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46 Cards in this Set
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Helminth reproduction
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cestodes: Each proglottied segment is hermaphroditic
Nematodes: distinct male and female sexes Trematodes: hermaphrodicit except fro schistosomes |
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Cestodes general
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Phylum Platyhelmenthes
Class cestoda = tapeworms Subclasses: Eucestoda (everything we usually think of adn CEstodaria (just a few, unusual species) |
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The Cestode lifecycle is complex and simple at the same time. Why
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Simple because no asexual phases, but complicated because at least 1 intermediate host AND a definitive host (except for hymenolepsis nana)
Many cestodes have a 2 phase life cycle with two host types |
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What are the cestode life cycle stages:
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Eggs, oncosphere, cysticeroid/cesticercus, coracidium, procercoid, plerocercoid, adult
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Cestode LIfe Cyce (general)
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Eggs laid by the adult pass out in the feces of the definitive host, and are eaten by the intermediate host.
Eggs develop into the intermediate stage which generages the adult when eaten by the definitive host. A tapeworm may pass through many intermediate hosts before finding the appropriate definitive host. |
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Cestode Anatomy/Morphology
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Cestodes are segmented and have 3 distinct regions: Scolex, Neck, Strobila
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Scolex
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Scolex is the anterior point of attachment structure on a cestode. Not a mouth. Different in the 2 orders
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Order pseudophyllidea: Scolex contains slit-like suckers or grooves
Order cyclophyllidea: Scolex contains suckers and sometimes hooks. This is a key difference in identifying tapeworms. |
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Neck (cestode)
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Undifferentiated/unsegmented region posterior to scolex. The narrowest part of the tapeworm. Site from which new proglottids form
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Cestode Strobila
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LIinear series of segments or proglottids. Proglottids are continuously fromed posterior to the neck region in a process called strobilization. As new proglottids form, the older ones move posteriorly and become sexually mature.
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Types of cestode proglottids
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Immature proglottids: Newly formed
Mature proglottids; Possess both male and female organs Gravid: develop after mating, contain hundreds to thousands of embryonated eggs. Each proglottid is an independantly functioning unit. |
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Cestode Male Reproductive organs
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Male system develops first. Strucutes begin to form in the immature proglottids, fully developed in mature proglottids.
They disappear in gravid proglottids |
Organs:
many testes (3 to 100's) vasa efferentia vas deferens (often coiled) cirrus sac w/ cirrus common genital pore |
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Cestode Female reproductive organs
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Structures form and become functional in mature proglottids.
Most female organs disappear in gravid proglottids except for the egg filled uterus. |
Structures:
Ovary, vitellaria (yolk gland, scattered or compact), Mehlis gland, uterus (contains eggs in branches) , vagina (carries sperm to ootype), common genital pore |
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Cestode reproduction points
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Self mating is unusual w/in segment
Sperm are transferred between mature proglottids lying next to each other. Gravid proglottids develop after mating and contain hundreds to thousands of embryonated eggs. Gravid proglottids detach from parent and exit the host. |
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Cestode Egg
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Eggs that are passed ar embronated and contain a hexacanth larva called an oncosphere. The oncosphere has 3 pairs of hooks, is encased in an inner envelope, which is surrounded by another membrane called the embryophore.
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the outer envelope is between the embryophore and the shell (or capsule). Eggs remeain viable externally for weeks to months.
SO: Oncosphere, inner envelope, embryophore, outer envelope, shell/capsule. |
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Hexacanth
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Six hooks on head
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Cestode Tegument:
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The tegument has to make up for the fact that the cestode has no gut. The external surface must function no tonly for protection, locomotion, and as sensory surface, but also as metabolically active layer taking up nutrients from the environment and as a layer through which secretions and excretions must pass
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the tegument also has to restist the attack of digestive enzymes and protect against the immune responses of the host.
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Glycocalyx
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The entire surface of the tegument is a layer of carbohydrate containing macromolecules called the glycocalyx. the glycocalyx protects the parasite against host digestive enzymes, enhances nutrient absorption, maintains the parasite's surface membrane,.
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The microvilli on the tapeworm surface increases the surface area of the parasite by about 20 times.
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Syntegument (Cestode)
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outer anucleate syncytial cytoplasmic layer containing mitochondria and secretory bodies.
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Syncytial:
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multinucleated mass of cytoplasm that is not separated into individual cells.
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Cytotegument:
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nucleated cell bodies lying beneath the tegumental muscles and connected to the syntegument.
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Cestode digestion
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Cestodes do not produce digestive enzymes of any kind, instead they rely on the digestive enzymes of their hosts to break down nutrients into low molecular weight compounds, which they can then absorb
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Cestode transport
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Cestodes have evolved a whole repertoire of transport mechansims in their tegument which can effectively compete w/ the uptake mechanimss of the hosts intestine
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Cestode Osmoregulation
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most cestodes behave like osmometers when placed in solutions of different osmotic pressure. All swell in dilute solutions and shrink in concentrated solutions. They appear to have little if any ability to regulate their body volume. Despite limited osmoregulatory ability, all cestodes appear slightly hypotonic to their surroundings in vivo (lower osmotic pressure)
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Cestode Nervous system
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arranged like a ladder w/ paired ganglia near the anterior end, nerves running anterioroly toward sensory or holdfast and longitudinal nerve trunks extending posteriorly to near the end of the body.
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The 'brain' is located in teh scolex, is a rectangluar or circular nervous tissure varying in complexity - from a simple ganglia and commissures (joints/seams). Th ebrain gives rise to short anterior and posterior nerves that richly support varioius portions of the scolex a/ more fibers and recieve sensory fibers from rostellum, suckers, and tegument.
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Cestodes: beef, pork, fish
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taenia solium (pork), Taenia saginata (beef), Diphyllobothrium latum (fish).
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Members of Order cyclophyllidea and pseudophyllidea
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Pseudophyllidea is the one w/ slit like suckers or grooves on scolex, and contains just the D. latum and Spirometra mansonoides
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Cyclophyllidea is the one with circular suckers or hooks on scolex and contains Taeniidae, Hyenolepididae, and Dipylidiidae
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Family Taeniidae:
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Contains
T. saginata: beef tapeworm and T. solium (pork) |
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Taenia saginata:
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Beef tapeworm of humans: umans are the ONLY definitive host, and cattle are the only eintermediate. 4-8 meters long. THe cysticercus (larva) is soybean shaped, iht the small scolex invaginated into the translucent cysticercus. It evagenates as the cysticercus develops into an adult.
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The scolex contains 4 suckers and lacks hooks - this is used to diagnose. Mature proglottids contain both male and female organs. Gravid proglottids are identified by teh presnce of 15 or more side branches on either side of the uterus. THis is the diagnositc stage. Eggs are NOT used for diagnosis because all Taenia have the same shaped ova.
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Taenia Saginata life cycle
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The adult lives in the human small intestine. The gravid proglottid (w/ hundreds of embryonated eggs) is shed in feces - it may actively crawl about in feces. It ruptures on land during drying and releases eggs into soil. a grazing cow ingests the eggs, and the oncosphere hatches form the egg into the cow small intestine, penetrates the intestine and enters circulation.
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Oncosphere reaches skeletal muscle and becomes cysticercus. Humans eat raw or undercooked beef. The scolex evaginates, attaches to wall of ileum and begins strobilization. Adult reaches maturity and maximum length in 3 months.
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Can cattle become infected with adult T. saginata?
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No, not even if they ingest the cysticerci. Humans cannot harbor the metacestode since T. sagniata will only hatch in cows.
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E. granulosus
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3-6mm long. Resides in teh small intestine of definitive host : dogs/other canids . Gravid proglottids release eggs that are passed in the feces. After ingestion by a suitable intermediate host, the egg atches in teh small bowel and releases an oncosphere. The oncosphere penetrates the intestine wall and migrates through the circulatory system into various organs, especially teh liever and lungs. Here, teh oncosphere develops into a cyst that enlarges gradually, producing protoscoleces and daugheter cysts that fill the cyst interior. The definitive host becomes infected by ingesting the cyst containing organs of the infected intermediate host. AFter ingestion, the prootcoleces evaginate, attach to the intestinal mucosa, and evelop into adult stages in 32-80 days.
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E. multilocularis:
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same life cycle as E. granulosus, but with some differences:
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The definitive hosts are foxes and sometimes cats, dogs, volves, and coyotes. THe intermediate hosts are small rodents and larval growth (whcih is in the liver) remains indefinitely in th eproliferative stage, resulting in invasion of surrounding tissues. Humans become infected by ingesting eggs whith the resulting release of oncospheres in the intestine adn the development of cysts in various organs.
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Family Hymenolepididae
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Large family of tapeworms in berids and mammals. Characterized by by proglottids that are wider than they are long. Mature proglottids contain a small number of testes (3-4). gravid proglottids disintegrate in host adn relesae eggs. INtermediate hosts are invertebrates.
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There are only two species that infect humans: Hymenolepsis nana , Hymenolepsis diminuta
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H. nana: dwarf tapeworm
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Worldwide distribution, mostly affects children. Small tapeworm, 15-45 mm. Adult has 150 -200 proglottids and lives in the lumen of the small intestine.
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The scolex has 4 suckers and a single row of hooks. Rodent are the resevoir host, this is the only tapeworm that does not necessarily require an intermediagte host for its life cycle.
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H. nana life cycle:
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eggs of H nana are immediately infective when passed w/ the stool and cannot survive more than 10 days in teh external enviornment. When eggs are ingested by an arthropod intermediate host, they develop into cysticercoids wchihc can infect humans or rodents when ingested. The cysticercoids grow to adults in small intestine. when eggs are ingested, the oncospheres contained in the eggs are released. Th eoncospheres prenetrate the intestinal villus and develop into cysticercoid larvae.
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Upon rupture of the villus, the cysticercoids return to the intestinal lumen, evaginate their scoleces, attach to the intestinal mucosa and develop into adutls that reside in teh ileum producing gravid proglottids. Eggs are passed in the stool when released from proglottids - either through the proglottid's genital atrium or when the proglottid disintegrates in the small intestine. An alternate mode of infection is internal autoinfection where the eggs release their hexacanth embryo, which penetrates the villus continuing the infective cycle w/o passage through the external environment.
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H. nana lifespan
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4-6 weeks, but internal autoinfection allwos teh infection to go on for years
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Hymenolepsis diminuta: rat tapeworm
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found everywhere, primarily infects children. Small, 20-60cm. scolex has 4 suckers and no hooks. Many resevoir hosts, including dogs, cats, rodents
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H. diminuta life cycle
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Eggs are passed in feces of infected definitive host (rodents, humans). The mature eggs are ingested by an intermediate host (various arthropods - adult or larva) na doncospheres are relesaed from the eggs and penetrate the intestinal wall of teh host, wchich develop into cysticercoid larvae.
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Teh cysticercoid larvae persist through teh arthropods orphogenesis to adulthood. H. diminuta infection is aquired by teh mammalian host after ingestion of an intermediate host carrying the cysticercoid larvae. Humans can be accidentally infected through teh ingestion of insects in precooked cereals or otehr food items, and directly from the environment. after ingestion, the tissue of the infected arthropod is digested releaseding the cysticercoid larvae in teh stomach and small intestine., Evagination of the scoleces occurs shortly afgter the cysticercoid larvae are released. Using the 4 suckers on the scolex, the parasite attaches to the small intestine wall. Matureation of the parasites occurs w/in 20 days adn the adutl worms can reach an avaerage of 30 cm in lenth. Eggs are released in the small intestine from gravid proglottids that disinitegrate after breaking off from teh adult worms. Teh eggs are expelled to the enviornment in the mammalean hosts feces.
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Family Dipylidiidae:
Dipylidium caninum |
The double-pored dog tapeworm. Proglottids of the adutl have genital pores on both sides (double pore). THe uterus breaks down into egg capsules, each containing several eggs w/ oncospheres. The gravid proglottids break free and pass out in feces, releaseing the egg capsules.
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The scolex has a rostellum with 4 rows of hooks, along w/ 4 suckers
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D. caninum life cycle
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The gravid proglottids are passed inact in feces from host. they release egg packets. sometimes proglottids rupture and egg packets are seen in stool samples. Following ingestion of eggs by an intermediate host (larval stages of cat/ dog ctenocephalides), each oncosphere is released into the flea's intestine.
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the oncosphere penetrates the intestinal wall, invades the insect's hemocoel (body cavity) adn evelops into a cysticercoid larva. the larva develops into an adult, and the adult flea harbors the infective cysticercoid. The vertebrate host becomes infected by ingesting the adult flea containing the cysticercoid. The dog is the principal defiinitive host for D. caninum. Other potential hosts include cats, foxes, and humans (mostly children). Humans aquire infection by ingesting the cysticercoid contaminated flea. This can be promulgated by clsoe contact between chidlren and their infected pets. in the small intestine of the vertebrate host teh cysticercoid larva devleops into an adult tapeorm which reaches matureity about 1 month after infection. The adult tapeworm resides in teh small itnnestine fo the host where they each attache by tehir scolex. they produce proglottids which have 2 genital pores. The proglottids mature, become gravid, detatch from teh tapeworm and migrate down to be passed by the stool.
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Order Pseudophyllidea:
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Contains Diphyllobothrium latum and Spirometra/Diphyllobothrium mansonoides
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Some of the largest tapeworms - can be more than 10 meters. Worldwide. Characterized by scolex containing 2 grooves (bothria) - slit-like adhesive organs. The bothria are the holdfast organs. These pinch teh intestinal wall to hld the worm in place in the gut.
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Order Pseudophyllidea reproduction
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Male and female genital openings are separate and located mid-ventrally in teh proglottid. Testes are scattered througout the proglottid
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Gravid proglottids do not detatch from the rest of the worm, but rather remain attached and shed eggs in to the gut through a uterine pore and are passed through the feces.
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Order Pseudophyllidea life cycle and distribution
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complex, 3 hosts:
First intermediate host: copepod (small crustacean) Second int. host: fish/amphibian Definitive host: fish eating mammal |
Distribution is world wide, but more prevalent in the northern hemisphere. human infections common in great lakes are and in norhtenr europe particularly finland. Eating raw/undercooked fish results in infection from ingesting the plerocercoid
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Diphylobothrium latum
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Broad Fish tapeworm
Proglottids wider than long. Definitive host is infected from fish. LIttle difference between mature and gravid proglottids. |
Definitive host: commonly human, bear, dog, cat, fox, mink, raccoon, wlarus, seal.
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D. latum has a unique affinity for what?
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vitamin B12: they use the tegumental receptro that has a high affinity, so it absorbs all the b12 from the host.
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b12 is normally involved in metabolism of a cell, affects dna synthesis and regulation, also fatty acid synthesis and energy production.
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D. latum eggs:
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oval or ellipsoidal, there is an operculum on one end that can be inconspicuous and the oppsoite end is a small knob, barely discernable. the eggsa repassedin stool unembronated.
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