Intraerythrocytic schizogony of Theileria sergenti in cattle

The characteristics of developing intraerythrocytic stages of T. sergenti were studied by light and transmission electron microscopy. The parasites with many ribosomes, acristate mitochondria, cytostome, and food vacuoles were morphologically regarded as the trophozoite stage. Although this type of parasites was frequently detected, intraerythrocytic merozoite stage with electron dense cisternae, rhoptries and small electron dense bodies was rarely observed in high parasitaemia. The intraerythrocytic stages of T. sergenti were divided mainly into four daughters by schizogony, and alternatively into two by binary fission. The daughter parasites in each division had the same ultrastructural features as of merozoites. As a result, it was suggested that T. sergenti trophozoites multiplied by schizogony to four organisms or by binary fission in the peripheral erythrocyte, and differentiated to the merozoites which acquired penetrating ability into the erythrocytes.     

Ultrastructure of developing Isospora suis in cultured cells

The ultrastructure of Isospora suis sporozoites, type-1 meronts, and type-1 merozoites was examined, using transmission electron microscopy of infected cultured cells. The ultrastructure of sporozoites and type-1 merozoites was similar. Each possessed trimembranous pellicles, subpellicular microtubules, a conoid, anterior and posterior polar rings, rhoptries, micronemes, a single vesicular nucleus, tubular mitochondria, Golgi complexes, ribosomes endoplasmic reticula, inactive micropores, amylopectin bodies, lipid bodies, dense bodies, and crystalloid bodies. Merozoites were produced by endodyogeny. Ultrastructural events associated with merozoite production by type-1 meronts are described.     

Development and use of hybridoma antibodies directed against Eimeria acervulina merozoites for cross-reactive and ferritin-labeling studies

Hybridoma antibodies (Hab) were produced against Eimeria acervulina merozoites that had been separated from extraneous intestinal material by a fiber column technique before injection into mice. The Hab demonstrated three different immunofluorescent-antibody (IFA) patterns of tip, surface, or surface-internal fluorescence in or on the merozoites. Some Hab reacted with round immature schizonts, which were also present in the fiber-cleaned merozoite material. Variations in cross-reactivity were seen with a number of Hab tested by IFA with merozoites, sporozoites, and immature schizonts of different coccidial species. Certain Hab were species- and stage-specific, whereas others cross-reacted with some or all stages or species tested. One Hab apparently reacted with only a small percentage of the E. acervulina merozoites in the fiber-cleaned material. The ferritin (Fe)-labeling technique showed that with one Hab, which gave a surface-internal IFA pattern, there was an irregular clumping of the Fe label along the surface of the immature schizont. A heavier deposit of Fe label was seen on the area of the schizont where the merozoite was beginning to form. A heavy uniform labeling of Fe was seen on the surface of the pellicle of the mature merozoites. These results demonstrate that stage-specific and cross-reactive antigens are present in or on the merozoites of E. acervulina, and as shown with one Hab, surface antigens present on the immature schizont are incorporated onto the mature merozoite.     

Fine structure and invasive behaviour of the early developmental stages of Theileria annulata in vitro

The interaction, in vitro, between bovine peripheral blood lymphocytes and sporozoites of Theileria annulata (Ankara) was studied by light and electron microscopy. Beginning five minutes following incubation, samples were taken for Giemsa-stained smears and glutaraldehyde-fixed pellets, for light and electron microscopy, respectively. Sporozoites of T. annulata measure an average of 0.9 microns long, 0.8 microns broad and possess a limiting unit membrane, the pellicle; a round-to-ovoid, eccentrically situated, non-chromocentric nucleus; double-membraned, tubular, acristate mitochondria; varying numbers of anisocytic, densely osmiophilic and pleomorphic organelles, the rhoptries which together with the polar ring form the apical complex; and numerous, loosely scattered, electron-dense ribosomal particles. As early as 5 min of incubation, sporozoites had made contact with, and penetrated, lymphocytes. Sporozoites consistently attached to the lymphocyte plasmalemma by their basal end, possibly at specific receptor sites. Apparently only a proportion of lymphocytes (up to 40% and more commonly 10-20%) were susceptible. Two subpopulations of the susceptible lymphocytes were observed; one which appeared to have receptor sites localized on one pole of the plasmalemma and the other subpopulation in which the receptor sites were distributed evenly around the plasmalemmal surface. Within individual susceptible lymphocytes, the number of interiorized sporozoites increased from 1 to 3 at 5-10 min to as many as 15 or more parasites at around 60 min of incubation. Theileria annulata sporozoites were interiorized by the invagination of the host cell plasmalemma which remained intact throughout the process but later fragmented. Within 30 min of interiorization, each sporozoite underwent dedifferentiation by the loss of its rhoptries and transformed into a trophozoite. Around 24 h, the trophozoite, a uninucleate, motile and feeding stage of the parasite, developed into a schizont by an acentric, closed mitosis.     

Studies on Globidial Schizonts in the Abomasum of Norwegian Sheep: The Fine Structure of One of the Four Merozoite forms Investigated

Norwegian sheep were investigated for globidial schizont infection in the abomasum. The frequency of infection was found to be 78.2 %. Light microscope studies of the various mature schizonts revealed the existence of four morphologically different merozoites, small A, small B, intermediate and long forms. Each globidial schizont was found to contain only one form of these merozoites. However, these four schizont types occurred in the same abomasum.The intermediate form of globidial schizont merozoites was investigated by the aid of an electron microscope, with the aim of comparing its internal morphology with that previously published for Eimeria species. A striking resemblance was observed between the fine structures of the intermediate merozoite and that of Eimeria species, particularly the first generation merozoites described in giant schizonts of Eimeria bovis.The present status of globidial schizonts infecting the abomasum of sheep was discussed. It was concluded that these four forms of merozoites could represent different generations of one Eimeria species or different E. species producing giant schizonts in the abomasum.Due to the practical difficulties in studying the life histories of the different Eimeria species infecting sheep, it was proposed that the in vitro propagation of the individual species in cultured cells may shed some light on the corresponding asexual, as well as the sexual, stages. This would offer a new approach to the study of the ultra-structure of the developing parasite.     

Ultrastructure of schizonts and merozoites of Sarcocystis neurona

The ultrastructure of Sarcocystis neurona schizonts and merozoites was studied in specimens derived from cell culture and from the brains of infected mice. Schizonts and merozoites were located in the host cell cytoplasm without a parasitophorous vacuole at any stage of development. Merozoites divided by endopolygeny. Fully formed merozoites had a pellicle, numerous polysomes and ribosomes, smooth and rough endoplasmic reticulum, 22 subpellicular microtubules, 9-16 dense granules, 25-75 micronemes, a plastid, a Golgi complex, 1-3 mitochondria, a conoid, 2 apical rings, 2 polar rings, 0-6 lipid bodies, a nucleus and nucleolus, but no rhoptries. Most micronemes were located anterior to the nucleus including 1-6 micronemes in the conoid. Merozoites were either slender (7.3 microm x 1.7 microm) or stumpy (7.7 microm x 3.1 microm). Dense granules appeared to arise from the maturation face of the Golgi complex. The ultrastructure of in vitro derived schizonts and merozoites were similar to in vivo derived organisms.     

An electron microscopic study of intra-erythrocytic stages of Babesia bovis in the brain capillaries of infected splenectomized calves.

Splenectomized vaccine donor calves undergoing primary reactions to Babesia bovis infections may develop cerebral babesiosis which leads to death if not treated in time. A brain biopsy was performed on an artificially-infected animal showing nervous symptoms and the tissue was immediately processed for electron microscopic examination. Virtually every erythrocyte in the brain capillaries sectioned was infected with B. bovis. Intra-erythrocytic merozoites, trophozoites and dividing trophozoites were indentified. Important features of the piriform merozoites included a reduced apical complex consisting of the anterior polar ring, microtubules, rhoptries and micronemes. Unidentified membrane-bound bodies, mostly spherical in shape, were observed anterior to the nucleus. The trophozoites showed very little structural differentiation and no food vacuoles or micropores could be detected. Each trophozoite produced 2 identical merozoites and the parent cell became totally incorporated in the daughter merozoites in the multiplication process. Projections were seen radiating from the surface of infected erythrocytes which appeared to adhere to other surfaces on contact. This probably resulted in the sludging of infected erythrocytes in the capillaries. The latter observations coincide with those described for Babesia argentina.     

柔嫩艾美耳球虫裂殖生殖阶段超微结构的研究

利用透射电镜对柔嫩艾美耳球虫（Eimeria tenella)裂殖生殖阶段的超微结构进行了观察描述。其第二次裂殖生殖方式为外裂殖生殖，裂殖子侵入宿主细胞后，裂殖子逐渐变圆形成裂殖体，此过程中裂殖子的棒状体首先消失，引后锥体和极环消失、最后微浅、淀粉颗粒和折光体消失。裂殖体长大后，细胞膜下陷，将裂殖体分成几个部分，随后裂殖体进行核分裂成多核裂殖体，此后在靠近细胞核处细胞膜加厚外突，临近部位的细胞膜凹陷，同时近突起部位内膜复合体加厚形成极环，随着时间的推移逐渐形成幼稚裂殖子，幼稚裂殖子后部与残体相连，此过程中裂殖子的锥、极环、微线、棒状体、淀粉颗粒、折光体依次逐渐形成。裂殖子成熟的标志为从残体脱离，裂殖子的膜下微管24根纵向贯穿裂殖子直达顶端和极环相连，裂殖子内部由锥体、锥体前环1、锥体前环2、极环、微线、线粒体、折光体和3－多个棒状体等组成。     

Ovine sporozoan encephalomyelitis linked to Sarcocystis infection

The unidentified sporozoan causing encephalomyelitis in sheep described by Hartley and Blakemore (1974) was restudied, and the parasite was identified as a Sarcocystis species based on its location and structure. The parasite was located free in the host-cell cytoplasm, divided by endopolygeny and mature merozoites lacked rhoptries.     

Hepatozoonosis in two species of Japanese wild cat

Hepatozoon sp. infections were detected in two species of Japanese wild cat, Iriomote wild cat (Felis iriomotensis) and Tsushima leopard cat (Felis bengalensis euptilura), between April 1993 and October 2005. The prevalence was 56.7% (17/30) and 14.3% (6/42), respectively. The most affected organ was the heart; all infected animals had organisms in their hearts. The parasitizing form was schizont and various developmental stages were observed. The size of schizont and merozoite was 22.3 +/- 3.1 x 15.3 +/- 2.2 mum and 6.1 +/- 0.6 x 2.3 +/- 0.2 mum, respectively. Few inflammatory reactions against the parasites were observed. Electron microscopically, organisms were located in parasitophorous vacuoles of unidentified host cells, and mature schizonts consisted of numerous merozoites. This is the first report of hepatozoonosis in Japanese felids.     

Dermatitis in a dog associated with an unidentified Toxoplasma gondii-like parasite

Protozoal dermatitis was diagnosed in a 6-year-old female Great Dane dog from Rio de Janeiro, Brazil. The dog died because of a chronic illness with an Ehrlichia-like organism. Numerous apicomplexan parasites were identified histologically in the section of dermal lesions. The protozoan reacted with Toxoplasma gondii polyclonal rabbit serum but not with Neospora caninum or Sarcocystis neurona antibodies. Ultrastructurally, the protozoa was not T. gondii because it had schizont-like structures with merozoites arranged around a prominent residual body, and the merozoites had several rhoptries with electron-dense contents; rhoptries in T. gondii tachyzoites are electron-lucent and a residual body is not found in groups of tachyzoites. This is the first report of unidentified T. gondii-like protozoa in the skin of a dog.     

Langerhans cells within the follicular epithelium and the intradermal sweat duct in equine insect hypersensitivity "Kasen"

Histopathologic and electron microscopic observations were given on Langerhans cells (LCs) within the follicular epithelium (FE) and intradermal sweat duct (ISD) of equine "Kasen". By light microscopy, LCs were present in the greatest numbers within the FE and ISD than within the epidermal layer and the normal skin, with an occasional formation of several aggregated foci. By electron microscopy, LCs within the FE and ISD widely extended their dendritic processes between the keratinocytes and contained Birbeck granules (Bgs), mitochondria, rough endoplasmic reticula and ribosomes in the cytoplasm. Numerous Type 2 LCs, with a number of Bgs and endocytosis, and Type 3 LCs, with multivesicular bodies and endosomes of various sizes, were recognized within the FE and ISD, although inactive Type 1 LCs, with a narrow and lucid cytoplasm, were rarely seen. LCs observed within the FE and ISD in the "Kasen" skin lesions might express the particular stage corresponded to recognize, intake and process the antigens which permeate them.     

Sarcocystis neurona and Sarcocystis falcatula: monitoring of schizogony in cell culture using fluorescent nuclear labeling

The nuclei of merozoites of Sarcocystis neurona and Sarcocystis falcatula were labeled with the fluorescent marker Syto21. It was shown that the marker would label the parasites and that they would retain the marker throughout schizogony. Thus, there was sufficient marker in the daughter merozoites to make them easily visible with fluorescence microscopy. This technique will be helpful in studying the developmental biology of these parasites in vitro.     

Penetration of equine leukocytes by merozoites of Sarcocystis neurona

Horses are considered accidental hosts for Sarcocystis neurona and they often develop severe neurological disease when infected with this parasite. Schizont stages develop in the central nervous system (CNS) and cause the neurological lesions associated with equine protozoal myeloencephalitis. The present study was done to examine the ability of S. neurona merozoites to penetrate and develop in equine peripheral blood leukocytes. These infected host cells might serve as a possible transport mechanism into the CNS. S. neurona merozoites penetrated equine leukocytes within 5 min of co-culture. Infected leukocytes were usually monocytes. Infected leukocytes were present up to the final day of examination at 3 days. Up to three merozoites were present in an infected monocyte. No development to schizont stages was observed. All stages observed were in the host cell cytoplasm. We postulate that S. neurona merozoites may cross the blood brain barrier hidden inside leukocytes. Once inside the CNS these merozoites can egress and invade additional cells and cause encephalitis.     

Ultrastructural study of globidian parasites infecting the abomasum of sheep in Germany.

Globidian parasites infecting the abomasum of sheep in Germany were investigated by means of electron microscopy. The frequency of infection was found to be 93 %. The globidian cyst-like bodies contained multinucleate schizonts, developing merozoites or fully developed merozoites. Among the latter there were two different types, namely short and long forms. The process of merozoite formation was described in detail. The giant schizonts were subdivided into multinucleate cell portions of irregular size and shape. Their nuclei were then arranged at the periphery of the cell portions and underwent their last division which was combined with the differentiation of merozoites. The long form merozoites were elongated cylindrical in shape with terminal nucleus. They measured 7.7 μm in length and 1.0 μm in width. The merozoites of the short type were spindle-shaped with a central nucleus. They were 5.0 μm long and 1.0 μm wide. The globidian parasites were located in a parasitophorous vacuole of an intact host cell.     

Schizogony and gametogony of Eimeria zuernii (Rivolta, 1878) Martin, 1909

Calves were infected with Eimeria zuernii given by stomach tube and also placed directly into surgically prepared pouches of small intestine. The calves were killed at 2 day intervals or less from the 2nd to the 21st day after injection. First generation schizogony occurred in the lamina propria of the lower ileum and the first generation schizont was a giant schizont. Second generation schizogony and gametogony took place in the epithelial cells of the caecum and proximal colon. Measurements of the various stages of the life cycle of E. zuernii are given.     

兔脑炎原虫的超微形态与发育

用电镜连续７代动态地观察了培养细胞中兔脑炎原虫的超微结构与发育状态。脑炎原虫含有细胞核，但无线粒体、内质网和高尔基复合体等细胞器，其表面有几根极丝。脑炎原虫在培养细胞中除二分裂增殖外，还有裂体增殖和配体增殖。由于脑炎原虫有３种增殖方式，故在光学显微镜下呈多形态结构。     

鹌鹑源火鸡隐孢子虫在小白鼠和雏鸡体内内生发育阶段的超微结构比较

用鹌鹑源火鸡隐孢子虫（Cryptos poridium meleagridis）卵囊分别感染昆明系小白鼠和固始雏鸡，用透射电镜和扫描电镜观察比较了C．meleagridis在两种试验动物体内的内生发育虫体超微结构和致病性的差异。利用扫描电镜观察发现，鹌鹑源火鸡隐孢子虫（C.meleagridis）在小白鼠和雏鸡体内的寄生部位有较大差异，在小白鼠体内寄生于十二指肠，但在雏鸡体内主要寄生于回肠；C．meleagridis深嵌于小白鼠肠微绒毛丛内，微绒毛较为完整；但在雏鸡回肠，C．meleagridis似黏附在肠黏膜表面，微绒毛脱落明显，对雏鸡致病性明显比对小白鼠的致病性强。利用透射电镜在两种试验动物的样品中均观察到不同发育阶段的滋养体、裂殖体和大配子体以及正在孢子化的卵囊。滋养体和裂殖体在发育过程中可明显见到粗面内质网结构，裂殖生殖中期阶段粗面内质网尤其发达；小白鼠体内的C．meleagridis虫体与肠黏膜接触处形成一凹陷，寄生部位较深，而在雏鸡体内无此现象。此外，利用透射和扫描电镜均观察到虫体寄生部位周围微绒毛密度高而且也比其它部位长。形成这些差异的原因有待于进一步探讨。     

An epizootic among knots (Calidris canutus) in Florida. II. Ultrastructure of the causative agent, a Besnoitia-like organism.

Multinucleated cysts near the luminal surface of the thoracic aortas of diseased knots (Calidris canutus) were similar to besnoitia cysts. Ultrastructurally, the cyst had four distinct layers. The central area included a vacuole that contained a sporozoan with a conoid, polar ring, micronemes, rhoptries, nucleus, mitochondria, dense bodies, a lipid-like vacuole and endoplasmic reticulum. External to the vacuole was a layer with organelles typical of vertebrate cells. The wall of the cyst was irregular in thickness and was bound by a strongly osmiophilic membrane. There was a loose, acellular area of intertwined strands between the cysts wall and layer of organelles.     

Light and electron microscopic observations on the development of Babesia bigemina in larvae, nymphae and non-replete females of Boophilus decoloratus

In Boophilus decoloratus infected by transovarian passage with B. bigemina, primary schizogony occurred as a continuous repetitive process in all 3 stages of the tick's life cycle spent on the host. The primary schizonts and the large merozoites (= vermicules) produced by them were observed in the gut epithelium, haemocytes, muscles, ad peritracheal cells. Secondary schizogony which led to the formation of small merozoites (= infective forms) occurred mainly in the salivary glands, but was also observed in the cortex of the synganglion. Mature small merozoites were observed in nymphal and adult ticks only. An infective stabilate was prepared from nymphae collected on Day 14 and Day 15 post larval infestation. The infections resulting from intravenous injection of the stabilate had a prepatent period of 8 days.