From encounter to disease - Parasitology and Mycology Flashcards
This deck contains the lectures about schistosomiasis and anti-fungal resistance
Lifespan of Schistosomes
~15 years
Epidemiological characteristics of schistosomiasis (3)
- Disease in tropical and subtropical areas
- Only 10% symptomatic
- Caused by flatworm (trematode): Schistosoma spp
Which species are infective to humans?
- S. Mansoni
- S. Japonicus
- S. Mekongi
- S. Intercalatum
- S. haematobium
Describe the lifecycle of Schistosoma mansion
- Eggs via stool/urine
- Eggs come in contact with fresh water
- Larvae (miracidia) hatches from egg
- Replication in intermediate host (fresh water snails)
- Cercariae release from snail
- Skin penetration of definite host
- Migration to mesenteric vains and pairing of male and female
Geography: Why is schistose weirdly/patchy distributed among the world?
Depends on where particle snails are present (intermediate host)
True or False: “Cercariae are produced by the parasite.”
False. Cercariae are produced by the snail
How can these cercariae find their way to the skin to penetrate?
Chemotaxis
What is needed for cercariae to penetrate the skin?
- Head structure with glands that produce proteases to degrade skin proteins
- Mechanical force of the tail movement
Why are the number of Schistosoma high
Fresh water is schaars, so lots of people visit these waters become infect
What happens to the head structure after penetrating the skin? Why?
They shed of their head structure –> because it’s an antigenic structure
Acquiring of a new head structure that is less/not antigenic
Which distinction can be made based on the colour of the worms?
White: males
Black: female –> digest erythrocytes, but cannot digest heem
Grey: -
How can you describe the movement of the worms?
Walking up and down the blood vessel system
Blooth clotting - thrombotic events
Turbulence
Pathogenesis of Schistosomiasis is really caused by…
Eggs produced by adult worms
How do schistosomiasis eggs cause pathology?
Trapped eggs contains eggshell which is cross-lit
Eggshell –> cross linked –> proteases cannot degrade it –> stays immunogenic –> ongoing immune response –> granuloma formation –> loss of tissue function
When do you treat schistosomiasis and why?
Before symptoms occur. Killing adult worms does not really do anything if their eggs have already caused symptoms
Which kind of Th response is the classical response against helminths?
Th2
What are the principal target cells during the host immune response?
Eosinophils
What are the major immune reactions against helminths?
- Eosinophil and mast cell activation
- Alternative macrophage activation
What kind of immune response is elicited against helminth infections and which cytokines are involved?
- Th2 reaction
- Cytokines IL-4, IL-5, IL-13
Describe the immune response to invasive helminths
- Eosinophils expand
- Bind and recognize helminth structures
- Granulate with anti-helminth components
- Induce antibodies (IgE)
- Crosslinking mast cells
What does the helminth directed Th2 response lead to?
Mucus synthesis leading to an increased barrier via which helminths can penetrate
How is a chronic schistosomiasis infection established?
Intensity of Th2 response is reduced, induction of regulatory T cell response
How can egg excretion factors induce a Th2 response?
25:25
Differences/Similarities Helminth/Allergy
- Allergy: high-income settings
- Helminth: low- income settings
What does the hygiene hypothesis mean with respect to helminth infections?
Helminth infection induces Th2 response, but at the same time it suppresses it by Treg response –> Negative-feedback mechanism in place
Most of the blood vessel is occupied by the adult worm-pair causing tremendous turbulence. Why does this not cause thrombosis?
What happens after when a thrombocyte binds to a schistosome egg? (6)
- Connect eggs to the underlying surface
- Endothelial cells overgrow it after binding
- Eggs excrete protein factors and attract leukocytes
- Leukocytes can’t phagocytose the egg
- Only degranulation and release of proteases
- Eggshell can’t be degraded –> your own external matrix is dissolved
- Egg has some room to move –> can go through tissue
Why can’t the egg be degraded by the leukocyte?
The eggshell is cross-linked
Do thrombocytes bind to eggs or adults?
Eggs, NOT adults
Why do thrombocytes bind to eggs and not adults?
Eggs and thrombocytes have a strong adhesion since they need to stay stuck in the blood vessel to migrate to the tissue to get excreted