Ultrastructural characterization and pathogenicity of Allovohlkamfia spelaea in a murine model: Neuropulmonary infections and therapeutic potential of ellagic acid.

Background: Allovahlkampfia spelaea (A. spelaea) is a free-living amoeba that has recently been recognized to cause Acanthamoeba-like keratitis, the treatment of which is complex. The pathogenic potential of Allovahlkampfia spp. remains unexplored. This study characterized A. spelaea through ultrastructural morphological analysis and investigated the pathogenic potential of the A. spelaea strain KS1, which was isolated from a patient with keratitis, in a murine model, with a focus on neuro-pulmonary infections. Additionally, this study assessed the therapeutic effectiveness of ellagic acid (EA) against tissue damage caused by amoebic infections.

Methods: Immunosuppressed male Wister rats were intranasally inoculated with A. spelaea trophozoites (1 × 10/ml) and divided into control, infected untreated, and infected treated (50 mg/kg EA daily) groups. Histopathological and ultrastructural analyses of brain and lung tissues were conducted by scanning and transmission electron microscopy. Additionally, the therapeutic effects of EA were assessed via comparative tissue pathology.

Results: A. spelaea infection induced A. spelaea-induced neural lesions resembling granulomatous amoebic encephalitis (GAE) in the brain, which was characterized by gliosis, vasculitis, and necrosis, in addition to severe pulmonary damage, including suppurative bronchopneumonia and abscesses. Trophozoites presented with pseudopodia, acanthopodia, and amoebostomes, whereas cysts presented with double-layered walls. EA-treated rats presented nearly normal brain and lung histology, with reduced inflammation and gliosis, highlighting the anti-inflammatory and antioxidant properties of EA.

Conclusion: This study highlights the neurotropic and pulmonary pathogenicity of A. spelaea, with ultrastructures parallel to those of Vahlkampfia spp. and Acanthamoeba spp. Ellagic acid significantly reduces infection-induced damage, underscoring its potential as a therapeutic agent for infections caused by free-living amoebae.