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Leishmaniasis


Leishmaniasis is an obligate intracellular protozoal infection. Human leishmaniasis can be caused by multiple species of Leishmania, classically divided into Old World (Eastern Hemisphere) and New World (Western Hemisphere).

It is transmitted by the bite of a sandfly and may be classified as Cutaneous, Mucosal (previously known as Mucocutaneous) and Visceral according to travel history and clinical presentation.

Cutaneous leishmaniasis is the most common form, resulting in skin nodules and often subsequent ulceration. Visceral leishmaniasis usually affects the spleen, liver, and bone marrow, and can be fatal if left untreated. Patients usually present with fever, weight loss, splenomegaly, hepatomegaly and pancytopenia.

Mucosal leishmaniasis can be a sequela of cutaneous leishmaniasis acquired in Latin America (most commonly, but not restricted to, the sub-genus L. Viannia).

The different species are morphologically indistinguishable, but can be differentiated by other diagnostic techniques detailed below.

Please do not send unfixed samples over the weekend (it is better to store samples in the fridge over the weekend before sending to reduce bacterial/ fungal growth).

Please send a travel history with all specimens (this is essential for species determination).


Diagnosis of Cutaneous and Mucosal Leishmaniasis by microscopy

  • Sample type: Punch Biopsy – Take from the edge of the lesion. Ideally placed in a small volume of sterile saline in a suitable sterile container (DO NOT FREEZE AND WHERE POSSIBLE AVOID FIXING SINCE THIS WILL AFFECT CULTURE AND PCR – see below).

If histology is required, please take a second biopsy, or cut original biopsy in half vertically through the epidermis and tissue. Put half in sterile saline for Parasitology and half in formal saline for histology.

  • Sample type: Slit skin smears; Take from the edge of the lesion, onto a slide. Air dry and then fix with methanol.


Diagnosis of Visceral Leishmaniasis by microscopy

  • Sample type: Bone marrow or Splenic aspirate – please provide two methanol fixed slides and a small amount (less than 1ml) of sample in a sterile EDTA tube ( e.g. Vacutainer purple top).
  • Sample type: e.g. Biopsies – Microscopy based diagnosis of Leishmaniasis may be performed on sample types other than bone marrow or splenic aspirate under consultation with the Department of Clinical Parasitology. Please phone for advice if considering such an investigation.

In cases of suspected visceral Leishmaniasis, an attempt should always be made to find Leishmania from aspirated/ trephine material (bone marrow or spleen) – contact laboratory for advice.

  • Sample type: Histology Sections – if histology is required, please contact the Department of Clinical Parasitology so this may be actioned as a referral test.

 

Diagnosis of Cutaneous, Mucosal and Visceral Leishmaniasis by PCR

PCR can be used to detect (with very high sensitivity) and identify the species of Leishmania when an accurate travel history is provided. Contact microscopy section of laboratory for advice.

  • Sample type: Unfixed tissue – see above for information on Biopsies, Bone marrow or Splenic aspirate and Slit skin smears. In addition Leishmania PCR may also be performed on additional unfixed samples such as Vitreous fluid and BAL under consultation with the Department of Clinical Parasitology. Please phone for advice if considering such an investigation.
  • Sample type: Fixed tissue – please send at least 6 normal thickness sections in a small screw capped or Eppendorf (snap lip) tube.
    The Fixation of tissue containing DNA is known to significantly decrease the sensitivity of PCR based diagnostics and therefore we request unfixed tissue where possible.


Diagnosis of Visceral and Mucosal Leishmaniasis by serology

  • Sample type: a minimum or 0.5ml of serum is required.

Note: negative serology does NOT exclude the diagnosis of visceral leishmaniasis in heavily immunosuppressed patients.

Serology is NOT helpful in the diagnosis of cutaneous infections.

Serology is usually positive in mucosal leishmaniasis, except in early cases.

A Direct Agglutination Test (DAT) for Leishmaniasis using formalinised promastigotes of Leishmania donovani stained with Coomassie blue is the standard serology test and a rapid test (rK39) antibody detection assay is also provided. The DAT is considered positive when the titre exceeds 1600 and in visceral leishmaniasis titres may rise to 51,000 or above. The rK39 antibody test is reported as positive or negative, with no titre available.