Biol 332 - Laboratory Sporozoa II. Coccidians
Required drawings.
Eimeria tenella

trophozoite


mature schizont with merozoites
Eimeria stiedae

trophozoite

gamonts

macrogametocyte

microgametocyte

oocyst
Plasmodium vivax

trophozoite - ring stage

schizont prior to nuclear division

late schizont after nuclear division

merozoite

gamonts

macrogametocyte

microgametocyte

exflagellation

oocysts
immature schizont with multiple nuclei
1-4. Eimeria tenella. Schizonts developing in the wall of the caecum of a chicken. The
infected cells contain a large (hypertrophied) nucleus, more than 10 times the size of
nuclei in non-infected host cells. In the cytoplasm is a large Eimeria schizont, a cell with
rather granular looking cytoplasm containing many nuclei. These nuclei have a light pink,
almost clear outer region and a dark pink inner region. The cytoplasm of the schizont is
clearly distinguishable from that of the host cell. To observe this or any of the specimens
of sectioned material it is necessary to focus up and down through the specimen as you
look at it, so that you can get some idea of its three dimensional organization.
5. Eimeria tenella. Mature schizonts with fully formed merozoites. In the lower part of
the field (5:00) a cluster of merozoites is being released by rupture of the host cell. Note
two other cells at 9:00 and half way between the center and the edge toward 1:00 which
are filled with merozoites. Notice free merozoites near the edge of the field between
10:00 and 1:00.
6-8. Eimeria tenella. Trophozoites - large round cells with a centrally located large
nucleus showing a prominent nucleolus. These cells have a homogenous finely textured
cytoplasm Schizonts are large cells with multiple nuclei. These are contained wholly
within enlarged host cellswith hypertrophied nuclei. These occur mainly in the left half of
the field. Mature schizonts with merozoites - At this stage the schizont has divided to
many elongated merozoites. Note small central nuclei in the merozoites.
9. - 11 Eimeria tenella. Macrogametocytes and oocysts. The thick walled cell are oocysts
These are post-zygotic cells which have not yet undergone meiosis or the sporogenic
divisions. The macrogametocytes are the large dark pink cells with a conspicuous central
nucleus).
12. - 17. Eimeria stiedae. this coccidian infects the epithelium of the bile ducts of rabbits.
These specimes show the sexual stages quite well but are not very good for the
schizogony stages that are well shown in E. tenella. All specimens contain the following
stages:
Trophozoites - small round cells contained entirely within host epithelial cells. centrally
located nucleus with prominent nucleolus, homogenous cytoplasm. Range in size from
very small to quite large.
Macrogametocytes - large elongated cells (circular in transverse section) with a single
centrally located nucleus with prominent nucleolus (often stained darkly). The peripheral
region of the cell contains many spherical granules. These contain cell wall precursor
material that will later be secreted to form the cell wall.
Microgametocytes. These are the cells that give rise to many small flagellated
microgametes. At maturity they have many hundreds of condenced small elongated nuclei
at the cell surface. At earlier stages there are multiple nuclei around the periphery of the
cell. They are the most difficult cell type to identify, but are easy to see, once that you
know what to look for.
Oocysts. These are the post-fertilization stages. The earlier ones look just like
macrogametocytes, but have a refractile cell wall. As the wall develops the number of
peripheral vesicles decreases. Eventually the cytoplasm condenses and shrinks to produce
an irregularly shaped oocyst with a condensed cytoplasmic mass inside. Spores later form
within the oocyst.
18. - 20. Eimeria Stiedae, schizonts with merozoites. At pointer. This stage is relatively
inconspicuous in this species. Identify schozont, merozoites. Focus carefully through the
specimen to get a sense of the three-dimensional organization.
21. - 22. Eimeria stiedae oocysts. Oocysts are thick-walled cells (often irregularly shaped)
with a central cytoplasmic mass. They are zygotes that have not yet undergone meiosis or
sporogenic divisions.
23-30 Plasmodium vivax. These specimens are human blood smears obtained from
infected patients.
Early trophozoites - ring stage - ring is endoplasmic reticulum material. Nucleus stains
darkly (dot). later trophozoites have larger rings.
Schizonts generally have several irregularly-shaped purple masses. These eventually
develop a number of round merozoites, which are released from the cell. Host cells
containing older schizonts and gamonts are filled with small redish or brownish dots.
These granules are calld Schüffner's dots and consist of haematin, a degradation product
of haemoglobin (which is eaten by the parasites). As schizonts develop the nuclei divide
and eventually the cells cleave to form a number of merozoites. These merozoites are
released by rupture of the membrane of the host cell. These late stage schizonts are shown
at stations 23 and 24.
Free merozoites are small cells with dark round nuclei that nearly fill the cell. These
occur in every specimen.
Gamonts are identifiable by their generally round shape. The inside of the cell is almost
entirely filled by the parasite. The Microgametocytes fill slightly less of the cell volume
(about 75%) than macrogametocytes which occupy >90%. See diagrams and color plate
for further hints.
24. - 27. Plasmodium vivax. Trophozoites Schizonts at various stages, gamonts both
macrogametocyte and microgametocyte. merozoites.
23. Plasmodium vivax. Early Schizont. Note four nuclei
24. Plasmodium vivax. Late Schizont with multiple nuclei prior to release merozoites.
11.3 x 109.
25. - 30. Plasmodium vivax. Trophozoites.
27. Plasmodium vivax. Gamont - macrogametocyte.
28. Plasmodium vivax. Gamont - microgametocyte
31. Plasmodium vivax. Ooccysts. In cells of the midgut. The round oocysts protrude on
the coelomic side of the midgut wall. Each of these large round cells will give rise to
hundreds of sporozoites. Examine first with 10 x, then use 40 x to look at one of the
oocysts. Best at the margin of the preparation.
32. Plasmodium vivax. Exflagellation - release of microgametes (the very long, thin
stained objects emanating from the microgametocyte. This occurs in the stomach of the
mosquito..