Parasitology-5 Flashcards
What are the 4 things which contribute to the pathogenesis of parasitic disease?
Nutritional competition or depletion of the host’s essential nutrients (spoliation or despoliation)
Mechanical damage through the bursting of cells, migration through tissues or altering the flow of bodily fluids and movements
Inappropriate of insufficient immunological response
In very few cases there is toxin mediated pathogenesis
How do nematodes exhibit disease through nutritional competition?
Competition is seen at all levels and it is affected by the nutritional status of the host which can cause malnutrition
This is most commonly noted with Acaris lumbricoides which is one of the most prevalent human intestinal parasites because it has the largest reproductive rate
Some worms such as Ancyclostoma duodenale and Necator americanus which are blood sucking parasites have more specific malnutrion symptoms such as anemia
How do nematodes cause disease through mechanical damage?
Some worms like Ascaris lumbricoides produces blockages and bowel distention or rupture
Ancyclo duodenale and Necator amercianus cause intestinal haemorrhage through their hooks
Trichuris trichiuria provokes rectal prolapse through use of a whip like projection which it uses to cut out pieces of the mucosa for digestion
Enterobius vermicularis commonly causes intense anal and vaginal pruritus, secondary bacterial infection along with disturbed sleep
How can cestodes cause disease?
They are largely asymptomatic, and often provide concomitant immunity preventing more than one from colonizing the host causing the infection to persist as a single individual
What extra-intestinal disesase can be caused by intestinal worms?
Some worms such as ascaris lumbricoides go through a developmental stage in the lungwhich can lead to inflammation and pneumonia
Some worms such as echinococcus granulosus larvae can trigger an allergic reaction leading anaphylactic shock
Chronic infection in a variety of tissues may be caused by the different stages of worms if they end up trapped and induce the formation of a granuloma
How can Schistosoma Mansoni cause disease?
The adults live in the intestinal mesenteric venules, if the eggs manage to find their way to the lumen there can be intestinal symptoms
The eggs may also be dragged back to the liver through the hepatic portal vein where they get stuck. This can lead to portal hypertension due to granulomas around the edge of the vein in the acute stage this causes ascites, hepatomegaly, esophagogastric varcies which can potentially be fatal, if the infection persists however it can still be lethal inducing either cirrhosis or cardiovascular complications
How can Taenia Solium cause disease?
The larvae of these cestodes can cause severe disease known as human cysticercosis as the cysticerci have a strong preference for human eyes and brain where they cause mechanical damage such as displacement of the retina, cerebral ischemia, and blockage or alterations o the flow of cerebrospinal fluid and associated granulomas leading to inflammatory destruction of host tissue
This can lead to blindness or neurological disease such as convulsions or hypertension
Why does Taenia Solium disease have a very bad prognosis?
Disease depends on the number and location of worms, drug treatment exacerbates symptoms and neurological damages which do not revert and surgery is not always possible
What are the features of giardia lamblia?
It resides in the small intestine in the duodenum and early jejunum which is a nutrient rich environment with few microbial competitors and only a thin protective mucin layer
It contains a ventral disc for host attachment
How can giardia lamblia cause disease?
It causes villus blunting of the gut which causes a barrier to form preventing the absorbtion of nutrients, lipids and lipid soluble vitamins as well as induction of mucus production and potentially inhibition of digestion
This results in malabsorbtion and malnutrition as well as fat-rich diarrhea with lots of mucus and lipids but no blood
What are the features of entamoeba histolytica?
It resides in the large intestine which is a nutrient poor environment full of microbial competitors and a thick protective mucin layer
How does entamoeba histolytica cause disease?
Unlike most parasites this parasite can produce toxins and can break through the intestinal mucosa to disseminate to other tissues both these features are closely associated with pathogenesis
What causes entamoeba histolytica to transform from asymptomatic to invasive?
This is not yet certain but it may have something to do with a microbiota pre condition, a pre-existent lesion in the mucosa or genetic background
What is the major adhesion of E. histolytica?
Lecthin Gal/GalNAc which binds to sugar residues on host proteins with the Gal-GalNAc motif
How does E. histolytica penetrate the protective mucin layer of the large intestine?
It can phagocytose intestinal bacteria and secrete glycosidases and cysteine proteases for the breakdown of fibrous proteins
Acid phosphatases are found inn both membrane bound and secreted forms used to alter the host cell surface to cause depolymerisation of cortical actin and affect cell junctions
It uses amebopores that can interact with lipids of cell membranes oligermise and insert themselves into the membrane promoting cell necrosis
