Why are animals immune to catching the cold or flu when the owner is contagious?
Due to the fact that dogs, cats, and humans share a litany of cold symptoms - including stuffy noses and irritability - the underlying causes are usually alien [1]. Although the germs that cause most colds and flues are species specific, some that cause cold- and flu-like symptoms are up for grabs [2]. Certain varieties of streptococcus - which causes a sore throat - are infectious among dogs, cats, and humans [2]. However, dog colds are not contagious to humans [3]. In addition, there are several viruses that can cause upper respiratory diseases in cats and dogs, none of which are transmitted to humans [6].
While people can catch illnesses from animals, the viruses that cause these illnesses in people are different from the ones that cause them in animals [1]. In fact, animals can catch flu and other illnesses from humans, but humans cannot catch these same illnesses from animals [2]. Scientists believe this is due to how animals' bodies are built and the way they interact with the world around them [4]. For example, dogs have a higher saliva pH and helpful bacteria in their saliva that allow them to eat bacteria that would normally make humans sick [3]. Additionally, most illnesses that humans contract do not spread to animals [3].