Superwanda, it is my understanding that there are different phases of this disease as HRP mentioned. Normally there it can start as a severe form (acute as she mentioned) and can come back cyclically which may not be as severe.
Clinical and laboratory findings
Clinical disease in dogs is most often associated with the acute, bacteremic phase of infection. The duration and severity of the clinical findings during the acute phase of the disease can vary greatly and can last from one to several days.5
Chronic, subclinical, persistent infections have been documented for more than five-and-a-half months in dogs experimentally inoculated with a Swedish isolate of A. phagocytophilum and for almost one year in dogs inoculated with a human isolate from New York (NY18).6,7 However, no confirmed reports of clinical disease occurring in animals known to be chronic carriers exist. It is unknown whether a chronic carrier state can later result in chronic disease.