Leishmania Flashcards
Which genera belong to the family Kinetoplastids?
Leishmania & Trypanosoma
Define kinetoplast
a disk-shaped mass of circular DNA inside a large mitochondrion that contains many copies of the mitochondrial genome
What are maxi-circles?
ktDNA encoding several genes, similar to mitochondrial DNA.
the mRNAs coming from the maxi-circles has many errors in it and requires editing
What are mini-circles?
ktDNA that encodes guide DNAs (gDNA), which corrects the mistakes in the mRNA from the maxi-circles
Where does the guide DNA correct the mRNA of maxi-circles?
in the mitochondrion of kinetoplasts
What does the extent of editing correlate with?
different parasite life cycle stages and the corresponding changes in metabolism
What are the mini-circles used for in the lab?
parasite detection and distinguishing different isolates
What is the glycosome and what are its features?
- organelle in which glycolysis occurs
- single membrane
- equivalent to peroxisome
- contains glycolytic enzymes
What are the four major morphological forms found in kinetoplastids that cause human disease?
trypomastigote, amastigote, promatigote, epimastigote
What are the features of the trypomastigote?
- kinetoplast located on posterior end
- flagellum emerges from posterior end from basal body and folds back along the body of the parasite to form the undulating membrane
- free flagellum emerges from anterior end
What is the function of the undulating membrane?
increases motility
In which direction does the parasite move?
In the same direction as the orientation of the flagellum (forward from anterior end)
What are the features of the amastigote?
- sphere-shaped
- no free flagellum = non-motile
- basal body at base of flagellum
- kinetoplast is near the nucleus
- nucleus is at posterior
What are the features of the promastigote?
- kinetoplast at anterior end
- free flagellum with no undulating body
What are the features of the epimastigote?
- kinetoplast is centrally located, just anterior to nucleus
- flagellum emerges near center from basal body
- forms a shorter undulating membrane (not observable under microscope
- epimastigotes are less motile than trypomastigotes
What are the four types of leishmaniasis?
cutaneous, mucosal, visceral, and nodular post-kala-azar dermal
Which species of sandflies transmits leishmania in the New World?
Lutzomyia
Which species of sandflies transmits leishmania in the Old World?
Phlebotomus
How is leishmania spread?
Mostly zoonotic but can also spread through humans
One species can usually infect several different animal species
How many sandfly species cause infection in humans?
21 out of 30 species that affect mammals
Which Leishmania species causes visceral leishmaniasis in humans and where is it found?
L. donovani. Asia & Africa
Which Leishmania species causes cutaneous leishmaniasis in humans?
L. tropica. Asia, Africa, & Mediterranean
Which Leishmania species causes mucocutaneous leishmaniasis in humans?
L. braziliensis. Central & South America
In America, which countries are not affected by leishmaniasis?
Canada, Uruguay, and Chile
Define digenetic life cycle
having two hosts, as in Leishmania
In which host are promastigotes found?
in the sandfly vector
In cutaneous leishmaniasis, where does the amastigote reside in the human body?
intracellularly in macrophages in skin lesions
In visceral leishmaniasis, where does the amastigote reside in the human body?
in the mononuclear phagocyte system of blood, liver, lymph nodes, spleen
Which stage is the motile stage of leishmaniasis?
promastigote
Which stage is the non-motile stage of leishmaniasis?
amastigote
How does leishmania move from the sandfly to the host?
through the bite of a female sandfly, via the pharyngeal valve
How does the pathogenesis affect the immune cells of the body?
decrease in WBC
increase in monocytes & lymphocytes
elevated IgM & IgG
What is the main difference between cutaneous and visceral leishmaniasis?
cutaneous is self-healing, visceral is often fatal without medication
Describe the sores formed in cutaneous leishmaniasis
open sores or nodules on the skin that are usually painless but can become painful if secondarily infected, can cause lymph nodes to swell, center encrusts while satellite papules develop at the periphery
When do skin nodules form?
2-8 weeks after the bite
How long does it take for ulcers to heal?
2-10 months, sometimes years
Can a person develop ulcers after a second infection of cutaneous leishmaniasis?
no, they become immune
What happens when a person gets mucocutaneous leishmaniasis?
they get the sore, like in cutaneous leishmaniasis, then the disease metastasizes and spreads to mucoid tissues and can destroy them. may occur months-years after skin lesion
Which species causes visceral leishmaniasis in the Old World?
L donovani (Asia & Africa L. infantum (Mediterranean - particularly affects infants)
Which species causes visceral leishmaniasis in the New World?
L donovani chagasi
What are some symptoms of visceral leishmaniasis and when do they occur?
chronic fever, weight loss, enlarged spleen and liver. can occur months after being bitten
Which part of the world has milder symptoms for the disease?
the Middle East
Who does L donovani chagasi affect the most?
mostly children in Latin America and North-Eastern Brazil
Describe the pathogenesis in visceral leishmaniasis
- from bite on skin, parasite moves rapidly internally
- may sometimes cause skin lesions in children (not common
- go to phagocytic cells of spleen, liver, lymph nodes, bone marrow, intestinal mucosa, etc
- 1-4 days later there is chronic fever, chills and sweating. spleen and liver become enlarged
- host becomes susceptible to other infections
How can leishmaniasis be diagnosed?
- look for skin lesions in all types
- biopsy lesion (stain with Giemsa dye) most common technique
- can test using PCR but does not say if parasite is alive
- Ab detection (limited value in cutaneous)
- immunoassays
How to prevent leishmaniasis?
- vaccinate stray dogs
- suppress small rodent population
- suppress the sandfly
- insecticide, protective clothing, permethrin treated clothes & bed nets. esp at night
Have vaccines been effective?
no
What are some common terms for visceral Leishmaniasis?
kala-azar and dumdum fever
