What is a zoonosis, and what is a vector-borne disease?

Thierry Boulinier: A zoonosis is an infectious disease that can be transmitted from animals to humans, and vice versa. The majority of infectious diseases are of animal origin: today some are transmitted exclusively among humans, while others can potentially be transmitted from animal reservoirs. Vector-borne diseases involve an arthropod — a mosquito or tick — that transmits the infectious agent. Numerous factors promote the emergence and spread of such diseases: the destruction of natural habitats, intensified contact with wildlife, globalized trade, the development of industrial animal farming, and global warming. These dynamics interact on a global scale.

Why did you choose marine birds as models for study?

T. B. : I have been working on marine birds for a long time, on their parasites and pathogens. These species reproduce in colonies that can sometimes be immense, on islands dispersed across the globe. In polar regions, reproduction is highly synchronized over short summer periods. These conditions create unique opportunities to study the transmission of infectious agents: high densities promote direct contact with parasites such as ticks, which can remain at sites awaiting the return of hosts; and low specific diversity simplifies analysis of transmission networks. These birds live for a long time (over 50 years for some albatross), and exhibit great fidelity toward their reproduction site. This makes it possible to study pathogen dispersion on an oceanic scale, as well as repeated interactions between a host and an infectious agent over time.

Some wild species transmit viruses to domestic animals more easily?

T. B. : It is a complex question. Species differ through their sensitivity or tolerance to infection, capacity to excrete the virus, migratory or gregarious behavior, and interactions with breeding farms. Understanding these differences requires in-depth ecological knowledge of species in relation to that of pathogens, which remains lacking for many wild taxons. For example, our research on the flaviviruses of marine birds, transmitted by specific ticks, shows that these viruses circulate largely independent of continental systems.  By studying them in TAAF as well as the Mediterranean, Brittany, and the Arctic, we are seeking to understand their continuance  and global dispersion. At the same time, we are working comparatively with colleagues on the circulation of such agents in terrestrial systems in mainland France, notably involving the ubiquitous tick Ixodes ricinus⁴.   

How is your research in keeping with a One Health approach?

T. B. : This approach is based on the notion that animal health, human health, and the health of ecosystems are closely linked. Scientifically, it requires interdisciplinary approaches. Attention long focused on systems closely connected to human activities, such as farm animals or hunted species. However, today’s HPAI, which led to unprecedented mortality among mammals and marine birds, underscores the importance of also including wild species that are remote from direct human activities. The evolution of immune systems, behaviours, and the movement of species to varying ecologies must be fully included in this approach.

What are the primary results of your research? For instance, should the vaccination of wild animals be seen as a preventive measure for some species?

T. B. : ANR funding allowed us to develop long-term monitoring and projects, doing so with continuity while combining basic and applied approaches, such as REMOVE_DISEASE⁵, ECOPATHS⁶, and WILDFLU⁷. REMOVE_DISEASE gauges the effect that island ecosystem restoration—via eradication of introduced mammals (rats, cats)—has on epidemiological dynamics threatening native species, notably on Amsterdam Island. ECOPATHS explores the circulation of infectious agents in TAAF by explicitly including management-related issues, such as optimised monitoring and the potential interest of vaccination in wildlife populations. Finally, WILDFLU analyses the diffusion and impact of HPAI among wildlife, marine birds in particular, as well as their role in dispersing the virus, their differential resistance, and their immune-related particularities.

We recently demonstrated that king penguins vaccinated with an messenger RNA vaccine for ducks developed a strong and persistent immune response observed over more than 250 days, covering the maturation period for chicks⁸. Our research also revealed that with a puffin species, maternal antibodies transmitted via the yolk persist for a number of weeks with the chicks. This discovery paved the way for vaccinating female albatrosses in order to indirectly protect their young against other highly lethal pathogens, such as avian cholera on Amsterdam Island.

This research, which was also conducted on the Crozet and Kerguelen Islands with support from the French Polar Institute (IPEV), aims to better understand long-term eco-epidemiological dynamics, and to fully include wildlife within a One Health approach that can anticipate global health crises. The vaccination of wild species also raises ethical questions. To what extent should we intervene? What risks should we accept? What balance should be struck between biodiversity conservation, ecosystem protection, and health prevention? These decisions must be made based on reliable scientific data and interdisciplinary approaches, and grow out of collective debate.

How can your research help guide public action?

T. B. : Some of my work has direct implications for animal or human health, such as research on the ticks that are vectors for the bacteria behind Lyme disease or HPAI. Other work chiefly involves conservation. The Amsterdam albatross, for instance, only reproduces on Amsterdam Island. However, each year avian cholera epizootics kill a large share of the chicks of other albatross species on the same island. Should they also be protected? These issues do not directly involve human health, but help prevent extinctions in systems already weakened by marine overexploitation, climate change, and the introduction of invasive species. Wildlife should also be better integrated within monitoring and management measures in order to anticipate crises rather than respond to them on an emergency basis.

¹ Du clade 2.3.4.4b.
² An epizootic is the rapid spread of an infectious disease among a large number of animals of the same species, or multiple species, in a given area. A panzootic is an epizootic that extends to the global or intercontinental scale.
³ Clessin A. et al. (2025) Circumpolar spread of avian influenza H5N1 to southern Indian Ocean islands, Nature Communications, 16(8463). https://www.nature.com/articles/s41467-025-64297-y
⁴ For example, as part of the ANR’s JCJC MoZArt project led by Raphaëlle Métras, an epidemiologist at Inserm: https://anr.fr/Project-ANR-22-CE35-0003
⁵ The REMOVE_DISEASE project is carried out on an international level with a Portoguese team (ISPA, MARE), South African teams (Nelson Mandela University, UCT), and an American team (Cornell University): https://anr.fr/Project-ANR-21-BIRE-0006
⁶ The ECOPATHS project is partnered with Anses (Bacterial Zoonoses Unit, Maisons-Alfort) and the Social Anthropology Laboratory (LAS, Collège de France/CNRS/EHESS): https://anr.fr/Project-ANR-21-CE35-0016
⁷ The WILDFLU project is partnered with Anses (Virology, Immunology, and Parasitology in Poultry and Rabbits Unit of the Ploufragan National Reference Laboratory on Avian Influenza), and LAS. These projects are also supported by an agreement with the Ceva Wildlife Research Fund, CNRS initiatives on H5N1 influenza, and SEE-Life long-term monitoring in ecology and evolution: https://anr.fr/Project-ANR-25-CE35-0691
⁸ Lejeune M. et al. (2026) Vaccination against H5HP avian influenza virus leads to persistent immune response in wild king penguins, Nature Communications, 17(1395). https://www.nature.com/articles/s41467-026-69094-9

Caption: Rapid field detection test for A fever antigens on a sea elephant carcass. Combined with virus sequencing and knowledge of host ecology, these approaches enabled a rapid scientific response to the emergence of HPAI in isolated territories rich in biodiversity. © Jérémy Tornos/Mathilde Lejeune/CNRS/IPEV