In the upper midwest, the risk of tick exposure is highest from late spring through autumn. The bacteria are transmitted to humans by the bite of infected ticks. The symptoms are generally nonspecific and can range from very mild to very severe illness. Most patients will experience fever, muscle pain, severe headache and shaking chills. Less frequent signs and symptoms include nausea, vomiting, acute weight loss, mental confusion, cough, and skin rash.
Symptoms typically begin between one and three weeks after exposure.
Certain laboratory test results can suggest a diagnosis of ehrlichiosis. These include a low white blood cell count, low platelet count, and an elevation in certain liver function tests. The definitive diagnosis involves specialized blood tests which detect the Ehrlichia agent itself or the presence of antibodies against the bacterium. Tests developed for E. chaffeensis infection will generally not be able to detect an infection with the agent of human granulocytic ehrlichiosis. The disease tends to respond very well to tetracycline type antibiotics like doxycycline.