Notes on the biological cycle of Leishmania
The infection is transmitted by the bite of infected sandflies. The promastigotes (flagellates elements, extracellular) in the insect’s saliva, penetrate through the skin, bind to macrophages of the skin and spread in the reticuloendothelial system of the whole organism. On the surface of the promastigote there are two molecules that have a prominent role in engaging the parasite-phagocytic cells: a glycoprotein (gp63) and a lipofosfoglycan. They activate the way alternates complement. Most parasites are destroyed by the body’s non-specific defenses, some are rapidly engulfed by macrophages, where they become amastigotes (aflagellati elements, intracellular), which begin to multiply in intracellular vacuoles. The amastigotes are oval forms of 2-4 microns in diameter. The lysosomes of macrophages release the hydrolasic enzymes to digest the parasite, Leishmania but offer some resistance to their action. Visceral leishmaniosis in the affected cells are soon to meet death and release the amastigotes that are themselves engulfed by other macrophages: this cycle is repeated several times until all organs containing macrophages are widely infected with Leishmaniae (spleen, liver, bone marrow, lymph nodes). When a subject is infected point from another phlebotomist not yet infected, the infection is transmitted at the time when it sucks the blood, through the circulating macrophages full of amastigotes. In the sandfly stomach amastigotes are released in a few hours and intestines are transformed into promastigotes, 10-15 microns long plagued shape and 1.5-3.5 microns wide: the scourge measures 15-28 microns. After many binary divisions they migrate into the pharynx and in the buccal cavity of the sandfly, ready to be placed on a new host. The cycle time in the mosquito is ten-day.