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Kala-azar, also known as black fever, Dumdum fever or visceral leishmaniasis, is a vector-borne tropical infection that is caused by protozoans that belong to the genus Leishmania. There are three forms of leishmaniasis: visceral or kala-azar which is the most fatal, cutaneous and mucocutaneous.
The vector responsible for the transmission of the disease is the sandfly of the Lutzomyia and Phlebotomus species.
Black fever is endemic in more than 60 countries but most of the cases are from rural areas of countries like India, Bangladesh, Brazil, Nepal and Sudan, where the populations are poor and many areas are remote with no or less political support and access to affordable drugs or preventive measures.  In India, states like Bihar, West Bengal and Uttar Pradesh are mostly affected by kala-azar.
According to the WHO, leishmaniasis is considered one of the seven most fatal tropical diseases as its clinical features involve a broad range of symptoms, with various degrees of severity and serious complications.
A study has shown that around 350 million people worldwide are at increased risk of acquiring kala-azar, with 1.5 to 2 million new cases occurring each year with 70000 deaths. 
Let's discuss the causes, symptoms, treatments and other details of kala-azar.
Causes Of Kala-Azar
The epidemiology of kala-azar depends on the characteristics of parasites, sandfly species, the ecological condition of the area, past and current exposure to the parasite and human behaviour. 
Kala-azar is mainly caused by the bite of the sandfly. Adult sand flies are about one-third the size of a small mosquito and thrive in moist climates and during the night. Female sandflies are the ones that require a blood meal to produce eggs and are responsible for the transmission of protozoa to the human host.
Sandflies acquire protozoan parasites by feeding on infected animals or humans. They use their saw-like mouthparts to create small wounds into the skin and suck blood. The protozoa from the infected host then enter the body of the sandflies and replicate.
Next time when sand flies feed on uninfected hosts-- be it canines, rodents or humans-- it transmits the infection to their bodies. The protozoa infection affects the phagolysosomes, immune cells that are involved in engulfing and destroying pathogens and start causing serious symptoms.
In kala-azar, the infection is spread to viscera such as the liver, spleen, bone marrow and lymph nodes of the intestines.
Symptoms Of Kala-Azar
The incubation period of kala-azar is 3-8 months. Its common symptoms include: 
- Fever for weeks or months.
- Splenomegaly or enlarged spleen.
- Hepatomegaly or abnormal enlargement of the liver.
- Hypergammaglobulinemia, elevated levels of certain immunoglobulins in the blood.
- Pancytopenia, low blood count of all the three blood cells; RBC's, WBC's and platelets.
- Loss of appetite leading to extreme weight loss
- Dry, thin and scaly skin
- Pale skin
- Asthenia or physical weakness
- Night sweats
- Swollen lymph nodes
Risk Factors Of Kala-Azar
Some of the risk factors of black fever include:
- Preschool children
- People with compromised immune systems such as in the case of AIDS.
- Malnourished people, especially due to the lack of iron, zinc and vitamin A.
- People who are intravenous drug users, suggesting transmission of the condition through contaminated syringes.
- Poor domestic sanitary conditions
- Staying in forest areas where the climate is humid and warmer.
Complications Of Kala-Azar
If not treated early, kala-azar can cause complications such as: 
- Chronic diarrhoea
- Growth retardation in children
- Multiple organ failure
- Cachexia or extreme weight loss and muscle wasting
- Superimposed infection
Diagnosis Of Kala-Azar
In areas where kala-azar is epidemic, diagnosing the condition is easy compared to areas where it is not. Common diagnostic methods include:
- Anti-K39 antibody test: To detect antibodies against the parasite in the blood. 
- Bone marrow aspirate: To examine the condition of the bone marrow whether it is healthy or not as parasites mainly infects the immune cells.
- Biopsy: To reveal the parasites inside macrophages.
Treatments Of Kala-Azar
Treatment methods of kala-azar depend on the parasitic species, areas where the condition is prevalent, type of sandflies and other factors. Common treatment methods include:
- Pentavalent antimonials: It is the first line of drugs used to treat kala-azar.
- Amphotericin B injections: It is an antifungal medication used for the treatment of fatal fungal infections and leishmaniasis. 
- Paromomycin oral drug: An aminoglycoside antibiotic as an alternative to amphotericin B. the drug is approved for some cases in India and Africa. 
- Other alternatives: It includes other medications like rifampicin, ketoconazole, metronidazole and azithromycin. 
Prevention Of Kala-Azar
Kala-azar can be prevented and controlled by the following strategies.
- Early diagnosis of the condition.
- Controlling the vector in the area such as spraying of DDT. 
- Monitoring of the disease in areas where the cases of infections are high.
- Monitoring and control of animal hosts such as dogs who can act as hosts for sandflies.
- Maintaining proper sanitation in the area.
- Social mobilisation and education of the community against the infection.
- Wearing long-sleeved clothes to prevent the bite of sandflies.
- Using insect repellents containing DEET.
- Sleeping under the bednet.
Kala-azar is a neglected disease associated with 90 per cent mortality as the treatment method is not so effective in completely treating the condition, followed by the lack of a vaccine and development of resistance by the protozoa against the drugs and DDT.
Therefore, controlling the vector and early diagnosis of the condition is the best approach to controlling kala-azar.