Study recommends integrated risk assessment for zoonotic and vector-borne diseases

A study published in the journal One Earth points out that risk assessments for diseases transmitted by infected animals (zoonotic) and by vectors (such as mosquitoes) need to be unified and integrated. Such actions could help prevent these diseases, which tend to increase due to climate change.

The study was led by researchers from the Nucleus of Analysis and Synthesis of Nature-Based Solutions (BIOTA Synthesis), supported by FAPESP within the scope of the Science Centers for Development (SCDs). 

Based at the Institute of Advanced Studies of the University of São Paulo (IEA-USP) in Brazil, the center also includes researchers from the Department for the Environment, Infrastructure, and Logistics of the State of São Paulo (SEMIL) and other universities and third-sector organizations.

The researchers conducted a survey of 312 published studies on the transmission risk of 39 pathogens and diseases. However, only 7.4% of the studies included all three risk components: hazard, exposure, and vulnerability.

“There’s no standardization in the studies conducted. The risk of transmission of the same disease, for example, may be assessed based only on the abundance of mosquito vectors in one study, while another takes into account human exposure to these organisms. This lack of uniformity compromises the production of reliable and accurate models that could guide public policies aimed at the early identification of risk areas,” explains Raquel Carvalho, first author of the study, conducted during her postdoctoral research with a scholarship from FAPESP at IEA-USP.

The article presents recommendations for organizing this rapidly expanding field of research in the context of environmental change. The guidelines emphasize the importance of paying closer attention to exposure and vulnerability and of defining specific indicators for each. The article also recommends redirecting international research funding and strengthening international cooperation to support scientific efforts focused on zoonotic and vector-borne diseases in tropical regions.

For her work, Carvalho also completed an internship at the University of Glasgow in Scotland. She is currently a professor in the Department of Zoology at the Institute of Biosciences (IB-USP) and a BIOTA Synthesis researcher.

The results of the study were also proposed to the State Plan for Climate Adaptation and Resilience (PEARC), an instrument that aims to structure, coordinate, and articulate the actions of the state of São Paulo in addressing the impacts of climate change.

State plan

In their contributions to the PEARC, the BIOTA Synthesis authors differentiate between the components of hazard, exposure, and vulnerability to zoonotic and vector-borne diseases.

According to the document, which follows the definitions used in the study, the hazard of infection occurs because of the “presence and/or abundance of zoonotic hosts, vectors, and reservoirs.” It also takes into account “the presence and/or prevalence of infection by pathogens in a given space and time, representing a potential threat to humans.”

In turn, “exposure” is defined as the “probability of human contact with danger, determined by the type, frequency, and probability of behaviors, activities, and other related variables that modulate contact with danger and may result in infection by a zoonotic or vector-borne pathogen.”

Finally, “vulnerability” is defined as the “probability of human infection, considering the chance that a person or group of people, in a given space and time, will be infected by a zoonotic or vector-borne pathogen after exposure to the hazard.”

“No component is more important than another. It’s the intersection between them that represents the overall risk. Therefore, to adequately estimate risk areas, it’s necessary to consider all of them, which rarely occurs simultaneously in studies that perform this type of assessment,” Carvalho explains.

According to the authors, omitting relevant components can lead to inaccurate or misleading estimates. This can result in inadequate spatial planning, such as defining irrelevant priority areas, as well as poor resource and management effort allocation. These issues prolong the exposure of vulnerable populations to preventable risks.

For example, places with a high human population density and many cases of dengue would need more awareness campaigns to prevent the reproduction of the Aedes aegypti mosquito, as well as the application of insecticide.

Similarly, the mere presence of a pathogen in the environment does not necessarily indicate a high risk. The presence of Hantavirus in wild rodents, for instance, poses a lower risk in rural areas because human exposure to infected animals is less frequent.

Practical measures

In the section on zoonotic and vector-borne diseases in the recommendations to the PEARC made by BIOTA Synthesis, the team of managers and researchers not only structures a unified and integrated risk assessment for these diseases, but also addresses a series of measures to be implemented.

One of these measures is improving the impact assessment of developments such as condominiums on zoonoses, which currently only considers spotted fever. Another recommendation aims to improve the laboratory network for diagnosing and actively surveilling wildlife, as well as improving communication, to optimize access to and availability of information.

Finally, the researchers and managers emphasize the need to improve the efficiency and rationality of water distribution. According to the authors, ample scientific evidence links vector-borne diseases, such as dengue, to a lack of water security.

About São Paulo Research Foundation (FAPESP)
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