Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 22 March 2005

The text below simply represents a crude lecture outline of one of the topics covered in class. It is not meant to substitute for attending lectures or ignoring the textbook. Additional material, including line drawings, kodachromes, and more extensive information on life-cycles and basic biology, will be supplied in the lectures.

TOPIC 26. Lumen dwelling flagellates (excluding opalinids)


Some general characteristics of flagellates

  1. flagella
    1. central axoneme
    2. surrounded by plasma membrane that continues from body of the cell
    3. 9 outer doublets surrounding inner 2 microtubules (9+2)
    4. base plate near level of cell where central doublet ends; then, continues as 9 triplets (kinetosome, basal body, or blepharoplast)
  2. most of the time, the active (feeding) stage is termed a "trophozoite."
  3. many, but not all, form resistant cysts which are the way most are transmitted between hosts
  4. longitudinal binary fission of the trophozoite is the main mode of reproduction (asexual)
  5. mastigont (flagellum, kinetosome, and all associated organelles)
  6. costa (striated rod of protein, runs from one kinetosome along margin of organism just under undulating membrane when present; support)
  7. axostyle (longitudinal rod of microtubules running length of some flagellates
  8. parabasal body (large, modified Golgi apparatus (=dictyosome) in some genera)
  9. parabasal filament (periodic fibril in some, runs from parabasal body in kinetosome in some)
  10. karyomastigont (entire complex of organelles of the mastigont plus nucleus)


ORDER: Retortamonadida

  1. 4 kinetosomes, associated as 2 pair
  2. 3 anterior flagella and a fourth lying in a cytostomal groove; or only 2 flagella
  3. mitochondria absent; Golgi absent
  4. typical life history
    1. Undergo longitudinal binary fission in intestinal tract
    2. Cysts produced, pass out feces into environment
  5. representatives of the genus Chilomastix
    1. trophozoites with single nucleus; 3 anterior flagella and a fourth small flagellum within the cytostomal groove
    2. trophozoites with oblique, spiral groove
    3. lemon-shaped cysts; mononucleate
    4. cytostomal fiber prominent and hook-like in both trophozoite and especially cyst (Shepherd's crook)
    5. representative species
      1. Chilomastix bettencourti (rodents)
      2. Chilomastix caprae (cattle, goats)
      3. Chilomastix mesnili (swine, primates)
      4. Chilomastix intestinalis (guinea pigs)
      5. Chilomastix cuniculi (rabbits)
      6. Chilomastix gallinarum (chickens)
  6. some representatives of the genus Retortamonas
    1. trophozoites with single nucleus; 2 flagella (1 anterior and a second that trails)
    2. lemon-shaped cysts; mononucleate
    3. some representative species in the genus
      1. Retortamonas gryllotalpae (mole crickets)
      2. Retortamonas caviae (guinea pigs)
      3. Retortamonas intestinalis (primates, including humans)
      4. Retortamonas kirbii (American woodchuck)
      5. Retortamonas ovis (sheep, cattle)
  7. Other species of importance
    1. Cochlosoma anatis (enteritis in various orders of birds)
    2. Cochlosoma soricis (shrews)


ORDER: Enteromonadida (you will not be tested over this taxon)

  1. 1 karyomastigont
  2. 1-4 flagella associated in the karyomastigont
  3. mitochondria absent; Golgi absent
  4. common species
    1. Caviomonas mobilis (guinea pigs and hamsters)
    2. Enteromonas caviae (guinea pigs)
    3. Enteromonas hominis (primates, including humans)
    4. Enteromonas intestinalis (rabbits)
    5. Enteromonas suis (swine)
    6. Enteromonas wenyoni (opossum)
    7. Trimitus ranae (frogs and salamanders)
    8. Trimitus trionici (tortoises)


ORDER: Diplomonadida

  1. 2 karyomastigonts (binucleate)
  2. polyploid, with a functional ploidy of at least 4
  3. each mastigont with 4 flagella (8 flagella total)
  4. mitochondria absent; Golgi absent
  5. free-living or parasitic
  6. common genera include Giardia, Hexamita, Spironucleus
  7. Giardia intestinalis (syns. Giardia duodenalis, Giardia lamblia)
    1. tear drop-shaped trophozoites with ventral adhesive disc (NOT a "sucking" disc), 8 flagella, and 2 nuclei
    2. about 80% of the trophozoites possess one or more median bodies, poorly defined microtubule-containing structure(s) that tend to be claw-shaped in this species
    3. ellipsoidal cysts with 4 nuclei when mature
    4. life-cycle
      1. quadrinucleate cysts ingested
      2. excyst; trophozoites complete division; attach to mucosa of small intestine with ventral adhesive disc
      3. divide by longitudinal binary fission
      4. some produce cysts (2 nuclei)
      5. nuclei and flagella in cyst divide; cytoplasm of trophozoite becomes arrested in middle of division
      6. in a wide variety of medium-large sized mammalian hosts
    5. pathology may include diarrhea, weight loss, abdominal pain; in humans, periodic (cyclic) passage of cysts in feces
    6. discovered in 1681 by Antoni van Leeuwenhoek who found the parasite in his own stools using the first successful simple light microscope (which he built himself)
    7. Giardia intestinalis is divided into different groups based on rRNA sequences, although groupings and taxonomy is changing rapidly from year to year
      1. human isolates can be typed into 2 different genotypes (group 1 or group 2). Other animals may also harbor these genotypes, however
      2. most dog isolates can be typed into 2 different genotypes (group 3 and group 4). Other animals rarely share these genotypes. However, dogs sometimes can be found to be passing group 1 or group 2 cysts.
      3. cats can be found to be passing group 1 cysts
      4. group 1 is more evolutionarily divergent; groups 2, 3, and 4 are more closely related
      5. this grouping system should be considered temporary and will certainly change very shortly
    8. other Giardia spp.
      1. Giarida muris in rodents (oval-shaped median bodies)
      2. Giardia agilis in amphibia (tear drop-shaped median bodies; elongate trophozoites)
      3. Giardia varani in varanids (claw-shaped median bodies)
      4. Giardia psittaci in parakeets (claw-shaped median bodies; no ventral flange at margins of ventral adhesive disc)
      5. probably many other species in mammals and birds; many other named species but status of each of these requires further studies.
  8. Spironucleus meleagridis (syn. Hexamita spironucleus)
    1. in turkey, quail, pheasant, duck, etc.
    2. trophozoites binucleate, with 8 flagella; ventral adhesive disk absent
    3. trophozoites undergo binary fission in intestine; cysts passed in feces
    4. pathology includes diarrhea, weight loss, ruffled feathers, death
    5. similar species
      1. Hexamita intestinalis (anurans and salamanders)
      2. Octomitus intestinalis (rodents)
      3. Octomitus neglectus (anurans and salamanders)
      4. Spironucleus columbae (pigeons)
      5. Spironucleus muris (rodents)


ORDER: Oxymonadida (you will not be tested over this taxon)

  1. 1-more karyomastigonts
  2. each karyomastigont with 4 flagella, typically arranged as 2 pair
  3. 1-more flagella recurrent
  4. 1-many axostyles
  5. mitochondria and Golgi absent
  6. in termites and woodroaches
  7. common genera Monocercomonoides, Oxymonas, Notila, Saccinobaculus, Pyrsonympha


ORDER: Polymonadida (you will not be tested over this taxon)

  1. multinucleate; each nucleus with associated set of flagella
  2. axostyles present
  3. parabasal body (large Golgi) present and associated with karyomastigont
  4. in termites
  5. common genera Calonympha, Cornonympha


ORDER: Hypermastigida (you will not be tested over this order)

  1. mastigont system with many flagella each
  2. mitochondria absent; many parabasal bodies (Golgi) present
  3. kinetosomes and associated flagella arranged in complete or partial rows, plates, spiral rows, longitudinal rows, etc.
  4. single nucleus per cell
  5. in wood eating insects such as termites, wood roaches, and cockroaches
  6. common genera Barbulanympha, Trichonympha, Spirotrichonympha


ORDER: Trichomonadida

  1. typically 1 karyomastigont
  2. variable number of flagella, 0-6, associated with karyomastigont; one flagellum often recurrent and associated as undulating membrane
    1. i.e. Pentatrichomonas (5 anterior flagella plus 1 recurved flagellum)
    2. i.e. Trichomonas (4 anterior flagella plus 1 recurved flagellum)
    3. i.e. Tritrichomonas (3 anterior flagella plus 1 recurved flagellum)
  3. mitochondria absent; parabasal body (Golgi) presesnt
  4. 1 axostyle
  5. true cysts rarely formed
  6. trophozoites undergo longitudinal binary fission in the intestinal tract; intestinal species can round up and resist passage through stomach
  7. urogenital species known to release proteases, dissolve epithelium, and utilize digested products
  8. representative species
    1. Dientamoeba fragilis (large intestine of humans)
      1. closely related to Histomonas meleagridis
      2. about 80% are binucleate
      3. may cause mild to moderate diarrheal illness; occasionally more severe symptoms
      4. no true cysts have been identified
      5. one study has shown the amoeboid stage probably occurs in Enterobius vermicularis eggs and may be transmitted by ingestion of infected eggs (1956, Am J Trop Med Hyg 5: 258-265).
      6. Multiple statistical studies have shown a strong correlation between the presence of Enterobius vermicularis when Dientamoeba fragilis is present
      7. In the mid-1970's, Ockert successfully infected himself and two other individuals by ingesting pinworm eggs from a child who was concurrently infected with Dientamoeba fragilis
      8. two distinct genetic variants have been noted which may (or may not) indicate two morphologically similar species
    2. Histomonas meleagridis
      1. in gallinaceous birds
      2. pleomorphic; amoeboid form with single flagellum in caecum (however, 4 kinetosomes)
      3. amoeboid form can be invasive; erodes mucosa
      4. transmitted in eggs of Heterakis gallinarum
      5. turkeys the most susceptible; 3-12 weeks of age; ulcerations in caecum; perforation of intestine; carried to liver and may cause hepatic abcesses; blackhead disease of turkeys; death (need Escherichia coli or Clostridium perfringens as well; no bacteria then no pathology)
      6. similar species, Parahistomonas wenrichi, also transmitted in Heterakis eggs but not pathogenic; 4 flagella
    3. Pentatrichomonas hominis (large intestine of humans)
    4. Trichomonas canistomae (mouth of canids)
    5. Trichomonas felistomae (mouth of felids)
    6. Trichomonas muris (caecum and colon of rodents)
    7. Trichomonas gallinae (upper GI tract of chickens, turkeys, pidgeons, and numerous other birds; can kill birds)
    8. Trichomonas tenax (mouth of humans)
    9. Trichomonas vaginalis (urogenital tract of humans; may cause erosion of urogenital epithelium)
    10. Tritrichomonas eberthi (intestine of chickens)
    11. Tritrichomonas equi (intestine of equids)
    12. Tritrichomonas foetus (urogenital tract of cattle; may cause endometritis and abortion). Some evidence suggests that this species also infects the intestinal tract of felids and may cause diarrhea. Recent evidence has also shown Tritrichomonas suis (intestine of swine) to be a synonym.


    ORDER: Proteromonadida (you will not be tested over this taxon)

    1. 1-2 pair of unequal flagella
    2. paraxial rods absent
    3. one mitochondrian, which curls around nucleus
    4. Golgi (dictyosome) present
    5. forms cysts
    6. known from amphibia, reptiles, and mammals
    7. representative species include Karotomorpha, Proteromonas

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