Zoonoses can jump from animal to human or from human to animal
Zoonoses include all situations where a pathogen, bacterium, virus or parasite can be transmitted from animals to humans and/or vice versa.
Zoonoses do not always cause disease in both humans and animals
Some animals carry pathogens that cause disease in humans.years showing symptoms. This is the case of poultry carrying bacteria Campylobacter and sometimes from Salmonella or bats carrying viruses of the coronavirus family.
Conversely, foot-and-mouth disease is most often asymptomatic in humans, whereas it affects cattle, goats, sheep and pigs.
Animals are reservoirs of pathogens
The great diversity of animal species results in a wide variety of pathogens, to which humans are not usually exposed and which might cause more or less serious illnesses in the event of transmission. It is thus estimated that 75% of emerging infectious diseases in humans come from animals.
The transmission of a pathogen from one species to another does not always result in the emergence of a new disease
Cases of transmission of pathogens between species are frequent. For one to speak of the emergence of a disease, the ptransmitted pathogen adapts to new host and spreads between individuals of the newly infected species. It can also be a re-emergence if the disease reappears in a territory from which it had been eliminated.
Not all emergencies result in a pandemic
Not all disease emergences result in an epidemic or a pandemic. An epidemic concerns an infection that spreads in a specific area.while the pandemic spreads worldwideI. The passage to the pandemic stage of an emergence is most often declared by the WHO. In the case of animal pathogens only, we speak of epizootics and panzootics.
The spread of an epidemic depends on many factors related to the pathogen, infected hosts and environmental conditions. The mode of transmission has a preponderant role: a respiratory illness is more likely to spread than a disease with another mode of transmission. International travel and trade in animals and products are also important factors.
For a pathogen to cross the species barrier, it must mutate.
Viruses, especially RNA virusesi.e. which use ribonucleic acid (RNA) as genetic material, mutate more frequently as bacteria or parasites. They are more likely to acquire a mutation allowing them to adapt to a new species. This explains why most of the zoonoses that have emerged in recent years such as avian influenza, Covid-19, or Ebola are RNA viruses.
Zoonoses are not only transmitted through direct contact between animals and humans.
Other modes of transmission are possible, such as through the environment (water and soil), food or vectors.
Vectors are a mode of disease transmission
A vector is an arthropod, a group comprising insects and arachnids (mosquitoes, ticks, etc.), that transmits a pathogen : a virus, a bacterium or a parasite. It acquires this pathogen by feeding on a host and then transmits it to other individuals.
Genomics tools help spot the progression of pathogens
Genetic sequencing of pathogens detected through epidemiological surveillance makes it possible to better detect the spread of new pathogens or variants and to adapt the means of control.
One health, One welfare et Ecohealth, trois concepts proches
The “One Health” concept or “a single health” in French, was highlighted with the awareness of the close links between human health, that of animals and the global ecosystem state. It therefore encourages consideration all disease emergence factorsboth through research on these diseases and their management.
The concept Ecohealth gives more importance to the role of the environment and the good state of the ecosystem on animal and human health.
Finally, the concept One welfare add the welfare to the health dimension: it highlights the fact that the well-being of animals and that of humans are linked, and that they interact with their physical and mental health.
