July 26th – Ehrlichia chaffeensis is an obligate intracellular gram-negative species of rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick (Amblyomma americanum). It is the causative agent of human monocytic ehrlichiosis. Genetic studies support the endosymbiotic theory that a subset of these organisms evolved to live inside mammalian cells as mitochondria to provide cellular energy to the cells in return for protection and sustenance. ATP production in the rickettsia is biochemically identical to that in mammalian mitochondria. Human monocytic ehrlichiosis caused by E. chaffeensis is known to spread through tick infection primarily in the southern, southcentral and mid-Atlantic regions of the United States. In recent years the lone star tick has expanded its range up the East Coast to New England, putting more humans at risk for tick-borne infections. It is named for Fort Chaffee where the bacteria was first discovered in blood samples of infected patients.