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Vector-borne diseases: challenges and responses

Read Kevin Keyaert, Konstantina Boutsika and Lina Heltsche describe the benefits of integrated and cross-board approaches to vector control.
© University of Basel
Malaria is not the only disease that is vectored by mosquitoes. You may have heard of such diseases as dengue, chikungunya, yellow fever or Zika, which also put a heavy burden on the public health and healthcare systems of tropical and subtropical regions.

These diseases, however, differ in the pathogens that cause them, and the mosquitoes that vector them. Malaria, for example, is a parasite spread by Anopheles mosquitoes, whilst dengue, chikungunya, etc., are arboviruses and are vectored between people by Aedes mosquitoes. Luckily, vector control measures can be implemented effectively in response to a variety of vector-borne disease outbreaks. Sometimes these outbreaks can occur unexpectedly, such as in the case of the 2015-2016 Zika epidemic, whilst others can hold their grip on communities for decades on end.

The mosquitoes that vector different vector-borne diseases are often adapted to different environments. The Aedes mosquitoes, which transmit dengue and chikungunya for instance, prefer urban environments and tend to bite earlier in the day.

Others, such as most Anopheles species, generally prefer rural settings and bite later in the evening. Hence, mosquito bed nets are more effective against Anopheles species. Each setting requires a different set of control measures.

However, in most cases the use of insecticides remains a key intervention. Nevertheless, for insecticides to work, mosquitoes need to be susceptible to them. Insecticide Resistance Management (IRM) is therefore important in all settings where insecticides are used. IRM programmes need to consider not only the different ecological settings, but also the behavioural characteristics of the targeted mosquito species.

Integrated approaches

Vector-borne diseases and the different mosquito species that transmit them do not necessarily exist in isolation. Multiple mosquito species and disease pathogens may be present in the same location. Therefore, a comprehensive public health programme requires an integrated approach to control the mosquitoes and vector-borne diseases.

Environmental factors such as climate change, deforestation, urbanisation, large-scale agriculture, global supply chains, etc., have led to a spread of invasive mosquito species. For example, Anopheles stephensi has spread to East Africa and Aedes albopictus has migrated into Southern Europe. This can lead to changes in the dynamics and epidemiology of existing vector-borne diseases such as malaria, or the potential for new vector-borne diseases to be introduced, such as dengue and chikungunya in Europe. Whilst insecticides should not necessarily be the first intervention used, where they are, IRM should be included in all vector control activities from the beginning.

No respect for borders

An integrated approach is needed to address vector-borne disease, not only between programmes targeting particular diseases, but also between countries and regions. Mosquitoes don’t respect borders.

There are several initiatives promoting and supporting this, such as the globally coordinated action of the RBM Partnership to End Malaria. Other initiatives operate at a continental level to foster best practice approaches to capacity-building and intersectoral collaboration in vector control. For example, the Pan-African Mosquito Control Association (PAMCA).

At the regional level, initiatives such as Elimination 8 and the Sahel Malaria Elimination Initiative (SaME) focus on Southern Africa and the Sahel region respectively. Some countries in Africa also invest in extensive national campaigns to create a strong environment for collaborative action, with Zambia being at the forefront through their Zero Malaria Starts With Me programme.

Integrated approaches that look at the wider ‘system’ in which vector-borne diseases exist, are gaining prominence. This is exemplified in the concept of One Health, where health governance for people, animals and the environment is addressed through a multisectoral and transdisciplinary approach.

Nested within One Health, vector control governance utilises the framework of Integrated Vector Management (IVM) to ensure that the coordinated efforts are efficient, cost-effective, and sustainable. For vector control to be sustainable in the long run, multisectoral collaboration also becomes necessary to ensure that insecticide resistance can be effectively managed and mitigated. Perhaps ‘Integrated Resistance Management’ would be a better name?

Commitment in a changing world

We have visited the fictional village of Nsuhyia at several points during this course. As with many similar, but real, towns and villages, malaria isn’t the only vector-borne disease they have to cope with. Changes to the environment, climate, demographics and infrastructure may change the vector-borne disease landscape, for better or worse.

But, until we no longer need to control the insect vectors of disease, entomologists and vector control practitioners will need to be trained, and new ways of controlling the mosquito vectors will need to be developed and implemented. This will take an ongoing commitment from the global community. Insecticide-based interventions will continue to play a key role. It is therefore vital that a holistic approach is taken, and that Insecticide Resistance Management is an integral part of all vector control programmes, ensuring that the greatest value from these public health interventions can be realised.

Authors: Kevin Keyaert, Konstantina Boutsika and Lina Heltsche

© University of Basel
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The Resistant Mosquito: Staying Ahead of the Game in the Fight against Malaria

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