The most common means of transmission is by exposure to infected fleas. The initial symptom is usually a swollen, inflamed and tender lymph gland in the body near where the infected flea bit the person. Fever is usually present. The disease may progress to a generalized blood infection that may result in pneumonia. People with pneumonic plague may transmit the disease to other people when coughing.
Symptoms usually begin within one to six days after exposure to the plague bacteria.
Immunity after plague recovery is variable, and may not provide complete protection. Certain antibiotics such as streptomycin, tetracyclines and chloramphenicol are effective in treating the disease. Animals in Montana may carry plague. Care should be taken by hunters and campers to avoid fleas from wild animals. Pets should be defleaed.