Tuesday, 15 May 2018

Leishmania donovani

Leishmania donovani
                                                            Phylum – Protozoa
                                                                      Class – Mastigophora
                                                                      Order – Protomonadina
                                                                      Genus – Leishmania
                                                                      Species — donovani


Leishmania is a genus of trypanosomes that are responsible for the disease leishmaniasis.Leishmania  donovani is a species of intracellular parasites belonging to the genus Leishmania, a group of haemoflagellate kinetoplastids that cause the disease leishmaniasis Leishmania donovani is a protozoan endoparasite inhabiting the cells of reticulo-endothelial system of human beings causing kala-azar or visceral leishmaniasis. It infects the mononuclear phagocyte system including spleenliver and bone marrow. Infection is transmitted by species of sandfly belonging to the genus Phlebotomus in Old World and Lutzomyia in New World.Therefore, the parasite is prevalent throughout tropical and temperate regions including Africa (mostly in Sudan), ChinaIndiaNepal, southern EuropeRussiaand South America. It is named after the discoverer, Leishman and Donovan. Leishman in May, 1903 from London and Donovan in July, 1903 from Madras, independently discovered the parasite in the spleen of the patients suffering from kala- azar.


Geographical distribution:

 Leishmania donovani has a wide distribution occurring in all continents except Australia It is endemic in many places in India, China, Africa, Southern Europe Mediterrean, South America and Russia.In India, it is more prevalent in Assam, Bihar, Orissa, Madras and Eastern Uttar Pradesh Although the disease is prevalent in persons of all ages, about 60% people suffering from this disease belongs to young adult group and rarely children below four years of age. In China and Brazil, dogs are the reservoir of infection for man.

EPIDEOMIOLOGY:
Leishmania currently affects 6 million people in 98 countries. About 0.9-1.6 million new cases occur each year, and 21 species are known to cause disease in humans.

STRUCTURE/LIFE CYCLE:
  1. The amastigote form is found in the mononuclear phagocytes and circulatory systems of humans. It is an intracellular and nonmotile form, being devoid of external flagella. The short flagellum is embedded at the anterior end without projecting out. It is oval in shape, and measures 3–6 µm in length and 1–3 µm in breadth. The kinetoplast and basal body lie towards the anterior end.

The promastigote form is found in the alimentary tract of sandflies. It is an extracellular and motile form. It is considerably larger and highly elongated, measuring 15-30 µm in length and 5 µm in width. It is spindle-shaped, tapering at both ends. A long flagellum (about the body length) is projected externally at the anterior end. The nucleus lies at the centre, and in front of it are the kinetoplast and the basal body.


Mode of Transmission:

Sand-flies act as the transmitting agent for the disease caused by L. donovani. In India sand-fly of the genus Phlebotomus argentipes is the common vector. An infected sand-fly when bites a person in order to take a blood meal liberate the parasitic flagellates into the wound caused by its proboscis. In this way, transmission of L. donovani from a kala-azar patient to a healthy one occurs. Besides this, the other mode of transmission are –
i. Transmission through blood transfusion.
ii. Congenital infection of a child from mother while still in uterus.
iii. Possible transmission during coitus (Symmers, 1960).Pathology:
The incubation period i.e., the period between the time of the initial infection and the appearence of clinical symptoms, generally varies from 3 – 6 months, but in certain cases it may exceed upto two years.
Leishmania donovani causes the disease kala-azar or visceral leishmaniasis, with following characteristics-
1. Pyrexia:
Continuous or discontinuous fever during initial phase of the disease, waves of pyrexia may follow later on.
2. Splenic enlargement:
The spleen shows various degrees of enlargement. In severe infection spleen may extend well below the level of the umbilicus. The capsule covering spleen is often thickened due to perisplenitis.
3. Liver enlargement:
Liver is less frequently enlarged than the spleen in kala-azar. The Kuffer’s cells are greatly enlarged both in size and number as their cytoplasm gets packed with the parasites. Normally jaundice does not appear in kala-azar unless liver is greatly damage.
4. Changes in bone marrow:
Leishmania infection causes hyperplasia (abnormal increase in the number of normal cells) and a profound disturbance in the haemopoietic activities of the bone marrow. Leucopenia (neutropenia) and monocytosis occurs which reduces the resistence of the body against other infections.
5. Skin:
In kala-azar patient the skin over the entire body become dry, rough, harsh and often darkened The hair tends to be brittle and falls out. In few cases cutaneous lessions may appear.
6. Anaemia in kala-azar:
Profound anaemia may occur in kala-azar. The possible reason for this is haemolysis and destruction of RBC’s in the spleen of the patient.
7. Changes in lymph nodes:
The lymphatic glands are frequently enlarged. Parasites have been observed in the lymph nodes from cases occuring in China and Mediterrean.
8. Changes in intestine:
Intestinal lession in kala-azar patients may appear as a secondary infection.

Treatment:

The mortality in untreated patients is high, from 90 to 95 per cent in adults and from 75 to 85 per cent in children. The patient usually die within two years. Death usually occurs from complications, anaemia or toxemia. Proper treatment through systematic chemotherapy, along with high protein and vitamin diet has reduced the mortality rate considerably.
Following drugs are used to treat the kala-azar patient-
1. Pentavalent antimony compounds like urea stibamine, neostum, neostibosan, aminostiburea, sodium-antimony-gluconate etc. are the drugs of choice.
2. Pentamidine isethionate-a synthetic non-metallic compound is also being recommended.
Prophylaxis:
The preventive measures are as follows-
1. Control of vector (sandfly) population by using effective insecticides.
2. Prevention of sandfly bite by using mosquito net, door and window screen, periodic fumigation and avoiding, the ground floor for sleeping purposes.
3. Effective treatment of patient by specific drugs.