Untitled Quiz

Parasitology

• Study of parasites, their hosts and the relationship between them
• One of the largest fields in parasitology deals with parasites that infect man, the diseases they cause, clinical picture, diagnosis, treatment, prevention and control
• Parasite: An organism that lives on or within another organism (called the host).

Important Terms

• Worm: A multicellular organism that is typically parasitic
• Protozoa: Unicellular eukaryotic organisms that are often parasitic
• Egg: The reproductive cell of a parasite, which may contain an embryo
• Cyst: A protective covering that surrounds a parasite, allowing it to survive outside of a host
• Larva: An immature stage of a parasite that can develop into an adult
• Trophozoite: The actively feeding and growing stage of a protozoan parasite.

Diagnostic Methods

• Stool Examination: Used to detect parasites or their eggs in feces
  • Macroscopic Examination: Visual inspection of stool for consistency, blood, mucus, worms, and proglottids
  • Microscopic Examination: Use of a microscope to identify parasites or eggs
    • Direct Wet Method: A small portion of stool is mixed with saline and examined for eggs and larvae
    • Stained Wet Method: A small portion of stool is mixed with Lugol’s iodine to detect protozoan cysts
    • Concentration Methods: These separate parasites from debris and increase visibility
      • Sedimentation Method: Sediment is resuspended in a formalin solution and examined
      • Floatation Method: Sediment is resuspended in a zinc sulfate solution and the top fluid is examined
      • Kato Technique: Stool is mixed with glycerin to clear fecal debris and allows for egg counting
• Urine Examination: Useful in diagnosing infections caused by Schistosoma haematobium
  • Eggs are often trapped in mucus or pus and are more commonly found in the last few drops of urine
• Sputum Examination: Used to identify parasites in sputum, which may indicate an infection in the lungs
• Blood Examination: Used to detect parasites and their stages in blood
  • Thin Film: Blood is spread thinly on a slide, allowing for visualization of red blood cells, white blood cells, platelets, and parasites
  • Thick Film: Red blood cells are lysed, allowing for easier visualization of parasites in cases of light infection
  • Staining: Giemsa stain is preferred for blood film staining
• ImmunoDiagnostics: Used to detect parasite antigens or antibodies in blood
  • Analytical Approaches: Classical agglutination, complement fixation, gel-diffusion methods, immunofluorescence, enzyme immunoassay (EIA), and Western blot assays

Parasitology Course Subjects

• Helminths: Multicellular parasites, e.g. tapeworms and flukes
• Protozoa: Unicellular parasites, e.g. amoebas and flagellates

Basic Terms

• Lifecycle: The developmental stages of a parasite throughout its lifespan
• Host: An organism that harbors a parasite
  • Definitive Host: Harbors the adult or sexually mature stage of a parasite
  • Intermediate Host: Harbors the immature or larval stage of a parasite, where the parasite multiplies asexually
  • Reservoir Host: An animal that harbors a parasite and acts as a source of infection
• Habitat: The place where a parasite lives within its host
• Diagnostic Stage: The stage of development where a parasite can be easily identified
• Infective Stage: The stage of development where a parasite can infect a host
• Mode of Infection: The manner in which a parasite enters its host

Types of Hosts

• Vector: Usually an arthropod (e.g. mosquito) that carries a parasite and transmits it to its host

Additional Helpful Information

• Unfertilized Egg: Will eventually die if not fertilized
• Fertilized Egg: Has the potential to develop into a mature, embryonated egg
• Embryonated Egg: Contains an embryo and is infective
• Larvated Egg: Ready to release larvae and is infective

Classification of Helminths

• Phylum Platyhelminthes (Flatworms)
  • Class Cestoda (Tapeworms)
    • Taenia saginata/solium
    • Echinococcus granulosus
    • Hymenolepis nana
  • Class Trematoda (Flukes)
    • Fasciola hepatica/gigantica
    • Fasciolopsis buski
    • Clonorchis sinensis
    • Heterophyes heterophyes
    • Schistosoma mansoni/hematobium
• Phylum Nemathelminthes (Roundworms)
  • Class Nematoda
    • Ascaris lumbricoides
    • Trichuris trichiura
    • Enterobius vermicularis
    • Ancylostoma duodenale
    • Trichinella spiralis
    • Loa loa
    • Wuchereria bancrofti
    • Onchocerca volvulus
    • Dracunculus medinensis

Nematodes - Part 1

• Nematodes are roundworms that are cylindrical, non-segmented, and have a well-developed digestive tract
• Sexes are separate: Males are typically smaller and more slender than females
• Intestinal Nematodes: Live in the intestines of their hosts
  • Small Intestine
    • Ascaris lumbricoides
    • Ancylostoma duodenale
    • Trichinella spiralis
  • Large Intestine
    • Trichuris trichiura
    • Enterobius vermicularis
    • Tissue Nematodes: Live in the tissues of their hosts

Ascaris lumbricoides (Giant Intestinal Roundworm)

• Disease: Ascariasis
• Hosts: Definitive host: Man
• Habitat: Small intestine
• Infective Stage: Embryonated eggs
• Mode of Infection: Ingestion of food and water contaminated with embryonated eggs
• Diagnostic Stage: Fertilized and unfertilized eggs (unembryonated eggs)
• Lab Diagnosis: Stool examination showing fertilized and unfertilized eggs. Occasionally, larvae can be found in sputum
• Life Cycle: Embryonated eggs develop in the soil, are ingested by the host, hatch in the small intestine, larvae migrate to the lungs, are coughed up and swallowed, and mature in the small intestine
• Additional Information:
  • Eggs take 18 days to several weeks to become embryonated
  • Larvae mature in the lungs in 10-14 days
  • Male worms are typically 15 cm long, and female worms are 30 cm long

Trichuris trichiura (Whipworm)

• Disease: Trichuriasis
• Hosts: Definitive host: Man
• Habitat: Large intestine
• Infective Stage: Embryonated eggs
• Mode of Infection: Ingestion of food and water contaminated with embryonated eggs
• Diagnostic Stage: Fertilized and unfertilized eggs (unembryonated eggs)
• Lab Diagnosis: Stool examination showing fertilized and unfertilized eggs

Enterobius vermicularis (Pinworm)

• Disease: Enterobiasis (Oxyuriasis)
• Hosts: Definitive host: Man
• Habitat: Large intestine
• Infective Stage: Embryonated eggs
• Mode of Infection: Ingestion of food and water contaminated with embryonated eggs; contaminated clothes or bed linens can also cause infection
• Diagnostic Stage: Eggs in the perianal area and occasionally the adult worms are found in the perianal area
• Lab Diagnosis: NIH swab, Scotch tape, or sticky paddle used to collect eggs from the perianal area
• Additional Information:
  • The female worm migrates to the anus at night to deposit her eggs
  • Autoinfection and Retro-infection possible
  • Adult female worms: 9-13 mm long
  • Adult male worms: 2-5 mm long

Other Information

• Ascaris Eggs (Diagnostic Stage)
  • Size: 60 x 40 µ
  • Oval shaped, bile stained (brown) with a striated wall containing a single fertilized ovum
  • Have a thick egg shell composed of three layers
• Intestinal Obstruction: Ascaris worm can cause intestinal obstruction
• Trichuris trichiura (Diagnostic Stage)
  • The egg is barrel-shaped, bile-stained, with transparent polar prominences
  • Inside the egg shell, there is a singe fertilized ovum