13. Nematodes infective larvae cont'd Flashcards
what are the nematodes with infective larvae (L3)?
Necator amercanus
Ancylostoma duodenale
Strogyloides stercoralis
Trichinells spiralis
what is the world’s largest intracellular parasite?
Trichinella spiralis
what is the distribution of Trichinella spiralis
worldwide
which areas are the exception, and do not have Trichinella?
Puerto rico
Australia
what is special about the life cycle of Trichinella spiralis?
the DH and the IH are the same individual
is T. spiralis host-specific?
NO
what is the size of the female worm of T. spiralis? male worm?
female: 3mm x 36µm
male: 1.5mm x 36µm
what is the size of the new born larvae?
80µm x 7µm
how many molts does Trichinella larvae undergo before developing into the adult?
4
how long does it take for T. spiralis to do 4 molts?
30 hours
where are larvae released from (T. spiralis)?
Nurse cells in the stomach
what is the habitat of the adults (T. spiralis)?
the small intestine
what is the domestic cycle?
- They are all zoonoses with humans becoming infected incidentally (i.e. eating raw or undercooked meat, pork) and not playing a role in the life cycle
- You can have the animals infecting themselves
where is sylvatic cycle found?
- temperate zone
- tropic zone
- arctic zone
How is trichinellosis acquired?
by ingesting meat containing cysts (encysted larvae) of Trichinella
what indices the releasing of larvae from their cysts?
- After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms
where do the larvae encyst?
in striated muscle
what larval stage is the one to encyst in striated muscle?
L1
which Trichinella species never encysts?
Trichinella pseudospiralis
how long does it take for encystment? how long are they viable for?
4-5 weeks, and several years
how is the cycle of Trichinella continued?
ingestion of the encysted larvae
what is the human’s role in the life cycle?
they are accidentally infected when they eat improperly processed meat
Where are Trichinella spiralis found?
in all tissues - eventually they reach the skeletal muscle
what are some of the most commonly invaded muscles of Trichinella spiralis?
Eye, tongue, masticator muscles, diaphragm, intercostal muscles, and the muscles found in arms and legs
Do nurse cells form in the heart?
NO
Do nurse cells form in the nervous system?
NO
why are the juveniles like a virus?
- they penetrate individual cells
- they subvert and redirect the host cell activities to their own survival
- they alter gene expression of the host cell of the contractile fibre to that of a nurse cell –> they remodel what the cell is supposed to be doing
what is a nurse cell?
- The nurse cell is a unique consequence of the host cell’s association with the infectious L1 larva of Trichinella spp.
- Its function us thought to nourish as well as protect it from host immune responses
- it is to make sure it survives and gets nourished as well – nurses the parasite
how long can the nurse cell-parasite complex can survive in the human host? how?
30 years - the worm immuno-supresses the host
what are the two distinct phases of the overall process of the nurse cell
- de-differentiation
2. re-differentiation
what are the steps leading to nurse cell survival?
- Larvae enter the muscle fibre cell
- Fibre loses its myofilaments
- Fibre mitochondria degenerates
- Fibre nuclei enlarges
- Fibre smooth endoplasmic reticulum increases
- Encapsulation of the unit with collagen
describe nurse cell formation?
- Larvae enters muscle, muscle proteins “leak” into bloodstream
- Mitochondrial damage – they start to break down, and nothing will have energy so everything that happens after this is coming from the larval stage of the parasite
- Secretion of parasite proteins – no longer a skeletal muscle, more a nerve cell
- DNA synthesis and nuclear enlargement – starts to produce specific proteins that it needs at that point
- Collagen type IV synthesis has a critical role in the regulation of angiogenesis
- Collagen type VI synthesis: a non-fibrillar collagen and forms a microfilament network – start remodelling the whole cell type
- Induction of vascular endothelial growth factor (VEGF) – triggers …
- Angiogenesis – nerve blood vessels that will surround the nerve cell and keep it alive
what is bad about angiogenesis
angiogenesis is required for spread of a tumour or metastasis
What is VEGF?
a signal protein produced by cells that stimulated angiogenesis (marker to know that angiogenesis has started)
what is the major reservoir for T. spiralis?
pig
what is the major reservoir for T. pseudospiralis?
pig
What species of Trichinella has no freezing resistance and a high reproductive capacity?
T. spiralis
What species of Trichinella has freezing resistance and low reproductive capacity?
T. native
T. britovi
T. nelsoni
T. pseudospiralis
What species of Trichinella has no cycts/nurse cells formation?
T. pseudospiralis
what is the stichosome?
The stichosome is a multicellular organ that apparently functions as a secretory gland and storage organ
what makes up the stichosome?
a single row of 45-55 cells called stichocytes
what do the antigens in the stichocytes cross-react with? what hypothesis was formulated in relation to this?
antigens present in the excretion-secretion products of living muscle larvae;
that secretory-excretory substances from the stichocytes not only are immunogenic but mediate alteration of host gene expression during the formation of the nurse cell
what do the stichocytes have?
- α and β stichocytes
- mitochondria, golgi-like apparatus, RER, 2 types of secretory granules
which 3 stages cause pathology in Trichinella?
- intestinal stage
- migrating larvae
- muscle
what is the pathology of the intestinal stage of Trichinella?
Worms migrating in the intestinal epithelium cause traumatic damage to the tissues. Inflammation causes nausea, vomiting, sweating, and diarrhea
what is the pathology of the migrating larvae stage of Trichinella?
- Juveniles damage blood vessels resulting in localized edema. They may cause pneumonia, myocarditis, encephalitis, eye damage, etc.
• L1, L2 and L3 are the things that will cause the most damage
• By going in and out of the cells, you cause the rupturing of cells and thus the edema
what is the pathology of the muscle stage of Trichinella?
- Formation of the nurse cell causes muscle pain, difficulty breathing, and swallowing. Presence of eosinophilia and edema in tissues
• Depending on how many of these larvae, you might have muscle pain
• A heavier burden – pain
what accompanies invasions of muscles by formation of nurse cells?
an intense inflammatory reaction
what raises the inflammatory reaction?
the release of the secretory-excretory antigens - the nurse cells are being developed and you have this release from the worm
can adult worms be detected in a stool specimen?
NO
can migrating juveniles be detected?
NO
how are muscle nurse cells detected?
- by biopsy
- muscle larvae can be seen easily by crushing the tissue between microscope slides
is serology a good method for diagnosis of Trichinella?
NO - false positives
what is PCR used for in Trichinella diagnoses?
epidemiology
what is given to relieve symptoms of Trichinella?
Analgesics and immunosuppressive drugs like corticosteroids
which drugs are used to eliminate the adult host from the intestine?
- mebendazole
- albendazole
are drugs recommended to eliminate nurse cells?
NO - only by surgery
