Leishmania

Biology and morphological forms

Leishmania reproduce by simple division and go through two developmental stages in their life cycle depending on the host.

• Flagellated form (promastigote). Inhabits the gut of the sandfly or artificial nutrient media. Has an elongated, spindle-like shape (10–20 µm in length) with a flagellum at the pointed end, ensuring motility. Contains a nucleus, cytoplasm, kinetoplast, and volutin granules. Amastigotes that enter the vector's body with blood transform into promastigotes within 6–8 days.
• Aflagellated form (amastigote). Found in the mammalian body (including humans). Parasitizes intracellularly within macrophages and cells of the reticuloendothelial system (RES) of the liver, spleen, and lymph nodes. These are small (2–5 µm) round or oval cells without a flagellum. Upon Giemsa staining, the cytoplasm becomes grayish-blue, while the nucleus and kinetoplast turn reddish-purple.

Clinical forms of leishmaniasis

Depending on the species of the pathogen, diseases are classified by the involvement of internal organs or body integument.

Visceral leishmaniasis Characterized by involvement of the RES (liver, spleen, bone marrow, lymph nodes) and the gastrointestinal tract.

• Indian variant (Kala-azar) caused by the L. donovani complex. This is an anthroponosis (the reservoir is human). Characterized by hypergammaglobulinemia, skin darkening due to adrenal involvement, and rashes (leishmanoids).
• Mediterranean-Central Asian variant caused by L. infantum. The reservoir is canids and rodents, with children being most frequently affected. The clinical picture resembles Kala-azar, but the skin becomes pale.

Cutaneous and mucocutaneous leishmaniasis

• Anthroponotic cutaneous leishmaniasis (oriental sore / "annual sore") caused by L. tropica. Incubation lasts for months; a nodule slowly forms on the face and hands, ulcerating after 3–4 months. It scars over about a year.
• Zoonotic cutaneous leishmaniasis (Pendinsky ulcer) caused by L. major (reservoir: rodents). Incubation is short (2–4 weeks), course is acute, and ulcers are weeping (most commonly on the legs).
• Mucocutaneous leishmaniasis (Espundia) caused by L. braziliensis. Found in South and Central America. Characterized by a granulomatous process with deep destruction of the skin and mucous membranes (e.g., "tapir nose" deformity).

Diagnostic methods

The basis of diagnosis is the detection of the pathogen or antibodies against it.

1. Bacterioscopic method (primary): microscopy of smears from ulcers, bone marrow punctates, or lymph nodes. Intracellular amastigotes are sought using Giemsa staining.
2. Culture method: inoculation of material onto NNN medium (containing defibrinated rabbit blood) and incubation for about 3 weeks.
3. Biological assay: inoculation of laboratory animals (hamsters, white mice).
4. Serology: IFA, ELISA (though insufficient specificity is noted).
5. Skin-allergy test: Montenegro test (using leishmanin). Based on delayed-type hypersensitivity, used for epidemiological purposes.

Class and exam questions

What else to study on this topic

• Features of immunity after recovering from leishmaniasis
• Treatment principles: use of pentavalent antimony drugs
• Detailed classification of pathogen complexes (L. mexicana, subgenus Viannia)
• Preventive measures and vaccination with live L. major culture

Other topics in "Flagellates (Leishmania, Trypanosoma, Giardia, Trichomonas)"

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