Kala-azar (Visceral Leishmaniasis) is transmitted from person to person by the bite of the infected female phlebotamine sandfly, Phlebotomus argentipes which is a highly anthrophilic species. Transmission may also take place by contamination of the bite wound or by contact when the insect is crushed during the act of feeding. Transmission of kala-azar has also been recorded by blood transfusion, veneral and transplacental but are very rare.
Different factors involved in the transmission of kala-azar
- Agents: Leishmania donovani, are intracellular parasites that infect and divide within macrophages is the causative agent of kala-azar.
- Reservoir of infection: There is a variety of animal reservoirs e.g. dogs, jackals, foxes, rodents and other mammals. Indian kala-azar is considered to be a non-zoonotic infection with man as the sole reservoir.
- Age: Kala-azar can occur in all age groups including infants below the age of one year.
- Sex: Males are affected twice as often as females.
- Population movement: Movement of Population between endemic and non-endemic areas can result in the spread of infection.
- Socio-economic movement: Kala-azar usually affects the poorest of the poor.
- Occupation: The disease strongly associated with occupation. People who work in various farming practice, forestry, mining and fishing have a great risk of being bitten by sandflies.
- Altitudes: Kala-azar is mostly confined to the plains, it does not occur in altitudes over 2000 feet.
- Season: High Prevalence during and after rains.
- Rural areas: The disease is generally confined to rural areas, where conditions for the breeding of sandflies readily exist compared to urban areas.
- Vector: Only the female sandfly transmits the protozoa, infecting itself with the Leishmania parasites contained in the blood it sucks from its human or mammalian host. Sand fly breed in cracks and crevices in the soil and buildings, tree holes, caves etc.