Clinical Use
Detection of Acanthamoeba
Background
Acanthamoeba species are free-living amoeba found commonly in soil, water, and air. Infection is relatively rare, but when it does occur it can present as amoebic keratitis and in some cases encephalitis.
Amoebic keratitis is associated with wearing contact lenses or ocular trauma. Presenting with severe pain, photophobia, tearing, blepharospasm, conjunctivitis, and blurred vision. If not treated promptly, it may lead to corneal ulceration, and eventually to blindness. Amoebic DNA is typically detected from corneal scrapings or contact lens fluid/storage cases via Polymerase Chain Reaction (PCR). However, Acanthamoeba spp. may be isolated from contact lens fluid from individuals with no signs or symptoms of disease.
Patient preperation
- Use aseptic technique.
- Collect specimens in appropriate CE marked leak proof containers and transport in sealed plastic bags.
- Collect swabs into appropriate transport medium and transport in sealed plastic bags.
- Compliance with postal, transport and storage regulations is essential.
Specimen requirements
Appropriate validated sample types:
- Corneal scrape
- Corneal swabs
- Contact lens cleaning fluid
- CSF in meningoencephalitis.
Be aware:
Scalpel blades will NOT be accepted and will be rejected
For liquid samples: 200 µL is the minimum required for testing, preferably 500 µL to facilitate additional extraction and testing.
- For tissue samples: please send a matchstick head sized piece of the appropriate tissue in a sterile container.
- Bilateral eye swabs should be clearly labelled ‘left’ and ‘right’ eye.
Limitations & restrictions
Superficial swabs, although not ideal, may be all that is available, but deep-seated samples are best and if available should be sought.
Molecular assays such as PCR cannot distinguish between infection and environmental contamination. Molecular assays are particularly sensitive and can detect DNA present from the environment. All positive results need to be interpreted with the clinical signs and symptoms. If there is concern or a requirement for further advice, please feel free to contact the Duty Microbiologist via switchboard.
Low volume samples may be diluted and tested, but reports will bear a caveat regarding the potential effect on assay sensitivity.
Please note:
Sending sufficient sample is imperative when requesting multiple tests
Turnaround time
Two working days on receipt to reference laboratory. Weekends and bank holidays are not included in the TAT calculation. Eye, and postmortem samples may incur some delay due to the nature of the sample type and Acanthamoeba PCR requires a manual extraction process which can lead to increased likelihood of delay.
Analysing laboratory
Micropathology Ltd, Venture Centre, University of Warwick Science Park, Sir William Lyons Road, Coventry, CV4 7EZ
For more information on Micropathology please visit their website: https://www.micropathology.com/
Additional information
The Acanthamoeba DNA identification is a UKAS accredited assay, providing the correct volume and sample type is provided. Anything outside of the scope which is laid out within this document may affect/ invalidate the results.
Additional information provided by the reference laboratory is shown on their website with list of tests, sample types, and turnaround times available: https://www.micropathology.com/Tests?testnamesearch=