Study of Leishmania donovani

 

Study of Leishmania donovani

 

Introduction

Leishmania donovani is a protozoan parasite responsible for visceral leishmaniasis (also known as kala-azar), a severe systemic disease affecting humans. It is transmitted through the bite of female sandflies of the genus Phlebotomus (Old World) and Lutzomyia (New World). The disease is characterized by fever, weight loss, hepatosplenomegaly, and anemia.

 

Morphology

Leishmania donovani exists in two main morphological forms:

1. Promastigote Form (Insect Stage):

 It is found in the gut of sandflies. They are Elongated, spindle-shaped with a flagellum for motility. Nucleus centrally placed, with a kinetoplast near the basal body. They are 10-20 μm in length and 1-3 μm in width.

2. Amastigote Form (Human and Mammalian Host Stage):

It is found inside macrophages of the mammalian host. They are Small, round, or oval, without an external flagellum. Their Kinetoplast and nucleus are distinct with a size of  2-4 μm in diameter.

 

Life Cycle

The life cycle of Leishmania donovani involves two hosts: sandflies and mammals (including humans).

Life Cycle in Sandfly

1. Ingestion of Amastigotes: When a female sandfly bites an infected host, it ingests amastigotes present in the blood.
2. Transformation into Promastigotes: Inside the midgut of the sandfly, the amastigotes transform into flagellated promastigotes.
3. Multiplication: The promastigotes multiply by binary fission and migrate to the proboscis.
4. Infective Stage: The sandfly becomes infectious and can transmit the promastigotes to a new host during its next blood meal.

Life Cycle in Humans

1. Transmission to Human Host: The infected sandfly bites a human, injecting promastigotes into the bloodstream.
2. Invasion of Macrophages: Promastigotes are phagocytosed by macrophages.
3. Transformation into Amastigotes: Inside macrophages, they transform into amastigotes and multiply within the phagolysosomes.
4. Dissemination: The amastigotes rupture the macrophages and spread via the blood and lymphatic system, infecting new macrophages.
5. Continuation of the Cycle: When another sandfly bites the infected host, amastigotes are ingested, completing the cycle.

Prevalence and Epidemiology

Leishmania donovani is primarily found in tropical and subtropical regions. It is endemic in parts of India, Bangladesh, Nepal, Sudan, Ethiopia, and Brazil.

Transmission is influenced by:

Ø  Presence of vector (Phlebotomus and Lutzomyia sandflies).

Ø  Poor sanitation and socioeconomic conditions.

Ø  Reservoir hosts like rodents and domestic animals.

Pathogenicity

Causes Visceral Leishmaniasis (Kala-azar)

Symptoms of  Leishmaniasis (Kala-azar):

1. Prolonged fever and malaise.
2. Hepatosplenomegaly (enlarged liver and spleen).
3. Severe anemia, weight loss, and immune suppression.
4. Hypergammaglobulinemia leading to renal and cardiovascular complications.
5. If untreated, the disease has a high mortality rate.
6. Can lead to Post-Kala-Azar Dermal Leishmaniasis (PKDL), a condition with skin lesions appearing months to years after treatment.

Prophylaxis (Prevention and Control)

1. Vector Control:

a)       Insecticide spraying in endemic areas.

b)       Use of insecticide-treated bed nets and protective clothing.

c)       Environmental management to reduce breeding sites.

2. Reservoir Host Control:

Controlling stray dogs and rodents that act as reservoir hosts.

3. Personal Protection:

Using insect repellents and avoiding outdoor activities at night when sandflies are active.

4. Vaccination and Drug Prophylaxis:

a)       No effective vaccine is currently available.

b)       Chemoprophylaxis using pentavalent antimonials and miltefosine in endemic areas.

5. Early Diagnosis and Treatment:

a)       Prompt detection using microscopic examination, serological tests (rk39 antigen test), and PCR.

b)       Treatment with drugs like amphotericin B, pentavalent antimonials, and miltefosine.

 

Conclusion

Leishmania donovani is a significant parasitic pathogen causing visceral leishmaniasis, a life-threatening disease if untreated. Effective control strategies, including vector management, personal protection, and early treatment, are crucial to reducing disease prevalence. Further research on vaccine development is essential for long-term control of this neglected tropical disease.

 

References:

1. Chappuis, F., et al. (2007). Visceral leishmaniasis: What are the needs for diagnosis, treatment and control? Nature Reviews Microbiology.
2. World Health Organization (WHO) Reports on Leishmaniasis.
3. Recent studies on Leishmania epidemiology and treatment strategies.