Leishmania Donovani (Haemoflagellates | Parasitology

In this article we will discuss about: 1. Systematic Position of Leishmania Donovani 2. Speciation of Leishmania Donovani 3. Types 4. Habits and Habitat 5. Vectors 6. Symptoms and Pathogenesis 7. Clinical Features 8. Prophylaxis.

Leishmania is an important pathogenic zoo-flagellate genus closely related to Trypanosoma. The genus Leishmania was created by Ross in 1903. The species L. donovani was reported simultaneously by Leishman from London (1903) and Donovan from Madras (1903), hence the name Leishmania donovani. Various species of Leishmania infect man, dog, cattle, horse, sheep etc. and cause serious diseases collectively known as Leishmaniasis.

Systematic Position of Leishmania Donovani:

Subphylum – Sarcomastigophora

Superclass – Mastigophora

Class – Zoomastigophora

Genus – Leishmania

Species – donovani

Speciation of Leishmania Donovani:

The speciation of the genus Leishmania has been considered by Hoare (1949), Biagi (1953) and Adler (1964).

Leishmania donovani Ross, 1903 (Syn. Piroplasma donovani; Leishmania infantum; L. chagasi). This organism is morphologically identical with other species. It is the cause of kala-azar, dumdum fever or visceral leishmaniasis in humans and dogs.

Biagi (1953) has classified the different kinds of kala-azar as follows:

i. Indian kala-azar:

Dumdum fever, the classi­cal form of L. donovani. It occurs in India, affecting young adults, 60 percent of infec­tion being in the age group 10-20 years. The infection is transmitted by sand-fly, Phlebotomus argentipes.

ii. Chinese kala-azar:

Chiefly occurs in northern China, mainly a condition of children with dog as a reservoir. Transmitted by P. chinensis and P. sergenti.

iii. Mediterranean kala-azar:

Chiefly occurs in the Mediterranean area, Southern Europe and parts of tropical Africa. 80 per cent of cases found in children under 5 years of age and 94 per cent in those under 10 years. Dog serves as a reservoir host and in this animal infection rates may be as high as or higher than, in the human population. The infection is transmitted by P. major, and P. perniciosus.

iv. African kala-azar:

Chiefly prevalents in Kenya and Sudan; 66 percent of cases occur in young adults. Natural infections have been found in a Cercopithecus mon­key, a gerbil and a ground squirrel. This is characterised by the early skin lesion and the infection is transmitted by P. orientalis and P. martini.

v. Russian kala-azar:

This is an infection with a zoonotic reservoir in dogs and jackals in the Caucasus, Turkistan and other Republics of U.S.S.R. Transmitted by P. arkaplensis.

vi. American kala-azar:

Occurs from Mexico to Southern Argentina and in U.SA. This disease occurs in humans and the fox serves as reservoir host. The transmitting flies are P. intermedins and P. longipalus.

Types of Visceral Leishmaniasis:

This is caused by L. donovani and may be classified as endemic, sporadic and epidemic.

i. Endemic visceral leishmaniasis:

Affects chil­dren of 1-4 years in the Mediterranean area, South-west Asia, China and Latin America. In India and East Africa, the peak age is 5-10 years or older. The common symp­toms are fever, malaise, weight loss, ano­rexia accompanied by anaemia, skin darke­ning and enlargement of the spleen.

ii. Sporadic visceral leishmaniasis:

This affects non-indigenous people and is characte­rized by a markedly sudden onset of fever, 3 weeks to 2 years after exposure.

iii. Epidemic visceral leishmaniasis:

All ages are susceptible except those who are old enough to have been affected during a pre­vious epidemic.

Habits and Habitat of Leishmania Donovani:

In man, Leishmanians live as intracellular parasite in W.B.C. or cells of liver, spleen, bone- marrow, lymphatic gland etc. This parasite occurs in man in the amastigote form only but in the insect vector the promastigote form is assumed.

It is the causative agent of the disease known as kala-azar resulting in fever, enlargement of spleen and a reduction in the number of leucocytes in blood. This parasite is transmitted through the bite of sandflies. It is essentially a parasite of the R. E. System.

Vectors of Leishmania Donovani:

Indian vector – Phlebotomus argentipes

Chinese vector – P. chinensis and P. sergenti

Mediterranean vector – P. perniciosus, P. major

Sudanese vector – P. orientalis

East African vector – P. martini

Russian vector – P. arpaklensis

Brazilian vector – Lutzomyia longipalpis

Symptoms and Pathogenesis of Leishmania Donovani:

Symptoms:

i. The incubation period of kala-azar is long and generally varies from 3-6 months and symptoms may appear even after 2 years.

ii. Pyrexia is often an early symptom and it may be continuous or remittent in type, becoming intermittent at a later stage.

iii. Splenic enlargement is one of the most striking features and the organ progres­sively enlarges.

iv. The liver is also enlarged but not as much as the spleen.

v. Irregular fever is also observed.

vi. In a fully developed case of kala-azar emaciation, anaemia due to reduction in number of blood cells become noticeable.

vii. The skin over the entire body is dry, rough and harsh and is often pigmented (darkened).

viii. The hair becomes brittle and falls out.

Pathogenesis:

If not properly treated, the patient dies within a period of 2 years. Death in kala-azar is due to some complications such as amoebic or bacillary dysentery, pneumonia, pulmonary tuberculosis, cancrun oris and other septic infec­tions. The dense mechanism of human body is so weak that the patient is unable to resist them.

Clinical Features of Leishmaniasis Donovani:

1. Kala-azar is caused by L. donovani and its sub-species and may be classified as endemic, sporadic or epidemic.

i. Endemic visceral leishmaniasis:

Affects children of 1-4 years in the Mediterranean area, Latin America, South-West Asia and China. In East Africa and India, the peak age is 5-9 years or older. The common symptoms are fever, malaise, weight-loss, anorexia accompanied by enlargement of the spleen, anaemia and skin darkening.

ii. Sporadic visceral leishmaniasis:

This affects non-indigenous people entering an epidemic area. It is characterised by a markedly sudden onset of fever, 3 weeks to 2 years after exposure.

iii. Epidemic visceral leishmaniasis:

All ages are susceptible except those who are old enough.

2. Post-kala-azar dermal leishmaniasis (PKDL):

PKDL is common in India which appears one to several years after apparent cure of kala-azar. The lesions consist of multiple ulceration.

3. Muco-cutaneous leishmaniasis:

Ulcers exhibit around the margins of mouth and nose which can mutilate the face so badly that victims may become social outcasts.

4. Cutaneous leishmaniasis:

There are several forms of cutaneous leishmaniasis; such as Zoonotic (rural) cutaneous leishmaniasis (ZCL), Anthroponotic (urban) cutaneous leishmaniasis (ACL), Diffuse cutaneous leish­maniasis (DCL) etc. This febrile disease is characterised by painful ulcers in the parts of the body exposed to sand-fly bites (legs, arms or face) inhibiting the victim’s ability to work. Here the agent is confined to skin. The disease may be mistaken for leprosy.

Prophylaxis of Visceral Leishmaniasis:

The preventive measures include the follow­ing:

i. Eradication of the insect vector:

In endemic areas low trees and bushes etc. should be cleared out. This consists of measures directed against the sand-fly, the transmitting agent.

ii. Attack on the parasite:

In areas where dogs serve as reservoirs of infection, all street dogs should be killed. In India, control measures should be campaign treatment.

iii. Personal prevention:

Use of mosquito-net or screen for avoiding bite of sandflies and avoid sleeping on ground floors. Periodic fumigation of sleeping quarters should be done.