Leishmania

Title: Leishmania — Leishmaniasis

Introduction: Leishmania is the protozoan parasite that is responsible for the disease Leishmaniasis.  There are around 20 different species of Leishmania. It is a vector borne disease transmitted to humans and other vertebrates by sand flies.  Symptoms of the disease range from confined skin ulcers (cutaneous Leishmaniasis) to potentially lethal systemic infection (visceral Leishmaniasis)¹.  Leishmaniasis is most common in Mexico, Central America, South America (excluding Uraguay and Chile), most parts of Asia, the Middle East, Africa, and Southern Europe.  Many different sand fly vectors have adapted to different climates and environments and have the potential to continue to adapt and extend their georgraphic range. ¹

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Symbiont Description:  Leishmania is the genus name of the protozoan parasite. There are over 20 different species of Leishmania that live in various subtropical/tropical regions of the world. 

Host Description:  In the first stage of life, sandflies serve as the host for leishmania.   The second stage of life occurs when a sandfly bites a vertebrate for a blood snack.  Common vertebrates that leishmania live in include humans, dogs, and other mammals. 

Life Cycle: There are two distinct stages during the lifecycle of Leishmania.  First, a sand fly infected with the parasite bites a human and injects the parasite (which is in the Promastigote stage) into the skin.  The Promastigote is phagocytized by macrophages, which transform the Promastigote into Amastigotes.   The Amastigotes multiply in various tissues throughout the body.  A sand fly bites an infected individual and the Amastigotes turns into the Promastigote stage when it reaches the midgut of the fly.  The Amastigotes multiplies throughout the sand fly and the cycle starts all over again.¹

Ecology:  Leishmaniasis occurs in two different forms, cutaneous and visceral.  Cutaneous Leishmaniasis is much more common and is characterized by skin ulcers.  Visceral Leishmaniasis is a lot more serious including extreme weight loss, inflammation of the liver and spleen and reduced red blood cell count which can ultimately lead to death.  90% of VL occurs in India, Bangladesh, Nepal, Sudan, Etiopia, and Brazil¹.  90% of CL occurs in Afghanistan, Algeria, Iran, Saudi Arabia, Syria, Brazil, Columbia, Peru and Bolivia¹.  The disease does not spread epidemically unless humans are involved. 

An Example of Vector Born Transmission:  Vector Born transmission occurs when the vector spreads the disease.  The most common vectors that spread diseases are arthropods, which account for 85% of all known animal species³.  The arthropods spread the disease by either biting or stinging.  In the case of Leishmaniasis, the sand fly is the vector.  It bites various vertebrates and injects the Leishmaniasis into the skin.

References:

1.    1.  http://www.cdc.gov/parasites/leishmaniasis/biology.html

2.    2.  http://www.iayork.com/Images/2008/7-27-08/070617_leishmania_300.jpg

3.    3.  http://www.enotes.com/vector-borne-diseases-reference/vector-borne-diseases