Acanthamoeba keratitis: an increasingly common infectious disease of the cornea

Acanthamoeba, a free-living protist that is ubiquitously distributed in the environment, is also an opportunistic pathogen and a host of phylogenetically distinct bacteria, fungi, viruses, and other protists. Acanthamoeba causes keratitis, a sight-threatening, painful, and difficult-to-treat ocular infection that is linked to contact-lens wear.1 The pathogen can also cause infections of the CNS and skin, which are associated with immunodeficiency,2 although these types of infection are less common than keratitis. Acanthamoeba has been recovered from the nasal mucosa and throat of healthy individuals, and might be part of normal human microbiota.3 Acanthamoeba keratitis is a rare eye disease, accounting for only 2% of corneal infections, but cases are increasing. Infamous for its resilience against anti-protozoal armamentaria, disinfectants, and harsh environments, Acanthamoeba poses a challenge to clinicians caring for patients infected with the pathogen. The lifecycle of Acanthamoeba includes an active trophozoite and a quiescent cyst stage, which can remain viable for several years.4 Acanthamoeba cysts can survive in corneal tissue and result in recurrent disease. Coinfections of Acanthamoeba and other pathogens such as Pseudomonas aeruginosa or Fusarium spp are reported in keratitis and could be due to the intracellular carriage of these microbes within the infecting Acanthamoeba.