Ehrlichia ewingii causes canine granulocytotropic ehrlichiosis. It can also infect humans, who usually have fever, headache, fatigue, and muscle aches within one to two weeks following a tick bite. The vector is Amblyomma americanum, the lone star tick. The disease is usually seen in immunocompromised patients from Missouri, Oklahoma, and Tennessee.
E. ewingii is antigenically similar to E. chaffeensis and E. canis and can only be distinguished from E. chaffeensis by PCR. A total of 302 cases of E. ewingii ehrlichiosis have been reported from 2008 to 2021. Before 2008, E. ewingii cases were included in E. chaffeensis cases because tests did not distinguish them. Morulae are found in granulocytes, not monocytes.
Ehrlichia muris-like is believed to be carried by Ixodes scapularis in Minnesota and Wisconsin. E. muris is found in Japan and Russia. This bacteria has now been formally named E. muris eauclairensis. One to two weeks after a tick bite, symptoms of fever, malaise, headache, lymphocytopenia, thrombocytopenia, and increased liver enzymes appear. PCR is the test of choice.
