Helminths and protozoal infections Flashcards
what sp of protozoa infect the small intestine
- Giardia lamblia
* Cryptosporidium parvum
what sp of protozoa infect the large intestine
Entamoeba histolytica
what is giardiasis
a cause of travellers’ diarrhoea
how is G. lamblia spread
drinking water and person to person
describe the life cycle of G.lamblia
- Trophozoite
- Flagellated and bi-nucleated
- Lives in upper part of small intestine
- Adheres to brush border of epithelial cells
- Cyst
- Formed when trophozoiteforms resistant wall
- Passes out in stools
- Can survive for several weeks
describe the pathogenesis of G. lamblia
- Present in the duodenum and upper ileum
- Attaches to the mucosa via ventral sucker
- Does not penetrate the surface
- Causes damage to the mucosa and villous atrophy
- Leads to malabsorption of food, esp. fats and fat soluble vitamins
- May swim up the bile duct to gall bladder
what are the stigmata of G. lamblia
- Mild infections are asymptomatic
- Diarrhoea is usually self-limiting (7-10 days)
- Chronic diarrhoea presents in immunocompromised patients
- Stools are characteristically loose, foul-smelling and fatty
how is C. parvum spread
faecally contaminated water
animal reservoir
opportunistic (e.g. aids)
describe the life cycle of C. parvum
- Asexual ; sexual development within host
- Ingestion of resistant oocysts
- Release of infective sporoziotesin small intestine
- Invasion of intestinal epithelium
- Division to form merozoiteswhich re-infect cells
- After sexual phase, oocytesreleased
describe the pathogenesis of C. parvum
- Enters cells of the microvillus border of small intestine
- Remains within vacuole of epithelial cell
- May multiply to give large numbers of progeny, especially in immunocompromised hosts
what are the stigmata of C. parvum infection
- Moderate to severe profuse diarrhoea
- Up to 25 litres of watery faeces / day
- Usually self limiting disease
- In HIV positive individuals with CD4+T-cell counts of
describe the features of E. histolytica
common in tropics and sub tropics via contaminated food or water or anal sex reproduce in the small intestine damage epithelia and red blood cells later on live in the large intestine cause colitis
describe the pathogenesis of E.histolytica
- Adheres to epithelium and acute inflammatory cells
- Resists host humoral and cell mediated immune defence mechanisms
- Produces hydrolytic enzymes, proteinases, collagenase, elastase
- Produces protein that lyses neutrophils, the contents of which are toxic to the host
what are the stigmata of E.histolytica infection
- Small localised superficial ulcers leading to mild diarrhoea
- Entire colonic mucosa may become deeply ulcerated leading to severe amoebic dysentery
- Complications include intestinal perforation
- Trophozoites may spread to the liver, and other organs
- Rarely, abscesses spread to overlying skin
what are the features of bacillary dysentery
- Many PMN in stool
- Eosinophilsabsent
- Many bacilli in stool
- Blood/mucus present in stool
what are the features of amoebic dysentery
- Few PMN in stool
- Eosinophils present
- Few amoebae in stool
- Blood/mucus present in stool
how is G. lamblia treated
- Mepacrinehydrochloride
- Metronidazole
- Tinidazole
how is C. parvum treated
- Nitazoxanide
* Spiramycin
how is E. histolytica treated
- Spiramycin
- Metronidazole
all treated with oral rehydration therapy
how can protozoal infections be treated
- Improved hygiene and water supplies
- Eating only freshly prepared food served hot
- Avoiding salads and fruit which cannot be peeled
- Avoiding tap water and ice cubes
what are nematodes
roundworms
bisexual and cylindrical
what are cestodes
tapeworms
elongated and flat, segmented, hermaphrodite
what are trematodes
Flukes
leaf shaped flat worms
mainly hermaphrodite
rare
how are nematodes transmitted
soil
either swallowing eggs or active skin penetration
what is S. stercoralis
pin worm
causes villous atrophy and loss of intestinal elasticity
what are the stigmata of pinworm
- Dysentery (persistent in immunocompromisedhosts)
- Dehydration
- Malabsorptionsyndrome
- Anal pruritis
- Association with appendicitis
how is whip worm transmitted
eggs on vegetables
what is A. lumbricoides
giant roundworm
what are the stigmata of giant roundworm
digestive upsets
malnutrition
intestinal blockages
may be allergic reaction
what is E. vermincularis
- Threadworm
* Small cylindrical nematodes
what is A. duodenale
hookworm
•Often picked up walking barefoot in infected areas
•Attaches to small intestine, suck blood and protein, often present in huge numbers
•Cause hypochromic anaemia
•Blood loss 0.03ml/day/worm (often 500-1000 worms)
what is T. solium
tapeworm •Acquired from ingesting worms or eggs in undercooked pork •Reside in large intestine •Can grow up to 7m long! •Scolex–for attachment
why are helminths and protozoa difficult to treat
- Large variety of species
- Complexities of their life cycles
- Differences in their metabolic pathways
- Drugs active against protozoa are inactive against helminths
what are the 3 types of Helminth
Nematodes, cestodes and trematodes
what are the two types of nematodes
blood and tissue
intestinal
what are the two types of cestode
taenia
echinococcus
what are the 3 types of trematode
lung, liver, blood
what is Onchocerciasis
a disease caused by infection with the parasitic worm Onchocerca volvulus.[1] Symptoms include severe itching, bumps under the skin, and blindness. it is spread by Simulium flies.
what is schistomaiasis
a disease caused by parasitic flatworms of the Schistosoma type. The urinary tract or the intestines may be infected.
what a the pathological mechanisms of helminth infections
- Inflammation
- Competition for nutrients
- Space occupying lesions
- Stimulation of fibrosis
what is Filariasis
an infection with roundworms of the Filarioidea type.[1] These are spread by blood-feeding black flies and mosquitoes.
can lead to elephantiasis
what worms compete for nutrition
- Hookworms
- Ascaris
- Tapeworms
- Trichiuris trichiura
- Major threat to health
- More severe with poor nutrition
- Intellectual development may be slowed
what is dysentery
inflammation of the intestine causing diarrhoea with blood and/ or mucus
what is trichiuris
aka whipworm infection
can cause dysentery, abdominal symptoms
growth and mental retardation
what does hookworm cause
anaemia due to worm consuming blood
abdo pain
what is ascariasis
caused by the parasitic roundworm Ascaris lumbricoides.
symptoms include SOB, fever, abdo symptoms, malnutrition, learning difficulties
hepatobiliary obstruction and jaundice, intestinal obstruction
what helminths can cause space occupying lesions
- Eggs in the wrong place
- Cysticercosis causing CSF obstruction
- Ascaris causing intestinal obstruction
what is cysticercosis
caused by pork tapeworm
may cause neuro problems and siezures
what types of fibrosis might occur from schistosomes
lung fibrosis leading to rt heart failure
liver fibrosis leading to portal hypertension
bladder fibrosis leading to bladder cancer
how are cestodes (tapeworms) treated
praziquantel
in cysticercosis anti epileptic drugs are given to treat the seizures
steroids to reduce inflammation
how are nematodes treated
albendazole is most effective
sometimes levamisole and piperazin
how does praziquantel work
Not fully known: probably increases calcium permeability of membranes depolarisingthem
•May interfere with purine synthesis
what is Hydatid disease
a cyst containing a tapeworm larva
what is praziquantel used to treat
- Hydatid disease
- Cysticercosis
- Schistosomiasis
- Clonorchis, Fascioliasis and Paragnomiasis
what are the pharmacological features of praziquantel
- Well absorbed orally
- 20 mg/kg
- On WHO essential medicine list
- Significant first pass effect
- Low systemic concentrations
- Excreted in the kidneys
- Short half life
what are the side effects of praziquantel
- Dizziness, headache, drowsiness and somnolescence, rarely seizures
- Abdominal cramps and nausea. Diarrhoea
- Transient asymptomatic rise in transaminases
- Urticaria, rash and pruritis
- Interacts with rifampicin (decreased concentrations), carbamazine, phenytoin (reducing praziquantelbioavailability)
what is albendazole used to treat
Treatment of nematode infections: trichiuriasis, filariasis, Enterobiusinfection, ascariasis, hookworm, toxocariasis, strongyloidiasis and some protozoa, some cestodes, mebendazol and thiabendazole
what is albendazole MOA
Binds to colchicine sensitive receptor or tubulin
•This prevents polymerisationinto microtubules
•Impaired glucose uptake and depleted glycogen stores
•Degenerative changes appear in the worm
what are the side effects of albendazole
- Concentrated in semen and may be teratogenic
- Persistent sore throat
- Headaches dizziness and seizures
- Acute liver failure
- Aplastic anaemiaand marrow supression
how does piperazine work
- Agonist activity against the gamma butyric acid receptor paralysingmuscular activity
- Orally active
- Metabolism in liver
- Variable half life
- Used to treat ascariasis and enterobiusinfection
- SE include GI tract upset and rarely hypersensitivity, dizziness
how does pyrantel work
- Treatment of hookworms and roundworms
- Causes depolarisingneuromuscular blockade
- Poorly absorbed providing selective toxicity
- Excreted unchanged in the faeces
- Antagonistic with piperazine
- Avoid in pregnancy
- Can cause intestinal obstruction if there is a heavy worm load
what is levamisole
- WHO List of essential medicine
- Nicotinic acetylcholine receptor antagonist
- Ascariasis and mixed ascarishookworm infection
- Rapidly absorbed
- Caution in pregnancy
- Abdominal pain, nausea and vomiting are reported
what is diethyl carbamazine
- A piperazinederivative
- WHO essential medicine list
- Inhibits arachidonic acid making parasites more susceptible to immune attack
- Filariainfection
- Associated with increase in inflammation: caution Mazzottireaction, loss of site in onchocerciasis
what is ivermectin used to treat
eradication of lymphatic filariasisand onchocerciasis
how does invermectin work
Ivermectinbinds glutamate-gated chloride increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the nerve or muscle cell resulting in paralsysisand death of the parasite either directly or by causing the worms to starve.
what is niclosamide
- Inhibits glucose uptake, oxidative phosphorylation and anaerobic metabolism
- Used for the treatment of tape worm infections only
- Causes dizziness, skin rashes, drowsiness and perianal itching
how can helminth infections be prevented
- Vector control for filariasis
- Meat inspection for cysticercosis
- Sanitation and hygiene for intestinal nematodes
what does pruritus mean
itching
