Nucleolar hypertrophy as an indicator of transcription in cells infected with second generation meronts of Eimeria tenella

Changes in nuclei and nucleoli of cells of chicken cecum infected with Eimeria tenella were studied in living cells by interference microscopy and in fixed and stained tissues using light level microscopy. As soon as merozoites began to transform into second generation meronts, there was an increase in the size of both the nucleus and the nucleolus of the host cell. The dry weight of the nucleus increased somewhat, but there was a greater increase and a correlation of the dry mass of the nucleolus with the size of the parasite as measured by interference microscopy. In fixed and stained tissues, there was a correlation between the area of the nucleolus and the area of the parasite. Removal of nucleic acids with DNase and/or RNase showed high concentrations of both in the nucleoli and a residue of protein. The increased nucleolar size indicates a high level of transcription in infected cells and allows the conclusion that the parasite somehow induces transcription to occur. Since transcription is a highly specific process, the high degree of host and site specificity shown by nearly all coccidia is consistent with a hypothesis that the coccidia share a portion of the host genome.

Effect of natural feedstuffs added to a semi-purified diet on Eimeria tenella infection

Experiments were conducted to study the effect of addition of natural feedstuffs to a semi-purified (SP) diet on Eimeria tenella infection of chickens. Chicks were fed the experimental diet throughout the experimental period and were orally inoculated with 200,000 sporulated oocysts of E. tenella at 14 days of age. Addition of corn, but not soybean meal, to a SP diet increased mortality and decreased body weight gain due to the coccidial infection in comparison with chickens fed the SP diet. Addition of corn gluten meal or replacement of poultry fat by corn oil or glucose by corn starch in the SP diet did not significantly change any of the parameters studied. Addition of 20% of corn fermentation solubles (CFS)-but not 20% of distillers dried grains with solubles, wheat bran, or rice bran-to the SP diet, resulted in significantly higher mortality from the coccidial infection. Addition of 5 or 10% of CFS to the SP diet significantly increased mortality in chicks compared to those fed the SP diet, but feeding the residue of CFS after extraction with chloroform-methanol followed by water did not increase mortality. These studies show that corn and CFS contain factors that enhance E. tenella infection in chicks fed a semi-purified diet, but other natural feedstuffs such as soybean meal do not.

Problems in the identification of species of Eimeria

The paper is concerned with the principles upon which coccidia of the genus Eimeria may be characterized. Reference strains for comparative purposes usually are not available and the limitations of morphological data for speciation are discussed. The value of other parameters are considered such as host and site specificity, pathogenicity, immunological specificity, pre-patent period, sporulation time, enzyme variation, and DNA buoyant density. The weight afforded to each of these parameters for specific identification may vary according to the parasite and host studied. Determinations of physiological and behavioral characteristics that are now becoming available should be included in species definitions wherever possible.

Eimeria tenella, Eimeria necatrix, and Eimeria adenoeides: peripheral blood leukocyte response of chickens and turkeys to strains adapted to the turkey embryo

The peripheral blood leukocyte responses of chickens and turkeys inoculated with one of three strains of a chicken Eimeria species adapted to the turkey embryo with their respective parent lines, or with E. adenoeides of the turkey were studied. The adapted lines tended to cause hematological changes in chickens and turkeys similar to those caused by E. adenoeides. These parasites caused the most significant increases in large mononuclear white blood cells = (monocytes) in both chickens and turkeys. These results provide further evidence for a monocyte/macrophage effector mechanism in the rejection of heterologous species of Eimeria from a nonspecific host. The results also agree with previous studies that show that increases in mononuclear white blood cells during parent E. tenella and E. necatrix infections in chickens occur during the periods of greatest tissue damage (3-4 days after inoculation). The generally unaffected lymphocyte numbers and increases in mononuclear white blood cells during infections with the adapted lines probably explain the reduced pathogenicity and the lack of immunogenicity seen previously in chickens inoculated with these three lines. Possibly, monocytes/macrophages play a role in the host specificity of the parasites.

Effect of selenium and vitamin E on the development of immunity to coccidiosis in chickens

Six experiments were conducted using broiler chickens to study the effect of selenium (Se) or vitamin E supplementation of a corn-soybean meal diet on the immune response to coccidiosis. Immunized chickens fed diets supplemented with .25 ppm Se or 100 IU vitamin E/kg of diet had increased body weight gain and feed intake and a tendency for lower feed conversion ratio than chickens fed unsupplemented diet after a challenge with 150,000 oocysts of Eimeria tenella. In two experiments, chickens fed .25 and .50 ppm of Se and immunized against E. tenella had higher body weight gain and a tendency for higher feed intake and lower feed conversion ratio than unsupplemented chickens when challenged with 150,000 oocysts of E. tenella. Except for a reduction on cecal lesion scores and blood packed cell volume in Experiments 1 and 4, respectively, no dietary effect was observed on cecal lesion score or blood packed cell volume of immunized chickens. Dietary supplementation with selenium or vitamin E reduced mortality and increased body weight gain of nonimmunized chickens infected with E. tenella in three of four experiments. These studies suggest that immunization of chickens against coccidiosis is enhanced by Se or vitamin E supplementation.

Effect of selenium on peripheral blood leucocytes of chickens infected with Eimeria

Experiments were conducted to study the effects of dietary selenium (Se) on peripheral blood leucocytes of chickens infected with coccidia. Primary coccidial infection significantly increased blood leucocyte number at 6 days postinfection (PI) in three of four experiments when chicks were fed a corn-soy diet, and in all four experiments at 11 days PI. When chickens were fed a semipurified (SP) diet, coccidial infection did not affect the blood leucocytes number at 6 days PI but significantly increased blood leucocyte number at 11 days PI. In the primary infection, Se significantly decreased blood leucocyte number in four of six experiments at 6 days PI and significantly increased the blood leucocyte number in three of five experiments at 11 days PI. In the secondary infection, chickens had significantly more blood leucocytes than chickens given a primary infection at 8 or 24 hr after challenge. Selenium significantly increased blood leucocyte number at 8 hr after challenge in one experiment and produced numerically higher leucocyte number in three other experiments. The results of these studies indicate that dietary Se supplementation modifies the number of peripheral blood leucocytes in chickens infected with coccidia.

The effect of feeding a semipurified diet to chickens infected with coccidia

Four experiments were conducted using broiler chicks to study the effects of feeding a semipurified diet on coccidial infection. Chickens fed a semipurified diet and inoculated with E. tenella had a very mild infection with little or no mortality and no effect on body weight gain, feed intake, feed conversion ratio, and blood cell loss as judged by hematocrit. At necropsy the infected chickens had light cecal lesions. However, no difference in response was observed between chickens fed either the corn-soybean meal or the semipurified diet and inoculated with a mixture of E. acervulina, E. maxima, and E. brunetti. Chickens fed a diet composed of 25% of the corn-soybean meal diet plus 75% of the semipurified diet and inoculated with E. tenella had the same mortality as chickens fed the corn-soybean meal diet. Feeding chickens the semipurified diet as early as 6 days before inoculation did not affect the severity of E. tenella infection. No difference was observed in the intestinal or cecal pH or food passage time of noninfected chickens fed either the corn-soybean meal or the semipurified diet. No differences were found in the number of oocysts discharged between 2 and 9 hr after inoculation expressed as a percentage of the infective dose. The results of these studies show that a semipurified diet ameliorates infection of chickens with the cecal parasite E. tenella but not coccidial infections of the small intestine.

Extraintestinal sporozoites of chicken Eimeria in chickens and turkeys

Oocysts were found in the feces of chickens (recipients) dosed orally with whole blood, liver, lung, or heart homogenates from chickens and turkeys (donors) inoculated 3 and 4 days previously with a mixture of 3.5 X 10(6) oocysts of chicken Eimeria. No oocysts were found in the feces of recipients given spleen homogenates from these same chickens and turkeys and none were found in the feces of recipients given similar material from uninoculated donors. Intracellular sporazoites were found in the peripheral blood of a turkey inoculated with chicken Eimeria. The results indicate that a small number of sporozoites are capable of invading and surviving for at least 4 days in the peripheral blood of chickens and turkeys.

Gordon memorial lecture. Coccidiosis control: past, present and future

Hygiene, management, chemotherapy and immunity all play a part in the control of coccidiosis. Under the conditions of modern intensive poultry rearing, special reliance is placed upon chemotherapy and since the introduction of the sulphonamides in 1939 a sequence of different types of drugs has been developed. At present the field is dominated by the ionophore antibiotics which have a special mode of action against the extracellular phases of the parasitic life cycle. Drug resistance is a continuing problem which has limited the effective life of most types of drug, although it has been most significant for particular compounds. So far it has not severely affected the efficacy of the ionophores. Immunity is involved in effective prophylaxis and the strong protective immunity which is a feature of most coccidial infections offers promise of a vaccination system. However, much more research will be necessary to bring this promise to fruition. Studies on immune mechanisms, antigenicity, biochemistry and in vitro cultivation may all contribute to the development of methods for controlling a series of infections which are an important obstacle to the development of modern husbandry methods.

Development of human and calf Cryptosporidium in chicken embryos

Cryptosporidium is a newly recognized, zoonotic protozoan that produces short-term, flu-like, gastrointestinal illness in immunocompetent humans and prolonged, severe, diarrhea in immunocompromised individuals. Successful completion of the life cycle, from sporozoite to infective oocyst, of isolates of Cryptosporidium from humans and calves was demonstrated in endoderm cells of the chorioallantoic membrane (CAM) of chicken embryos maintained at 37 C. The human and calf isolates of Cryptosporidium were morphologically and developmentally indistinguishable when grown in chicken embryos. The human isolate also completed its entire life cycle in the CAMs of chicken embryos maintained at 35 C and 41 C. Oocysts recovered from endoderm cells of infected CAMs produced heavy infections in suckling mice. The timing, presence, and morphology of developmental stages in CAM cells during the first eight days after inoculation of sporozoites were similar to those in enterocytes of mice inoculated with oocysts. The method described is safe and convenient for cultivating and studying Cryptosporidium in a bacteria-free environment; the system also lends itself to well-established procedures for evaluating antiprotozoan drugs.

Studies to determine the taxonomic status of Eimeria mitis, Tyzzer 1929 and E. mivati, Edgar and Seibold 1964

We have examined several taxonomic features of a number of strains of Eimeria from many sources world wide. The strains were isolated on the basis of their small spherical (or sub-spherical) oocysts. From a study of mean oocyst dimensions, electrophoretic variation of enzymes, ability to develop in embryonated eggs, absence of gross lesions in heavily infected chickens, and cross-immunity, all the strains were found to belong to one species. For convenience, the parasites when isolated, were referred to as strains of E. mitis/mivati-type, but after characterization they were clearly found to be E. mitis. In contrast, a laboratory strain of E. mivati supplied to one of us (M.W.S.) was found to be a mixture of E. acervulina and E. mitis. Evidence from these and other studies supports the notion that E. mivati is a nomina dubia.

Attenuation of Eimeria necatrix and E. tenella of U.S. origin by serial embryo passage

Two lines of Eimeria tenella (PS and FS65) and one line of E. necatrix (FS144) of U.S. origin were passaged in chicken embryos. The embryo-passaged line of E. tenella PS was significantly less pathogenic than the parent line when tested in chickens after 33 embryo passages. After 29 embryo passages, E. tenella FS65 was just as pathogenic to chickens as the parent line. A comparison of the immunogenicity of the embryo-adapted lines and the parent lines in chickens showed that embryo-passaged E. tenella PS and E. tenella FS65 were as immunogenic as parent lines. The embryo-passaged line of E. necatrix FS144 was significantly less pathogenic when tested in chickens after 30 embryo passages. Although there was also some loss of immunogenicity in the embryo-passaged line of E. necatrix, immunity to this parasite could be achieved by increasing the dose of oocysts.

Serial passage of Eimeria tenella and E. necatrix in turkey embryos

The serial passage of 3 strains of Eimeria from the chicken in embryonating turkey embryos is reported here. All 3 strains increased their reproduction in turkey embryos; reproduction being equal to or better than the same lines maintained in chicken embryos. Pathogenicity and immunogenicity trials conducted in chickens using these 3 strains of Eimeria showed that all 3 turkey embryo-adapted lines were significantly less pathogenic than the parent lines. Only 1 of the lines (E. tenella (PS) turkey embryo-adapted) maintained its immunogenic potential.

Amelioration of pale bird syndrome in chicks by vitamin E and selenium

Vitamin E and/or selenium supplementation of a corn-soybean diet fed to broiler chicks in floor pens ameliorated the effect of an outbreak of pale bird syndrome diagnosed when the chicks were 3 weeks old. Supplementation significantly reduced both mortality and the effects of disease on body weight gain. The added nutrients only partly overcame the effect of the disease on body weight gain when infected chicks were compared with uninfected chicks.

Studies on the stage of action of ionophorous antibiotics against Eimeria

Sporozoites of Eimeria tenella were treated with different anticoccidial drugs in vitro and their subsequent viability was tested by inoculating them into chicken embryos. Monensin, salinomycin, lasalocid, and arprinocid, at concentrations between 0.01 and 1.0 micrograms/ml, greatly reduced sporozoite viability as judged by mortality, hemorrhage and specific lesions in the embryo chorioallantois. Monensin was also effective in reducing the viability of sporozoites of E. mivati and E. tenella as judged by oocyst production occurring in embryos; activity of monensin was greater against E. tenella than against E. mivati. Monensin (0.1 mg) inoculated into embryos inhibited development of E. tenella. Oocysts which were produced in the presence of the drug sporulated normally and sporozoites obtained from them were fully infective. By initiating treatment of chickens with monensin at different times in relation to infection, it was shown that the drug exerts its anticoccidial effect on the primary invasive stage and on the gametogonous stage of E. tenella and E. necatrix. The effect of gametogony was tested by initiating infections with second generation merozoites of E. tenella. Significant reduction in oocyst production occurred in three of four strains of E. tenella tested. Medication with monensin initiated before merozoite inoculation was effective in inhibiting oocyst production, but medication starting 5 hr after merozoite inoculation was not. This differed from the effects of arprinocid and sulfaquinoxaline which were expressed both before and 5 hr after merozoite inoculation. The results show that the ionophorous anticoccidial drugs exert their anticoccidial action primarily against the invasive stages of Eimeria.

The effect of feeding variable concentrations of monensin on the control of coccidiosis

Chickens were given concentrations of monensin in the feed which increased at weekly intervals (60 to 121 ppm). This resulted in a fairly constant intake of drug (mg/k body weight). Such chickens consumed less drug than those given monensin at 121 ppm. Chickens given variable concentrations of drug in the food were well protected against coccidiosis judged by the parameters of lesion scores and mortality. Total body weight of these chickens was greater and lesion scores at 28 days were lower compared with chickens given constant levels of monensin, but the differences were not significant. These results suggest that adequate control of coccidiosis in broilers could be achieved by administering a relatively low concentration of an anticoccidial 0 to 3 weeks followed by a high concentration.

Attenuation of a strain of Eimeria mivati of U.S. origin by serial embryo passage

A strain of Eimeria mivati (FS50) isolated in Georgia was purified and serially passaged in groups of developing chicken embryos. Starch gel electrophoresis using glucose phosphate isomerase and lactate dehydrogenase showed the parasite to be similar to another strain of E. mivati isolated in the U.S. The embryo-passaged line of E. mivati (FS50) was less pathogenic than the parent line but retained its immunogenicity. This strain may be suitable for inclusion in an improved coccidiosis vaccine. The status of E. mivati and E. mitis is discussed.

The biology and pathogenicity of a recent field isolate of Eimeria praecox Johnson, 1930

A recent isolate of Eimeria praecox, strain G, was obtained from Georgia and purified. Studies of the life history, pathogenicity, and cross-immunity of the isolate were conducted to verify its identity. In inoculated three-week-old chickens, the occurrence of merogony and gametogony was limited to the superficial epithelium of the upper intestine. Oocysts, 23 x 19.5 microns, with a shape index of 1.17 were first observed 83 h after inoculation. Mortality and morbidity were not observed in any of the experimental birds. However, there was a positive correlation between dose of oocysts, reduced weight gain, and the incidence of exudative diathesis. These studies showed that E. praecox depresses weight gains in chickens and may be of economic importance. Although complete immunity to avian coccidiosis is believed to be species specific, chickens immune to E. praecox (G) or E. acervulina had a degree of cross-immunity to a heterologous challenge. Electrophoretic analysis of glucose phosphate isomerase and lactate dehydrogenase prepared from the European strain of E. praecox and E. praecox (G) showed no differences, confirming the identity of the isolate as E. praecox.

Eimeria tenella: clinical effects in partially immune and susceptible chickens

Chickens made partially immune to E. tenella infection exhibited cecal lesions after challenge. Some of the chickens had cecal lesions of severity similar to those of birds having their first infection with the parasite. The presence of severe cecal lesions in the partially resistant birds was not accompanied by lowered body weight gain or packed erythrocyte volumes and prothrombin time was not extended. It is suggested that there are at least three stages of immunity to E. tenella; birds may be totally resistant to parasite and no development occurs, birds may be resistant to a degree where oocysts are discharged after challenge but no lesions occur, or birds may be resistant to the clinical effects of the disease despite having severe lesions.

The use of sentinel birds to monitor coccidial infection in litter pens

Two-week-old chickens susceptible to coccidiosis were introduced into litter pens for periods up to 48 hr in order to estimate the potential coccidial challenge. They were then transferred to cages and the infections acquired were estimated by oocyst output or by body weight gain and lesion scores. Moderate to severe infection occurred even when about 1,000 oocysts/gram were present in the litter. The results suggest that the brief introduction of "sentinel" birds into an infected environment may be a valuable method of assessing the actual coccidial challenge which groups of chickens acquire from exposure to litter. The technique may be used to monitor the effectiveness of anticoccidial drugs or the immune status of chickens kept in litter pens by comparing infections in "sentinels" and "in-pen" birds.

Immunological differences in Eimeria maxima: effect of a mixed immunizing inoculum on heterologous challenge

The immunological differences known to exist between laboratory strains of Eimeria maxima was confirmed. Protection against challenge with different strains or field isolates of the species could be achieved by including small numbers (25 oocysts) of each in the immunizing inoculum. Similar protection was obtained when 4 distinct populations which were allowed to interbreed were used in the immunizing inoculum. This hybrid mixture of E. maxima was used to immunize chickens against challenge with 7 new isolates of E. maxima from poultry houses in different parts of England. The results show that although immunological differences exist within E. maxima good protection against many strains of this species may be achieved by initial infection with the hybrid mixture of E. maxima.