The telltale signs of a problem are a fever and persistent pain that's disproportionate to the injury: Sometimes it's "the worst pain they've ever experienced, " he said.

CNN: Surviving a flesh-eating disease

Symptoms include mild headaches, muscle pain, fever, a persistent cough and sometimes vomiting and diarrhoea.

BBC: Legionnaires' Disease bacteria

Symptoms are similar to those felt by humans: a persistent cough, thick nasal discharge and in severe cases, fever and respiratory distress.

WSJ: A New Breed of Flu Shot to Avoid Getting Sick as a Dog