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2. Parasitic diseases and their laboratory investigation
Parasites requiring special methods and/or sampling techniques are listed separately; others are listed under general headings. All are listed in alphabetical order below; select a link to view the related information - you will be able to return to this list.
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Amoebiasis
Intestinal amoebiasis/ amoebic dysentery and invasive amoebiasis
Organisms investigated: Entamoeba histolytica (pathogenic) or Entamoeba dispar (non-pathogenic)
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| Diagnosis: |
formol-ether concentration and microscopical examination of faeces for cysts
direct microscopy of fresh faeces /pus for trophozoites
amoebic culture from faeces or pus
Specific antigen ELISA for the differentiation of E. histolytica from E. dispar from faeces, pus and culture
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| Specimens: |
faeces in plain container for concentration and culture
fresh faeces or rectal scrapings for trophozoite investigation to be carried out within 1 hour of sample being taken - please inform laboratory in advance
pus from liver or lung abscess for microscopy and culture*
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* Please telephone laboratory for advice before taking sample.
Free living amoebae
Granulomatous amoebic encephalitis (GAE)
Primary amoebic meningoencephalitis (PAM)
Causative organisms; Acanthamoeba sp., Balamuthia sp. (GAE), Naegleria fowleri (PAM)
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| Diagnosis: |
microscopy and culture
serology for antibodies (IFAT)
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| Specimens: |
CSF for culture and antibodies
serum (1ml) for antibodies
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NB These infections require urgent diagnosis; telephone advice should be obtained as soon as infection is suspected.
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Amoebic keratitis
Causative organism Acanthamoeba spp
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| Diagnosis: |
microscopy and culture
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| Specimens: |
contact lens and/or wash fluids
corneal scrapes
submitted cultures
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NB Culture media and a method sheet are available on request.
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Babesiosis
Causative organism Babesia spp.
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| Diagnosis: |
microscopical examination of thin and thick blood films for parasites stained with Giemsa and Field's
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| Specimens: |
2 thin (methanol-fixed) and 2 thick (unfixed) blood film sent in a slide container.
Blood should be taken at peak of parasite density as indicated by fever; however parasites may be found in the absence of fever and the examination of blood films should NOT be delayed. Repeat blood films may be necessary to demonstrate infection.
Blood should be taken into EDTA and films made with a minimum of delay.
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| NB Travel history and splenic status is important in the diagnosis of this infection. |
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Cryptosporidiosis
Causative organism Cryptosporidium spp.
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| Diagnosis: |
Microscopy after acid fast staining of faecal smears using a modified Ziehl-Neelsen stain or fluorescent microscopy after phenol auramine staining. Both for detection of oocysts.
immunochromatographic rapid antigen test
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| Specimens: |
faeces in a plain container or fixed in SAF (or less suitable, formalin)
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Cyclosporiasis
Causative organism Cyclospora cayetanensis.
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| Diagnosis: |
microscopical examination of faecal smears stained by modified Ziehl-Neelsen for oocysts and direct microscopy following formol-ether concentration
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| Specimens: |
faeces in plain container
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NB up to 3 specimens may be required to exclude Cyclospora cayetanensis due to the intermittent nature of oocyst excretion
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Enterobiasis
Threadworm or Pinworm
Causative organism Enterobius vermicularis
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| Diagnosis: |
microscopical examination for ova
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| Specimens: |
adhesive tape smear of perianal skin
perianal swab
faeces in clean container (low sensitivity)
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Adhesive tape or swab preferred.
Cut a 10cm strip of sellotape, or similar, and press middle 3-5cm firmly against the right and left perianal folds, sticky side down. Stick tape onto a microscope slide and place in a slide box.
or
Moisten a swab in sterile saline and repeatedly roll over the whole of the perianal area; break off into a small volume of saline in a sterile universal.
Carry out either procedure first thing in the morning before bathing or defaecation. Repeated samples over 4 to 6 consecutive days may be necessary to exclude diagnosis.
BEWARE eggs are highly infectious and resistant to drying!
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Filariasis
Of particular importance are Loa loa, Wuchereria bancrofti. Brugia malayi, Onchocerca volvulus
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| Diagnosis: |
membrane filtration and microscopical examination of peripheral blood for microfilaria (except O. volvulus)
examination of skin snips for microfilariae of O. volvulus
examination of histological material for adults
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| Specimens: |
10 - 20 ml of citrated (preferred anticoagulant) blood (observe periodicity if known, if not take at any time)
for Loa loa take sample between 12 noon and 2 pm
for W. bancrofti take around midnight
skin snips for O. volvulus placed into physiological saline
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Advice should be sought before taking skin snips.
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Giardiasis
Causative organism G. intestinalis (syn., G Giardia lamblia. duodenalis)
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| Diagnosis: |
microscopy of fresh faeces for trophozoites and cysts
formol-ether concentration and microscopical examination for cysts
immunochromatographic rapid antigen test
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| Specimens: |
faeces in plain container
if fresh and for trophozoites, examination should be carried out within 4 hours of specimen being produced.
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NB Due to the intermittent nature of cyst shedding it may be necessary to examine 3 or more samples collected on alternate days to exclude a diagnosis.
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Hydatid infection
Causative organisms, Echinococcus granulosus and E. vogeli for cystic hydatid and E. multilocularis for alveolar hydatid.
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| Diagnosis: |
microscopical examination for hooks and protoscolices in hydatid sand
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| Specimens: |
fluid/contents of cysts
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NB advice from a centre expert in the management of hydatid disease should be sought before considering aspiration of a cyst as leakage of fluid may cause further dissemination or an anaphylactic reaction.
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Insects and other arthropods
Living insects, ticks and mites for identification should be sent in a plain tube without fixation.
If specimen is not living then it should be sent in 70% ethanol.
Larvae (maggots) etc. should be sent live if possible, or in 70% ethanol .
Where specimen has been excised from patient and there is a risk of infection, then specimen should be fixed in 10 buffered formalin (as used for histology) or 10% formol water/saline, then rinsed in distilled water and transferred to 70% ethanol.
Allow specimen to remain intact if possible, giving full clinical details including travel history and site of extraction if relevant.
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Intestinal parasitic infections with helminths and protozoa (general)
A wide range of nematodes, cestodes, trematodes and protozoa are dealt with; some are listed individually e.g. amoebiasis, cryptosporidiosis, cyclosporiasis, giardiasis, microsporidiosis, schistosomiasis.
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| Diagnosis: |
macroscopical examination of faeces for adult worms and segments
direct microscopy of fresh faeces for trophozoites
formol-ether concentration of faeces and microscopy for ova, cysts and larvae
iron-haematoxylin staining and microscopy of SAF-fixed faeces for protozoal trophozoites
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| Specimens: |
faeces in plain container for adult worms, segments and concentration
SAF fixed faeces for trophozoites (especially suitable when a fresh sample is not practical and for fragile organisms e.g. Dientamoeba fragilis
fresh faeces for trophozoites
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NB It may be necessary to submit 3 samples collected on alternate days to exclude a diagnosis.
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Leishmaniasis
Visceral and Cutaneous leishmaniasis
Causative organism Leishmania spp. (several species involved in both forms of the disease
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| Diagnosis: |
microscopy of stained marrow/spleen/liver impression smears.
histological examination of tissue sections for presence of parasites
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This laboratory only performs microscopy of impression smears or tissue sections.
For a full investigation of cutaneous or visceral leishmaniasis please contact the Department of Clinical Parasitology at the Hospital for Tropical Diseases, telephone number 0845 155 5000 ext. 5418, who offer range of investigations including culture, serology (visceral) and PCR
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Malaria
of human importance are Plasmodium falciparum (malignant tertian), P. vivax (benign tertian), P. ovale (benign tertian) and P. malariae (quartan)
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| Diagnosis: |
microscopical examination of thin and thick blood films for malaria parasites and for species determination using Giemsa and Field's stain
parasitaemia estimation to indicate severity of infection and effectiveness of treatment
immunochromatographic techniques for the detection of malaria antigen in blood
PCR for malaria confirmation and species determination when required
serology is no longer performed by this laboratory, but may be obtained from the Department of Clinical Parasitology at the Hospital for Tropical Diseases, telephone number 0845 155 5000 ext. 5413
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| Specimens: |
2 thick (unfixed) and 2 thin (methanol fixed) ready made films sent in a slide box and a sample of EDTA blood (minimum 100 microlitres) for PCR
Blood is ideally collected during fever, however parasites are found at all stages of the infection and therefore blood films without delay are mandatory in all cases of suspected malaria. If the first films are negative, blood should be taken and films made and checked at least two times over the first 24 hours and further films examined every 12 hours after that if strongly clinically indicated.
Blood taken into anticoagulant (EDTA should be used) should have films made as soon as possible to minimise morphological changes in the parasites, and certainly within 2 hours. However, parasites can be detected even after extended exposure to anticoagulant (exceptionally up to 24 hours) and no sample will be rejected unexamined.
1 -2 ml of whole blood (EDTA) for antigen detection methods
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NB serology has no place in the diagnosis of acute malaria.
BLOOD FILMS ARE ESSENTIAL IN CASES OF ACUTE FEVER OR OTHER SYMPTOMS WHERE MALARIA IS SUSPECTED
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Microsporidiosis
Causative organisms including Enterocytozoon bieneusi, Encephalitozoon intestinalis
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| Diagnosis: |
microscopical examination of strong trichrome stained faecal/urine smears for microsporidial spores
Histology of bowel biopsy tissues from other sites of the body
Electron microscopy (EM) of biopsies
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| Specimens: |
faeces
urine
biopsy material fixed in buffered formol-saline for histology
Special fixation required for EM, please contact laboratory in advance
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Schistosomiasis
Bilharzia
Parasite: Schistosoma mansoni, S. haematobium, S. japonicum, S. intercalatum, and S. mekongi
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| Diagnosis: |
formol-ether concentration and microscopy of faeces for ova
microscopical examination of urine after concentration or filtration
microscopical examination of squash preparations of tissue for ova
histology
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| Specimens: |
faeces in plain container
urine in a plain, sterile container.
either a midday urine specimen (between 10.00 and 14 00hrs) or a 24-hour collection of terminal urine
NB peak egg excretion occurs between noon and 3pm, eggs may be found trapped in the blood and mucus in the terminal portion of the urine specimen.
tissue - unfixed biopsy material (rectal, sigmoid, bladder) material for squashes and histology.
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NB when screening after return from an endemic area, it is advisable to examine both urine and faeces.
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Trichinosis
Causative organism Trichinella spiralis
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| Diagnosis: |
microscopical examination for larvae by squash or/and histology
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| Specimens: |
unfixed/fixed muscle biopsy
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NB it is widely considered unnecessary to perform biopsy for the diagnosis of this parasite, the alternative being serology (performed at HTD)
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Trypanosomiasis - African
Sleeping sickness
Causative organisms Trypanosoma brucei rhodesiense, T.b. gambiense
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| Diagnosis: |
microscopical examination of blood films for trypomastigotes
microscopical examination of cerebrospinal fluid where neurological involvement *
concentration techniques - DEAE column or microhaematocrit
serology is no longer performed by this laboratory, but may be obtained from the Department of Clinical Parasitology at the Hospital for Tropical Diseases, telephone number 0845 155 5000 ext. 5413
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| Specimens: |
thin and thick blood films for microscopy
CSF
Heparinised blood for concentration techniques
1ml serum for IFAT
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* Advice should be sought before attempting to take CSF sample for diagnosis, due to risk of introducing trypanosomes into the CNS from the blood
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Trypanosomiasis - South American
Chagas' Disease
Causative organism Trypanosoma cruzi
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| Diagnosis: |
blood film in the acute stage (extremely rarely seen in the UK)
serology by IFAT or ELISA for antibodies in the chronic phase (occasionally seen in the UK)
xenodiagnosis (using laboratory reared vector)
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| Specimens: |
1ml serum for IFAT or ELISA
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NB it is not usual to look for trypanosomes in blood or other fluids, however it is possible to perform xenodiagnosis with prior arrangement, please contact the reference laboratory for details. Serology is the usual method for diagnosis
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