CESTODES

Question 1

State some of the major morphological features of members of Class Cestoda.

Answer 1

• They have a segmented, elongated tape like body .
• Lack an alimentary canal.
• Have a complete set of reproductive organs in each segment / proglottid.

Question 2

What are the 3 major body parts of Cestodes?

Answer 2

• Scolex - rounded head.
• Neck - connects the proglottids to the scolex.
• Proglottids - segmentations.

Question 3

What is the role of the Scolex in Cestodes?

Answer 3

This is the attachment organ , which has specialized structures such as suckers, hooks and sucking grooves , through which the tapeworm attaches itself onto the intestinal wall.

Question 4

How do members of Class Cestoda grow ?

Answer 4

By adding new proglottids from its germinal center, which lies next to the scolex.

Question 5

State the arrangement of worms in the Proglottids of Cestodes.

Answer 5

• Youngest/ immature forms - found anteriorly, close to the germinal centers.
• Mature forms with functional testes and ovaries - found in the middle.
• Oldest / gravid forms -; found posteriorly towards the distal end . The gravid forms produce many eggs which are excreted in the feces and transmitted to various intermediate hosts e.g cattle, pigs & fish.

Question 6

State the 2 orders into which members of Class Cestoda are categorized.

Answer 6

• Cyclophyllidea
• Pseudophillidea

Question 7

Outline 5 Cestodes that belong to Order Cyclophyllidea.

Answer 7

• Taenia Genus e.g Taenia saginata ( beef tapeworm) , Taenia solium ( pork tapeworm).
• Hymenolepis genus e.g Hymenolepis nana, Hymenolepis dimunita.
• Dipylidium genus e.g Dipylidium caninum.
• Echinococcus genus e.g Echinococcus granulosus.
• Multiceps - lungs e.g Multiceps multiceps .

Question 8

Outline some of the Cestodes that belong to Order Pseudophillidea.

Answer 8

– Bilobed ovary.
* Diphyllobothrium species e.g Diphyllobothrium latum ( fish tapeworm)
* Spirometra ssp e.g Spirometra mansoni , Spirometra proliferum

Question 9

State some of the major distinguishing features between Cestode members of Cyclophyllidae and Pseudophillidae.

Answer 9

• Pseudophillidea are parasites of fish and fish eating vertebrates while Cyclophyllidea are parasites of birds and mammals.
• Pseudophillidea eggs give rise to oncospheres ( larvae ) which are ciliated while Cyclophyllidea eggs give rise to oncospheres which are not ciliated .
• Pseudophillidea have no uterine branching while Cyclophyllidea have uterine branching.
• Pseudophillidea have uterine pores while Cyclophyllidea lack uterine pores.

Question 10

The 6- hooked embryo contained in the eggs of Cestode species is called?

Answer 10

Hexacanth embryo / oncosphere.

Question 11

State the causative agents of Alveolar and Cystic Echinococcosis .

Answer 11

• Cystic Echinococcosis is caused by infection with the larval stages of Echinococcus granulosus.
• Alveolar Echinococcosis is caused by infection with the larval stages of Echinococcus multilocularis.

Question 12

How do humans acquire Echinococcus granulosus infections?

Answer 12

By ingesting eggs in food or water contaminated with dog feces which may contain hydatid cysts.

Question 13

State one difference between the cysts formed by Echinococcus granulosus and those formed by Echinococcus multilocularis.

Answer 13

• Echinococcus granulosus - forms fluid filled unilocular cysts, with exogenous budding.
• Echinococcus multilocularis - forms fluid filled free multilocular cyst with exogenous budding.

Question 14

Briefly describe the life cycle of Echinococcus granulosus.

Question 15

Definitive host of Echinococcus granulosus?

Answer 15

Dogs and other canids.

Question 16

Intermediate hosts of Echinococcus granulosus?

Answer 16

Domestic animals e.g
* Sheep
* Cattle
* Camels

Question 17

Briefly describe the pathogenesis of Cystic Echinococcosis caused by Echinococcus granulosus infections.

Answer 17

• Persons remain assymptomatic until the hydatid cysts containing the Larval parasites grow large enough to cause pain , discomfort, nausea and vomiting.
• E. granulosus forms one large fluid filled cyst ( unilocular) which contains thousands of protoscolices+ many daughter cysts within the large cyst.
• The individual scoleces lying at the bottom of the large cyst are called Hydatid sand.
• The cysts grow over the course of the years and are found in organs such as liver, lungs , spleen, kidneys, heart, bone and CNS , including the brain and eyes.

Question 18

What are some of the clinical findings associated with Echinococcus granulosus infections?

Answer 18

• Many people with Hydatid cysts are asymptomatic.
• The cysts can also act as Space Occupying Lesions, exerting pressure on adjacent tissues.
• Presence of the cysts in the liver may cause : compression, atrophy, portal hypertension from mechanical obstruction, liver cirrhosis and hepatic dysfunction.
• Presence of the cysts in the lungs - can erode into a bronchus, causing coughing of bloody sputum.
• Cerebral cysts - can cause headaches and focal neurological signs, as well as epileptiform seizures.
• Rupture of the cysts can cause fatal anaphylactic shock.
• The brood capsules can metastasize to form additional Hydatid cysts.

Question 19

State the major preventive measures that are effective in reducing the spread of Echinococcus granulosus infections.

Answer 19

• Avoid consumption of any food or water which may be contaminated with fecal matter from dogs.
• Avoid feeding the entrails of slaughtered sheep or other domestic animals to dogs , because they may be infected with cysts.
• Limiting the areas where dogs are allowed to prevent them from contaminating human food and water sources through their feces.
• Washing hands with soap and warm water after handling dogs and before handling food, to reduce the risks of contamination.
• Prevent dogs from feeding on carcasses of infected sheep .
• Controlling of stray dog populations.
• Restricting the home slaughter of sheep and other livestock.
• Health education on the importance of washing hands properly with soap and warm water to prevent infections.

Question 20

List the major techniques useful in diagnosis of Echinococcus granulosus infections.

Answer 20

• Presence of a cyst like mass in a person with history of exposure to dogs’ fecal matter, or living in an area where E.granulosus is endemic.
• Imaging techniques such as CT Scans, ultrasonography, Biopsies and MRIs used to detect the cysts.
• After a cyst has been detected, serological tests may be used to confirm the diagnosis.
• Microscopic examination demonstrating the presence of brood capsules containing multiple protoscolices.

Question 21

What are the major drugs effective in the treatment of Echinococcus granulosus infections?

Answer 21

• Albendazole - kills the larval stages/ Hydatid cysts.
• Praziquantel - can be used e.g in Veterinary practice to kill the cysts in sheep .
• Paromomycine.
• Rhizome of male Fern ( Dryopteris filix ) - herbal preparation that also kills the worms.

Question 22

Besides prescribing medications , what are other steps are useful in the treatment and management of Echinococcus granulosus infections?

Answer 22

• Surgery and chemotherapy for Hydatid disease - surgical removal of the cyst.
• Cyst puncture.
• PAIR - Percutaneous Aspiration Injection of Chemicals , Reaspiration.
• Some cysts are also assymptomatic and inactive, they often go away without any treatment.

Question 23

What precaution should be taken while conducting surgical procedures to excise the cysts caused by Echinococcus granulosus?

Answer 23

• Extreme care must be exercised during surgery . This is to prevent the cysts from rupturing as cyst rupture may cause release of protoscolices.
• A protoscolicidal agent should be injected into the cyst to kill the microorganisms in order to prevent their dissemination.

Question 24

State the result of Cyst Rupture in Echinococcus granulosus infections.

Answer 24

• Cyst rupture may be caused by trauma.
• This may result in mild to severe anaphylactic reactions, which may also be life threatening.
• The cysts contain Hydatid fluid which is highly immunogenic resulting in serious anaphylactic reactions that may be life threatening. ( Contain the parasite antigens)

Question 25

List down 3 protoscolicidal agents.

Answer 25

• Hypertonic saline.
• Silver nitrate.
• Cetrimide.

Question 26

Dwarf tapeworm?

Answer 26

Hymenolepis nana

Question 27

State the distinctive features of the egg of Hymenolepis nana species.

Answer 27

• The egg is oval , colorless and almost transparent.
• Has polar filaments - 8-10 polar filaments lie in between the membrane of the 6-hooked larva and the outer shell.

Question 28

State two ways in which the Hymenolepis nana species are different from other common tapeworms.

Answer 28

• Its eggs are directly infectious to humans i.e the ingested eggs can develop into adults worms without an intermediate host.
• In contrast to other tapeworm infections where only one adult worm can be found in the human host, hundreds of Hymenolepis nana adult worms can be found.

Question 29

Briefly describe the Indirect life cycle of Hymenolepis nana parasites.

Answer 29

• Eggs of Hymenolepis nana are passed in the feces and immediately become infective.
• The eggs are ingested by an intermediate host - arthropods e.g beetles and flies.
• The eggs develop into cysticercoids in the insect, and may infect humans or rodents when the cysticercoids are ingested in cysticercoid-infected arthropods.
• The cysticercoids reside in the small intestine wall.
• Upon rupture of the villus, the cysticercoids return into the intestinal lumen .
• They evaginate their scoleces , and attach to the intestinal mucosa, where they develop into adults.
• The adults reside in the ileac portion of the small intestines, producing gravid proglottids .
• The gravid proglottids detach , disintegrate and release fertilized eggs , or may release the eggs though their genital atria.
• The eggs are then passed into feces and cycle is completed if they are ingested by arthropods.

Question 30

State some of the clinical conditions associated with Hymenolepis nana infections.

Answer 30

Most infections are light and assymptomatic. Heavy infections are associated with symptoms such as :
* Weakness
* Headaches
* Anorexia
* Abdominal pain and discomfort
* Diarrhea
* Weight loss
* Irritability
* Pruritus Ani

Question 31

State four major parasites whose infections are associated with Pruritus Ani.

Answer 31

• Taenia saginata
• Taenia solium
• Hymenolepis nana
• Enterobius vermicularis

Question 32

Basis of diagnosis of Hymenolepis nana infections?

Answer 32

• Demonstration of the eggs in the stool. Concentration techniques and repeated examinations will increase the likelihood of detecting light infections.

Question 33

State 3 drugs effective in the treatment of Hymenolepis nana infections.

Answer 33

• Praziquantel
• Niclosamide
• Nitazoxanide

Question 34

What measures may be effective in preventing the spread of Hymenolepis nana infections?

Answer 34

• Maintaining good personal hygiene.
• Proper disposal of human wastes in toilets and latrines.
• Washing hands properly with soap and warm water after using the washrooms , to prevent contamination of food and water.
• Health education on the prevalence of the disease.

Question 35

How does internal autoinfection occur in cases of Hymenolepis nana ?

Answer 35

• After the embryonated eggs of Hymenolepis nana are passed in the feces, some eggs may remain in the small intestines.
• These eggs release their oncospheres - 6hooked larvae, which penetrate the intestinal villus and continue with their infective cycles, without passage through the external environment.

Question 36

Briefly describe the direct life cycle of Hymenolepis nana parasites.

Answer 36

• Embryonated eggs of Hymenolepis nana are passed in the feces and immediately become infective.
• The embryonated eggs may be ingested by humans from contaminated food, water or hands.
• After ingestion, the oncospheres contained in the eggs hatch and are released.
• The oncospheres penetrate the small intestines and develop into the Cysticercoid larvae within the duodenum.
• Upon rupture of the villus, the cysticercoids return into the intestinal lumen .
• They evaginate their scoleces , and attach to the intestinal mucosa, where they develop into adults.
• The adults reside in the ileac portion of the small intestines, producing gravid proglottids .
• The gravid proglottids detach , disintegrate and release fertilized eggs , or may release the eggs though their genital atria.
• The eggs are then passed into feces and cycle is completed if they are ingested by arthropods.

Question 37

Rat tapeworm?

Answer 37

Hymenolepis diminuta

Question 38

State 3 ways in which Hymenolepis diminuta species are different from Hymenolepis nana.

Answer 38

• The worms are longer compared to Hymenolepis nana worms.
• Their scolex does not have a hooked rostellum like the Hymenolepis nana species.
• The oncospheres are almost similar to those of H.nana species , but lack hair like filaments in their inner membrane, and are also twice their size.
• Hymenolepis diminuta eggs have no polar filaments extending into the space between the oncosphere and the outer shell.

Question 39

State the definitive and intermediate hosts of Hymenolepis diminuta.

Answer 39

• Definitive hosts - rodents, humans.
• Intermediate hosts - arthropods e.g fleas .

Question 40

Briefly describe the life cycle of Hymenolepis diminuta parasites.

Answer 40

• Eggs are passed out in the faeces of the infected definitive hosts e.g rodents/ man.
• Mature eggs are ingested by a suitable intermediate host e.g arthropods like fleas .
• Oncospheres contained in the eggs hatch and are released from the eggs .
• They penetrate the intestinal wall and develop into Cysticercoid larvae, which persist through the arthropod’s morphogenesis to adulthood.
• Humans accidentally become infected by ingesting the infected insects e.g in precooked cereals, other food items , or directly from the environment by children.
• After ingestion, the tissue of the infected arthropod is digested, releasing the Cysticercoid larvae into the stomach and small intestines.
• Eversion of the Scolex occurs , and the parasite attaches to the small intestine wall, using the 4 suckers on their scolex.
• The larvae mature into adult worms in the small intestines.
• Adults produce gravid proglottids, which detach, disintegrate and break off from the body of the adult worms.
• The proglottids then release eggs which are expelled into the environment through the faeces.

Question 41

State the attachment apparatus of Hymenolepis diminuta parasites onto the intestinal wall.

Answer 41

They attach onto the intestinal wall through the 4 suckers on their scolex.