An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment.

Free-living amoebae of the genus Acanthamoeba are causal agents of a severe sight-threatening infection of the cornea known as Acanthamoeba keratitis. Moreover, the number of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Interestingly, Acanthamoeba keratitis has remained significant, despite our advances in antimicrobial chemotherapy and supportive care. In part, this is due to an incomplete understanding of the pathogenesis and pathophysiology of the disease, diagnostic delays and problems associated with chemotherapeutic interventions. In view of the devastating nature of this disease, here we present our current understanding of Acanthamoeba keratitis and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be potential targets for improved diagnosis, therapeutic interventions and/or for the development of preventative measures. Novel molecular approaches such as proteomics, RNAi and a consensus in the diagnostic approaches for a suspected case of Acanthamoeba keratitis are proposed and reviewed based on data which have been compiled after years of working on this amoebic organism using many different techniques and listening to many experts in this field at conferences, workshops and international meetings. Altogether, this review may serve as the milestone for developing an effective solution for the prevention, control and treatment of Acanthamoeba infections.

Treatment of early Acanthamoeba keratitis with alcohol-assisted epithelial debridement.

PURPOSE: To study the safety and efficacy of treating early-stage Acanthamoeba keratitis (AK) with 20% alcohol-assisted epithelial debridement. METHODS: Four consecutive patients (2 wearing orthokeratology lenses and 2 wearing soft contact lenses) presented with pseudodendrites, radial keratoneuritis, and epithelial irregularities. Using a technique similar to laser-assisted subepithelial keratomileusis, we performed alcohol-assisted full-thickness debridement of the corneal epithelium and sent portions for smears, histopathologic and ultrastructural examinations, and culture for evidence of Acanthamoeba. Patients were then started on topical propamidine isethionate and 0.02% polyhexamethylene biguanide. RESULTS: Immediately after debridement, minimal underlying anterior stromal infiltrate or haze was seen. Dosages of antiamoebic agents were tapered as corneal defects reepithelialized (in 1-3 weeks) with no evidence of post-debridement corneal infection. At the final follow-up, 1 cornea was transparent and the other 3 corneas had very faint subepithelial haze. Cultures of all epithelial debridement specimens yielded Acanthamoeba trophozoites and cysts, and histopathologic and electron microscopic examinations revealed Acanthamoeba organisms within corneal epithelial layers. CONCLUSIONS: Alcohol-assisted epithelial debridement facilitates detachment of the full-thickness corneal epithelial layer in a controlled manner and seems to be effective in the treatment of early-stage AK. Unlike the fragile fragmented specimens obtained by mechanical scraping without alcohol soaking, epithelial sheets detached easily and the architectures were well preserved, permitting histopathologic and ultrastructural examinations. Most importantly, 20% alcohol-assisted epithelial debridement did not prevent culturing of Acanthamoeba from the removed epithelial specimens.

Intrathecal administration of p-hydroxymercuribenzoate or phosphoramidon/bestatin-combined induces antinociceptive effects through different opioid mechanisms.

The antinociceptive effect of intrathecally (i.t.) administered protease inhibitors was tested against capsaicin (800 ng) injected into the dorsal surface of a hindpaw. Both p-hydroxymercuribenzoate (2-8 nmol), a cysteine protease inhibitor, and phosphoramidon (1-4 nmol), an endopeptidase 24.11 inhibitor in the presence of bestatin (0.25 nmol) an aminopeptidase inhibitor, administered i.t. 60 min prior to the injection of capsaicin produced a dose-dependent reduction of the capsaicin-induced paw licking and biting response. p-Hydroxymercuribenzoate (4 nmol)-induced antinociception was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. On the other hand, phosphoramidon (4 nmol) /bestatin-induced antinociception was significantly antagonized by naltrindole, but not by nor-binaltorphimine. The results indicate that the antinociceptive effect of p-hydroxymercuribenzoate may be due to the inhibition of a cysteine protease degrading endogenous dynorphins whereas phosphoramidon in the presence of bestatin blocks the degradation of enkephalins.