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Persistence of acanthamoeba antigen following acanthamoeba keratitis
Y F Yang1, M Matheson, J K Dart
1Moorfields Eye Hospital, London, UK.
Aim:
To investigate the hypothesis that persistent corneal and scleral inflammation following acanthamoeba keratitis is not always caused by active amoebic infection but can be due to persisting acanthamoebic antigens
Methods:
24 lamellar corneal biopsy and penetrating keratoplasty specimens were obtained from 14 consecutive patients at various stages of their disease and divided for microscopy and culture. Histological sections were immunostained and screened for the presence of Acanthamoeba cysts by light microscopy. Cultures were carried out using partly homogenised tissues on non-nutrient agar seeded with E coli. Clinical data were obtained retrospectively from the case notes of these patients.
Results:
Of the 24 specimens, 20 were obtained from eyes that were clinically inflamed at the time of surgery. Acanthamoeba cysts were present in 16 (80%) of these 20 specimens, while only five (25%) were culture positive. Acanthamoeba cysts were found to persist for up to 31 months after antiamoebic treatment.
Conclusion:
These findings support the hypothesis that Acanthamoeba cysts can remain in corneal tissue for an extended period of time following acanthamoeba keratitis and may cause persistent corneal and scleral inflammation in the absence of active amoebic infection. In view of these findings, prolonged intensive antiamoebic therapy may be inappropriate when the inflammation is due to retained antigen rather than to viable organisms
Insights
Persistent inflammation after acanthamoeba keratitis may stem from residual Acanthamoeba cysts, not active infection. These cysts can remain in corneal tissue for months, potentially causing ongoing inflammation without viable organisms.
Area of Science:
- Ophthalmology
- Infectious Diseases
- Microbiology
Background:
- Acanthamoeba keratitis (AK) is a severe corneal infection.
- Persistent inflammation post-AK treatment poses a clinical challenge.
- The role of residual Acanthamoeba antigens in chronic inflammation is not fully understood.
Purpose of the Study:
- To investigate if persistent inflammation in AK is due to active infection or remaining Acanthamoeba antigens.
- To determine the duration of Acanthamoeba cyst persistence in corneal tissue.
Main Methods:
- Analysis of 24 corneal biopsy and keratoplasty specimens from 14 AK patients.
- Histological examination with immunostaining for Acanthamoeba cysts.
- Microbiological culture of tissue samples to detect viable Acanthamoeba.
Main Results:
- Acanthamoeba cysts were detected in 80% of inflamed specimens.
- Only 25% of specimens were culture-positive for viable Acanthamoeba.
- Cysts persisted for up to 31 months post-treatment, indicating long-term presence.
Conclusions:
- Acanthamoeba cysts can persist in corneal tissue long after treatment for AK.
- Persistent inflammation may be caused by these residual cysts (antigens) rather than active infection.
- Prolonged antiamoebic therapy might be unnecessary if inflammation is antigen-driven.