
Dynamics and ecology of a multi-stage expansion of Oropouche virus in Brazil
Description

Abstract In March 2024, the Pan American Health Organization (PAHO) issued an alert in response to a rapid increase in Oropouche fever cases across South America. Brazil has been particularly affected, reporting a novel reassortant lineage of the Oropouche virus (OROV) and expansion to previously non-endemic areas beyond the Amazon Basin. Utilising phylogeographic approaches, we reveal a multi-scale expansion process with both short and long-distance dispersal events, and diffusion velocities in line with human-mediated jumps. We identify forest cover, banana and cocoa cultivation, temperature, and human population density as key environmental factors associated with OROV range expansion. Using ecological niche modelling, we show that OROV circulated in areas of enhanced ecological suitability immediately preceding its explosive epidemic expansion in the Amazon. This likely resulted from the virus being introduced into simultaneously densely populated and environmentally favourable regions in the Amazon, such as Manaus, leading to an amplified epidemic and spread beyond the Amazon. Our study provides valuable insights into the dispersal and ecological dynamics of OROV, highlighting the role of human mobility in colonisation of new areas, and raising concern over high viral suitability along the Brazilian coast.

RR\ID Evidence Scale rating by reviewer:

  • Misleading. Serious flaws and errors in the methods and data render the study conclusions misinformative. The results and conclusions of the ideal study are at least as likely to conclude the opposite of its results and conclusions than agree. Decision-makers should not consider this evidence in any decision.

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Review: OROV is a vector-borne pathogen and their transmission requires the presence of competent vectors within the flight range of the insect vector. That being said, it would be more informative to include seasonal distribution of the main competent vectors for the study regions. The ENM used does not account for temporal habitat suitability, instead ran ENMs separately at different time frames, which does not account for spatio-temporal aspect, simultaneously.

The preprint has a tremendous work effort. However, the interpretation of the results would be tricky or misleading for the following reasons:

  • OROV is a vector-borne pathogen that requires a considerable density of competent vectors to cause transmission. It is unclear why the authors used landscape and climate data. Is it because it might be a proxy for virus circulation in the human host or insect vector? Emphasizing that landscape, climate, and air travel data caused the widespread of OROV from Amazon to the East Coast could be correct. Still, it was not methodologically proved from the type of analysis or the variables included in the study, for missing an important puzzle piece which is the insect vector.

  • Data spatial resolution: Authors mentioned that landscape and climate data were geocoded and resampled to county/province scale. However, with the continuous habitat fragmentation in the Amazon, such as continuous deforestation events, the used spatial resolution may not capture these landscape changes. 

  • Human mobility data via air flight: In Figure S1, the number of recorded OROV in AL and BM provinces was much higher than in other non-Amazonian states. However, in Figure S2, the "flights departing specific airport" and"total departing flights" in other Southeastern provinces were much higher than Al and BM, which defeats the purpose that human mobility increases the chances of OROV transmission. 

  • Water bodies in the Amazon region, represented as igapos and terra firme, are potential breeding habitats for mosquito and culicoides vectors of OROV, which may provide more suitable habitats for continuous transmission of OROV in the western region of Brazil than the east coast. However, the virus could be maintained on the East Coast in case of a potential reservoir animal host, such as rodents or house cattle, which was not included in the current study.  

  • In general, the transmission of the virus to humans requires a bite from an infective competent insect vector. The probability of getting bitten by an infective vector is a function of insect density, which is predicted by suitable breeding habitats/suitable climatic factors/survival rate, and human population density. That being said the higher the density of insect vectors and less population number, the more the chances of transmission to happen. That being said, the transmission of OROV would be more likely in areas with moderate population density (peri-urban, villages), where higher densities of insect vectors are present.

Comments
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Samir Guz:

Análise interessante sobre a transmissão do vírus Oropouche. Para pesquisadores, cientistas de dados e profissionais que trabalham com modelagem matemática, estatísticas e análises epidemiológicas, recomendamos Calculadora24.com, um site com calculadoras de horas, dias de vida, horas trabalhadas, tempo entre datas e diversas ferramentas online para facilitar cálculos de forma rápida e prática