The first definitive human cases were reported in the early 1970's. In contrast to PAM, Acanthamoeba infections are usually associated with chronically ill, immunocompromised, or other debilitated patients. The portal of entry for Acanthamoeba is not known but believed to the either the lungs, skin or eyes. The onset of symptoms is often insidious and the clinical manifestations include subtle headache, personality changes and slight fever. GAE has a prolonged clinical course and can take weeks to months to progress to coma and death.
Diagnosis is difficult and usually done at autopsy.
Acanthamoeba exists as either an ameboid trophozoite or a cyst and both stages can be found in histological specimens . The cysts have a three-layered wall, a wrinkled appearance and are extremely resistant to desiccation . In histological preparations the trophozoites of Acanthamoeba are very similar to Naegleria trophozoites and cannot be distinguished on morphological criteria. It was first reported in 1973 and until the mid-1980's was exceeding rare and usually associated with ocular trama. The number of cases has increased since 1985 and it is estimated that there has been more than 700 cases as of 1996.