In the Pacific states, California ground squirrel fleas are the most common source. Domestic cats can be infected by fleas or by eating infected wild rodents and can be a direct source of infection to people. Dogs rarely suffer severe illness and have yet to be shown to be sources of infection for humans. When a person is bitten by an infected flea or is infected by handling an infected animal, the plague bacteria move through the bloodstream to the lymph nodes. Other symptoms are fever, headache, chills, and extreme tiredness.
Some people have gastrointestinal symptoms.
Signs and symptoms are fever, chills, tiredness, abdominal pain, shock, and bleeding into the skin and other organs. Untreated septicemic plague is usually fatal. Pneumonic plague, or plague pneumonia, develops when the bacteria infect the lungs. People with plague pneumonia have high fever, chills, difficulty breathing, a cough, and bloody sputum. Plague pneumonia is considered a public health emergency because a cough can quickly spread the disease to others.