What Is Kala Azar? Key Facts for Biology Students
Kala-Azar is the second biggest parasitic killer in the world and infects around 3 lakh people annually. Along with Chagas disease and sleeping sickness, kala-azar is one of the most lethal and neglected tropical diseases (NTDs). Only malaria is more dangerous. Kala Azar is known to be endemic in 47 countries with approximately 200 million at risk. The parasite spreads to humans by the bite of infected female sand flies. It is known to attack the immune system and can be fatal if not treated. Between 2-400,000 cases, 90% of cases are found in India, Bangladesh, Nepal, Sudan, and Brazil.
What is Kala Azar Disease?
Kala-Azar or Visceral Leishmaniasis is a slow progressing indigenous condition that is caused by a protozoan parasite. The disease-causing parasite belongs to the genus Leishmania. The parasite infects the reticuloendothelial system and may be found in abundance in bone marrow, spleen, and liver. In India, generally, the parasite that causes this disease is Leishmania donovani.
Post-Kala-Azar dermal leishmaniasis is a condition in which Leishmania donovani parasites invade the skin cells. The parasites stay, and develop in the skin cells and evolve as dermal lesions. In this section, we will learn more about the causes of kala-azar and kala-azar symptoms
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Kala-Azar Causes
In India, there is only one sand fly vector of kala-azar- Phlebotomus argentipes which is the cause of kala-azar. Sandflies are tiny insects that are about ¼ the size of a mosquito. The length of a sand fly can range from 1.5 mm to 3.5 mm.
These sand flies breed in high relative humidity, warm temperatures, high subsoil water, and an abundance of vegetation. Micro-climatic conditions are the ideal breeding grounds for sandflies. The high organic matter available in such places serves as food for its larvae.
These sand flies are ecologically sensitive insects, fragile, and cannot bear desiccation or the removal of moisture.
The leading cause of kala-azar is a bite from female phlebotomine sand-flies which is the vector or transmitter of the Leishmania parasite. Listed below is how the infection occurs:
The sand flies feed on animals and humans for blood which they need to develop their eggs.
If blood having Leishmania parasite is drawn from an animal or human, the next person to receive a bite will become infected and develop Leishmaniasis.
After months of the initial infection, the disease can progress into a severe form called Visceral Leishmaniasis or Kala-Azar.
Kala-Azar Symptoms
In the beginning, Leishmania parasites cause skin sores or ulcers at the site of the bite. As the disease advances, it attacks the immune system. Kala-azar presents itself in full form after two to eight months, with general signs and symptoms such as prolonged fever, and the following:
Recurring fever with a double rise in temperature.
Loss of appetite and weight loss.
Weakness and fatigue.
Dry, thin, scaly skin, and hair loss. Grayish discoloration of the skin of hands, feet, face, and abdomen in light-skinned people, hence the name kala-azar or black fever.
Rapid deficiency in red blood cells or hemoglobin.
Enlargement of the spleen.
Liver enlargement.
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Kala-Azar Diagnosis
Kala-azar can be diagnosed based on symptoms such as a case of fever lasting more than two weeks. And no response to anti-malarial or antibiotics. Lab findings may include anemia and progressive leucopenia.
In the lab, the following test may diagnose kala-azar:
Serology test – this standard test for kala-azar is based on relative sensitivity; specificity and feasibility include Direct Agglutination test (DAT), rk39 dipstick, and ELISA. All these tests detect IgG antibodies that are long-lasting. The aldehyde test is a non-specific test.
Parasite detection in bone marrow/spleen/ lymph node aspiration or culture medium is the confirmatory diagnosis. Sensitivity varies with the organ selected for aspiration. Spleen aspiration has the highest sensitivity and specificity, with precaution, expertise, and better hospital facilities.
Kala-Azar Treatment
The treatment of kala-azar is about the killing of the parasite with effective drugs that are cheap and less toxic. Pentavalent antimonial is the first-line drug, and pentamidine and amphotericin B are the second-line drugs. These medicines can only be given through injection. They are toxic and have many side effects. The treatment extends to a period of 30 days.
Conclusion
This is all about Kala Azar, a tropical disease, its causes, symptoms, and treatment process. Focus on how this disease spreads and how the patients are treated.
FAQs on Kala Azar Disease: Causes, Symptoms & Treatment
1. What is Kala-azar and what organism causes it?
Kala-azar, also known as visceral leishmaniasis, is a slow-progressing but serious disease caused by a protozoan parasite called Leishmania donovani. It is a vector-borne disease, meaning it is transmitted to humans through the bite of an infected insect, specifically the female sandfly (Phlebotomus argentipes). The parasite primarily attacks the internal organs like the spleen, liver, and bone marrow.
2. What are the main symptoms of Kala-azar?
The symptoms of Kala-azar develop gradually over several weeks to months after the infective sandfly bite. Key signs to watch for include:
Recurrent high fever that comes and goes.
Significant and unexplained weight loss.
Enlargement of the spleen (splenomegaly) and liver (hepatomegaly), leading to a swollen abdomen.
Anaemia, which causes weakness and fatigue.
Darkening or grayish discoloration of the skin, especially on the hands, feet, and face.
3. Why is Kala-azar also called 'black fever'?
Kala-azar gets its name 'black fever' from one of its most characteristic symptoms. The term 'Kala' in Hindi means black, and 'azar' means fever. In advanced stages of the disease, patients often experience hyperpigmentation, which is a significant darkening of the skin on the face, hands, feet, and abdomen. This grayish, dark discoloration of the skin, combined with the persistent fever, led to the common name 'black fever'.
4. Is Kala-azar transmitted by mosquitoes like malaria is?
No, this is a common misconception. While both are serious vector-borne diseases caused by protozoan parasites, they are transmitted by different insects. Malaria is spread by the bite of the female Anopheles mosquito. In contrast, Kala-azar is transmitted exclusively through the bite of an infected female sandfly (genus Phlebotomus). Sandflies are much smaller than mosquitoes and are most active from dusk to dawn.
5. How is Kala-azar diagnosed and treated?
Diagnosing Kala-azar requires clinical suspicion based on symptoms, followed by laboratory confirmation. The most definitive diagnostic method involves identifying the Leishmania parasite in tissue samples, typically obtained through a bone marrow or spleen aspiration. Treatment involves a course of specific anti-leishmanial drugs, such as liposomal amphotericin B or miltefosine, which must be administered under medical supervision. Early diagnosis and complete treatment are crucial for recovery and preventing complications.
6. What are the most effective ways to prevent Kala-azar infection?
Since no vaccine is available for Kala-azar, prevention focuses on avoiding sandfly bites. Key preventive measures include:
Personal Protection: Wear long-sleeved shirts and long pants, and use insect repellent on exposed skin, especially during evening and night-time hours.
Indoor Protection: Sleep in well-screened rooms or under bed nets treated with insecticide. Spraying living areas with residual insecticides can also help kill sandflies.
Vector Control: Community-level efforts to reduce the sandfly population through indoor residual spraying (IRS) are critical in endemic areas.
7. What is the role of the sandfly in the Leishmania life cycle?
The sandfly acts as the biological vector, playing an essential role in the parasite's development and transmission. When a female sandfly bites an infected person, it ingests blood containing the non-motile form of the parasite (amastigotes). Inside the sandfly's gut, these parasites transform into a motile, infective form (promastigotes). When the infected sandfly bites another person, it injects these promastigotes into the new host, thus completing the Leishmania life cycle and spreading the disease.
