Clinical Diagnostic Parasitology Laboratory (CDPL)

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Blood parasites

Malaria

Samples are screened using thick blood films. Thin films are examined on positive samples. If P.falciparum is found, parasitaemia is performed. Rapid diagnostic tests (RDTs) are available.

Sample requirements:

• Thick and thin films (unstained but thin-film methanol fixed) made from a fresh blood sample.
• Thick and thin films made and stained from a fresh blood sample.
• Original EDTA sample.

Key factors affecting tests:

Malaria parasites collected into anticoagulants such as EDTA deteriorate and morphological changes occur within a few hours.

Complete the malaria reference laboratory form and the report form, and enclose them with the sample. Include sample date and patient travel history.

Microscopic image showing red blood cells infected with malaria parasites. Several cells display dark-stained ring forms of Plasmodium species within the pale circular red blood cells, typical of malaria infection.

Filaria

A definitive diagnosis of filariasis is usually made by the demonstration of microfilariae in the peripheral blood. The exception to this is Onchocerca volvulus which is diagnosed by demonstration of microfilariae in skin snips.

Blood filariasis:

A wet preparation is examined and samples are filtered using a Nuclepore membrane. If  W.bancrofti is suspected, blood collection time should be between 22.00 and 02.00. For a Loa loa diurnal blood sample, 12.00 is preferred.

Sample requirements:

  • EDTA blood.
  • Sample size is not critical but ideally it should be between 5ml and 10ml.
  • The larger the sample filtered, the greater chance of demonstrating the microfilariae.

Key factors affecting tests:

Sheathed microfilariae may ex-sheath if the blood sample is not examined within two to three days of collection. All microfilariae may last up to 72 hours in EDTA blood before disintegration.

Scientific illustration of a parasitic roundworm showing its elongated, coiled body with detailed internal structures. The drawing highlights the worm’s smooth outer surface and looping form, typical of nematode anatomy.

Trypanosomiasis

Thick blood films are used and concentration technique is applied if films are negative. Blood samples for concentration should be examined on the day of collection.

Sample requirements:

  • Unstained thick/thin films.
  • EDTA blood sample.

Key factors affecting tests:

Trypanosomes may not survive for more than a few hours in EDTA tube, so posted samples can show false-negative results.

If a CSF sample is to be examined for trypanosomes, this should ideally be done within 20 minutes of L.P.

3D medical illustration showing a Trypanosoma parasite among red blood cells. The elongated, spiral-shaped parasite with a visible nucleus and flagellum contrasts against the smooth, disc-shaped red blood cells, representing the cause of African trypanosomiasis (sleeping sickness).

Babesia

Sample requirements:

  • Thick and thin films (unstained but thin-film methanol fixed) made from a fresh blood sample.
  • Thick and thin films made and stained from a fresh blood sample.
  • Original EDTA sample.
3D illustration showing a red blood cell infected with Babesia parasites. The image depicts four teardrop-shaped protozoa with purple nuclei arranged in a cross-like formation inside the red blood cell, characteristic of Babesia infection.

Borrelia

Sample requirements:

  • Thick and thin films (unstained but thin-film methanol fixed) made from a fresh blood sample.
  • Thick and thin films made and stained from a fresh blood sample.
  • Original EDTA sample.
Microscopic image showing spiral-shaped Borrelia bacteria under dark-field illumination. The bright, corkscrew-like organisms stand out against a dark blue background, characteristic of spirochete bacteria associated with Lyme disease and relapsing fever.

Leishmania

Sample requirements:

  • Thick and thin films (unstained but thin-film methanol fixed) made from a fresh blood sample.
  • Thick and thin films made and stained from a fresh blood sample.
  • Original EDTA sample.
3D medical illustration showing Leishmania parasites among red and white blood cells inside a blood vessel. The elongated, purple, flagellated protozoa stand out against the red cells, representing the causative agent of leishmaniasis.