Free-living Amoebae
This section on free living amoebae refers to human infection with any of the following amoebae:
- Naegleria fowleri,
- Acanthamoeba spp.
- Balamuthia mandrallis.
Naegleria fowleri is a free living amoeba found in warm, fresh water. Infection is contracted via inhalation of infected water, often during recreational activities. It causes primary amoebic meningoencephalitis which is a rapidly progressive, haemorrhagic meningocephalitis. Symptoms resemble bacterial meningoencephalitis with fever, headache, altered mental state, seizure and coma. The disease follows a fulminant course with an exceptionally high associated mortality. Trophozoites can be visualised in the CSF.
Acanthamoeba spp and Balamuthia mandrallis cause granulomatous amoebic encephalitis. Infection is more common in immunocompromised hosts and aquisition of the amoeba is via inhalation of the cysts from the environment. The syndrome follows a sub-acute course with a headache, low grade fever, focal neurological deficit and behavioural change, typically evolving over a period of weeks and months. Examination of CSF or brain tissue is usually required for diagnosis.
If infection with free living amoebae is suspected, please discuss the case with the Parasitology consultant or registrar.
Diagnosis of primary amoebic meningoencephalitis or granulomatous amoebic encephalitis by Microscopy
- Sample type: CSF – please send a fresh sample (as much as you are able to spare) without fixative for microscopy. CSF microscopy may detect Naegleria fowleri, but is much less sensitive for the detection of Acanthamoeba or Balamuthia mandrillaris.
Diagnosis of primary amoebic meningoencephalitis or granulomatous amoebic encephalitis by Culture
- Sample type: CSF or brain tissue without fixative and received in the laboratory as soon as possible.
Culture is available for Naegleria fowleri and Balamuthia mandrillaris on discussion with the Consultant Parasitologist or Parasitology registrar.
Diagnosis of of primary amoebic meningoencephalitis or granulomatous amoebic encephalitis by PCR
- Sample type: CSF or brain tissue without fixative and received in the laboratory as soon as possible.
A PCR is available upon discussion with the Consultant Parasitologist or registrar for the diagnosis of Naegleria fowleri, Balamuthia mandrillaris and Acanthamoeba spp.
Molecular detection of free living amoebae is not currently validated as a clinical test or covered under our accreditation by UKAS. Please phone the Consultant Parasitologist or registrar to discuss its relevance to patient management.
Diagnosis of amoebic keratitis by culture and PCR for Acanthamoeba spp.
Samples should be referred directly to:
Diagnostic Parasitology Laboratory
The London School of Hygiene and Tropical Medicine. Keppel Street, London WC1E 7HT
DX address: HPA Malaria Reference Lab DX 6641200
Tottenham Crt RD92WC
Tel: +44 (0)207 927 2427 Fax: +44(0)207 637 0248
This is best diagnosed by sending corneal scrapings suspended in a small volume (0.2ml) sterile saline or sterile distilled water.
They can also perform culture from contact lenses or fluids; isolation from these specimens, whilst suggestive, does not necessarily implicate the amoeba as causing the patient’s symptoms.
Request forms can be found at: http://www.parasite-referencelab.co.uk/