Biology 625
Fall semester lecture note outline

Updated: 24 October 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 33. Coccidia and Cryptosporidium spp.

Characteristics of the suborder: Eimeriorina (coccidia)

  1. homoxenous or heteroxenous
  2. macrogamonts and microgamonts develop independently (without syzygy)
  3. microgametocytes usually produce many microgametes
  4. sporozoites develop within resistant oocyst, or within a series of membranes analogous to the oocyst wall
  5. normally, zygote is not motile
  6. merogony, gamogony, and sporogony normally present
  7. many have life-cycles where resistant oocysts are passed in the feces
    1. homoxenous. One host (i.e. direct) life-cycle.
    2. heteroxenous. More than one host used in the life-cycle.
    3. prepatency. The length of time between ingestion of oocysts until the first new oocysts are detected in the feces.
    4. patency. The total length of time oocysts are shed in the feces.

Taxonomy of the suborder: Eimeriorina

  1. Family: Spirocystidae (you will not be tested over this taxon)
    1. homoxenous
    2. with coiled, vermicular meronts
    3. one species; in an oligochaete
  2. Family: Selenococcidiidae (you will not be tested over this taxon)
    1. homoxenous
    2. life-cycle poorly defined
    3. one species, in the Atlantic lobster
  3. Famiy: Aggregatidae (you will not be tested over this taxon)
    1. heteroxenous
    2. oocysts usually polysporic
    3. most species marine
    4. 3 genera, the most well known in Aggregata where merogony occurs in decapod crustaceans and gamogony and sporogony in cephalopods. Other genera traditionally placed within this family now within the Eimeriidae.
  4. Lankesterellidae (you will not be tested over this taxon)
    1. heteroxenous
    2. merogony, gamogony, and sporogony in vertebrate
    3. oocysts without sporocysts
    4. sporozoites exit thin-walled oocysts and invade blood cells; become dormant
    5. blood sucking vectors, i.e. mites, dipterans, or leeches ingest sporozoites in blood
    6. parasites transmitted to new vertebrate host by ingestion of vector; apparently no development in invertebrate
    7. genera (distinctions between the genera becoming clouded)
      1. Atoxoplasma
        1. in birds
        2. oocysts with many sporozoites
        3. most vectors dipterans or mites
      2. Lankesterella
        1. mainly in amphibia; few in reptiles
        2. oocysts with more than 32 sporozoites
        3. most vectors leeches
      3. Schellackia
        1. mainly in reptiles; few in amphibia
        2. oocysts with 8 sporozoites
        3. most vectors dipterans or mites
  5. Eimeriidae
    1. most species homoxenous
    2. some form monozoic cysts in paratenic host
    3. merogony, gamogony, and oocyst wall formation in same host
    4. in vertebrates or invertebrates
    5. most genera distinguished by numbers of sporocysts and sporozoites within oocyst
    6. 15-25 genera, depending upon author. Most important genera as follows:
      1. Eimeria (4 sporocysts in oocyst, each sporocyst with 2 sporozoites)
      2. Isospora (2 sporocysts in oocyst, each sporocyst with 4 sporozoites)
      3. Several others include Caryospora, Cyclospora, Pfeifferinella, Pseudoklossia, Tyzzeria, Wenyonella
  6. Family: Sarcocystidae
    1. heteroxenous
    2. all with oocysts containing 2 sporocysts, each sporocyst with 4 sporozoites
    3. all species have at least one asexual stage comprised of large tissue cysts containing thousands of dormant merozoites. This cyst stage is responsible for transmitting infection to definitive host
    4. 2 subfamilies, distinguished by presence or absence of metrocytes
    5. 6 genera, which include Toxoplasma, Neospora, Hammondia, Frenkelia, Sarcocystis, Besnoitia

Eimeria spp. or Isospora spp. (Eimeriidae)

  1. oocysts ingested by host
  2. excystation in gut
  3. sporozoite penetrates intestinal epithelium cells (occasionally in renal, biliary, or respiratory epithelium in some species)
  4. merogony (1-7 asexual generations; 2-4 common)
  5. last generation merozoites develop into gamonts
  6. most become macrogametes
  7. some become microgametocytes
  8. flagellated microgametes develop, leave microgametocyte, and fertilize macrogametes
  9. zygote lays down resistant wall
  10. unsporulated oocysts passed in feces; sporulation (some sporulate endogenously but most species sporulate exogenously)
  11. representative species (over 2,500 described to date)
    1. Eimeria bovis, Eimeria zuernii in cattle
    2. Eimeria leuckarti in horses
    3. Eimeria tenella, Eimeria acervulina, Eimeria maxima in chickens
    4. Isospora canis, Isospora ohioensis in dogs
    5. Isospora felis, Isospora rivolta in cats

Sarcocystis spp. (Sarcocystidae)

  1. heteroxenous
  2. each oocysts with 2 sporocysts, each sporocyst with 4 sporozoites
  3. sporulation endogenous, so that oocysts (often free sporocysts) passed fully sporulated
  4. oocysts usually with very thin wall, which often ruptures in gut so that free sporocysts passed in feces of many species
  5. large, elongate tissue cysts in muscle of intermediate host
  6. life-cycles usually involve predator/prey or scavenger type life-cycles; merogony in intermediate host and gamogony and sporogony in predator or scavenger
  7. life-cycle
    1. oocysts ingested by intermediate host
    2. excystation in gut
    3. penetrate mucosa; invade extraintestinal organs; endothelial cells of hepatic capillaries a favorite target
    4. 1-2 generations of merogony
    5. merozoites invade striated muscle fibers
    6. form elongate cysts, termed sarcocysts, each filled with numerous slow dividing merozoites termed bradyzoites. Division of the bradyzoites via endodyogeny within dividing zoites termed metrocytes
    7. sarcocysts gradually increases in size and numbers of bradyzoites increase in number
    8. sarcocyst ingested by carnivore or scavenger
    9. bradyzoites penetrate mucosa and usually enter lamina propria
    10. macrogametes and microgametocytes develop
    11. flagellated microgametes produced by microgametocyte; exit and and penetrate macrogamete
    12. zygote lays down resistant wall; endogenous sporulation
    13. oocysts gradually liberated in feces over period of weeks
  8. most species not pathogenic; very little immunity develops in definitive host
  9. representative species
    1. Sarcocystis bertrami (equine/canid)
    2. Sarcocystis cruzi (bovine/canine)
    3. Sarcocystis capracanis (goats/canids)
    4. Sarcocystis fayeri (equine/canid)
    5. Sarcocystis hemionilatrantis (deer/canid)
    6. Sarcocystis hirsuta (bovine/feline)
    7. Sarcocystis hominis (bovine/human)
    8. Sarcocystis miescheriana (swine/canids)
    9. Sarocystis muris (mouse/felid)
    10. Sarcocystis odoi (deer/felid)
    11. Sarcocystis rileyi (ducks/skunk)
    12. Sarocystis tenella (sheep/canid)

Toxoplasma gondii (Sarcocystidae)

  1. facultatively heteroxenous
  2. definitive hosts felids
  3. intermediate hosts over 350 known species of mammals and birds
  4. tissue cysts throughout body, especially concentrated in CNS. Tissue cysts generally spherical
  5. life-cycle in felid
    1. oocysts, or tissue cysts from infected intermediate hosts, ingested
    2. sporozoites (or bradyzoites if from cysts) penetrate intestinal epithelial cells
    3. 5 generations of merogony in gut
    4. macrogametes and microgametocytes form
    5. flagellated microgametes liberated from microgametocytes; penetrate macrogamete
    6. zygote develops; resistant wall layed down
    7. unsporulated oocysts liberated and passed in feces
    8. sporulation exogenous, in about 72 hours
  6. life-cycle in intermediate host (this also occurs in felids)
    1. oocysts or tissue cysts ingested
    2. sporozoites (from oocysts) or bradyzoites (from tissue cysts) penetrate intestinal wall
    3. dissemination throughout body
    4. penetrate cells; under endodyogeny as tachyzoites. "Groups" of tachyzoites develop in host cells
    5. tachyzoites rupture from cells and initiate new infections
    6. eventually, some tachyzoites transform into slower dividing bradyzoites; cyst wall layed down around parasitophorous vacuole derived from both the ER and host cell mitochondria
    7. tissue cyst gradually increases in size; bradyzoites increase in number by undergoing slow endodyogeny; metrocytes absent
    8. eventually, cysts become dormant; occasionally rupturing and liberating bradyzoites. If immunity has waned, bradyzoites may transform into tachyzoites and increase in numbers. If still immune, bradyzoites destroyed.
  7. pathology includes no clinical signs to lymphadenopathy, muscle pain, fatigue, birth defects (tachyzoites can cross placenta), abortion, blindness, seizures, and occasionally death
  8. prevention
    1. litter boxes should be changed every 48 hours to keep sporulated oocysts from accumulating
    2. all meat should be cooked thoroughly, especially meat fed to cats
    3. new cats should not be obtained in households with pregnant females
    4. childrens sandboxes should be kept covered when not in use
  9. Martina Navratilova, tennis star, developed acute toxoplasmosis in 1982.
  10. Tennis star Arthur Ashe developed neurologic problems in 1988 due to toxoplasmosis. Further tests revealed he was HIV positive.
  11. British actress Leslie Ash developed toxoplasmosis when she was two months pregnant
  12. Ariel Daye, porn star, left the business in 1996 due to acute toxoplasmosis
  13. Miriam Pires, Brazilian actress, died of toxoplasmosis in 2004

Family: Cryptosporidiidae

  1. homoxenous
  2. intracellular, but project from lumenal side of cell and attached to cytoplasm of host cell by "feeder organelle."
  3. oocysts with 4 naked sporozoites
  4. single genus Cryptosporidium
    1. oocysts with 4 sporozoites, without sporocysts
    2. develop intracellulary, but in peripheral location on lumenal side of intestinal epithelial cell; projects into lumen
    3. recent molecular evidence suggests this taxon derived from gregarines, and is more closely related to gregarines than to most other members of the suborder
    4. two types of autoinfective stages hypothesized; type I merozoites capable of forming new type I meronts and thin walled oocysts that may liberate sporozoites to initiate new infections
    5. life-cycle of Cryptosporidium parvum
      1. oocysts ingested by host; in the case of Cryptosporidium parvum it usually involves neonates and over 150 different mammalian hosts have been found to be suitable
      2. sporozoites excyst from suture at one pole
      3. penetrate epithelial cells; preferred site ileum
      4. type I meronts (with 8 merozoites); capable of recycling and producing more generations of type I meronts
      5. some merozoites penetrate cells and undergo development into type II meronts with 4 merozoites
      6. type II merozoites liberated, infect new cells
      7. macrogametes and microgametocytes
      8. 16 non-flagellated microgametes arise from microgametocyte; exit and penetrate macrogamete
      9. zygote
      10. resistant wall layed down around zygote; endogenous sporulation
      11. about 20% oocysts thin walled, and may ruture releasing sporozoites to initiate new (autoinfective) cycles
      12. exit with feces
  5. life-cycle ended when host immune response eliminates the reproductive cycle. If animal immunosuppressed, parasite overwhelms host due to recycling of type I meronts
  6. pathology involves severe diarrheal illness, weight loss, abdominal cramping, and electrolyte imbalance
  7. related species
    1. Cryptosporidium andersoni in gastric glands of cattle (2000, J. Euk. Microbiol. 47: 91-95)
    2. Cryptosporidium baileyi in cloaca and bursa of chickens (1986, J. Protozool. 33: 289-296)
    3. Cryptosporidium bovis in older calves (2005, J. Parasitol. 91: 624-629)
    4. Cryptosporidium canis in canids (2001, J. Euk. Microbiol. 87: 1415-1422)
    5. Cryptosporidium felis in felids (1979, Jap. J. Parasitol. 28: 285-307)
    6. Cryptosporidium hominis in humans (2002, J. Euk. Microbiol. 49: 433-440)
    7. Cryptosporidium meleagridis in turkeys (1955, J. Comp. Pathol. 65: 262-266)
    8. Cryptosporidium molnari in fish (2002, Int. J. Parasitol. 32: 1007-1021)
    9. Cryptosporidium muris in gastric glands of rodents and other mammals (1910, J. Med. Res. 23: 487-509; 1986, Jpn. J. Parasitol. 35: 521-526)
    10. Cryptosporidium nasorum in fish (1981, J. Fish Dis. 4: 425-428) is a nomen nudum. The term is commonly used so I mention it here, but no taxonomic description occurs within the paper
    11. Cryptosporidium saurophilum in reptiles, especially lizards (1998, Folia Parasitol. 45: 93-100) (technically, this appears to actually represent Cryptosporidium varani)
    12. Cryptosporidium scophthalmi in turbot (2004, Dis. Aquat. Org. 62: 133-145)
    13. Cryptosporidium serpentis in gastric mucosa of reptiles, especially snakes (1989, J. Wildlf. Dis. 25: 20-30; 1996, J. Parasitol. 82: 748-751; 1998, J. Parasitol. 84: 1298-1300)
    14. Cryptosporidium wrairi in guinea pigs (1971, J. Protozool. 18: 243-247; 1991, Can. J. Microbiol. 37: 949-952; 1994, Folia Parasitol. 41: 97-100)

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