10 Questions
What is the primary mechanism of transmission for Leishmania parasites?
The bite of infected sandflies
What is the correlation between the leishmanin skin test and the progression of leishmaniasis?
A positive leishmanin skin test correlates with resistance to leishmaniasis
What is the primary immune response responsible for defense against Leishmania?
Cell-mediated immunity
Which species of Leishmania is commonly associated with mucosal leishmaniasis in the New World?
Leishmania braziliensis
What is the typical duration of infectivity in sandflies that transmit Leishmania?
The entire lifespan of the sandfly
What is the primary mechanism by which promastigotes are introduced into a vertebrate host?
During a blood meal by an infected sandfly
What is the characteristic shape of amastigotes?
Round- or oval-shaped structures
Which of the following is a characteristic of visceral leishmaniasis?
Fever, wasting, pancytopenia, and hypergammaglobulinemia
What is the primary site of amastigote multiplication?
Phagolysosomes within reticuloendothelial cells
Which species complex of Leishmania parasites is typically associated with visceral leishmaniasis?
Leishmania donovani complex
Study Notes
Leishmaniasis
- Caused by protozoan parasites of the genus Leishmania, transmitted by sandflies of the genera Phlebotomus (Old World) and Lutzomyia (New World)
- Results in diverse group of cutaneous and visceral clinical syndromes
Life Cycle
- Promastigotes in the female sandfly are introduced into the skin of a vertebrate host during a blood meal
- Promastigotes invade reticuloendothelial cells, transform into amastigotes (2-5 μm in diameter) within reticuloendothelial cells
- Amastigotes multiply within phagolysosomes, invade other reticuloendothelial cells
- Sandflies feeding on infected individuals ingest parasitized cells, amastigotes transform into promastigotes, multiply in the gut, and migrate to the proboscis, completing the cycle
Clinical Classification
- Separates into three major syndromes: visceral leishmaniasis, cutaneous leishmaniasis, and mucosal leishmaniasis
- Visceral leishmaniasis: fever, wasting, pancytopenia, hepatosplenomegaly, and hypergammaglobulinemia
- Cutaneous leishmaniasis: localized, nonhealing ulcerative skin lesion
- Mucosal leishmaniasis: primary cutaneous lesion followed by destructive nasopharyngeal lesions (espundia)
Transmission and Epidemiology
- Sandflies are inactive in daylight, seeking shelter in dark, moist places
- Female sandflies feed on various warm- and cold-blooded hosts, acquiring Leishmania with their first blood meal
- They can transmit disease 7-10 days later and remain infective throughout adult life
- Other routes of transmission: blood transfusion, needle-sharing, congenital transmission, sexual contact, and laboratory accidents
Immunology
- Protective immune response is primarily cell-mediated
- High titers of antibodies in visceral leishmaniasis play no part in defense against the parasite
- Positive leishmanin skin test correlates with resistance to leishmaniasis
- Cell-mediated immunity (CMI) causes tissue destruction and correlates with the onset of ulceration in cutaneous leishmaniasis
Visceral Leishmaniasis
- Most often caused by species of the L. donovani complex: Leishmania donovani and Leishmania infantum
- Transmitted by phlebotomine sandflies of the genera Phlebotomus (Old World) and Lutzomyia (New World)
- Regional epidemiology depends on the interaction of sandflies, reservoir hosts, and susceptible humans
Learn about the biology and life cycle of Leishmania parasites, transmitted by sandflies, and their role in causing diverse clinical syndromes. Understand the different stages of the parasite's life cycle and how it affects vertebrate hosts.
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