Kala-azar (Visceral Leishmaniasis) – Causes, Symptoms, Diagnosis, Treatment, and Prevention
~Introduction
Kala-azar, also known as visceral leishmaniasis, is a severe parasitic disease caused by protozoa of the genus Leishmania. It is transmitted through the bite of infected female sandflies (Phlebotomus species in the Old World and Lutzomyia species in the New World). The name “Kala-azar”, meaning “black fever” in Hindi, comes from the darkening of the skin observed in some patients.
Visceral leishmaniasis is the most severe form of leishmaniasis and, if left untreated, is almost always fatal. It primarily affects the internal organs—especially the spleen, liver, and bone marrow—causing long-lasting fever, weight loss, enlargement of the spleen and liver (splenomegaly, hepatomegaly), and anemia.
This disease is one of the neglected tropical diseases (NTDs), with significant health and socioeconomic impacts in parts of Asia, Africa, South America, and the Mediterranean region. Despite being treatable, kala-azar continues to affect the poorest populations, often in rural areas with limited healthcare access.
This article provides a comprehensive overview of kala-azar, including its causes, transmission, symptoms, diagnosis, treatment, prevention, and global impact.
~What is Kala-azar?
Kala-azar is a systemic parasitic infection caused by Leishmania donovani complex, which includes:
-
Leishmania donovani – predominant in the Indian subcontinent and East Africa.
-
Leishmania infantum (also called L. chagasi in Latin America) – found in the Mediterranean basin, parts of Asia, and South America.
Unlike cutaneous and mucocutaneous leishmaniasis, which affect the skin and mucous membranes, visceral leishmaniasis targets internal organs, leading to life-threatening complications.
~Transmission
Kala-azar is transmitted through the bite of an infected female sandfly. The transmission cycle can be explained as follows:
-
A sandfly bites an infected host (human or animal) and ingests parasites in their blood.
-
Inside the sandfly, the parasites (amastigotes) develop into promastigotes in the gut.
-
When the sandfly bites another person, it injects these promastigotes into the bloodstream.
-
The parasites invade macrophages and multiply inside them, spreading throughout the body.
Reservoirs of Infection
-
In the Indian subcontinent, humans are the primary reservoir (anthroponotic transmission).
-
In the Mediterranean and South America, dogs and wild canines are the main reservoirs (zoonotic transmission).
~Epidemiology
-
Kala-azar is found in more than 80 countries.
-
Around 50,000–90,000 new cases occur each year worldwide (WHO, 2023).
-
More than 90% of cases occur in seven countries: India, Bangladesh, Sudan, South Sudan, Ethiopia, Brazil, and Kenya.
-
India alone once contributed to half of the world’s cases, but major elimination programs have reduced its burden drastically in recent years.
Risk factors include:
-
Poverty (poor housing, malnutrition).
-
Living in rural areas with sandfly habitats.
-
Weakened immunity (especially in people with HIV/AIDS).
~Pathophysiology
Once inside the human body, Leishmania parasites invade macrophages (a type of immune cell). They transform into amastigotes, multiply, and spread to:
-
Spleen → massive enlargement.
-
Liver → hepatomegaly.
-
Bone marrow → suppression of blood cell production, leading to anemia, leukopenia, and thrombocytopenia.
The weakened immune system makes patients highly vulnerable to secondary infections, which are often the actual cause of death.
~Clinical Features
The disease usually develops slowly, within weeks to months after infection. The main clinical features include:
-
Fever – Prolonged, irregular, and intermittent fever is the hallmark symptom.
-
Splenomegaly – Spleen enlargement is massive and progressive.
-
Hepatomegaly – Liver is also enlarged, though less than the spleen.
-
Weight loss and cachexia – Patients appear extremely thin and malnourished.
-
Anemia – Due to bone marrow suppression, nutritional deficiencies, and chronic disease.
-
Darkening of the skin – Characteristic of kala-azar, more common in Indian patients.
-
Weakness and fatigue – Due to chronic illness and anemia.
-
Bleeding tendencies – From low platelet count.
-
Opportunistic infections – Pneumonia, tuberculosis, and diarrhea may complicate the condition.
If untreated, kala-azar is almost always fatal within 2 years, often due to secondary infections.
~Post-Kala-azar Dermal Leishmaniasis (PKDL)
In some patients, especially in East Africa and India, a condition known as PKDL develops months or years after treatment.
-
Characterized by skin lesions, including hypopigmented patches, nodules, or rashes.
-
PKDL is important because it can serve as a reservoir for parasites, sustaining transmission in communities.
~Diagnosis
Accurate diagnosis is crucial to differentiate kala-azar from other diseases like malaria, typhoid, or tuberculosis. Diagnostic methods include:
1. Clinical Diagnosis
-
History of prolonged fever, weight loss, and residence in an endemic area.
-
Physical examination showing splenomegaly and hepatomegaly.
2. Parasitological Diagnosis
-
Microscopy: Demonstration of Leishmania amastigotes in:
-
Splenic aspirate (most sensitive but risky).
-
Bone marrow aspirate.
-
Lymph node aspirate.
-
3. Serological Tests
-
rK39 Rapid Diagnostic Test – Widely used in the Indian subcontinent.
-
Direct Agglutination Test (DAT).
-
ELISA and IFAT – Useful but less common in field settings.
4. Molecular Methods
-
Polymerase Chain Reaction (PCR) – Highly sensitive but costly.
~Treatment
Treatment depends on geography, drug resistance patterns, and patient condition. Common drugs include:
1. First-line Treatments
-
Liposomal Amphotericin B (AmBisome):
-
Highly effective with fewer side effects.
-
Single-dose regimens are used in India.
-
-
Miltefosine:
-
First oral drug for kala-azar.
-
Effective but teratogenic (not safe in pregnancy).
-
-
Paromomycin:
-
An injectable aminoglycoside.
-
Used in combination therapy.
-
2. Combination Therapy
-
Preferred to prevent resistance.
-
Example: Amphotericin B + Miltefosine, or Paromomycin + Miltefosine.
3. Second-line Treatments
-
Conventional Amphotericin B (deoxycholate form): Effective but toxic to kidneys.
-
Pentavalent Antimonials (Sodium Stibogluconate):
-
Previously the main treatment, but resistance (especially in India) has limited its use.
-
~Complications
-
Severe anemia and pancytopenia.
-
Malnutrition.
-
Secondary infections (bacterial and viral).
-
Bleeding disorders.
-
Post-kala-azar dermal leishmaniasis (PKDL).
-
Death if untreated.
~Prevention and Control
Since no vaccine is available, prevention focuses on vector control, early diagnosis, and treatment.
1. Vector Control
-
Indoor residual spraying with insecticides.
-
Use of insecticide-treated bed nets.
-
Environmental management (removing breeding sites such as cracks in walls, rodent burrows).
2. Personal Protection
-
Using mosquito nets.
-
Wearing long-sleeved clothing.
-
Applying insect repellents.
3. Reservoir Control
-
In zoonotic areas, dogs (reservoirs) may be treated or culled.
4. Active Case Detection
-
Screening of communities in endemic areas.
-
Early treatment to reduce transmission.
5. Health Education
-
Raising awareness about symptoms and availability of free treatment programs.
~Global Burden and Elimination Efforts
-
Kala-azar is a major public health problem in India, Nepal, Bangladesh, Sudan, South Sudan, Ethiopia, and Brazil.
-
The Indian subcontinent has made remarkable progress through the Kala-azar Elimination Programme, reducing cases by over 95% since 2005.
-
WHO aims to eliminate kala-azar as a public health problem globally by 2030.
~Socioeconomic Impact
Kala-azar disproportionately affects the poorest communities:
-
Health impact: High mortality and disability if untreated.
-
Economic burden: Families spend heavily on treatment and lose income due to illness.
-
Education impact: Children miss school when affected or when caring for sick relatives.
-
Social stigma: Skin changes in PKDL can lead to discrimination.
~Research and Future Directions
-
Vaccine development: Still under research, but promising.
-
New drugs: Safer, shorter-course oral therapies are being explored.
-
Better diagnostics: Rapid, field-friendly tests to improve early detection.
-
Integrated programs: Combining kala-azar control with other neglected tropical disease (NTD) programs.
~Conclusion
Kala-azar, or visceral leishmaniasis, remains one of the deadliest parasitic diseases if untreated. Caused by Leishmania parasites and transmitted by sandflies, it leads to fever, organ enlargement, anemia, and darkening of the skin. With effective drugs like liposomal amphotericin B, miltefosine, and combination therapies, treatment is now highly successful if patients are diagnosed early.
However, challenges remain in the form of drug resistance, relapses, and PKDL cases. Vector control, early detection, and community education remain central to prevention.
With ongoing efforts, particularly in South Asia, the elimination of kala-azar as a public health problem is within reach. Global cooperation, investment in research, and sustained healthcare support will be crucial to make kala-azar a disease of the past.