Classification of diseases
Leishmania cause three main groups of diseases:
- Visceral leishmaniases (affect internal organs).
- Cutaneous leishmaniases (affect the skin).
- Mucocutaneous leishmaniases (deep lesions of the skin and mucous membranes of the nose, nasopharynx, and respiratory tract).
Depending on the source of infection, anthroponotic (source is humans) and zoonotic (source is animals, e.g., rodents or canids) types are distinguished.
Life cycle and pathogenesis
In the body of vertebrate hosts (humans and animals), Leishmania parasitize strictly intracellularly in the non-flagellated (amastigote) form. Blood-sucking insects — sandflies — serve as vectors of the infection.
The developmental process depends on the species of the causative agent:
- Upon the bite of an infected sandfly, the parasites invade the tissues.
- Leishmania are engulfed by macrophages and actively multiply within them.
- L. donovani affects the cells of the reticuloendothelial system (bone marrow, liver, spleen).
- L. tropica localizes in skin cells, causing local inflammation and the formation of a specific granuloma — leishmanioma, which eventually ulcerates and then scars.
Cutaneous leishmaniasis (Leishmania tropica)
There are two main types of cutaneous leishmaniasis, which differ in epidemiology and clinical course.
| Sign | Anthroponotic (urban) | Zoonotic (rural) |
|---|---|---|
| Causative agent | L. tropica minor | L. tropica major |
| Reservoir | Humans | Rodents (gerbils, susliks) |
| Incubation period | 2–6 months (up to 1 year) | 1–4 weeks |
| Ulcer characteristics | Dry, late ulceration | Wet, early ulceration |
| Parasite load | Many | Low |
Visceral leishmaniasis (Leishmania donovani)
This type of leishmaniasis affects internal organs. There are two main clinical forms:
- Mediterranean (infantile): Zoonosis, with members of the canine family (especially infected dogs) acting as the source of infection. Preschool-aged children are predominantly affected.
- Indian: Typical anthroponosis, with humans as the reservoir. Adults are mostly affected. Characterized by darkening of the skin (hence the name "black fever") and frequent detection of parasites in peripheral blood.
Briefly: answers to topical questions
Which morphological form of Leishmania parasitizes in the digestive tract of the vector?
In the digestive tract of the vector (sandfly), Leishmania parasitize as promastigotes (the flagellated form).
The life cycle of the parasite in the vector's body includes the following stages:
- Transformation — after the sandfly ingests macrophages with amastigotes, they enter the insect's stomach (midgut), where they transform into promastigotes.
- Multiplication and migration — promastigotes divide and gradually migrate from the stomach to the pharynx, and then accumulate in the proboscis.
It is the accumulation of promastigotes in the proboscis that makes the sandfly infectious and capable of transmitting the infection to vertebrate hosts.
Class and exam questions
In which cells do Leishmania parasite in humans?
In humans, Leishmania parasites intracellularly within macrophages and cells of the reticuloendothelial system (in the amastigote form).
Who is the vector of leishmaniases?
Vectors are sandflies (members of the genus Phlebotomus).
What is a leishmanioma?
A leishmanioma is a specific granuloma that forms in the skin during cutaneous leishmaniasis at the site of parasite entry. It includes the tubercle, ulcer, and scarring stages.
What else to study on this topic
- Morphological differences between amastigote and promastigote forms
- Features of the pathogenesis of mucocutaneous leishmaniasis (L. brasiliensis)
- Natural focality of zoonotic forms of leishmaniasis
- Methods of laboratory diagnosis of leishmaniases
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