Do humans contract more physical sicknesses and diseases than animals do?
The issue is more a matter of research focus than anything else. People care more about people than other organisms. Hence, more money is available for research and more money goes around in medical healthcare than in veterinary care. Research and drug development, in turn, focus on where the money is. The diseases of animals other than humans have simply not been investigated in such detail as in humans, because less effort has been done to document them as exhaustively as has been done for humans. Thus, when something is not in the literature, that doesn't mean it doesn't exist.