Life Cycle of Isospora rivolta (Grassi, 1879) in Cats and Mice*

SYNOPSIS. The endogenous development of Isospora rivolta (Grassi) was studied in cats fed oocysts, and was compared with the endogenous cycle after feeding them mice infected with I. rivolta. For the mouse-induced cycle, 14 newborn cats were killed 12 to 240 h after having been fed mesenteric lymph nodes and spleens of mice. Asexual and sexual development occurred throughout the small intestine, in epithelial cells of the villi and glands of Lieberkuhn. The number of asexual generations was not determined with certainty, but there were at least 3 structurally different meronts. Type I meronts appeared at 12–48 h postinoculation (HPI). They were 8.5(6–13) × 5.1(3–6) μm, contained 2–8 merozoites, and divide by binary division or endodyogeny. Type II meronts were multinucleate merozoite-shaped meronts within a single parasitophorous vacuole. They were found at 48–172 HPI and measured 12.6(9–18) × 9.8(9–13) μm. Individual multinucleate merozoite-shaped meronts were 7–13 × 3–5 μm in sections and contained 2–30 slender (5.5 × 1.0 μm) merozoites. Type III meronts occurred at 72–192 HPI and gamonts at 72–96 HPI. Mature microgamonts measured 11.3(9–15) × 8.0(6–9) μm in sections and up to 21.5 × 14 μm in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11–18) × 9.0(5–13) μm in sections and 18 × 16 μm in smears. Oocysts were 10–15 × 9–15 μm in sections and 19.8(17–24) × 18.0(17–23) μm in fixed and stained smears. Unsporulated oocysts in feces were 22.3(18–25) × 19.7(16–23) μm and spomlated oocysts 25.4(23–29) × 23.4(20–26) μm. Sporulation was completed within 24 h at 22–26 C. For the study of the oocyst-induced cycle in cats, 18 newborn cats were killed between 6 and 192 HPI. The endogenous development was essentially similar to the mouse-induced cycle, but merogony and gametogony occurred 12–48 h later than in the latter cycle. Isospora rivolta was pathogenic for newborn but not for weaned cats. Newborn cats fed 10⁵ sporocysts or infected mice usually developed diarrhea 3–4 days after inoculation. Microscopically, desquamation of the tips of the villi and cryptitis were seen in the ilium and cecum in association with meronts and gamonts. For the study of the development of I. rivolta in mice, mice were killed from day 1 to 23 months after having been fed 10⁵–10⁵ sporocysts, and their tissues were examined for the parasites microscopically, and by feeding to cats. The following conclusions were drawn. (A) Isospora rivolta most frequently invaded the mesenteric lymph nodes of mice and remained there for 23 months at least. It also invaded the spleen, liver, and skeletal muscles of mice. This species could not be passed from mouse to mouse. Sporozoites increased in size from ?6.8 × 4.9 μm on day 1 to ?13.4 × 6.9 μm on day 31 postinoculation. Division was not seen. Prepatent period was 4–7 days and patent periods ranged from 2 to several weeks.     

Life cycle of Isospora rivolta (Grassi, 1879) in cats and mice

The endogenous development of Isospora rivolta (Grassi) was studied in cats fed oocysts, and was compared with the endogenous cycle after feeding them mice infected with I. rivolta. For the mouse-induced cycle, 14 newborn cats were killed 12 to 240 h after having been fed mesenteric lymph nodes and spleens ofmice. Asexual and sexual development occurred throughout the small intestine, in epithelial cells of the villi and glands of Lieberkühn. The number of asexual generations was not determined with certainty, but there were at least 3 structurally different meronts. Type I meronts appeared at 12-48 h postinoculation (HPT). They were 8.5(6-13) x 5.1(3-6) micrometer, contained 2-8 merozoites, and divide by binary division or endodyogeny. Type II meronts were multinucleate merozoite-shaped meronts within a single parasitophorous vacuole. They were found at 48-172 HPI and measured 12.6(9-18) x 9.8(9-13) micrometer. Individual multinucleate merozoite-shaped meronts were 7-13 x 3-5 micrometer in sections and contained 2-30 slender (5.5 x 1.0 micrometer) merozoites. Type III meronts occurred at 72-192 HPI and gamonts at 72-96 HPI. Mature microgamonts measured 11.3(9-15) x 8.0(6-9) micrometer in sections and up to 21.5 x 14 micrometer in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11-18) x 9.0(5-13) micrometer in sections and 18 x 16 micrometer in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11-18) x 9.0(5-13) micrometer. Sporulation was completed within 24 h at 22-26 C. For the study of the oocyst-induced cycle in cats, 18 newborn cats were killed between 6 and 192 HPI. The endogenous development was essentially similar to the mouse-induced cycle, but merogony and gametogony occurred 12-48 h later than in the latter cycle. Isospora rivolta was pathogenic for newborn but not for weaned cats. Newborn cats fed 10(6) sporocysts or infected mice usually developed diarrhea 3-4 days after inoculation. Microscopically, desquamation of the tips of the villi and cryptitis were seen in the ilium and cecum in association with meronts and gamonts. For the study of the development of I. rivolta in mice, mice were killed from day 1 to 23 months after having been fed 10(5)-10(6) sporocysts, and their tissues were examined for the parasites microscopically, and by feeding to cats. The following conclusions were drawn. (A) Isospora rivolta most freqeuntly invaded the mesenteric lymph nodes ofmice and remained there for 23 months at least. Ii also invaded the spleen, liver, and skeletal muscles of mice. This species could not be passed from mouse to mouse. Sporozoites increased in size from approximately 6.8 x 4.9 micrometer on day 1 to approximately 13.4 x 6.9 micrometer on day 31 postinoculation. Division was not seen. Prepatent period was 4-7 days and patent periods ranged from 2 to several weeks.     

Isospora Species of the Cat and Attempted Transmission of I. felis Wenyon, 1923 from the Cat to the Dog*

SYNOPSIS Fecal samples from 130 domestic cats from Illinois were examined for coccidia. Three species of Isospora were found: (1) I. felis Wenyon, 1923, with oocysts 38-51 by 27-39 μ with a mean of 41.6 by 30.5 μ and sporocysts 20-26 by 17-22 μ with a mean of 22.6 by 18.4 μ; it was found in 13% of the cats; (2) I. rivolta (Grassi, 1879) Wenyon, 1923, with oocysts 21-28 by 18-23 μ with a mean of 25.0 by 21.1 μ, and sporocysts 14-16 by 10-13 μ with a mean of 15.2 by 11.6 μ; it was found in 3% of the cats; and (3) I. bigemina (Stiles, 1891) Lühe, 1906, with oocysts 12-15 by 10-13 μ with a mean of 13.2 by 11.8 μ. and sporocysts 8-10 by 6-8 μ with a mean of 8.8 by 6.5 μ it was found in 1.5% of the cats. Four coccidia-free puppies 1.5 months old were inoculated with 100,000 oocysts each of I. felis from the cat, but patent infections did not occur. Partial development of I. felis was not seen in tissue sections of the small intestine of a 5th pup killed 96 hours after inoculation with 150,000 I. felis oocysts. This coccidium is therefore presumably host-specific.     

Development and Ultrastructure of First-Generation Meronts of Sarcocystis cruzi in Calves Fed Sporocysts from Coyote Feces*

SYNOPSIS. The development of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) meronts was studied in seven 7- to 10-day-old calves killed 4, 7, 11, 15, 22, 25 and 28 days postinoculation (DPI) with 5 × 10⁷ sporocysts from feces of coyotes. No meronts were found 4 and 7 DPI. Young and intermediate meronts with 1–16 nuclei were found in endothelial cells of arteries in mesenteric lymph nodes, but not in kidneys 11 DPI. Mature meronts were noted in endothelial cells of arteries, arterioles, or capillaries of many organs of calves killed 15 to 25 DPI. No first-generation meronts were found 28 DPI. By electron microscopy, all stages of the first-generation merogony were found free within the host cell cytoplasm and not within a parasitophorous vacuole. The appearance of intranuclear spindles preceded the formation of merozoites by endopolygeny. Mature meronts measured 41.0 × 17.5 (34–50 × 15–24) μm, contained ～ 100–350 merozoites, and had 2 to 4 relatively small residual bodies, 2.8 μm in diameter. Merozoites measured 6.3 × 1.5 (5.5–7 × 1 μm) and contained most of the organelles characteristically found in coccidian merozoites. Micropores were observed in merozoites, but not in young and intermediate meronts. Merozoites were seen free in the lumen of blood vessels, in intracellular areas, and free within the host cell cytoplasm.     

The asexual pre-cyst development of Sarcocystis tenella in experimentally infected specific pathogen-free lambs

Twenty-two lambs raised under sporozoa-free conditions were infected at weaning with 0.25–2.0 million Sarcocystis tenella sporocysts obtained from dogs and then necropsied at intervals between 1.3 h and 41 days post-inoculation (dpi). Fixed and frozen sections from 47 different tissues from each lamb were examined respectively by a variety of histochemical stains and by indirect fluorescent-antibody staining. The remnants of excysted sporocysts were found within the gastro-intestinal tract between 1.3 h and 3 dpi. No enteric proliferative stage of the parasite was detected. First-generation meronts (schizonts) were detected from 6 to 19 dpi within the endothelial cells of arterioles in most organs and tissues. The meronts were undifferentiated from 6 to 9 dpi but were mature in appearance from 12 to 19 dpi (measuring 22.3 × 13.4 μm and containing 18–28 merozoites). Second-generation meronts were detected from 21 to 34 dpi within the endothelial cells of capillaries throughout the entire body. They were undifferentiated from 21 to 23 dpi but appeared mature from 25 to 34 dpi (measuring 15.2 × 10.6 μm and containing 18–38 merozoites). Several smaller meronts were then detected at 36 dpi within cells of the mononuclear phagocytic system. They were all mature in appearance (measuring 7.4 × 5.1 μm and containing 6–9 merozoites) and are thought to have formed facultatively following the incorporation of some second-generation merozoites into phagocytic cells. Only developing cysts were then detected at 41 dpi throughout the cardiac and skeletal musculature. Elements in both first- and second-generation merozoites stained markedly with haematoxylin and eosin, periodic acid-Schiff's, alkaline Giemsa-colophonium and basic fuchsin stains. However, only second-generation meronts and developing cysts exhibited strong specific reactions with the fluorescent-antibody stain.     

Transmission studies with Sarcocystis idahoensis of deer mice (Peromyscus maniculatus) and gopher snakes (Pituophis melanoleucus)

Transmission studies with Sarcocystis idahoensis of deer mice (Peromyscus maniculatus) and gopher snakes (pituophis melanoleucus) were conducted to determine host specificity of various stages of the parasite. Sporocysts were not passed by four dogs or four cats fed infected skeletal muscle from deer mice. Seven white mice (Mus musculus) and 34 white-footed mice (Peromyscus leucopus) were negative for sarcocysts and liver meronts following oral inoculation with S. idahoensis sporocysts; however, excystation of sporocysts occurred in two white-footed mice killed four hours post inoculation (PI). A gopher snake orally inoculated with sporocysts remained negative for coccidia for two months PI. Three deer mice orally inoculated and three intraperitoneally (IP) inoculated with tachyzoites from liver meronts developed sarcocysts in their skeletal muscles similar to those seen in deer mice orally inoculated with sporocysts. Liver meronts were not found. Ten deer mice orally inoculated and 10 deer mice inoculated IP with bradyzoites from S. idahoensis sarcocysts remained negative for sarcocysts and liver meronts at necropsy 17 days PI.     

New Observations on First-Generation Merogony of Eimeria tuskegeensis in Sigmodon hispidus1

First-generation development of Eimeria tuskegeensis was evaluated using light microscopy. Sporozoite-shaped meronts containing a prominent refractile body were observed in small intestinal cells of an experimentally infected cotton rat at 24 h post inoculation (PI). Mature spherical or subspherical meronts containing crescent-shaped merozoites were observed at 36 h PI. Refractile bodies were observed in some of these merozoites. Sporozoite-shaped meronts that were isolated from host intestinal cells and inoculated onto human fetal lung cell cultures penetrated the cultured cells by 2 h PI. A mature, subspherical, first-generation meront containing seven merozoites was observed at 9 h PI in cell culture, indicating that sporozoite-shaped meronts isolated from the host retained their infectivity.     

Development of the Swine Coccidium Eimeria debliecki Douwes, 1921 in Mammalian Cell Cultures1

Sporozoites of Eimeria debliecki entered human fetal lung and porcine kidney cells grown in cultures and underwent one merogenous cycle, terminating in the production of second-generation trophozoites. Sporozoites were intracellular 1 h post-inoculation (PI) and developed into sporozoite-shaped meronts at 40 h PI. These meronts, one of which was motile, had from two to ten nuclei. Sporozoite-shaped meronts then developed into elongate or spheroidal meronts with 10 to 24 nuclei by two days PI. Ten to 26 first-generation merozoites were formed by budding from the meront surface. Mature first-generation merozoites were most numerous three days PI. Most meronts had ruptured and released nonmotile merozoites into the culture medium by four days PI. Merozoites that were not released became rounded and developed into second-generation trophozoites. Refractile bodies were present in all developmental stages. No further development was observed five through eight days PI.     

Development of Eimeria funduli in Fundulus heteroclitus1

Laboratory-reared Fundulus grandis and F. heteroclitus were experimentally infected with Eimeria funduli by being fed Palaemonetes pugio (grass shrimp) collected from endemic areas. Histological sections were made of heart, liver, hepatopancreas, spleen, gall bladder, kidney, intestine, peri-intestinal fat, reproductive organs, and brain from F. grandis sacrificed at 1, 2, 6, 12, 18, and 24 h and from F. heteroclitus at 5, 6, 9, 14, 19, 24, 29, 34, 39, and 44 days after consuming naturally infected shrimp. We first found merogonous stages at day 9 postinfection (p.i.). No developmental stages of the parasite could be positively identified in the tissues of experimentally infected fish prior to day 9 p.i. Mature meronts were found 14 days p.i. The majority contained 8–16 (mean, 13) merozoites, but a few meronts had 18–26 (22) merozoites. Gamonts first appeared on day 14, were mature by day 19, and fertilization was completed by day 24 p.i. After sporoblast formation, sporopodia appeared during sporocyst wall formation, between days 24 and 29 p.i. Sporozoite formation was completed by day 44 p.i. in most sporocysts. Most endogenous stages occurred in hepatocytes; however, pancreatic and spleen cells were sometimes infected with gamonts.     

An Ultrastructural Study of First- and Second-Generation Merogony in the Coccidian Sarcocystis tenella1

ABSTRACT. Sporocysts of the coccidian Sarcocystis tenella were originally isolated in the feces of a coyote. Sporocysts used for inoculation of lambs were obtained from experimentally infected dogs. At 14, 16, and 19 days postinoculation (DPI) of lambs with the sporocysts, various developmental stages of first-generation meronts were found within cells located between the endothelium and internal elastic membrane of mesenteric arteries. At 19, 21, and 25 DPI, second-generation merogony occurred in cells associated with capillaries and arterioles of kidney glomeruli and convoluted tubules. Meronts of both generations were bounded by a double pellicular membrane and were situated free in the host cell cytoplasm. Merozoites formed by endopolygeny that involved multiple intranuclear spindles of a single, large irregular nucleus. First-generation meronts measured 22.6 × 17.1 μm (19–28.7 × 7.5–24 μm) and contained 120–240 merozoites, which measured 7.1 × 1.6 μm (4.8–7.5 × 1.3–1.8 μm). Corresponding values for second-generation meronts were 13.2 × 9.2 μm (8.3–15 × 7–13.5 μ), 32–80, and 5.8 × 1.7 μm (5.6–6.2 × 1.4–2.2 μm).     

Electron microscope study of merogony preceding cyst formation of Sarcocystis sp. in roe deer (Capreolus capreolus)

Precystic merogony of Sarcocystis sp. was studied in roe deer fawns 33, 45, and 49 days postinoculation (pi) with 2 X 10(4)-10(5) sporocysts recovered from dogs. Single merozoites, but no meronts, were found 33 days pi in liver, spleen, and lymph nodes. Transforming merozoites and meronts were found in myofibroblasts, satellite cells, and endothelial cells of muscle tissue on 45 and 49 days pi; they were surrounded by two membranes. Typical coccidian merozoites differentiated simultaneously around an enlarged, lobed nucleus.     

Sarcocystis Idahoensis Sp. N. In Deer Mice Peromyscus Maniculatus (Wagner) and Geopher Snakes Pituophis Melanoleucus (Daudin)*,†

SYNOPSIS Deer mice Peromyscus maniculatus (Wagner) were trapped near Hammett, Idaho, as a possible source of Besnoitia jellisoni Frenkel and species of Sarcocystis to be used for life cycle studies. Forty-nine deer mice were necropsied; 20 (40.8%) were positive for sarcocysts structurally identical with those of Sarcocystis idahoensis sp. N. the source of S. idahoensis used for life cycle studies was a Great Basin gopher snake Pituophis melanoleucus deserticola Stejneger killed near Hammett, Idaho; 20 sporulated sporocysts measured 11.1 × 13.4 (11-12 × 13-14) μm. Structurally identical sporocysts were found in 7 of 14 Pacific gopher snakes P. m. catenifer (Blainville), and in 6 of 10 San Diego gopher snakes, P. m. annectens Baird & Girard. Totals of 148 deer mice and 17 gopher snakes were necropsied in the course of life cycle studies. Development of the first generation meronts took place within the hepatocytes of deer mice 2-10 days post-inoculation (PI) with sporulated sporocysts. Rosette-shaped meronts (6-8 days PI) contained tachyzoites attached by their posterior poles to a residual body. After release from the residual body, tachyzoites were initially retained in a meront wall and later released from the hot cells Within muscle cells a single tachyzoite-shaped structure was found 11 days PI and PAS-negative metrocyte-containing sarcocysts (2nd generation meronts) 13-34 days PI. PAS-positive material was first seen in sarcocysts 34 days II at which time bradyzoite formation became apparent. At 160 days PI, 10 sarcocysts measured 0.4 × 5.8 (0.2-0.9 × 1.8-9.9) μ and appeared to be mature and structurally identical with those from naturally infected deer mice. After ingestion of S. idahoensis-infected deer mice by gopher snakes, bradyzoites developed directly into microgamonts and macrogametes. These stages were first seen 5 days PI. Microgamonts were generally located above and macrogametes below the epithelial host cell nucleus. Seven to 11 days PI microgamonts were seen with mature microgametes, and oocysts which had not yet begun sporogony were found with oocyst walls. Clinical signs of illness were generally not observed in infected gopher snakes; however, one snake developed anorexia and cachexia, and became moribund after repeated ingestion of heavily infected deer mice. Acute hepatitis associated with developing meronts often was noted in deer mice given over 15,000 sporocysts each. Five to 6 days PI anorexia, weakness, ataxia, and dyspnea were observed: these clinical signs increased in severity until 6-8 days PI, when mice became recumbent and died, or were killed while moribund. Hepatosplenomegaly, petechial hemorrhage o the serosal and cut surfaces of the liver, and icterus were common. Diffuse coagulative necrosis with cellular infiltration (primarily neutrophils) was noted on microscopic examination.     

The Ultra‐Structural Similarities between Cryptosporidium parvum and the Gregarines

Using a transmission electron microscopy‐based approach, this study details the striking similarities between Cryptosporidium parvum and the gregarines during in vitro axenic development at high ultra‐structural resolution. C. parvum zoites displayed three unusual regions within uninucleated parasites: epimerite‐like, protomerite‐like, and the cell body; these regions exhibited a high degree of morphological similarity to gregarine‐like trophozoites. The presence of a mucron‐like bulging structure at the side of the free ovoid gregarine‐like zoites was observed after 2 h of cultivation. An irregular pattern of epicytic‐like folds were found to cover the surface of the parasites 24 h postcultivation. Some extracellular stages were paired in laterocaudal or side‐side syzygy, with the presence of a fusion zone between some of these zoites. The present findings are in agreement with phylogenetic studies that have proposed a sister relationship with gregarines. Cryptosporidium appears to exhibit tremendous variety in cell structure depending on the surrounding environment, thereby mimicking the “primitive” gregarines in terms of the co‐evolution strategy between the parasites and their environments. Given this degree of similarity, different aspects of the evolutionary biology of Cryptosporidium need to be examined, considering the knowledge gained from the study of gregarines.     

Extra-Intestinal Stages of Isospora felis and I. rivolta (Protozoa: Eimeriidae) in Cats*

SYNOPSIS. Evidence is presented that Isospora felis and I. rivolta invade the extra-intestinal tissues of cats. Kittens were fed sporocysts of I. felis and I. rivolta. At specific intervals the kittens were killed and suspensions of extra-intestinal tissues were fed to indicator kittens less than a day old. Oocyst production by the indicator kittens within the regular prepatent period was taken as evidence that coccidian stages were present in the inoculum consisting of extra-intestinal tissues of cats. Tissues of kittens infected with I. felis for 5–104 days were infectious to newborn kittens as follows: liver and spleen mixture 3 out of 5 times, mesenteric lymph nodes 4 out of 4 times, brain and muscle mixture 1 out of 5 times, lungs 1 out of 5 times. The prepatent period in kittens consuming oocysts of I. felis was 7-11 days; after consuming extra-intestinal tissues of kittens it was 4–8 days. Distinct coccidian stages unlike those present in the gut were found singly and in groups of 2–15 in lymphoreticular cells of mesenteric lymph nodes of 2 kittens infected for 2–4 days. Tissues of kittens infected with I. rivolta for 5–21 days were infectious to newborn kittens as follows: liver and spleen mixture 3 out of 5 times, mesenteric lymph nodes 1 out of 5 times, brain, muscle and lung mixture none of 5 times. The prepatent period in kittens consuming oocysts of I. rivolta or extra-intestinal tissues of cats was 5–7 days. Coccidian stages occurred singly or in pairs, intracellularly or free in the mesenteric lymph nodes of 3 out of 10 kittens infected for 1–8 days.     

In Vitro Cultivation of the Vascular Phase of Sarcocystis capracanis and Sarcocystis tenella1

ABSTRACT. Sporozoites of Sarcocystis capracanis and S. tenella (Apicomplexa) penetrated all four cell types tested (bovine monocytes, BM; bovine pulmonary artery endothelial cells, CPA; Madin-Darby bovine kidney; and ovine monocytes). Sporozoites of S. tenella developed to meronts in BM and CPA; those of S. capracanis developed to meronts in BM only. Both species of Sarcocystis developed to large first-generation meronts followed by small meronts. At 40 to 50 days after inoculation (DAI) of sporozoites, considerably more merozoites of S. tenella were harvested from CPA (24.9 × 10⁶ merozoites/75-cm² flask; n = 4) than from BM (1.9 × 10⁶ merozoites/75-cm² flask; n = 4). Merozoites of S. capracanis were most numerous in BM at 88 to 100 DAI during which time 2.1 × 10⁶ merozoites/75-cm² flask (n = 4) were harvested.     

Eimeria gastrosauris n. sp. (Apicomplexa: Eimeriidae) from the stomach epithelium of Australian geckoes

Eimeria gastrosauris n. sp. exhibited endogenous development in the stomach lining and secretory epithelia of Heteronotia binoei from the Mt Isa region, northern Queensland. Morphologically similar coccidians were found in the stomach of Oedura monilis from the Mt Speke region, northern Queensland. Oöcysts were oblong-ellipsoids, with bivalved sporocysts, two distinct residua and endogenous sporulation. Oöcysts of similar shape and size were also found in faeces of Gehyra australis from the Townsville region of northern Queensland. Developmental stages, consisting of meronts, merozoites, microgamonts, macrogamonts and developing oöcysts, were observed in H. binoei and O. monilis, and are described.     

The Life Cycle of Cryptosporidium baileyi n. sp. (Apicomplexa, Cryptosporidiidae) Infecting Chickens

ABSTRACT. The life cycle and morphology of a previously undescribed species of Cryptosporidium isolated from commercial broiler chickens is described. The prepatent period for Cryptosporidium baileyi n. sp. was three days post oral inoculation (PI) of oocysts, and the patent period was days 4–24 PI for chickens inoculated at two days of age and days 4–14 for chickens inoculated at one and six months of age. During the first three days PI, most developmental stages of C. baileyi were found in the microvillous region of enterocytes of the ileum and large intestine. By day 4 PI, most parasites occurred in enterocytes of the cloaca and bursa of Fabricius (BF). Mature Type I meronts with eight merozoites first appeared 12 h PI and measured 5.0 × 4.9 μm. Mature Type II meronts with four merozoites and a large granular residuum first appeared 48 h PI and measured 5.1 × 5.1 μm. Type I meronts with eight short merozoites and a large homogeneous residuum first appeared 72 h PI and measured 5.2 × 5.1 μm. Microgamonts (4.0 × 4.0 μm) produced 16 micro-gametes that penetrated into macrogametes (4.7 × 4.7 μm). Macrogametes gave rise to two types of oocysts that sporulated within the host cells. Most were thick-walled oocysts (6.3 × 5.2 μm), the resistant forms that passed unaltered in the feces. Some were thin-walled oocysts whose wall (membrane) readily ruptured upon release from the host cell. Sporozoites from thin-walled oocysts were observed penetrating enterocytes in mucosal smears. The presence of thin-walled, autoinfective oocysts and the recycling of Type I meronts may explain why chickens develop heavy intestinal infections lasting up to 21 days. Oocysts of C. baileyi were inoculated orally into several animals to determine its host specificity. Cryptosporidium baileyi did not produce infections in suckling mice and goats or in two-dayold or two-week-old quail. One of six 10-day-old turkeys had small numbers of asexual stages only in the BF. Four of six one-day-old turkeys developed mild infections only in the BF, and sexual stages of the parasite were observed in only one of the four. All seven one-day-old ducks and seven two-day-old geese developed heavy infections only in the BF with all known developmental stages present.     

Early Development and Tissue Distribution of Pseudoloma neurophilia in the Zebrafish,Danio rerio

The early proliferative stages of the microsporidian parasite, Pseudoloma neurophilia were visualized in larval zebrafish, Danio rerio, using histological sections with a combination of an in situ hybridization probe specific to the P. neurophilia small‐subunit ribosomal RNA gene, standard hematoxylin‐eosin stain, and the Luna stain to visualize spores. Beginning at 5 d post fertilization, fish were exposed to P. neurophilia and examined at 12, 24, 36, 48, 72, 96, and 120 h post exposure (hpe). At 12 hpe, intact spores in the intestinal lumen and proliferative stages developing in the epithelial cells of the anterior intestine and the pharynx and within hepatocytes were observed. Proliferative stages were visualized in the pancreas and kidney at 36–48 hpe and in the spinal cord, eye, and skeletal muscle beginning at 72 hpe. The first spore stages of P. neurophilia were observed at 96 hpe in the pharyngeal epithelium, liver, spinal cord, and skeletal muscle. The parasite was only observed in the brain of larval fish at 120 hpe. The distribution of the early stages of P. neurophilia and the lack of mature spores until 96 hpe indicates that the parasite gains access to organs distant from the initial site of entry, likely by penetrating the intestinal wall with the polar tube.     

Development and ultrastructure of first-generation meronts of Sarcocystis cruzi in calves fed sporocysts from coyote feces

The development of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) meronts was studied in seven 7- to 10-day-old calves filled 4, 7, 11, 15, 22, 25 and 28 days postinoculation (DPI) with 5 x 10(7) sporocysts from feces of coyotes. No meronts were found 4 and 7 DPI. Young and intermediate meronts with 1-16 nuclei were found in endothelial cells of arteries in mesenteric lymph nodes, but not in kidneys 11 DPI. Mature meronts were noted in endothelial cells of arteries, arterioles, or capillaries of many organs of calves killed 15 to 25 DPI. No first-generation meronts were found 28 DPI. By electron microscopy, all stages of the first-generation merogony were found free within the host cell cytoplasm and not within a parasitophorous vacuole. The appearance of intranuclear spindles preceded the formation of merozoites by endopolygeny. Mature meronts measured 41.0 x 17.5 (34-50 x 15-24) microgram, contained approximately 100-350 merozoites, and had 2 to 4 relatively small residual bodies, 2.8 microgram in diameter. Merozoites measured 6.3 x 1.5 (5.5-7 x 1 microgram) and contained most of the organelles characteristically found in coccidian merozoites. Micropores were observed in merozoites, but not in young and intermediate meronts. Merozoites were seen free in the lumen of blood vessels, in intracellular areas, and free within the host cell cytoplasm.     

Fine Structure of Sarcocystis cruzi Schizonts

SYNOPSIS Schizogony of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) takes place in vascular endothelial cells 26 to 33 days after cattle ingest sporocysts from dogs. Kidney cortex from a heavily infected, dexamethasone-treated bovine was fixed for electron microscopy to determine the method of schizogonie development. Schizogony takes place by endopolygeny characterized by marked enlargement of the parasite nucleus, formation of nuclear lobes, presence of numerous spindles with adjacent pairs of centrioles along the nucleus, and simultaneous formation of daughter merozoites in the cytoplasm adjacent to the spindle poles. Endopolygeny in S. cruzi differs from that in other Sporozoa in that merozoite anlagen are seen in the cytoplasm before any nuclei divide. The resultant merozoites continue development and, when mature, resemble other sporozoan zoites. Upon release from the host cell into capillaries, they travel to muscle tissue to continue the life cycle by forming sarcocysts.