Transmission and Life Cycle

Classification of parasite : Kinetoplastida (order); Tryapnosomatidae (family), Leishmania (genus)

Parasite morphlogy: The amastigote, which contains a nucleus, kinetoplast, and internal flagellum, is an oval body and is about 2-5 microns by 1 - 3 microns (see left photo). The promastigote form measures 14 - 20 microns by 1.5 - 4 microns and is longer and thinner than the amastigote form. Promastigotes contain a central nucleus, a kinetoplast, and an anterior flagellum (see right photo).

 

Sources (L-R):http://www.emedicine.com/derm/topic219.htm , http://www.yamagiku.co.jp/pathology/case/case176.htm

Transmission: Mainly occurs through inoculation by the vector; some reports of tranmission by blood transfusions and contaminated needles; rarely spread from mother to baby

Vector: Female sandflies (30 species of Phlebotomus and Lutzomyia) in inter-tropical and temperate regions

Sources (L-R): http://www.who.int/leishmaniasis/disease_epidemiology/en/, http://pathmicro.med.sc.edu/lecture/trypanosomiasis.htm

Vector morphology: About 1/3 of the size of a mosquito (2-3 mm)

Life Cycle:

Source: http://www.dpd.cdc.gov/dpdx/HTML/Leishmaniasis.asp?body=Frames/G-L/Leishmaniasis/body_Leishmaniasis_page1.htm

1. While taking a blood meal, the sandfly releases promastigotes through the proboscis into the skin.

2. Macrophages phagocytize the promastigotes.

3. Promastigotes transform into amastigotes.

4. Amastigotes proliferate in cells and macrophages and during this time, the signs and symptoms of the disease become particularly prevalent.

5./6. The sandfly takes a blood meal and ingests macrophages containing amastigotes.

7. Amastigotes reach the infective stage when they transform into promastigotes in the sandfly's midgut.

8. Promastigotes migrate to the proboscis, ready to be released during the next blood meal.

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Sources:

http://www.who.int/tdr/diseases/leish/lifecycle.htm (animated life cycle)

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.4376

http://pathmicro.med.sc.edu/parasitology/blood-proto.htm

http://www.leishdomus.org/leish.htm?