Leishmania donovani
Classification
- Phylum- Protozoa
- Sub-phylum- Plasmodroma
- Class- Mastigophora
- Sub-class- Zoomastigophora
- Order- Protomonadina
- Genus- Leishmania
- Species- donovani
This specie of Leishmania is a causative agent of Kala-azar or visceral leishmaniasis. This disease is widespread in India, South China and in the Mediterranean countries.
Life Cycle :
The life cycle of this parasite is similar as other species with the only difference that this species migrates to the reticular endothelial cells of the liver, spleen, bone marrow and visceral lymph nodes.
The vector for this species is sand fly (Phlebotomus argentipes) and a few related species. The leptomonas stage of the parasite is introduced into the outer dermis. As parasites reach the skin of man, they are engulfed by phagocytes of the connective tissues. The phagocytes commonly involved in the act of engulfing are the macrophage (a large lymphoid wandering cell). The Leishmania bodies are not destroyed by the phagocytes but they reproduce to pack the infective cells which burst soon. In this way parasite bodies spread from phagocyte to phagocyte. This slow spread of parasites among the phagocytic cells continues from a period of few weeks to a year or more. Now some monocytes reach into the blood stream via the lymphatics and are further carried to different organs. When the parasites parasitize the phagocytes of liver, spleen, kidney and bone marrow, the symptomatic Kala-Azar is developed. The liver is enlarged and the number of Kupffer cells increase especially in the portal spaces. The spleen is also enlarged. In this stage irregular fever, weakness, headache and changed number of blood cells have been noticed. Due to the destruction of large number of monocytes, the red bone marrow produces many monocytes at the expense of other defensive cells, such as neutrophils. So, due to reduction in all types of white blood cells except monocytes a condition “Monocytosis with leucopenia” develops which reduces the resistance of the body and ultimately the victim of kala-azar dies of some infections which the victim would normally be able to counter act.
The complications usually observed in kala-azar are mainly those of the digestive and respiratory tracts. It has been noted that diarrohea and dysentery are intercurrent in origin. An important disorder is the respiratory syndrome. Children with kala-azar are commonly hospitalized primarily because of bronchopneumonia rather than for kala-azar.
Prevention and control :
In India where reservoir hosts are not important the treatment of human cases and destruction of sand fly alone can greatly reduce the amount of visceral leishmaniasis.
In areas where dogs constitute a constant source of infection for sand flies, campaign to destroy all street dogs and other with obvious skin lesions will effectively reduce the reservoir of this disease.
The supportive or symptomatic treatment by good nursing care, enriched diet and even blood transfusion is important in severe cases of infection, like bronchopneumonia, severe diarrhoea and dysentery. The advents of sulfa drugs and especially the antibiotics has greatly reduced the hazard.
Two types of drugs are given in the treatment of kala-azar e.g., antimonials and diamidines. The use of sodium and potassium antimony tartrates have been replaced by pentavalent antimonials of which ethyl stibamine (Neostibosan), urea stibamine and sodium antimony gluconate (solustibosan) have been the most effective drugs. Neostibosan and sodium antimony gluconate may be given intramuscularly, which is advantageous is mass treatment.
The diamidines are common in the cases where antimony drugs are not responding positively.
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