Zoonoses pose a growing threat to human health. How can this be explained? And what exactly does the term "zoonosis" mean?
The term "zoonosis" originates from Ancient Greek:
zôon, meaning "animal," and
nosos, meaning "disease." It refers to infectious and parasitic diseases that are transmitted between animals and humans.
This concept has evolved over time, with distinctions based on the mode of transmission or the animals involved, but these differences are becoming less relevant in the perspective of
"One Health," which recognizes that animal and human health are interconnected.
Examples of zoonoses still present in the world include rabies, transmitted through bites from infected dogs, which causes
nearly 60,000 deaths per year, or
brucellosis, transmitted through contact with infected animals or consumption of unpasteurized dairy products. Brucellosis induces fever, joint pain, and can lead to severe complications if left untreated.
Lyme disease is another example. It is transmitted to humans through bites from infected ticks. These ticks acquire the bacteria by feeding on certain animals, like rodents or deer, which act as natural reservoirs for the pathogenic bacteria. In this case, early symptoms can include fatigue and skin rashes. However, if untreated, it can also cause neurological or cardiac problems.
Multiple and complex causes
The threat posed by zoonoses is rising sharply. Approximately
60% of human infectious diseases are zoonotic, while 75% of emerging diseases originate from animals.
Recent examples that have led to pandemics include SARS (SARS-CoV), Ebola, and
Covid-19 (SARS-CoV-2), highlighting the increased vulnerability of human populations in an interconnected world.
Avian influenza (H5N1 influenza virus) is another example of a zoonosis with the potential to trigger a major health crisis.
The underlying causes of the rise in zoonoses are
multiple and complex. Among the primary factors are the loss of
biodiversity, which increases the chances of contact between wildlife and human populations, and climate change, which alters the habitats and behaviors of animal species, including vectors (mosquitoes, midges, ticks) of diseases.
However, these phenomena are not purely biological. They are also influenced by
socio-economic factors, such as lifestyle, poverty, cultural practices, or beliefs, as well as international travel and movement.
The
intensive farming of domestic animals, certain hunting practices, the farming of wildlife, and
live animal markets may also increase transmission risks, especially in regions with weak sanitary regulations.
How can zoonoses be prevented?
Global efforts are underway to
monitor and prevent these zoonoses. The "One Health" approach, which integrates various disciplines (human and veterinary medicine, epidemiology, social sciences, ecology, microbiology), has become essential in this fight. However, the level of response varies across regions. Some high-risk areas, particularly in the Global South, lack resources for surveillance and prevention.
To address this, international initiatives like
PREZODE (Prevention of Zoonotic Disease Emergence) aim to anticipate and manage future risks by strengthening surveillance networks and engaging local communities.
This initiative relies in part on regional research platforms like the
GREASE network (Management of Emerging Risks in Southeast Asia). The Greater Mekong region, rich in biodiversity, is a hotspot for the emergence of new zoonoses due to the close interaction between human and animal populations and environmental degradation.
To tackle this growing threat, it is crucial to focus on prevention, as well as to reinforce surveillance, research, and intervention capacities. The "One Health" approach provides an
integrated framework for understanding and countering these threats. It enables scientists, local authorities, and rural communities to combine efforts to prevent new global health crises.
Many challenges remain. However, by strengthening
international cooperation and adopting solutions based on biodiversity preservation and ecosystem management, we can hope to reduce the impact of zoonoses on human populations.
Authors:
François Roger - Regional Director Southeast Asia, veterinarian and epidemiologist, Cirad
Flavie Luce Goutard - Epidemiologist, Cirad
Marisa Peyre - Deputy Head of the ASTRE research unit, epidemiologist, Cirad