All dogs can get all dog diseases. That said, Chihuahuas are prone to becoming overweight or obese. Obesity can not only shorten their lifespan, it may also make other diseases worse. Other conditions they're predisposed to include periodontal disease, heart disease, orthopedic problems with their hips and knees, cataracts, corneal ulcers, bladder stones, cryptorchidism (failure of one or both testicles to descend—this can lead to cancer if not addressed), neurological issues (usually something they are born with), pregnancy issues, and tracheal collapse.