Echinococcus species


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Echinococcus species

  1. 1. By Mwamkoa MJ (BScHLS) 1
  2. 2. Learning Objectives By the end of this session, students are expected to be able to: Explain the geographical distribution Echinococcus granulosus Explain the habitat of Echinococcus granulosus Describe morphology of Echinococcus granulosus. Describe the mode of transmission & life cycle of Echinococcus granulosus Explain the diseases caused by Echinococcus granulosus. Explain the prevention and control of Echinococcus granulosus Explain the laboratory diagnosis of Echinococcus granulosus 2
  3. 3. Geographical Distribution The parasite has a worldwide distribution especially where sheep has close association with dogs and wild carnivores. High rates of infection occurs in East Africa (Turkana region in Kenya), North Africa, South Africa,, India, Eastern Mediterranean, Middle East and parts of Southern America and Australia. 3
  4. 4. Habitat Eggs – May be found in faeces of host (dogs and herbivores, domestic and wild animals which eat meat) or passed in gravid segment or may adhere to the coat of host when gravid segment disintegrates. It is infective to man. Larvae stage (hydatid cyst) – found in varying organs in herbivores (e.g. sheep, goats, cattle and man). Adult worm - lies attached to the mucus of small intestine of carnivores(e.g. canines & felines) 4
  5. 5. Morphology E. granulosus & E. multilocularis are smallest cyclophyllidean cestode, Measures 3 – 5 mm in length. Body divided into: Scolex having 4 suckers, armed with 2 rows of hooked rostellum bearing about 22-28 hooklets. Short neck. Strobila contains 3 proglottids. (One immature, one mature and one gravid). The size of the gravid segment is more than a ½ of the body length. The uterus is unbranched Genital pore is positioned behind the middle line of gravid segment Eggs are rounded and indistinguishable to those of Taenia spp. 5
  6. 6. Morphology… The body plan of adult Echinococcus In strobila several organs like the excretory system extend through the entire worm Proglottid: an individual segment Uterus Gravid Proglottid By Mwamkoa MJ (BScHLS) 6
  7. 7. Scolex 7
  8. 8. Hydatide sand 8
  9. 9. Life cycle Intermediate hosts acquire infection through ingestion of eggs in contaminated substances Eggs hatch in small intestine releasing an oncosphere which penetrate the intestinal wall & carried along the body by blood circulation to be trapped in organs like liver, lungs etc. These are then transformed into protoscolices in a (hydatid) cyst Infection of the definitive host (dog) is when hydatid cyst(s) in the intermediate host (e.g. sheep) is eaten. 9
  10. 10. Life cycle… The cyst wall is digested, the protoscolices are liberated, which develop into adults. The gravid proglottids break away and are expelled singly (may force their way out through anal sphincter). On drying they rupture releasing eggs with fully developed larvae. Hydatid cyst is a bladder that contains inverted scolices, brood sacs with scolices, and within those brood sacs, daughter cysts with their own inverted scolices. 10
  11. 11. Life cycle… If the scolices separate from the inner lining of the capsule, they are called hydatid sand. Hydatid cyst may be unilocular, osseous (E.granulosus) or alveolar/multilocular (E. multilocularis) Unilocular has a single compartment with 2 layers, the inner layer produces protoscolices & brood capsules, when these detach they are termed as hydatid sand Osseous are smaller found in vertebrae & marrow cavities Alveolar have multiple divisions of the cyst into 11 compartments
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  14. 14. Pathogenesis & pathology The pathology is primarily due to impairment as a result of pressure from the growing cyst, symptoms are subject to organs affected, size & number of the cyst. Pulmonary infection result into coughing & allergic responses. Seizures & comma may be a result of brain invasion. Rupture of the cyst release the protoscolices to the circulation, which may lead to secondary echinococcosis. 14
  15. 15. Pathogenesis & pathology… Fluid from the cyst may lead to severe allergic reactions (anaphylactic shock). Like osseous, alveolar cysts are usually difficult to remove, the former may lead to spontaneous fracture of bones where the later may lead to strong impairment & obstruction of infected organ and is fatal. May cause calcification of tissue when the cysts die. Few patients are reported to have generalized eosnophilia. 15
  16. 16. Diagnosis Laboratory diagnosis - post-surgical Microscopic demonstration of scolices in hydatic fluid Immunodiagnosis Casonis’ test, involves skin/intradermal injection of irradiated cystic fluid, which on presence of antibodies a burning swelling will be formed Serodiagnosis Detection of antibodies & antigens due to the parasite by ELISA, etc Imaging methods X-rays, ultrasounds, etc show presence of the hydatid cysts in organs 16
  17. 17. Casoni Test: Intradermal Test Antigen is prepared from filtered hydatid fluid or saline extraction of ground If 0.2mls of hydatid fluid is sterilized by filtration is injected intradermal into the patient suffering from hydatid cysts a wheel is produced in about 15 minutes surrounded by concentric erythromatous zone, which later disappear with a wheal. A second similar reaction (i.e. after 20 minutes) frequently takes place at the same point a few hours (or minutes) later. Between 50% and 100% of infected individual react positively 17
  18. 18. Prevention Regular treatment of dogs with anthelmintics. Elimination of stray dogs Preventing dogs from eating infected offal's of dead animals through disinfecting or disposal of refuse from slaughterhouses. Avoiding contact with infected animals (dogs & cats). Improving personal hygiene through hand washing especially after feeding or contacting dogs. 18
  19. 19. ECHINOCOCCUS MULTILOCULARIS Most of the E. multiculoris are said to be sterile because they don’t have protoscolices in their parent cyst. Although there may be few if any protoscolices produced In genera the rupture of hydatid cyst release the hydatid sand. 19
  20. 20. Differences btn E.granulosus & E.multilocularis E. granulosus E. multilocularis Strobila 3 segment only 3-5 segment Size 3 - 9mm long 1.2 – 5.5 mm long Genital pore Behind the middle line Anterior to the middle of gravid segment of gravid segment Length of gravid segment Hydatid cyst > ½ of the body length Unilocular Contain scolices Testis Host 46 – 60 16 – 26 Sheep, Cattle, Horses Rodents, foxes, etc. Wolves etc. < ½ of the body length Alveolar No scolices 20