Parasites of The GIT

Transcription

1 - No need to refer to the handout while studying this sheet. Nematodes continuation.. 1- HOOKWORMS : - They are nematodes. - They measure 1 cm in length. - They are called hookworms because of their hooked anterior end. Two main species pathogenic to Humans are : 1. Ankylostomaduodenale. 2. Necatoramericanus. We can differentiate between them by 3 points : 1. Ankylostoma is present in the old world Asia, Europe, Africa. While Necator is present in the new world as its name implies. 2. Morphologically :Necator has a pair of semilunar cutting plates dorsally in the mouth with a concave dorsal median tooth. it has cutting edges or discs just like teeth. While duodenale has hooks two ventral pair of teeth. 3. Duodenale s life span is longer ( 5-6 years ), while Necator disappears in within 2 years. Hookworms live in the GIT, in the small intestines. 1

2 The worm holds villus with its teeth and mouth, stays attached there. It feeds on blood and some of the fluids of tissues that are there.but mainly it feeds on blood. They can also move from one villus to another and by Eggs : doing this, they leave a raw area which leads to bleeding. So that, the main pathology that maybe produced by hookworms is the LOSS OF BLOOD ( either by feeding of worms on blood OR leaving a raw area ). Note : Its believed that maybe around 1 million liters of blood are lost everyday in the world because of these kinds of worms. - Have a thin transparent shell. - Its already embryonated when passed in the feces.( 2-8 cell stage ). Characteristic Life Cycle : - Female and male copulate and produce eggs. - Eggs reach the soil, giving rise there to larvae which are usually thick and are known as Rhabditiform larvae.these larvae feed on bacteria and debris in the soil and mature to the next stage which is Filariform Non feeding infective larvae that penetrates skin mainly the dorsum of feet or between the toes otherwise they die. - Note :Thigmotaxis is the attraction to skin. 2

3 - Once they go in, they gain access to blood or lymphatics to lungs where they ll stick and have other maturation, then to trachea swallowed to settle in duodenum continuing the cycle. Diagnosis : Eggs in fresh feces ( embryonated ). Symptoms : - Itching - Pneumonitis if there s a lot of larvae - Malaise - Eosinophilia - Occult bleeding * Main symptom is IRON DEFICIENCY ANEMIA * Cutaneous Larvae Migrans : - Hookworms belong to animals just like visceral larvae migrans. - Birds and animals affected by hookworms, if you get them into your skin, they ll give rise to : 1. Itching. 2. Rash. - They cant mature any further in your body and will die eventually. 3

4 3.StrongyloidesStercoralis : The smallest nematodes. ( 2-3 mm long ) Present in small intestines. Humans are the principal host. In the parasitic stage there s no male. ( Parthenogenesis: is that this kind of worms has no male, just an adult female that gives rise to eggs ) Produce eggs that very quickly start hatching to larvae that breakout through the wall into the lumen. Most UNLIKELY to see eggs in feces because they are released and very quickly hatched to larvae. Note : feces examination will show us larvae not eggs which is a good distinguishing feature of this worm. Life Cycle : The adult female worm is a filariform nematode lays eggs. The deposited egg hatch into Rhabditiform larvae( rod shaped ) that get out in the feces. It has three types of cycles : 1. Direct cycle : ( like hookworms ) Rhabditiform hatch in the soil into infective filariform larvae that penetrate the skin to blood and lungs then get swallowed to GIT becoming adults. 2. Indirect cycle : Rhabditiform larvae develops into free living male and female larvae that will copulate and produce eggs that will hatch to rhabditiform larvae then filariform or repeat the free living cycle. 4

5 3. Autoinfection : the infective filariform in the intestine and reinfect the host by penetrating the mucosa or the perianal skin Without going out to soil. A rare example :helminth multiplying within the host, what explains the persistence of the infection in people for 40 years! Diagnosis: - We look for the larvae in feces. Symptoms : - Itching - Abdominal pain - Skin rash As a result of autoinfection the larvae may become disseminated all over the body leading to what is known by :Hyperinfection Syndrome which may be fatal and associated with steroid use. Now that we finished up Nematodes, we ll start talking about Tapeworms ( cestodes ) - A very quick revision of the structure of tapeworms : They are made of units called proglottids. Most anteriorly they have scolex that havesuckers or hooks. Distally, the neck region. - The genus name is Taenia ( not the fungal ones ) 1. Taeniasaginatum : beef (cow) tapeworm 2. Taeniasolim : pork tapeworm 5

6 1. TaeniaSaginatum : Life cycle :( for both ) - Worm is present in the small intestine, it releases gravid proglottids that get out with the feces, disintegrate releasing the eggs which will be eaten in the grass by the intermediate host. Those eggs will release the oncosphere( hexacanth ) which penetrates the wall into blood and lymphatics distributed all over the body. Wherever it settles, it produces a cysticercus ( distended balloon filled with fluid yellow in color, inside it there is an invaginatedrudimentaryscolex.) - So when someone eats a live cysticercus, the scolexevaginates and attaches to the wall of GIT and develops into an adult worm. To differentiate between both : Saginatum is longer ( 4-6 meters ), Solium is almost ( 2-4 meters ). Number of proglottids in Solium is less due to its length.( 1000proglottids while saginatum reaches 3000 ). Scolex :Saginatum has 4 suckers but no hooks ( rostellum ), while Solium has 4 suckers with hooks. Cysticercus and eggs are the same for both. 6

7 Radially striated embryophore surrounds a hexacanth embryo. Mature proglottids are rectangular for solium but more square for saginatum. Two ovaries for saginatum and three for solium( trilobed ). Gravidproglottid is distinguished by lateral branches of the uterus.saginatum has more branches (15-30). Note: 1- Usually we find one worm in the small intestine. 2- You may require it for a long time up to 20 years without developing any disease. 3- No significant symptoms.sometimes its alarming when the motile proglottids pass through the anal canal involuntarily. 4- Rarely intestinal obstruction and perforation. 5- The proglottids in the worm are called strobila. Diagnosis: Look for proglottids in feces. 2.TaeniaSolium : Symptoms : - Slight intestinal irritation. - Rarely perforation. 7

8 - Humans can be the intermediatehost by eating the eggs, the cysticerci settle in muscles and brain, they can reach eyes, heart and lungs. - Serous damage can result in eye and brainconvulsions. - Epilepsy - Cyticercosis 3.DiphyllobothriumLatum : 8 The largest human tapeworm, reaches 10 meters. Fish tapeworm 3000 or more proglottids Has two longitudinal suckers No hooks and no rostellum Eggs : -They are operculated on one end, with a thickening on the opposite end. Life cycle : -There are two intermediate hosts. Eggs pass into water through defecation. They hatch a ciliated embyrophore that is ingested by Cyclops inside which it develops into larvae. - Cyclops are eaten by fresh water fishand the larvae will go to the organs developing into an adult worm in the intestines of the host.

9 Symptoms: - Very minor because it s one worm - Vague abdominal - Megaloblasticanemia. ( B12 deficiency ) - Intestinal obstruction with several worms. Freezing the worm for few day will be enough to kill it. Your colleague, Lina Baker. 9