Leishmania

Question 1

What is the respective incidence of VL and CL (numbers)?

Answer 1

0.5m (VL) and 10m (CL)

Question 2

Where do the promastigotes go once they are injected by the sandfly? What happens to them?

Answer 2

Are phagocytosed by macrophages in the liver and spleen in VL and in the skin in CL.
The promastigotes transform into amastigotes by losing their flagellum. Amastigotes multiply in the host macrophage and eventually lyse the cell to infect more cells.

Question 3

How do amastigotes within phagocytes avoid activating macrophage defence mechanisms?

Answer 3

By residing in the phagolysosome/ parasitophorous vacuoles

Question 4

How long after feeding does the leishmania invasion process occur?

Answer 4

50 days

Question 5

How do leish promastigotes use their flagella to move?

Answer 5

Use their anterior flagella to move forward!

Question 6

Describe the metacyclogenesis of leishmania parasites within the sandfly. From injection into host.

Answer 6

• Flagellated promastigotes injected
• Form aflagellar amastigotes in macrophages
• Forms procyclic promastigote
• Surface coat changes over time to make them more infective and change sandfly behaviour

Question 7

What is the role of PDG (proteophosphoglycan)?

Answer 7

Blocks stomodeal valve and has an immune effect on host cells (affects macrophage recruitment).

Question 8

What is the role of LPG (lipophosphoglycan)?

Answer 8

Role unknown but speculated to determine if the infection becomes VL or CL.
The LPG is different for each species and is diagnostic.
Also aids in resistance to lysis via complement -therefore enabling silent entry into macrophages.

Question 9

How does the amastigote survive in the hostile environment of the parasitophorous vacuole?

Answer 9

Has a proton pump to maintain pH

Question 10

How do amastigotes facilitate intracellular survival?

Answer 10

-Downregulate immune response molecules
-Damp down ROS and NO production by macrophage
-

Question 11

How many Leishmania species infect humans?

Answer 11

Around 20

Question 12

What are the subcategories of CL?

Answer 12

• Diffuse
• Mucocutaneous
• Recidivans
• Mucosal lesions (do not damage mucous membranes like ML does).

Question 13

What is PKDL? What are the two forms?

Answer 13

A complication of VL caused by L donnovani occurs following cure or resolution of VL. Consists of skin manifestations months or years after the apparent cure.

Can be papular (papules) or macular (flat).

Question 14

What is the incidence of PKDL in E Africa?

Answer 14

Around 50-60% of VL patients go on to develop PKDL.

Question 15

What is the response to treatment of PDKL?

Answer 15

Responds badly to treatment and persists for a long time.

Question 16

How may people be a reservoir for leishmaniasis/ be responsible for disease persistence within a community?

Answer 16

Papules and nodules may contain amastigotes.

Question 17

How do CL lesions from major and tropica present? How do brazilensis lesions present?

Answer 17

Dry, round lesions.

Wet lesions which may get secondary infections with bacteria.

Question 18

Why should infections with Mexicana and amazonensis always be treated?

Answer 18

Although they can self-cure, they can progress to ML if untreated.

Question 19

Which species is ML mainly caused by?

Answer 19

Aethiopica

Question 20

What is the difference in TH response in BALB/c mice (used for testing) vs human response?

Answer 20

The mice have a strong TH1/TH2 dichotomy whereas this does not occur in humans, we are more likely to have a balance between TH1 and TH2.

Question 21

Describe the typical cytokine response early in infection (although depends on the infective species). What impact does this have on macrophage defence?

Answer 21

Decrease in TNF alpha
Decrease in IFN gamma
Increase in IL10 (anti-inflammatory)

All lead to a decrease in macrophage defence (is beneficial to the pathogen).

Question 22

Describe the typical shift in cytokine response later in infection.

Answer 22

Switches to increased TNF alpha and IFN gamma and a decrease in IL10, causing macrophage activation to attack the parasite.

Question 23

Where is infection with diffuse CL focused?

Answer 23

Ethiopia.

Question 24

What is the T helper cell skew in diffuse CL and how does this allow the spread of parasites/ facilitate the infection’s diffuse nature?

Answer 24

TH2 is stronger than TH1 which leads to a lot of macrophage recruitment but little macrophage activation. Leads to ANERGY. This allows the spread of parasites and their diffuse nature.

Question 25

What is the response of DCL to treatment?

Answer 25

Highly refractive to treatment and therefore has a poor prognosis.

Question 26

How and why does recidivans develop?

Answer 26

Develops after cutaneous lesions have healed. Parasites are kept under control but persist in scars, these can be reactivated e.g. through trauma. This causes lots of tissue damage and spreading.

Question 27

How do we confirm a case of recidivans?

Answer 27

PCR to diagnose as leishmania. This is hard as parasites are sparse within the lesions.

Question 28

Which parasites are the cause of ML? What do the ulcers of ML contain?

Answer 28

Viannia. Ulcers are full of immune and inflammatory cells. This inflammation causes lots of tissue damage, despite the parasite burden often being low.

Question 29

What are the risk factors for ML?

Answer 29

• Males affected more than females
• Age
• Immune status
• If lesions were cured on the upper body

Question 30

In which demographic is complex VL most common? Why is this?

Answer 30

Those with HIV. Each exacerbates the other: leishmania promotes the progression to AIDS and latent leishmania in HIV patients will reemerge.

Question 31

What is the cascade leading to a decrease in cell mediated response that most commonly occurs in HIV coinfections with leishmania?

Answer 31

CD4 cells decrease due to HIV/ immunosuppression –> this leads to a decrease in the production of IFN gamma –> produces a TH2 response and a decrease in cell-mediated response (shift away from cellular response).

Question 32

How can pregnancy complicate leishmania infection?

Answer 32

The decrease in cellular immunity associated with pregnancy may make leishmania more aggressive.
The decrease in cellular immunity makes the individual prone to relapse.
If the newborn becomes infected they may have delayed symptoms.

Question 33

Look at notes for cases of atypical leishmania infection!

Answer 33

-

Question 34

How is VL diagnosed?

Answer 34

Microscopy is the gold standard. Using microscopy/ parasitology requires skillset and training for amastigote identification.
a sample is taken from aspirating the spleen and liver or bone marrow.

Also ELISA, antigen detection, DNA probe/ molecular tools.

Question 35

How is CL diagnosed?

Answer 35

Aspiration of the lesion from an undisturbed edge. Smear on a slide, fix and stain and microscopy diagnose.

Question 36

What is the benefit and disadvantage of using antigen detection when diagnosing leishmania?

Answer 36

• Distinguish between quiescent and active infection

- Does not work as well in HIV + individuals (because of the suppressed immune response)

Question 37

Why is a serology test not often used for diagnosis? How does it work?

Answer 37

Directly agglutinates if the antigen is present.

Not widely used as test results can be ambivalent.

Question 38

Descrive the katex test that can be used to identify leish infection. What is the difficulty with this?

Answer 38

Coat beads in Abs which detect antibodies in urine samples. Agglutination if present.
Hard to get a standardised leish antigen as there is so mush variability. Also requires skill.

Question 39

What is the RK39 test? How has this been modified? What is the problem with this?

Answer 39

Diagnostic elisa style test using kinesin like gene which is conserved.
Made into a dipstick test (RDT). Must use a secondary means e.g. parasitology to confirm.

As an Ab based test, it cant distinguish between current and past infections but we assume it is a current infection if the patient is showing symptoms.