Nematodes Flashcards
What is a parasite
A parasite is an organism that is entirely dependent on another organism referred to as its host for all or part of its lifecycle and metabolic requirements at the detriment of its host
Helminths are generally divided into
Nemahelminths- intestinal and tissue nematodes
Plathyhelminthes- trematodes and cestodes
The intestinal nematodes include
E- Enterobium vermicularis
A- Ascaris lumbricoides
T- Trichuris trichura
S- Strongyloides stercoralis
A- Ancyclostoma duodenal
N- Necator americanus
D- Capillaria phillipensis
General Characteristics of nematodes
Cylindrical non segmented worms with a body cavity and a body surface covered with non chittinous cuticle
Variation in sizes from <5mm In S.stercoralis to about 1m in D.medinensis
Diecious, males are smaller than females
Females are either viviparous or oviparous
Typically geohelminths
Mouth covered with lips or papillae
May have tooth palate
Rudimentary excretory and nervous
Seen mostly in tropics and subtropical
Poor hygiene
General chx of Ascaris
Largest intestinal nematode (25cm or more)
Low worm burden are asymptomatic, heavy infxn problematic especially in children where they impair development
Typically referred to as common roundworm
Causative agent of Ascariasis
Difference between male and female ascaris
Males are smaller than females
Males have a pointed and coiled end whereas females have a blunt and straight end
Cloacal and genital apertures are not separate in Males but aren’t in females
Presence of penal setae in males
Eggs of ascaris lumbricoides are typically golden brown with serrated edges. T/F
T
Tell me about the lifecycle of A.lumbricoides😎
Infection is through faeco oral route. A mature ascaris female lays about 200000 eggs a day and these are passed out through faeces into the soil where they embryonate and become infective. It is important to note that unfertilized eggs are also present in the feces but these however are not infective. The eggs enter the body through ingestion of contaminated food and water to the intestine. Here, a single rhabditiform larvae hatches from the egg and pierces the gut mucosa to enter the blood vessels , they then make their way through the portal vein to the liver, heart and then to the pulmonary circulation where they pierce to enter the lungs. At the lungs they undergo two moultings afterwhich they make their way up through the trachea, coughed up into the pharynx and are swallowed back down to the small intestine. Here the worms become mature, move further down and mate , producing eggs in the large intestine which are then passed out as feces contaminating the soil , undergo their first moulting and the cycle begins again
Nematodes are ubiquitous because of the presence of a lipid layer that prevents them from being affected by chemicals, acids etc..T/F
T
Pathogenic effects of A.lumbricoides
Ascaris pneumonia(loefflers syndrome)
Invasion of pancreatic and biliary tracts
Intestinal obstruction in heavy infection
Malnutrition and failure to thrive in children
Diagnosis of Al
Identification of eggs in stool
Treatment of A.lumbricoides
Mebendazole and pyrantel pamoate
Trichuris trichura general chx
Also known as whip worm because of its appearance
Typically seen with Ascaris
Morphology of T.trichura eggs
Brown eggs with a characteristic band shape with an outer shell and mucoid plugs at each end giving it a tea tray appearance
Egg contains a single embryo
Tell me about the lifecycle of T.trichura😌
Infection is through faeco oral route
Adult female lays about 10-20000 eggs per day and these are passed out in feces, emvryonate and contaminate food and water which are ingested by man. They reach the small intestine where the rhabditiform large hatches , penetrator the villi and continue to mature. The young worms then go down to the caecum of the large intestine penetrate the mucosa and complete development as adult worms which then mate and lay eggs which are passed out in feces.
In the lifecycle of T.trichura there are two migratory phases to the lungs and SI respectively
T/F
False, there is NO migratory phase
Pathogenic effect of T.trichura
Trivial
Causes rectal prolapse in children with associated dysentry
Diagnosis of T.trichura
Eggs in stool using direct smears or concentration
heavy infections (>30000 eggs)can be diagnosed clinically in rectum using proctoscope
Treatment of T.trichura
Mebendazole drug of choice
Enterobius vermicularis general chx
Infects children worldwide
Has the simplest lifecycle
Adults live in the large intestine may be found in the appendix
Entir lifecycle of E.vermicularis takes place in the human GIT . T/F
T
Lifecycle of E.vermicularis
Molts 4 times, first 2 within the egg and two before becoming adult worms
Infection occurs via ingestion of eggs either due to inadequate hand washing,nail biting etc. Eggs hatch in the duodenum afterwhuvh the emerging larvae grows and migrates toward the colon. During this migration, they moult twice and become adults. The male and female then mate in the ileum after which the male dies and is passed out in the feces.
The gravid female then settles in the ileum caecum appendix etc then crawl to the Anus at night where they lay their eggs. After all eggs have been laid the female becomes opaque and dies. Eggs become infective within hours after deposition at the anus
Pathogenic effects of E.vermicularis
Pruritus ani
Diagnosis of E.vermicularis
Graham swabs and scotch tape impression for the characteristic eggs on perianal area
