Leishmania

Question 1

Describe the Leishmania life cycle

Answer 1

1 - Sandfly takes blood meal and injects promastigotes into skin
2 - Promastigotes are phagocytized by macrophages or other phagocytic cells
3 - Promastigotes become amastigotes
4 - Amastigotes multiply in cells of various tissues, rupture the cell and begin infecting other cells
5 - Sandfly takes blood meal and ingests macrophages infected with amastigotes
6 - amastigotes become promastigotes in the gut of sandfly
7 - Divide in the gut and migrate to the proboscis

Question 2

How many species of Leishmania are there and how many can infect mammals?

Answer 2

30 species

20 can infect mammals

Question 3

What are the 4 diseases called that are collectively known as Leishmaniasis?

Answer 3

Cutaneous leishmaniasis (CL)
Diffuse cutaneous leishmaniasis (ADCL)
Mucocutaneous leishmaniasis
Visceral (kala-azar)

Question 4

Main points about CL

Answer 4

Caused by the parasite living in macrophages on the skin at the site of the sandfly bite
Main causitive agents are: L.major, L.tropica, L.infantum and L.mexicana spp. complex
Cutaneous lesion looks somewhat like a volcano with raised edges containing amastigotes

Question 5

Main points about ADCL

Answer 5

Diffuse cutaneous leishmaniasis
In the immunocompromised the parasite diffuses from the site of the sandfly bite to other areas of the body surface producing numerous lesions
Can occur (rarely) with L.aethipoica, L.mexicana and L.amazonensis
Responds poorly to chemotherapy

Question 6

Main points about mucocutaneous leishmaniasis?

Answer 6

Caused by the parasite living in macrophages of the soft mucous membranes within the mouth and nose or after spreading from a nearby cutaneous lesion (very rare)
Main causative agents are Vianna subgenus but can also be caused by L.amizonensis
Progressively invades the nose, leading to the destruction of the nasal septal cartilage and causing the collapse of the nose and disfigurement of the face

Question 7

Main points about kala-azar?

Answer 7

Caused by the parasite living in the macrophages of visceral organs such as the liver, spleen, lymph glands or bone marrow
Main causative agents L.donovani and L.infantum
Often accompanied by fever, weight loss, enlarged spleen, liver and glands, anaemia, low white blood cell and platelet counts
Opportunistic infection in areas where it coexists with HIV and tuberculosis

Question 8

What is PKDL?

Answer 8

Post kala-azar dermal leishmaniasis
Occurs sometimes after an apparent successful treatment with drugs, some patients develop multiple cutaneous lesions or non-ulcerating papules full of amastigotes on the skin
Caused by L.dovani and L.infantum

Question 9

How many people are affected with Leishmania?

Answer 9

Endemic in 98 countries - mainly in the tropics
~350 million people live in these areas and are at serious risk
12 million people infected with 2 million new cases anually
0.5 million with VL and 1.5 million with CL annually
0.5 million deaths annually

Question 10

What factors lead to the increase in risk of Leishmania?

Answer 10

Poverty
Poor housing - damp earthen floors (prolonged survival of vector)
Cracked mud wall (day time resting of vector)
Sleeping out doors (increased exposure)
Deforestation and intrusion of immunologically naive populations
Migration of rural poor to major cities
Poor environmental sanitation

Question 11

In what ways does Leishmania worsen poverty?

Answer 11

Income loss for patients and families due to absence from work
Death to wage earners
Transport to medical centres
Medical costs of anti-leishmanial medicine - in India average cost is 1.4 times the annual per capita income for 1 patient
Malnutrition and anaemia increase severity of the disease

Question 12

What control strategies can be put in place to help reduce the parasite?

Answer 12

Alleviate poverty - improved housing, living wage
Improved diagnosis - increase awareness in communities about disease and control
Community participation in development of control strategy
Vector control is impossible
No vaccines in routine use

Question 13

What is the main method of treatment?

Answer 13

Chemotherapy
Antimonial - current frontline drug
- discovered by trial and error
- mode of action unknown, toxic and with side effects
- intravenous fusions over long periods in hospitals
- requires continuous monitoring in hospital making treatment expensive
- patient non-compliance, treatment failure and drug resistance major factors
- new drug required

Question 14

What are the two life cycle forms of Leishmania?

Answer 14

Promastigotes - extracellular form

Amastigotes - intracellular form

Question 15

What are the anti-leishmanial drugs and their targets?

Answer 15

Meglumine antimoniate - Activated within amastigote but not promastigote, A-L activity may be due to action on host macrophage
Amphotericin B - Induces pores which alter ion balance and lead to cell death
Pentamidine - Accumulated by parasite, Effects include binding to kinetoplast DNA PMoA uncertain
Poromycin - affects mitochondrian of leishmania
Miltefosine - PMoA uncertain - various methods proposed
Sitamaquine - PMoA uncertain - may effect mitochondrial electron transport

Question 16

What alternate methods of treatment are available for leishmaniasis?

Answer 16

Immunotherapy - aimed at modulating the host immune response
Thermotherapy - aimed at using heat to effect killing
Nanotherapy - use of nanoparticles for drug delivery to increase efficacy and effect killing

Question 17

What are the desired characteristics of a new drug for leishmaniasis?

Answer 17

Discovered via a rational drug development strategy
Mode of action should be known
Non-toxic
No need for monitoring in hospital
Cheap
Oral administration
Short treatment regimes
Patient non-compliance
Does not lead to drug resistance

Question 18

What potential targets are there for a newly developed drug to affect in leishmania?

Answer 18

Sterol biosynthesis - formation of sterols e.g. cholesterol
Autophagy - destruction of cells
Purine salvage pathway
Glycolytic pathway

Question 19

How can Leishmaniasis be quickly diagnosed?

Answer 19

Biopsy - allows parasite detection, materials dried, fixed with methanol and staind with Giemsa or hematoxylin and eosin stains and observed by microscopy
- does not allow species identification

Question 20

What molecular techniques are there for species identification of leishmania?

Answer 20

Isoenzyme analysis - digestion of PCR products produces distinctive species-specific banding patterns

Question 21

What are the immunologic methods for species identification of leishmaniasis?

Answer 21

Anti-K39 antibody detection in immunochromatographic strip test

• 5 minute incubation of a drop of finger prick blood and buffer onto strip will produce a second pink band indicating the presence of anti-K39.
• Antibody detects visceral but not cutaneous leishmaniasis as patients lack the K39 antibody