Generations Of Schizogony Research Articles

Study on the pathogenicity, immunogenicity, endogenous development and drug sensitivity of Eimeria kongi.

Following the discovery of Eimeria kongi, we investigated the pathogenicity, immunogenicity, endogenous development and drug sensitivity of this coccidian. Coccidia-free rabbits were inoculated with 1 × 102 to 5 × 104 sporulated oocysts of E. kongi before challenge 14 days post inoculation. E. kongi was moderately pathogenic and induced good immunity against re-infection. All inoculated doses results in reduced food intake and body weight gain, and an inoculation oocyst dose of 1 × 103 or higher caused various degrees of diarrhea. Except for one death of the highest dose group, all rabbits recovered 12 days post inoculation. An inoculation dose of 1 × 103 or 1 × 104 oocysts conferred the most effective protection from re-infection, which reduced oocyst output by approximately 99% and maintained body weight gain. Four generations of schizogony were observed, and the endogenous development mainly occurred in the jejunum and ileum of rabbits. E. kongi was most sensitive to sulfachloropyrazine sodium, followed by decoquinate; it is resistant to diclazuril. Both decoquinate and sulfachloropyrazine sodium may be effective in the control of E. kongi infection.

Selection and identification of a precocious line of Eimeria intestinalis with enlarged oocysts and deletion of one generation of schizogony.

Rabbit coccidiosis is a common parasitic disease and responsible for enormous economic losses in the rabbit industry. Eimeria intestinalis, one of the highly pathogenic and common Eimeria species infecting rabbits, is considered as an indispensable species for the development of live oocyst vaccines against rabbit coccidiosis. In this study, we report the successful selection of a precocious line (EIP8) from a wild-type strain of E. intestinalis (WT) by successively collecting and propagating the early excreted progeny oocysts. The EIP8 line had a prepatent period of only 132h compared to 204h for the WT. Oocysts of EIP8 were notably different from those produced by the WT strain by their significantly larger size (mean length: 29.3 vs 27.6μm and mean width 20.5 vs 19.8μm). Examination of tissue sections prepared from EIP8-infected rabbits revealed that this precocious line undergoes only two generations of schizogony before differentiating into gametocytes by 120h post-infection. In contrast, WT parasites undergo three generations of schizogony and gametocytes are present by 168h post-infection. EIP8 multiplication capacity reduced by more than 35-fold and a concomitant decrease in pathogenicity was detected. Interestingly, immunization with 103 or 104 EIP8 oocysts provided sufficient protection against homologous challenge with wild-type parasites, as body weight gain of immunized and challenged rabbits was similar to that of untreated animals, as well as more than 90% reduction of oocyst output was detected in immunized and challenged animals when compared to unimmunized and challenged animals. Together, these results show that the EIP8 precocious line of E. intestinalis is an attenuated immunogenic strain and a suitable candidate for the development of a live vaccine against rabbit coccidiosis.

Eimeria hermani Farr, 1953 of the Canada goose, Branta canadensis: endogenous development, including intranuclear schizogony, in the domestic goose (Anser anser domesticus)

All endogenous stages of Eimeria hermani were found throughout the small intestine of experimentally infected domestic goslings. At least two generations of schizogony were seen to occur prior to gamogony, and mature schizonts were seen from 36 to 84 h postinfection. Developing gamonts were seen between 96 and 120 h postinfection and oocysts were seen in histological sections by 132 h. All schizogonic stages occurred within the nuclei of epithelial cells whereas the sexual stages were found within the cytoplasm of epithelial cells. Infected nuclei appeared close to the brush border of epithelial cells, in contrast to the basal position occupied by uninfected nuclei. The schizonts and the resulting merozoites lay within a parasitophorous vacuole bounded by a vacuolar membrane. In infected nuclei a dissociation of the granular and fibrillar portions of the nucleolus was apparent and the heterochromatin was concentrated near the nuclear membrane. The ultrastructure of the merozoites is described and the intranuclear development of the asexual stages of E. hermani is discussed in relation to previously described intranuclear coccidian parasites.

Some aspects of Leucocytozoon caulleryi reinfection in chickens.

The role of first- and second-generation schizonts in acquired immunity to Leucocytozoon caulleryi in chickens was studied. The chickens, which had recovered from a primary infection with various doses of sporozoites at 22-95 days of age, were challenged with sporozoites. First-generation merozoites were found in all of the challenged chickens, but no second-generation merozoites and gametocytes were seen in 30 of 32 chickens challenged with sporozoites. Almost all of the chickens that had recovered from a primary infection with sporozoites showed complete resistance to reinfection, and those that had recovered from a primary infection with first-generation merozoites showed resistance to reinfection with sporozoites. These results indicate that the second-generation schizont of L. caulleryi appears to be more immunogenic than the first-generation schizont and that some immune factors acquired by the chickens in the second generation of schizogony may inhibit the development of second-generation schizonts.

Eimeria tenella and E. necatrix: A Third Generation of Schizogony Is an Obligatory Part of the Developmental Cycle

The latter part of endogenous development of Eimeria tenella and E. necatrix was examined in sections of cecal tissue taken from chickens infected either by giving oocysts orally or by injecting merozoites into the cecum. The findings, with 3 strains of E. tenella and 1 of E. necatrix, indicate that the majority, if not all, of the parasite populations undergo a third generation of schizogony and then embark upon gametogony.

Eimeria tenella: immunogenicity of the first generation of schizogony.

The life-cycle of a precocious and attenuated line (WisF96) of Eimeria tenella, derived from the Wisconsin (Wis) strain, contained only the first of the three generations of schizogony undergone by the parent strain. The reproductive capacity of WisF96 was less than that of the parent strain by a factor of about 2000, but inoculation of chickens on two occasions with a large number of its oocysts induced resistance against challenge with oocysts, or with second-generation merozoites of Wis. The immunizing abilities of the attenuated line and its parent were compared by priming groups of chickens with numbers of oocysts of WisF96 or Wis, designed to produce infections of equal magnitude in terms of oocysts production (standard inocula), and then challenging with oocysts of Wis. The results suggested that an equivalent parasite mass of WisF96 was more immunogenic than Wis. This was confirmed by the finding that, even when the priming dose of Wis was increased 10-fold, the standard inoculum of WisF96 still produced the greater protective effect. These results indicate that the first generation of schizogony of E. tenella is highly immunogenic.

Eimeria maxima: Characteristics of attenuated lines obtained by selection for precocious development in the chicken

Both the Weybridge strain and a mixture of six laboratory and field strains of Eimeria maxima have been attenuated by selection for early maturation of oocysts during serial passage in chickens. The prepatent times of the resultant precocious lines produced after selection were reduced from approximately 120 hr to less than 107 hr, and their reproduction and pathogenicity were less than those of the parent strains. Chickens which had been inoculated with a small number of oocysts of the Weybridge precocious or mixed field isolate precocious lines were immune to subsequent challenge with the parent strains. In a comparison made between the endogenous development of the precocious lines and their parent strains, it was found that asexual multiplication of the precocious lines was reduced, due to the earlier onset of gametogony. The results of this study also indicate that the parent (i.e., normal) strains of E.maxima probably undergo a minimum of four generations of schizogony.

Infectivity of sarcocystis from donkey for horse via sporocysts from dogs

The dog is the final host for sarcosporidia cysts from the oesophagus and diaphragm of donkeys from Sardinia. The prepatent period lasted 9 to 10 days. Sporocysts measured 12.2-13.8 X 9.2-9.9 microns. Infection of a horse with 10(5) donkey/dog sporocysts increased the rectal temperature to more than 40 degrees C on days 10 and 20 after infection. On day 138 p.i. predominantly immature cysts containing metrocytes were found, especially in the oesophagus. Infection on day 117 p.i. with 2 X 10(5) horse/dog sporocysts did not give rise to a temperature increase during the following 21 days. The final host of sarcosporidia cysts from the oesophagus and diaphragm of horses from Sardinia is the dog. The prepatent period lasted 9-10 days. Sporocysts measured 12.2-13.8 X 9.2-9.9 microns. The rise in the rectal temperature of three foals infected with horse/dog sporocysts did not differ from that of the foal infected with donkey/dog sporocysts. In both cases rectal temperature increased to more than 40 degrees C on days 10 and 20 following infection with 10(5) sporocysts. Because of the occurrence of two temperature peaks following infection, two generations of schizogony are postulated. The presence of a sarcosporidia species occurring in the donkey only is doubtful.

Endogenous Stages of Eimeria tuskegeensis (Protozoa: Eimeriidae) in the Cotton Rat, Sigmodon hispidus

Endogenous stages of Eimeria tuskegeensis were studied in experimentally infected cotton rats, Sigmodon hispidus. Almost all parasites were located on the basilar side of the nucleus in epithelial cells on the sides and tips of villi of the small intestine. The endogenous cycle consisted of three generations of schizogony followed by gametogony. First-, second-, third-generation schizonts could be distinguished by time of appearance, size and shape of the schizont, and number, size, shape, and arrangement of merozoites. Immature gametogonous stages appeared to 84 hr postinoculation (PI) and developed into mature microgametocytes and macrogametes by 96 hr PI. Microgametocytes had a mono-centric type of development. Intermediate macrogametes had small, basophilic wall-forming bodies and mature macrogametes had large, eosinophilic wall-forming bodies. It was not possible to determine whether these were two distinct types of wall-forming bodies or whether they were different stages of a single type. Two nuclei were seen in the host's epithelial cells parasitized by schizonts, microgematocytes, macrogametes, and oocysts. This binucleate condition was apparently parasite-induced.