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Introduction to Parasitology By Sh. Ghaffari September 2012.

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2 Introduction to Parasitology By Sh. Ghaffari September 2012

3 Parasitology: definition Parasitology: study of parasites Animals: Free-living Symbiotic Symbiosis

4 Parasitism Parasite ( parasitos para: beside; sitos: grain or food) Host Parasitism: a form of symbiosis in which one organism (parasite) benefits at the expense of another organism of different species (host). Must be: 1. Animals 2. Different species

5 Medical Parasitology Life cycle 1.Direct life cycle 2.Indirect life cycle Larva Adult Egg Transfer or paratenic host

6 Medical Parasitology Host specificity Host: 1. Reservoir host 2. Incidental host Zoonosis Transmission : Direct contact Indirect contact Vector (carrier): often an arthropod, 1. Biological V. 2. Mechanical V.

7 Medical Parasitology Medical Parasites: 1. Protozoa 2. Helminthes: 1. Nematodes(Roundworms) 2. Trematodes(flukes) 3. Cestodes(tapeworms) 3. Arthropoda Ectoparasites Endoparasites Platyhelminthes

8 Classification Kingdom (Animal) Phylum (Platyhelminthes) Class (Trematoda) Order (Digenea) Family (Schistosomidae) Genus (Schistosoma) Species (heamatobium)

9 Binomial nomenclature The scientific naming of species whereby each species receives a Latin or Latinized name of two parts, the first indicating the genus and the second being the species. the genus (capitalized) and species (lowercase) names, both written in italics. For example: Sarcocyctis bovis, Leishmania donovani,

10 Nematodes

11 Parasitic nematodes Life cycle: Cylindrical, Complete digestive system, Male < Female Large (parsites) Long life molting

12 Ascaris lumbricoides Ascariasis

13 Ascaris lumbricoides: like Lumbricus Female: 20-35cm, Male: 10-20


15 Anterior end of Ascaris lumbricoides showing mouth, esophagus, and intestine.



18 Importance Worldwide Very common parasitic worm in human: 1/6 of world population Tropical and subtropical, poverty

19 worms

20 Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks, depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.

21 Need wet warm soil Resistant to cold weather Resistant to acids and alkalis as well as other chemicals Fertilized eggs oval to round, albumin thick outer shell Unfertilized eggs


23 Small intestine: Ascaris larva emerging from egg


25 Ascariasis Infection or disease? Number of worms

26 Ascariasis: Symptoms and signs 1- Migrating larvae: allergic and respiratory symptoms (Loffler syndrome): Cough Sever hemorrhagic pneumonia allergic hypersensitivity reactions(parasite proteins are allergenic): Asthmatic attacks. Pulmonary infiltration. Urticaria. Edema of the lips. Eosinophilia

27 Ascariasis: Symptoms and signs 2- Adult parasites in the intestine: A vague abdominal discomfort. Nausea. Colic Lactose Malnutrition Intestinal obstraction


29 Ascariasis: Symptoms and signs Adult worms outside of the intestine (wandering worms: High infection, Only male / Fever, Drugs) : carry intestinal bacteria to these sites Bile duct: jaundice, hepatitis Appendix and peritonea: appendicitis, peritonitis Migrate forward through the intestinal tract: vomited up or emerging through the nose.


31 Diagnosis Stool Examination: appearance of the eggs in feces Treatment Albendazole : single dose 400 mg/ 200 mg under 2 years Mebendazole: 100mg Bid x3 days Ivermectin pyrantel pamoate: single dose


33 Biliary ascariasis

34 Transmission Children 5-9 years old poor sanitation (sewage disposal) places where human feces are used as fertilizer poor personal hygiene consuming contaminated vegetables or fruits


36 Control Effective sewage disposal systems. Wash, peel, or cook all raw vegetables and fruits grown in soil Periodic treatment

37 Enterobius vermicularis Pinworm, Oxyur Enterobiasis


39 Enterobius vermicularis World wide distribution The most prevalent worm in USA and Western Europe Incidense: 11.4% among people of all ages in USA Most in School-age children (30-60%) Not associated with social class, or culture

40 Enterobius vermicularis Female: about 1 cm sharply pointed tail Male: About 0.5 cm curved tail


42 Contains developing embryo or a larva Colorless Adheres to environmental objects Enterobius eggs

43 Infective in 4-6 h remain active up to three weeks 11

44 Clinical manifestations No symptoms in most people Anal itching in children Restless sleep Itching and vaginal discharge in girls Irritated or infected skin around the anus

45 Diagnosis Treatment Tape test (Scotch ) transparent adhesive tape Done in the morning, before defecation and washing Adult worms in perianal skin Mebendazole Albendazole pyrantel pamoate single dose entire household be treated repeated after 2 weeks

46 Control Eggs can be transferred from fingers to clothing, bedding, towels, toilets, and other objects in the environment. Spread by children to schoolmates or family members. Dust containing eggs can become airborne personal hygiene. laundering of bedding

47 close contact Finger sucking and nail biting Autoinfection(infection from the original host to itself): anus-to-mouth rout retroinfection,(larvae may hatch on the anal mucosa, and migrate up the bowel)


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