Kala azar is transmitted by: March 2007

Ans. A: Sand fly Kala-azar is spread through an insect vector, the sandfly of the Phlebotomus genus. The sandfly vector becomes infected when feeding on the blood of an infected individual or an animal reservoir host. The leishmania parasites live in the macrophages as round, non-motile amastigotes (3-7 micrometers in diameter). The macrophages are ingested by the fly during the blood- meal and the amastigotes are relesed into the stomach of insect. Almost immediately the amastigotes transform in to the motile, elongated (10-20 micrometers), flagellate promastigote form. The promastigotes then migrate to the alimentary tract of the fly, where they live extracellularly and multiply by binary fission. Four to five days after feeding the promastigotes move forward to the oesophagus and the salivary glands of the insect. When the sandlfy next feeds on a mammalian host, it's proboscis pierces the skin and saliva containing anticoagulant is injected into the wound to prevent the blood from clotting, the leishmania promastigotes are transferred to the host along with the saliva. Once in the host the promastigotes are taken up by the macrophages where they rapidly reve to the amastigote form. The leishmania are able to resist the microbiocidal action of the acid hydrolases release form the lysozymes and so survive and multiply inside the macrophages, eventually leading to the lysis of the macrophages. The released amastigotes are taken up by additional macrophages and so the cycle continues. Ultimately all the organs containing macrophages and phagocytes are infected, especially the spleen, liver and bone marrow.