Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 11 October 1999

1. numerous species in mammals and birds; some in reptiles
2. small, piriform, spheroid, rod-like, or amoeboid in shape
3. conoid absent, although there has been some discussion that a remnant may be present in some species (exisiting as a "third pre-conoidal ring").
4. oocysts, sporocysts, and and pseudocysts absent
5. flagella absent
6. polar rings and rhoptries present
7. in erythrocytes and sometimes other cells of host
8. heteroxenous, with merogony and probably gamogony in vertebrate host, and fertilization, sporogony, and sometimes merogony in invertebrate host (known vectors ticks)
9. taxa
   1. family: Anthemosomatidae (you will not be tested over this taxon)
      1. meronts in erythrocytes
      2. 5-32 merozoites produced by budding
      3. gamonts spheroid or ovoid
      4. in mammals
      5. genus Anthemosoma; one species
   2. family: Babesiidae
      1. binary fission and merogony in erythrocytes, or in some species in lymphocytes, histiocytes, or other cell types
      2. sexual reproduction probably occurs but is poorly defined
      3. transovarian and transstadial transmission occurs in most species
      4. genera
         1. Babesia
            1. about 115 named species, most of which occur in mammals (hosts are mammals and birds)
            2. binary fission in erythrocytes of vertebrate hosts so that pairs of merozoites are formed; in some species merogony forming tetrads
            3. no filaments on erythrocytes
         2. Echinozoon (you will not be tested over this taxon)
            1. one species, in a mammal
            2. multiplication in vertebrate host by binary fission so that pairs of merozoites produced in erythrocytes
            3. filaments occur on parasitized erythrocytes
   3. family: Theileriidae
      1. merogony in vertebrate host in various cell types such as lymphocytes, histiocytes, erythroblasts, or other cells prior to invasion of erythrocytes; lymph nodes common site.
      2. stages invade erythrocytes, which may or may not divide; if they divide, produce 2-4 daughter cells
      3. binary fission and merogony occur in tick
      4. transovarian transmission does not occur
      5. all known vertebrate hosts mammals
      6. two genera
         1. Theileria; about 40 known species
            1. small-medium exoerythrocytic meronts; 10-20 micrometers in diameter
            2. meronts in lymphocytes
            3. in ruminants
         2. Cytauzoon; only 4 known species
            1. large exoerythrocytic meronts; some larger than 50 micrometers in diameter and divided into cytomeres when mature
            2. meronts in vascular endothelium
            3. 3 species in African ungulates; C. felis in felids in North America
            4. this genus is sometimes considered a synonym of Theileria
   4. family: Haemohormidiidae (you will not be tested over this taxon)
      1. merogony present, involving binary fission or merogony
      2. nucleus without endosome (nucleolus)
      3. in fish, reptiles, and birds; vectors unknown
      4. two genera; Haemohormidium, Sauroplasma (I doubt whether Sauroplasma is actually an apicomplexan, though)

Babesia bigemina (Babesiidae)

1. merozoites (often termed vermicules) transmitted into cattle when the tick, Boophilus annulatus and related species feed. Merozoites 2-3 micrometers in length
2. merozoites enter erythrocytes
3. undergo binary fission; repeated process
4. some merozoites appear to develop into gamonts, which remain dormant in erythrocytes; tend to be more ellipsoidal than merozoites
5. ingested by tick
6. gamonts develop protrusions (pseudopodia-like projections) and the resulting gametes are termed "rays."
7. rays of two different morpholgical types fuse to form a zygote
8. zygote an ookinete (termed a "primary kinete") and enters intestinal mucosa
9. "merogony" (actually, this is sporogony)
10. "merozoites" (vermicules, but actually sporozoites) liberated and migrate to hemocoel
11. merogony apparently in Malpighian tubules, muscles, hemocytes
    1. some merozoites (vermicules) migrate to salivary glands
    2. rapid merogony when tick begins feeding
    3. merozoites (vermicules) enter salivary ducts
    4. can be transmitted with bite into new bovid
12. some merozoites (vermicules) enter eggs in ovary
13. 2 generations of merogony
14. larval tick born with merozoites (vermicules) in salivary ducts
15. similar species
    1. Babesia microti in rodents, and Babesia equi in horses, do not undergo transovarian transmission and may be more closely related to the Theileriidae
    2. Babesia divergens in european cattle
16. pathology involves high fever, anemia due to erythrocyte destruction, fatigue, weight loss, internal organ damage, renal failure, jaundice, discolored (red) urine, and death in 50% or more of untreated cases. Termed "Texas cattle fever" or "red-water fever."

Theileria parva (Theileriidae)

1. sporozoites injected into cattle with bite of ixodid ticks, especially Rhipicephalus appendiculatus.
2. enter lymphocytes
3. merogony in lymphocytes; about 90 "macromerozoites" per "macromeront."
4. liberated merozoites enter lymphoid tissues and undergo merogony; about 80-90 "micromerozoites" per second generation "micromeront."
5. micromerozoites liberated in lymphoid tissues may invade new lymphoid cells and under merogony as micromeronts; if micromerozoites invade erythrocytes, undergo binary fission (some species undergo erythrocytic merogony)
6. micromeronts can induce clonal expansion of the infected host cells
7. some merozoites now initiate gamont formation
8. gamonts ingested along with blood meal by tick
9. in lumen of tick, gamonts differentiate into macrogametes and microgametocytes ("ray bodies")
10. 4 microgametes produced; one fertilizes macrogamete; zygote produced
11. ookinete (motile zygotes) form and migrate through gut wall
12. ookinete enters hemolymph, migrates to salivary glands
13. sporogony in acini of salivary glands, releasing numerous sporozoites which remain dormant in salivary glands
14. pathology involves high fever, nasal discharge, swollen lymph nodes, runny eyes, weakness, diarrhea, emaciation, and death in 25-90% of the cases, depending upon the strain. Disease termed East Coast cattle fever in Africa.
15. similar species include Theileria annulata in cattle (Mediterranean coast fever)