Basics of Leishmania Spp

Vector

Sandflies are pool feeders — they prick their victim and suck up the resulting pool of blood. They are infected upon ingesting infected macrophages.

Transmission

Life Cycle

Amastigote

Macrophage	Amastigotes are within the macrophages.
Ingestion	Upon ingestion by the sandfly, amastigotes transform into promastigotes.

Promastigote

Gut	The promastigotes in the gut of the female sandfly attach to the midgut-hindgut epithelium where they divide by binary fission for 8-20 days after initial ingestion of blood.

Metacyclic Promastigote

Pharynx	A decline in tetrahydrobiopterin triggers metacyclogenesis, whereby the promastigotes move forward to the pharynx.
Blockage	Metacyclic promastigotes secrete the promastigote secretory gel (aka PSG) to block the pharynx. The PSG plug forces the stomodeal valve open and extends into the pharynx region. Metacyclic promastigotes are concentrated at the anterior pole of the plug but are found along the foregut in both the cibarium and proboscis.
Feeding	When such a sandfly attempts to feed, it must egest the plug by regurgitating a bolus of metacyclic promastigotes — “clearing its throat”. This bolus is injected into the bite wound. There is no infection of the sandfly’s salivary glands.

Disease

Leishmaniasis	Species	Patient	Reservoir	Vector
Old Localized Cutaneous	L. major (moist) L. tropica (dry)	Human	Dog, rodent	Phlebotomus spp (Sandfly)
New Cutaneous	L. mexicana	Human	Dog, rodent	Phlebotomus spp (Sandfly)
Diffuse Cutaneous	L. aethiopica	Human	Hyrax	Phlebotomus spp (Sandfly)
New Dry Cutaneous	L. amazonensis	Human	Dog, rodent.	Lutzomyia
Muco-Cutaneous	L. braziliensis L. guyanensis (both viannia)	Human	Dog, rodent.	Phlebotomus spp (Sandfly)
Visceral	L. donovani	Human	Human	Phlebotomus spp (Sandfly)
Visceral	L. infantum	None, zoonosis	Dogs	Phlebotomus spp (Sandfly)
Leishmania/HIV	Co-infection is an emerging disease, particularly in southern Europe where 25-70% of adult Visceral Leishmaniasis are related to HIV infection, and 1.5-9.5% of AIDS cases suffer from from newly acquired or reactivated Visceral Leishmaniasis.

Parasite	Distribution
L. tropica	Urban areas of Mediterranean, Middle East, Pakistan and parts of India.
L. major	Rural (esp desert) areas of Central Asia, South Russia, Middle East and Africa.

Parasite	Distribution
L. braziliensis L. mexicana	Central and South America.
L. infantum	Africa, Asia and South Europe.
L. chagasi	South America

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