LEISHMANIA DONOVANI

Kingdom- Animalia.

Sub Kingdom- Protozoa.

Phylum- Mastigophora (flagellates).


HABITAT- 

In man, the leishmania are found in cells of monocytes- macrophages (reticuloendothelial) system.

MORPHOLOGY-

Leishmania donovani exist in 2 morphological forms-
i) Amastigote.
ii) Promastigote.

I) AMASTIGOTE (non-flagellate form)-

  • Habitat- At this stage, parasite recite in the cells of R-E  system of man.
  • Shape & Size- It is round or oval and measures about 2-4  um in diameter.
  • Cell membrane- Delicate.
  • Nucleus- It is over or around situated on the side of the cell wall. It is a little less than 1 um in diameter.
  • Kinetoplast- (Parabasal body + blepharoplast)-
  • It lies at right angles to the nucleus contains DNA and a  mitochondrial structure.
  • Axoneme- A delicate filament extending from the kinetoplast to the margin of the body.
  • Vacuole- Unstained clear space lying alongside the axoneme. 

II) PROMASTIGOTES (flagellate form):

  • Habitat- It occurs in the digestive tract of insect vector (sandfly) or lab culture.
  • Shape and Size- It is slender, spindle-shaped, and measures about 15- 20 um in length and 1-2 um in breadth.
  • The nucleus is situated centrally.
  • Kinetolpast near the anterior end.
  • Eosinophilic vacuole lying in front of kinetoplast over which the root of flagellum runs.


LIFE CYCLE:


Leishmania donovani passes its life cycle in two host- a vertebrate and an insect host (sandfly).

The infected form for the human being is PROMASTIGOTES, they enter into the tissue by the bite of an infected sandfly.
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They enter macrophages, lose their flagella, and transformed into AMASTIGOTES.
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AMASTIGOTE form resides in the cell of the R E system and they multiply in the cell by binary fission.
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Multiplication goes on continuously till the cell become pack with the parasite.
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Host cell enlarges and Rupture liberating parasite into the circulation.
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Either taken up by the fresh cells or parasites invade the fresh cells.
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Cycle is repeated
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In this way entire R E system progressively infected.
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In the bloodstream, some of the amastigote forms are phagocytosed by the neutrophilic granulocytes and monocytes.
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At this stage, blood-sucking insect (female sand flies) ingest this free amastigote form from the infected person during its blood meal.
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In certain species of the sandfly, these Amastigote forms change into promastigote form in the midgut.
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Multiply rapidly by binary fission
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Producing a numerous number of flagellates.
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Multiplication proceeds in the midgut of the sandfly.
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Flagellates forward to the interior part of the alimentary canal (pharynx or buccal cavity).
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A heavy pharyngeal infection is observed in 6th and the 9th day of its infective blood meal known as anterior station development.
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At this stage, transmission effected through the bite of an infected sandfly.
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Thus, the life cycle is repeated.

PATHOGENECITY-

Incubation period- 3 to 6 months.

Pathology of Kala Azar is due to blockage and destruction of the R-E system, mainly bone marrow, spleen, liver, and lymph nodes.

Bone marrow- Multiplication of parasite in the bone marrow leads to the destruction of hemopoietic tissue resulting in leukopenia and thrombocytopenia, bleeding gums. If untreated in 90% of cases death occurs within 2 years.

Spleen- The reticular cells of Billroth cords of the spleen are greatly increased and packed with the MST good forms of L. donovani.

Liver- Kupfer cells are greatly increased in size and number. The cytoplasm of Kupfer cells is packed with LD bodies.

Lymph nodes- Lymphadenopathy is seen.

Anemia in Kala Azar-
  • Hemolysis- Destruction of red cells in the spleen.
  • Autoimmune basis- Presence of anti-red cell antibody and antibody against leukocytes and platelets.
  • Skin- Changes are seen on the face, hands, feet, abdomen, there is pigment dark skin develops.
  • A nodular, ulcerative, cutaneous, mucocutaneous lesion may occur. 

LAB – DIAGNOSIS:

Direct Evidence-

a) Peripheral blood thick,  thin film.
b) Blood culture NNN medium-
  • Liver.
  • Bone marrow aspiration.
  • Splenic puncture.
  • Lymph node aspirate.

c) Biopsy/ aspiration smear.

Indirect Evidence-

a) Blood Examination- 
  • Leucopenia.
  • Thrombocytopenia.
  • RBCs decreased.


b) Serological test.
  • Aldehyde test.
  • Anti-Leishmanial antibody (ELISA).


c) Leishmanian skin test.

ALDEHYDE TEST or ANTIMONY TEST:

PRINCIPLE- 

The test depends on increase of non-specific serum gamma globulin in the patient's serum.
The aldehyde test becomes positive only when the disease is more than 3 months duration.

TEST-

To 1-2 ml of a serum sample, add 2 drops of concentrated formalin (40% v/v) and mix well. Allow to stand up to 20 min.

INTERPRETATION-

A positive reaction is indicated by the jellification of milk-white opacity like white of a hard-boiled egg usually in 2-20 min. The reaction is called strongly positive.

CULTIVATION-

  • L. Donovani can be cultivated in a medium composed of two parts of salt agar and one part of defibrinated Rabbit's blood.
  • This is first introduced by the Novy, Mac Neal, Nicolle, called a NNN medium.
  • Incubated at 22 -24-degree Celcius.
  • In the NNN medium, the amastigote form changes into promastigote which is multiplied actively by longitudinal fission to produce a large number of flagellates.