Medical and veterinary entomology is a holistic science. Very early on in the history of human society, people became aware that there was a link between insects, diseases and health. Today's entomologists, distant heirs of Aristotle, are required to take a new approach to these "vectors" by placing them in a historical, medical, socio-economic and environmental context and drawing on a wide range of complementary disciplines, from taxonomy to public health.
Entomologists themselves are often unaware of the importance of this historical dimension. Our predecessors trod a long and difficult path before eventually reaching the conclusion which today seems so obvious: hematophagous arthropods can transmit pathogens that are responsible for diseases in animals and humans. Young entomologists will do well to reflect on the foresight, dedication and bravery displayed by those who went before them to provide us with the body of knowledge we take for granted today. We should draw inspiration from our forebears when we are called to investigate a new research question. The book by Erik Orsenna will no doubt inspire more to follow in their footsteps, at all stages of their career. Who knows, some readers may even see their own names go down in history as a result of their discoveries and research!
Medical and veterinary entomology
It was only in the late 19th century that medical and veterinary entomology developed as a discipline. So it was generally only after this period, in which scientists began to understand the role of vectors in the spread of pathogens and diseases, that historians were able to reflect on how vector-borne diseases have shaped the development of our societies. Examples of the influence of these diseases include the conquests of Alexander the Great, brought to an abrupt end in 323 BC by his death – attributed by authors to malaria (Anopheles) or West Nile virus (Culex) ; the Arab invasions and the spread of Islam to Sub-Saharan Africa, which were limited by equine trypanosomiasis (Glossina); human losses mostly as a result of malaria during the second Madagascar expedition by colonial troops in 1895 (Anopheles); the three million deaths attributed to typhus in World War I (lice); not to mention the Black Death pandemics in Europe from the 14th century onwards (fleas). Since the mid-19th century, hundreds of vector-borne diseases have been described in humans, pets, livestock and wild animals. The pathogens involved include viruses, bacteria, protozoa and filarial worms, and the vectors belong to several groups of arthropods. But there are many arboviruses whose vectors are yet to be pinpointed or whose vertebrate hosts (if they have only been isolated in arthropods) have not yet been identified. Medical and veterinary entomologists still have plenty of discoveries to make!
Inevitable new infectious diseases
In his book The Destiny of Infectious Diseases, Charles Nicolle wrote back in 1933 that "there will be new infectious diseases – that is a fatal truth." There is no doubt that some of the diseases that are currently emerging and will continue to emerge in wild animal populations as a result of upheavals related to environmental, climatic, demographic, societal, cultural, medical, economic and other factors will be vector borne. Changes in vector systems – in other words, variations in the presence, distribution and quantity of vertebrate hosts, vectors and pathogens and the relations between them – come about when their general environmental situation is altered in some way.
These phenomena can have a variety of causes. If we are to understand and control vector-borne diseases, it is vital that we adopt a One Health approach, which takes account of balances and imbalances in terms of health, not only in humans and domestic animals but also in other animal and plant species. This complexity should not discourage entomologists but rather stimulate them – there is great satisfaction to be found in elucidating a transmission cycle, identifying a new vector or developing a technique to tackle vector-borne diseases based on new knowledge in vector biology and genetics. Each stage in the process from infection to vector-borne transmission is a separate event with its own environmental and socio-economic factors. Global changes have any number of repercussions, and the consequences at local level can vary enormously – they do not necessarily lead to increased health risks. The worst-case scenario remains just a scenario – but it must be taken into consideration.
And that is the role of entomologists, alongside their partners in other disciplines: to adopt a historical perspective, identify the parameters involved in disease transmission, evaluate the importance of different factors – without over- or underreacting – and, ultimately, assess the risks and make recommendations for surveillance, protection or control measures based on the available knowledge and tools.
By Didier Fontenille, IRD Director of Research and Director of the Institut Pasteur in Cambodia, Vincent Robert, IRD Director of Research, and Gérard Duvallet, Professor at Paul Valéry University of Montpellier.
This text illustrates the report “The Geopolitics of the Mosquito” - Go further with our experts!, published to coincide with the release of Erik Orsenna's book, Géopolitique du moustique, Ed. Fayard.
Excerpt from the book: Duvallet G., Fontenille D., Robert V., eds, 2017. Entomologie médicale et vétérinaire. Marseille-Versailles, IRD Editions- Quae, 650 p.