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Introduction to Parasitology

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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 Phoresis (to carry) Commensalism (eating at the same table) Mutualism positive reciprocal relationship Parasitism Metabolic dependence

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: Animals Different species

5 Life cycle 1.Direct life cycle 2.Indirect life cycle
Medical Parasitology Life cycle 1.Direct life cycle 2.Indirect life cycle Parasite Adult form/ Sexual reproduction Larva/ Asexual reproduction Host 1-Definitive or final host 2-Intermediate host Larva Adult Egg Transfer or paratenic host

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

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

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,
Adults egg L1 L2 molting Life cycle: Cylindrical, Complete digestive system, Male < Female Large (parsites) Long life

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


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 Treatment Stool Examination: appearance of the eggs in feces
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


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

43 remain active up to three weeks
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 ) Mebendazole Albendazole
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 Finger sucking and nail biting
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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