• We will be looking at these slides:
  • a1, a3, 6a, a7, a9, 9a.
• You need to know:
  • how to identify the organism in a slide.
  • what group the organism belongs to (nematode, cestodes, amoeboid protozoan, flagellate, etc).
  • what superkingdom they belong to (most are eukaryotes).
  • their common or scientific name. (Most others require scientific name.)
  • diagnostic criteria of patients that have them.
  • on most also know the mode of transmission.
     
• Parasites
  Parasites belong to two kingdoms: protists and animals.  Although the parasitic protists are microbes, the parasitic animals (worms) are not.  Microbiologists still study them partially because they are often diagnosed by their microscopic eggs.  These parasites often have complex life cycles that may involve two or more species.  The definitive host is the species where the parasite can mature and reproduce sexually.  The intermediate host is a species where an immature (or juvenile) parasite can live and reproduce asexually.

• Parasitic Protozoans
  All of the parasitic protists are protozoans, a grouping of animal-like protists.  We will use a clinical approach to classification because this is how diagnosis is often determined.  Parasitic protozoans usually have two or more life stages.  In protozoans that follow the fecal to oral route of transmission, the trophozoite stage is the motile, reproductive form of the parasite that may damage the host.  When environmental conditions become unfavorable, the trophozoite changes into the immobile cyst stage.  The cyst has a tough outer membrane that allows the parasite to survive harsh environments, such as when the parasite is outside of its host or in the acids of the stomach.  In the cyst stage, the parasite is in stasis (sort of like hibernation).
  • Entamoeba histolytica: (variant spelling: Endamoeba) cyst and trophozoite (slides none, Amoeboid protozoan)
    causes severe and painful diarrhea, and amoebic dysentery (amebiasis).  Transmission is fecal to oral route.  P.
    Atlas p. 176.  cyst1, cyst2, cyst3, cyst4, three trophozoites, trophozoite2, trophozoite with ingested RBC's, trophozoite4 in human gut.
    Entamoeba life cycle.
     
    
  • Balantidium coli: cyst & trophozoite life stages (slides A-1, Ciliate protozoan). 
    cause of balantidiasis (ulceration of colon, bloody-mucoid stools, diarrhea, constipation).  Transmission is fecal to oral.  P.
    Atlas p. 179.  cyst1, cyst2, trophozoite1, trophozoite2, trophozoite in a wet mount

  • Giardia lamblia: (or Giradia intestinalis) cyst and trophozoite life stages (slide 10, Flagellate protozoan)
    causes diarrhea, dehydration, and abdominal pain.  Transmission is fecal to oral. 
    Atlas p. 180.  cyst, trophozoite1, trophozoite2.  (Note, the flagella do not show up well if at all in a normal stain and a compound microscope.)

  • Trichomonas vaginalis: a trophozoite life stage (slide a3, Flagellate protozoan) 
    causes trichomoniasis, inflammation of the genitourinary mucosa.  Symptoms are more common in women than men.  Transmission is through sex.
    Atlas p. 181.  This parasite does not have a cyst stage.  trophozoite1, Trichomonas2, Trichomonas3, Trichomonas4,  life cycle.
    
    
  • Plasmodium vivax: has a comples life cycle (a3-slide is missing, Sporozoan protozoan)
    is one of four species that causes malaria.  Transmission is by the bite of the genus Anopheles (a-nawf'-a-lez). The life cycle of this parasite is much more complex than the two stages above.  This parasite is rather difficult to learn without slides, so just know this information.  Appearance of Plasmodium in infected blood, how heavy the parasite burden can be.
    Atlas p. 183.

 

• Parasitic Helminthes
  Helminthes are worms which is not a monophyletic group, it includes three phyla: Annelids, Nematodes, and Platyhelminthes.  Many are free-living organisms, but we'll only study the parasitic helminthes.  The life cycle of parasitic helminthes is often complex involving two or more species.  An immature parasite in an intermediate species can encyst in a tissue and wait to be consumed by the definitive or another intermediate host.  This cyst is very different from a protozoan cyst, but it has one similarity, it can survive stomach acids.  Once it passes the stomach, it may develop into a mature parasite in the definitive species or into another immature parasite in an intermediate species.  Depending on the parasite, diagnosis is often made by checking the patent's feces or anal region for characteristic eggs.  There are three types of parasitic helminthes in two phyla: Platyhelminthes (flatworms) and Nematodes (roundworms).  Parasitic Platyhelminthes often lack or only have a partial digestive system, absorbing food through their skin. They may also lack other systems, such as a system for locomotion.  

   

  1. Trematodes (flukes are parasitic flatworms, all flukes are parasites):
     • Attaches to its host with suckers.  Appearance is flat and leaf-like and they contain only a partial digestive system.
     • Clonorchis sinensis, adult, egg (oriental liver fluke, slides a7) 
       causes liver disease (especially in the bile ducts).  P.  Transmission is by consumption of undercooked or raw fish.
       Atlas p. 187.  Oriental liver fluke.
      
  2. Cestodes (tapeworms are parasitic flatworms, all tapeworms are parasites)
     • Attach to their host with a scolex that may have hooks or suckers or both.  Proglottids follow the scolex, each having an ovary and a testis.  When the proglotid matures, it is full of eggs and may break off and be shed in the feces.  Life cycle.  All cestodes lack a digestive system
       
     • Taenia saginata, adult, eggs, proglottid  (beef tapeworm, slides 9a or a9).  P.  
       Though we call this the beef tapeworm, cattle are the intermediate host, humans are the definitive host.  Symptoms are usually mild stomach problems and weight loss.  Transmission is by consumption of a cyst in undercooked beef.  Note the absence of hooks.
       Atlas p. 194.  Beef tapeworm1, ova. 
       
     • Taenia solium (slides 9a)
       Though we call this the pork tapeworm, swine are the intermediate host, humans are usually the definitive host.  Symptoms are usually mild stomach problems and weight loss.  Yet, juvenile tapeworms sometimes migrate to other parts of the body (when humans are an intermediate host), causing symptoms that vary depending on the tissue infected, but they are usually mild.  Transmission is by consumption of a cyst in undercooked pork or by consumption of eggs in contaminated food.  Tapeworm1, scolex, proglottids.
       
     • Taenia pisiformis (adult scolex, slide 9a or a9) 
       Not in the Atlas (has hooks and 4 suckers).  This is the dog tapeworm.
       pisiformis1, pisiformis proglottids, pisiformis scolex1, scolex2.
       
     • Echinococcus granulosus,  adult, hydatid cysts  and eggs (slides 6a) 
       Is the tapeworm of carnivores, humans can be an intermediate species.  P.  Juvenile parasites migrate through human tissue forming hydatid cysts which damages tissue, symptoms depend on what tissue is damaged and its extent.  Transmission is by consumption of eggs usually in contaminated food or hands or by consumption of a cyst in an undercooked intermediate species (such as sheep or cow).
       Atlas p. 192.  Tapeworm, cyst, mature cyst showing a scolex, life cycle.
      
  3. Parasitic Nematodes (parasitic round worms)
  • Most nematodes are free-living, not parasitic, they are also the most abundant animal.
  • Parasitic Nematodes have separate male and female individuals and they have a complete digestive system..
  • Enterobius vermicularis, eggs, adult female and adult male (pinworms of humans, slides a7 or 7a) 
    causes mainly peri-anal itching though other symptoms may occur.  P.  Humans are the only host.  Atlas p196.  Transmission is by (usually accidental) consumption of eggs.  This is the most common parasitic helminthes in the USA.  Enterobious infection on colon, ova.

Hyperlinks are to give you additional pictures and pronunciation, do not spend a lot of time memorizing text on these links.  Also, some of the links require a fast internet connection.  If there is a blue P. by the parasite, it means that there is an oral pronunciation of the parasite at my hyperlink (its the same web page for all of them, so you have to find the parasite on the page and click a link to hear it).