Early warning systems for vector-borne diseases

Climate change can have an influence on vector-borne disease (VBD) transmission as climatic conditions affect the life cycle of disease vectors (e.g., mosquitos, ticks,...) and the replication rates of viruses and parasites inside the vectors. Increased temperatures may shorten vector reproduction cycles and incubation periods for vector-borne pathogens, leading to larger vector populations and increased transmission risks. Changes in temperatures, precipitations and humidity could affect both the geographic distribution and seasonal activity of vectors and host animals, as well as human behaviours and land use patterns, and as such the overall prevalence of VBDs. 

Over the past decades, VBD outbreaks have occurred in Europe and climate change could be one of the drivers of these outbreaks. For example, in the summer of 2010, the unprecedented increase in the number of West Nile virus infections in humans in south-eastern Europe was preceded by a period of extreme hot weather in that region. In the subsequent years, high temperature anomalies were identified as contributing factors to the recurrent outbreaks (EEA 2016).

To prevent possible health risks to the population, signals from Early Warning Systems (EWS) can be used to structure effective vector control programmes. Actions following early warning include analyses of pathogens spreads, their detection (based on monitoring of the presence and spatial distribution of the pathogens), forecasting of potential further spread of infections through the use of predictive modelling, and finally dissemination of warnings, decision making and implementation of responses. These actions involve a wide variety of actors such as policy makers, national, regional and local authorities (e.g., the ministry of health, medical epidemiological units,...), medical staff (e.g., physicians, clinicians and laboratory staff) and researchers.

IPCC categories

Social: Informational, Structural and physical: Technological options

Stakeholder participation

The design and implementation of an EWS on VBDs involves a wide range of skills, secured by involvement of experts from areas such as traditional environmental and infectious disease epidemiology, public health, and environmental change. For this reason, several administrations and institutions at various spatial scales tend to be involved, including national ministries of health, national public health agencies, national medical entomological units, national/regional/local blood safety authorities, doctors, laboratory technicians, veterinarians and others.

At the European level, the European Centre for Disease Prevention and Control (ECDC) is implementing an information resource hub, called European Environment and Epidemiology Network (E3). The E3 Network is a collaborative network through which E3 Network users and partners can exchange data and information on the topic. Through the E3 Network, ECDC aims to promote activity in this field by collecting and distributing climatic, environmental, demographic and infectious disease data that have been produced by a wide range of primarily European research projects, institutes, and government agencies. The overarching objective of establishing the E3 Network is to permit Europe-wide analyses of the impending risks to infectious disease spread due to environmental change. The result of these analyses are disseminated to policy makers, public health practitioners, European Union and international agencies, other governmental sectors, and non-governmental organisations. National and sub-national systems can be integrated in a broader system (such as the E3) in order to monitor and homogenize the input data, as well as the outputs (such as maps) for vector monitoring.

Success and Limiting Factors

EWS on VBDs only function well if the monitoring network of disease occurrence, and climatological and environmental factors is well-established and accordingly maintained. There may be different variables to consider when monitoring and analysing VBDs (e.g., local temperature, humidity, state of vegetation, water index,...), and the methodologies available today may not be able to monitor all of them. Identification of health outcomes using these surveillance methods suffers from significant delays due to delays in data retrieval (such as climatic, ecological or epidemiological, epidemiological data), as well as delays in case identification, diagnosis, reporting, or other elements, which can lead to exposure misclassification.

The absence of, or faulty EWSs for VBDs could result in a significant increase of the impacts for the affected population. Therefore a correct implementation and management of an EWS on VBDs is of key importance. EWSs for VBDs require continuous updating and improvement, based on recent insights from research on climate change or epidemiology. To date, although there are several VBD alert systems already in place (e.g., West-Nile virus infection prevention in Greece), there are several challenges that are difficult to overcome. Among these, of primary importance is the difficulty to collect climate and epidemiological data (i.e., input data), but also to prove the evidence of cost-effective control measures. Also comparison and extrapolation of analyses is difficult.

Costs and Benefits

The cost of EWSs for VBDs is non-negligible in absolute terms. Yet, it is relatively low in comparison with the potential amount of losses that these systems allow to reduce. In fact, by intercepting the emergence and spread of vector-borne diseases, the human and financial costs of a potential epidemic can be contained. EWSs on VBDs entail costs related to several components of the surveillance systems as well as costs of vector control biocides, which can be related to human resources, blood safety measures (e.g., screening processes) or virus testing in humans, animals or vectors. In addition, resources are needed to maintain the system and further improve it.

Legal Aspects

The EU Strategy on Adaptation to Climate Change highlights the importance of limiting the emergence and spread of infectious diseases and allergens linked to geographical shifts in vectors and pathogens. The Strategy aims “to pool and connect data, tools and expertise to communicate, monitor, analyse and prevent the effects of climate change on human health, and on the health of animals and the environment (i.e., 'One Health' approach”). In this context, the European Food Safety Authority (EFSA) — an independent European agency which produces scientific opinions and advice on food safety, nutrition, animal health/welfare, plant protection, and plant health — in collaboration with the European Centre for Disease Prevention and Control (ECDC), collects data on vectors and vector-borne diseases, and analyses their spread in the European Union.

Implementation Time

Design and implementation of an early warning system for VBDs typically require 1 to 5 years, depending on the specific objective and characteristics of the system.

Life Time

Prevention and response activities, including the surveillance of human VBD infections, are generally implemented on an annual basis and surveillance systems are continuously operated.

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