Leshmania donovani - Classification, History, Habitat, Morphology, Culture

Introduction of Leishmania donovani

Leishmania donovani is protozoa causing the zoonotic infection called leishmaniasis. They are transmitted by the bite of an infected female sandfly during a blood meal to humans and other mammals. In humans, the incidental hosts of the intracellular parasite, infect the mononuclear phagocytes.

Leishmania donovani causes leishmaniasis which is also known as Dum-Dum fever, Asian fever, Assam fever, or infantile splenomegaly.

Classification of Leishmania donovani

Classification of Leishmania donovani can be done as:

Domain: Eukaryota

Phylum: Euglenozoa

Class: Kinetoplastea

Order: Trypanosomatida

Genus: Leishmania

Species: L. donovani

History of Leishmania donovani

Historically, Leishmaniasis is an ancient disease ad has been described in India and Africa since the eighteenth century. In 1903, both Leishman and Donovan reported observing the parasite simultaneously. Donovan discovered the parasite in the spleen smear of a patient suffering from kala-zar in India. At the same time, Leishman demonstrated the parasite in the spleen smear of a soldier in English who had died of Dum-Dum disease contracted in Kolkota.

From 1931 to 1934, the Indian Kala-zar Commission first identified the sand fly, Phlebotomus argentipes as the vector for Leishmania donovani.

Habitat of Leishmania donovani

Leishmania donovani are intracellular parasites that inhabits as intracellular amastigotes in the reticuloendothelial cells of the host spleen, mesenteric lymph nodes, bone marrow, intestinal mucosa, and liver.

Morphology of Leishmania donovani

The protozoa parasites, Leishmania donovani, exist in two morphological forms- amastigote and promastigote form

Amastigote form

• amastigote form is found in humans and other mammal hosts

• small, round to oval bodies, also known as Leishman Donovan (LD) bodies

• each amastigote form measures 2-3μm in length

• resides inside monocytes, endothelial cells, polymorphonuclear leucocytes of the host

• the nucleus is large and lies at a right angle to the kinetoplast which is slender, rod-shaped

• Leishmania donovani axoneme arises from the kinetoplast and extends to the margin of the amastigote

• vacuole, which is not stained lies alongside the axoneme

• stained well in Giemsa and Wright stain

• in Giemsa-stained preparations, the nucleus, and kinetoplast, are stained red

Promastigote

• promastigote form occur naturally in the digestive tract of sand fly (vector)

• mature promastigotes are long, slender, and spindle-shaped

• measures 15 μm to 25 μm in length and 1,5 μm to 3.5 μm in breadth

• a single nucleus is centrally located

• kinetoplast located transversally near the anterior end

• the presence of a single flagellum measuring 15μm -28 μm

• Leishman stain stains the cytoplasm blue, the nucleus pink, and the kinetoplast bright red

Culture of Leishmania donovani

The culture of Leishmania donovani can be done in biphasic media, liquid media, or laboratory animals.

Biphasic media

• consists of two parts of salt agar and one part defibrinated rabbit blood

• Novy and McNeal (1904) and Nicolle (1908) (NNN) medium was the first biphasic medium for the culture of Leishmania donovani

Liquid media

• includes Schneider’s, Grace’s, and Mituhasi-Maramorosh media- which are insect cell culture media

• liquid media do not contain any blood

• usually used for the preparation of a large volume of promastigotes

• Schneider’s medium which contains 20% fetal calf serum (FCS) is more sensitive to culture than the NNN biphasic medium

Laboratory animals

Chinese hamsters and golden hamsters are routinely used in the culture and diagnosis of Leishmania donovani.