What Diseases Can Squirrels Transmit to Humans? Since squirrels rarely bite unless they've been cornered or feel threatened, the pests are typically able to coexist with humans with little issue. However, they do carry and transmit a handful of diseases, which makes their presence undesirable and occasionally dangerous: Salmonellosis - Salmonella bacteria found in their droppings causes diarrhea, abdominal cramps, and fever. Lyme disease - spread by the ticks squirrels carry and symptoms include nerve pain, stiffness, and inflammation of the brain or spinal cord. Tularemia - an unpleasant condition that brings about swollen lymph nodes and ulcers. Leptospirosis - symptoms include fever, headache, vomiting, jaundice, and rash. Rabies - though rare, sometimes squirrels pass this virus onto humans via biting or scratching.