Natural barriers to the spreading of diseases in wild animals

The concept of natural barriers to the spread of animal diseases is a very ancient one. It incorporates not only the phenomenon of genetic resistance to pathogens, but also the influence of various other factors affecting the capacity of the pathogens to infect or to live as a parasite on certain animal species.After having recalled historical data on the subject, the author described the three main parts composing these natural barriers: difficulties associated with wild animals coming into contact with the pathogen, the innate resistance of the host animal to penetration by the pathogen and, finally, the acquired resistance of the animal, based on cellular or humoral immune resistance mechanisms.The author then examined possible weaknesses of these three components, which are linked to a variety of factors: modification of living conditions, biological rhythm or diet, penetration of skin or mucous barriers, adverse environmental conditions, etc.He concluded that natural barriers were relatively fragile and highlighted the risk that spontaneous mutations of pathogens represent for these barriers.