Observations on the gross pathology of Eimeria praecox infections in chickens.

Challenge infections with 10(3), 5 x 10(4), 10(5), or 5 x 10(5) sporulated Eimeria praecox oocysts caused moderate but significant weight gain reduction at all infective doses. Substantial reduction in plasma carotenoids and moderate but significant increases in plasma NO2(-) + NO3- were observed only at the two higher doses when measured at day 6 postchallenge (PC). Daily monitoring of chickens after challenge with 5 x 10(4) oocysts revealed an inflammatory response in the duodenum and jejunum beginning at day 1 PC that was associated with a significant increase in levels of plasma NO2(-) + NO3-, which peaked at day 4 PC. A moderate, uniform hyperplasia of the small intestine and significant depression of plasma carotenoids were observed on days 4-6 PC. Plasma NO2(-) + NO3- decreased to control levels by day 6 PC. All infections were accompanied by production of a mucoid exudate in the duodenum and jejunum, which became thick and opaque by 4 days PC and tended to obscure mildly inflamed areas. These observations indicate that the acute host response to primary infection with E. praecox is both different from and occurs earlier than the response to experimental infections with other Eimeria spp., such as Eimeria acervulina, Eimeria maxima, or Eimeria tenella. These factors need to be considered in observations of pathology arising from co-infections of E. praecox with other Eimeria species, especially in drug sensitivity testing of Eimeria oocysts recovered from litter and in the evaluation of live oocyst vaccines.

Development of a protective index to rank effectiveness of multiple treatments within an experiment: application to a cross-protection study of several strains of Eimeria maxima and a live vaccine.

Vaccination of chickens with live oocysts has become a more widely used method for controlling avian coccidiosis as resistance to anticoccidial medication increases. However, some coccidia strains are not useful in multispecies vaccines because antigenic variation has made them generally less protective. In order to experimentally test a number of strains for the best cross protection, we have devised an evaluation method using four independently measured variables: weight gain, lesion score, plasma carotenoids, and plasma NO2- + NO3-. These values, when measured at 6 days postchallenge, tend to be significantly correlated. A protective index (PX) is calculated for each chicken using the following algorithm: PX = (Ngain + Ncarotenoids) - (Nsqrls + N[NO2- + NO3-]), where the prefix N indicates values for a variable normalized against a mean of that variable from a control group. Nsqrls values are normalized values of the square roots of lesion scores. The PX can then be treated as a dependent variable. In this study, mean PX values of unchallenged groups cluster around 0. Mean PX values of protected chickens are statistically close to those from unchallenged groups, whereas unprotected chickens have highly negative mean PX values.

The effect of dietary betaine on intestinal and plasma levels of betaine in uninfected and coccidia-infected broiler chicks.

Chicks fed betaine supplemented diets and infected with Eimeria acervulina and Eimeria maxima had markedly higher levels of betaine in the duodenum and mid-gut than unsupplemented, infected chicks. Uninfected chicks fed betaine exhibited almost twice the levels of betaine in the gut as infected chicks. Plasma betaine levels were lower in E. maxima-infected chicks than in E. acervulina-or Eimeria tenella-infected chicks. Betaine supplementation reversed the decrease in weight gain in E. maxima- infected chicks but had no effect on the decrease in weight gains in E acervulina- and E. tenella-infected chicks. Coccidia-infected birds on normal diets regularly exhibit increases in plasma NO(2)(+)NO(3). This increase was abolished in E.tenella-infected birds on betaine supplement. Betaine feeding did not alter this effect in E. acervulina- and E. maxima-infected birds. Results indicate that betaine supplementation has a positive effect on gut betaine levels in birds infected with E. acervulina and E. maxima. In all treatment groups, infection lowered the levels of betaine.

Mapping quantitative trait loci associated with resistance to coccidiosis and growth.

To map QTL associated with disease resistance to avian coccidiosis and growth, two commercial broiler lines with different degrees of resistance to the disease were crossed to generate an F1 generation that was intercrossed to produce 314 F2 generation offspring. The F2 offspring were inoculated with sporulated oocysts of Eimeria maxima. Five disease-associated phenotypes were measured after the infection. Intertrait comparisons revealed that oocyst shedding was a good parameter for evaluating disease resistance or susceptibility. One hundred nineteen microsatellite markers, covering 80% of the chicken genome with an average marker interval of 25 cM, were used for genotyping of F1 parents and F2 offspring. Statistical analysis based on the data of four families revealed a locus on chromosome 1 associated with oocyst shedding (logarithm of odds = 3.46). The genetic mechanism of this locus appeared additive. The genomic scan also identified three potential growth QTL on chromosomes 1, 6, and 8. These results provide the foundation for further investigation to validate the QTL.

Interaction of dietary vitamin E with Eimeria maxima infections in chickens.

In two trials, broiler chickens, processed similarly to those placed in commercial operation, were fed, from 1 d of age, a range (13 to 200 ppm) of DL-alpha-tocopheryl acetate (VE-AC) levels, and the effects on the pathology of Eimeria maxima infections were assessed at 6 d postinoculation (PI). In Trial 1, dietary levels of VE-AC had little significant effect on variables characterizing pathology except for the number of oocysts shed, which was significantly increased in chicks treated with higher VE-AC levels. The infection was judged to be mild based on moderate lesion scores (2.2+/-0.2), lack of significant effects on weight gain (7+/-1.6% decrease), moderate reduction in plasma carotenoids (21+/-2%) and small increases in plasma NO2-+NO3- (141+/-12%). In uninfected and infected chickens, plasma alpha-tocopherol (AT) increased with dietary levels of VE-AC; however, E. maxima infection caused a fairly constant decrease in AT of 35.3+/-3.2% across these levels. Plasma gamma-tocopherol (GT) levels were unaffected by dietary VE-AC or E. maxima infection. In Trial 2, pathology, again, was relatively unaffected by dietary VE-AC level. The infection was judged to be severe based on lesion scores (3.5+/-0.1), reduction in weight gain (30.7+/-3%), plasma carotenoids (72.4+/-1.5%), uric acid (16.3+/-3.4), albumin (37.8+/-2.8%), large increases (261+/-8%) in plasma NO2-+NO3-, and high numbers of oocysts shed per chick (4.12+/-0.4 x 10(7)). Plasma AT again increased with increasing dietary VE-AC levels in uninfected and infected chicks, but the mean decrease across VE-AC levels caused by E. maxima infection was 73.14+/-3.3%. GT levels were erratic and unrelated to dietary VEAC or infection. Thus, in processed broiler chickens, high dietary VE-AC did not prevent or lessen the pathology caused by mild or severe infections with E. maxima. The main effect of E. maxima infection appeared to be reduction in plasma AT levels. We postulate that this reduction may be due to malabsorption of AT, which results from physical damage to the absorptive mucosa, reduction in esterases required to hydrolyze the VE-AC, and a generalized lipid malabsorption, preventing movement of the free AT to circulating blood and infected tissues.

Recent advances in biology and immunobiology of Eimeria species and in diagnosis and control of infection with these coccidian parasites of poultry.

Avian coccidiosis, an intestinal disease caused by protozoan parasites of the genus Eimeria, occurs worldwide. It is considered to be one of the most economically important diseases of domestic poultry. For many years, prophylactic use of anticoccidial feed additives has been the primary means of controlling coccidiosis in the broiler industry and has played a major role in the growth of this industry, which now can produce about 7.6 billion chickens annually. However, development of anticoccidial resistance has threatened the economic stability of the broiler industry. Although there has been little effort by the pharmaceutical industry to develop new anticoccidials, the mounting problem of drug resistance of Eimeria species has prompted major research efforts to seek alternative means of control through increased knowledge of parasite biology, host response, and nutritional modulation. As a consequence, important advancements have been made, particularly in defining parasite antigens that have potential use in vaccines, defining the Eimeria genome, understanding the immunology of coccidial infections, and the practical applications of live vaccines. This review describes the progress in these areas, most of which has occurred within the past 10 to 15 years.

Eimeria tenella infection in chickens: effect on plasma and muscle 3-methylhistidine.

To assess muscle breakdown during avian coccidiosis, the level of the nonmetabolizable amino acid 3-methylhistidine (3MH) was determined in muscle and plasma from chickens infected with the cecal parasite Eimeria tenella. The change in 3MH level during infection was determined in birds, each inoculated with 0 to 200,000 sporulated oocysts. The effect of levels of parasitism was evaluated at 6 d postinoculation. The 3MH levels of plasma and muscle were determined by HPLC after derivatization with fluorescamine. Weight gains, packed cell volumes, and gross lesion scores were also determined. E. tenella infected birds with lesion scores of 3 or 4 had significantly elevated plasma and muscle 3MH, whereas infected birds with lesion scores of 0, 1, or 2 did not have elevated plasma and muscle 3MH; however, there was a linear inverse relationship between weight gain and both plasma and muscle 3MH. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, was elevated during the acute stage of E. tenella infection and was most likely associated with anorexia caused by infection. However, the correlation of 3MH levels with severity of infection was not as strong as that previously observed for E. acervulina infection, most likely due to the differences in pathology caused by the two species.

Effects of treatments with cyclooxygenase inhibitors on chickens infected with Eimeria acervulina.

Reduced weight gains and feed conversions are major sources of economic losses from avian coccidiosis. Experiments were conducted to determine possible involvement of up-regulation of cyclooxygenase (COX) activity during coccidia infections that might contribute to reduced weight gain. In a series of trials, young (3 to 5 wk of age) cockerels infected with Eimeria acervulina, a duodenal parasite, received oral treatments with indomethacin (IM), an inhibitor of both COX-1 and COX-2, or nimesulide (NIM), a specific inhibitor of COX-2. Infection doses varied with experiment (from 10(5) to 10(6) oocysts per chick). Effects of infection on weight gain, duodenal lesions, plasma carotenoids, and levels of NO2+ NO3- were determined at 6 d postinoculation. Total oocysts were enumerated in feces collected from 5 through 8 d postinoculation from separate replicate groups. In no trials did treatment with IM reverse effects of infection on weight gain or significantly reduce lesion scores. However, in all trials, IM treatment reduced oocyst output per chick (Trial 1, 15%; Trial 2, 19%; Trial 3, 53%; Trial 4, 29%; Trial 5, 28.5%). Supplementation of feed with 400 and 100 ppm NIM significantly reduced weight gain of, and increased oocyst output from, infected chicks, whereas supplementation with 50 ppm NIM had no beneficial effects on weight gain or lesion scores, but reduced oocyst shedding. The inability of the IM and NIM treatments to reverse infection-associated weight gain suppression suggests that this pathological effect is not linked to increased prostanoid synthesis as a result of COX-2 up-regulation during infection. The inhibitory effects of IM treatment on oocyst shedding suggest that COX-2 products may have immunosuppressive effects in coccidia infection at local sites of infection. The stimulating effects of high-dose NIM treatments on oocyst shedding suggest that this compound may inhibit synthesis of other prostanoids as well.

Effect of Eimeria acervulina infections on plasma L-arginine.

As part of a program to study the pathological effects of coccidia infections on growth, we have examined the relationship of plasma L-arginine (ARG) levels to infective doses of Eimeria acervulina and infection-associated changes in weight gain, plasma carotenoids, and plasma NO2- + NO3-. Chickens consuming a starter ration containing 1.68% ARG were infected with a range of doses of E. acervulina. At 6 d postinoculation (PI), weight gains were significantly reduced by infections with 5 x 10(5) and 1 x 10(6) oocysts per chick (OPC). Gross lesion scores of chickens infected with 5 x 10(4) through 1 x 10(6) OPC were significantly greater than scores of chicks infected with 1 x 10(3) OPC. Compared with levels from uninfected controls, plasma NO2- + NO3- concentrations were significantly increased by infection with 5 x 10(5) and 1 x 10(6) OPC, plasma concentrations of ARG were significantly decreased by infection with 5 x 10(4) through 1 x 10(6) OPC, and plasma carotenoids were significantly decreased by all infection doses. Plasma arginine was significantly correlated with plasma carotenoids (P > 0.0187), but not with infection dose or weight gain; plasma NO2- + NO3- was positively correlated (P > 0.0043) with infection dose and negatively correlated (P > 0.0158) with weight gain. Regression analysis of the measured variables indicated that the strongest relationship existed between plasma ARG and carotenoids. This finding suggests that in this infection model, reduction in plasma ARG is most likely associated with nutrient malabsorption that accompanies infection and is likely not significantly impacted by synthesis of nitric oxide that is associated with the immune response.

Eimeria acervulina infection elevates plasma and muscle 3-methylhistidine levels in chickens.

To assess muscle breakdown during avian coccidiosis, the level of the nonmetabolizable amino acid 3-methylhistidine (3MH) was determined in muscle, plasma and excreta from chickens infected with Eimeria acervulina. The changes in 3MH levels during infection were assessed at 1-29 days postinoculation (DPI) in animals given 5 x 10(5) oocysts per bird. The effect of levels of parasitism were evaluated at 8 DPI in birds receiving 5 x 10(3), 5 x 10(4), 5 x 10(5) or 1 x 10(6) oocysts each. The 3MH levels of plasma, muscle, and excreta samples were determined by high-pressure liquid chromatography after derivatization with fluorescamine. Weight gains, breast muscle weight, eviscerated weight, plasma carotenoid levels, dry weight of muscle, and gross lesion scores were also determined. Infected birds had significantly elevated plasma and muscle 3MH at 4 and 8 DPI following a single dose of E. acervulina. The increase in 3MH levels had an inverse relationship with the time course of weight gain and plasma carotenoid levels. Plasma and muscle 3MH levels returned to control values by 15 DPI and remained unchanged from control values through the remainder of the experiment (29 DPI). Breast weight was decreased in infected birds, but the ratio of breast weight to eviscerated body weight was unchanged. Excretion of 3MH decreased relative to controls at 4 and 8 DPI and returned to control levels on 15 DPI. The plasma and muscle levels of 3MH were related to severity of infection; however, levels of excreted 3MH were not. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, increased during the acute stage of E. acervulina infection. The underlying causes for this muscle breakdown was unclear but could involve a physiological response to anorexia and decreased food intake during the acute phase of infection. Levels of excreted 3MH did not increase during infection and this may be the result of decreased excreta output during infection. Plasma and muscle levels of 3MH were correlated with severity of E. acervulina infections but may not be as sensitive an indicator of infection as plasma carotenoid levels or other physiological parameters.

Analysis of disease resistance-associated parameters in broiler chickens challenged with Eimeria maxima.

To determine an optimal dose for coccidial inoculation and to evaluate genetic resistance or susceptibility in individual chickens, broilers were inoculated with four different doses of Eimeria maxima oocysts. Body weight gain, fecal oocyst shedding, concentrations of plasma NO2- + NO3-, carotenoid, and interferon-gamma were measured at two different time periods postinfection. The results showed significant dose and sex effects on most parameters and interaction between dose and sex in some parameters. The dose effects were generally linear; however, some significant quadratic effects were also observed. The measurements from chickens inoculated with 10(4) oocysts displayed the highest correlation coefficients among oocyst shedding, body weight gain, and concentrations of carotenoid and NO2- + NO3-. An infection index, calculated from the correlated parameters, displayed high correlation coefficients with the parameters. The infection index may be a better parameter for evaluating individual genetic resistance against coccidial infection.

Effects of nutritionally balanced and stabilized flaxmeal-based diets on Eimeria tenella infections in chickens.

Twenty Sex Sal cockerels were randomly assigned to each of eight groups; each of four nutritionally balanced diets were fed to two groups from 1 d through 4 wk of age. These diets contained 0, 2, 5, or 10% stabilized flaxseed meal that provided a calculated 0, 0.45, 1.11, or 2.22% n-3 fatty acids, primarily linolenic acid. At 3 wk of age, one group of chickens from each diet treatment was infected with Eimeria tenella and was housed in separate but similar conditions to uninfected control chickens. At 6 d postinfection, chickens were weighed, bled, killed, and scored for lesions. No level of dietary flaxmeal tested provided protection against weight gain depression, increased feed conversion ratios, or lesions. We concluded that these diets did not protect against E. tenella infection because levels of linolenic acid were not high enough, and the oxidative potentials were well suppressed by vitamin E and other stabilizers present.

Effects of daily oral doses of L-arginine on coccidiosis infections in chickens.

L-arginine is an essential amino acid for chickens, as well as the substrate for biosynthesis of nitric oxide (NO), a bioregulatory free radical molecule known to have antimicrobial activity. Biosynthesis of NO by induced nitric oxide synthase (iNOS) can be stimulated during immunological response to infection. Therefore, in chickens, production of NO as a response to an infection should be influenced by dietary levels of L-arginine. Two experiments were carried out to determine whether oral dosing with L-arginine during coccidia infections could influence the associated pathology or the development of the parasites. Neither single nor dual daily doses (500 mg/kg) of L-arginine reversed weight gain reduction, augmented plasma NO2- + NO3- levels, or lessened lesion scores in chicks infected with Eimeria acervulina, Eimeria maxima, or Eimeria tenella. Although the oocyst shedding from E. maxima (1x dose) or E. acervulina (2x dose) infections were not affected, the oocyst shedding from E. tenella infections was significantly reduced by both dose regimens.

Comparisons of the intraocular tissue distribution, pharmacokinetics, and safety of 125I-labeled full-length and Fab antibodies in rhesus monkeys following intravitreal administration.

Access of recombinant proteins to the retina following intravitreal administration is poorly understood. A study was conducted in male Rhesus monkeys (15 to 28 mo of age; 2.8-3.3 kg) in order to compare the intraocular tissue distribution, pharmacokinetics, and safety of 125Iodine (I)-labeled full-length humanized rhuMAb HER2 antibody (148 kD) and of 125I-labeled humanized rhuMAb vascular endothelial growth factor Fab antibody (48.3 kD) following bilateral bolus intravitreal injection on day 0 (5 animals/group). The dose administered to each eye was 25 microg (9-10 microCi) in 50 microl. Animals were euthanatized on day 0 (1 hr postdose) and on days 1, 4, 7, and 14. Safety assessment included direct ophthalmoscopy, intraocular pressure measurements, clinical observations, body weight, and hematology and clinical chemistry panels. Blood and vitreous samples were collected daily (blood only) and at necropsy for pharmacokinetics and analysis for antibodies to the test materials; the ocular tissue distribution of the test material was evaluated by microautoradiography. All animals completed the study. Microautoradiography demonstrated that the full-length antibody did not penetrate the inner limiting membrane of the retina at any of the time points examined. In contrast, the Fab antibody fragment diffused through the neural retina to the retinal pigment epithelial layer at the 1-hr time point and persisted in this location for up to 7 days. Systemic exposure to test material was low but variable: the highest plasma concentration of the full-length antibody was 20.3 ng/ml, whereas plasma concentrations for the Fab antibody remained below the limit of quantitation (i.e., <7.8 ng/ml). An immune response to the test material was not evident in either treatment group. The half-life in vitreous was 5.6 days for the full-length antibody and 3.2 days for the Fab antibody. The shorter intravitreal half-life of the Fab antibody is related to its smaller size and its significant diffusion through the retinal layers. The differences in pharmacokinetics and tissue distribution that are noted between the full-length and Fab antibodies in this study identify potential therapeutic approaches that may be exploited in specific disease conditions.

Effects of dietary supplementation with n-3 fatty acid ethyl esters on coccidiosis in chickens.

The ethyl esters of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were added to a broiler starter diet singly or in combination [as bulk purified ethyl ester concentrate from menhaden oil (n3FAC)] in quantities similar to those found in a diet supplemented with 5% menhaden oil (MO). Diets were fed to chickens from 1 d of age through 3 wk of age. At 2 wk of age, the chickens were infected with Eimeria tenella, Eimeria acervulina, or Eimeria maxima. At 6 d postinfection (PI), the effects of the diets were assessed on weight gains, plasma carotenoids, gross lesion scores, and histological parasite scores in gut cross sections, or oocyst output. Significant ameliorating effects of diet on lesion scores and parasite scores were only seen in E. tenella infections and were only produced by the n3FAC and MO supplements. These two supplements, which contained higher molar concentrations of double bonds than the other supplements, also significantly reduced plasma carotenoids in uninfected chickens, indicating that they promoted a state of oxidative stress. These results are consistent with previous reports on the interaction of coccidiosis with dietary n-3 fatty acids and strengthen the hypotheses that dietary-induced oxidative stress is an effective deterrent against cecal coccidiosis in chickens.

Dietary modulation of avian coccidiosis.

During the past several years, our laboratory has been investigating the anticoccidial activities of various natural products that have potential use as dietary supplements for coccidiosis control. Sources of fats containing high concentrations of n-3 fatty acids such as menhaden oil and flaxseed oil and flaxseed, when added to starter rations and fed to chicks from one day of age, effectively reduce lesions caused by the caecal parasite Eimeria tenella, but not lesions caused by Eimeria maxima. Our results are consistent with reports of effects of diets high in n-3 fatty acids on other protozoan parasites which suggest that the state of oxidative stress induced by these diets in the cells of both host and parasites is responsible for their parasitic actions. Artemisinin, a naturally occurring (Artemisia annua) endoperoxide and effective antimalarial significantly lowers lesions from E. tenella when given at low levels as a feed additive. The mechanism of its action is also considered to involve induction of oxidative stress. Diets supplemented with 8 p.p.m. gamma-tocopherol (abundant in flaxseeds) or with 1% of the spice tumeric, reduce mid-small intestinal lesion scores and improve weight gains during E. maxima infections. These compounds may exert their anticoccidial activity because they are effective antioxidants. Betaine, a choline analogue found in high concentrations in sugar beets, improves nutrient utilisation by animals under stress. When provided as a dietary supplement at a level of 0.15% it has enhanced the anticoccidial activity of the ionophore, salinomycin. Betaine may act as an osmoprotectant whereby it improves the integrity and function of the infected intestinal mucosa. In in vivo studies, betaine plus salinomycin significantly inhibit invasion of both E. tenella and E. acervulina. However, subsequent development of E. acervulina is inhibited more effectively with this combination treatment than development of E. tenella.

Genetic influence on nitric oxide production during Eimeria tenella infections in chickens.

Studies were carried out to assess the importance of nitric oxide (NO) production in vivo in resistance to Eimeria tenella infections through treatment of resistant SC and susceptible TK strains of chickens with compounds proven to be effective inhibitors of induced nitric oxide synthase. The SC strain produced higher levels of plasma NO2- + NO3- in response to primary infection than did the TK strain. SC chickens were also more responsive in reduction of NO2- + NO3- levels and increased oocyst output in response to treatments with S-methylisothiourea or NG-methyl-L-arginine (LNMA) during primary infection. However, the SC strain, regardless of drug treatment, consistently yielded higher oocyst output during primary infection, indicating it could be susceptible to a higher parasite burden. On the other hand, the SC strain seemed to develop immunity more rapidly than the TK strain, in that oocyst output was decreased in both untreated and LNMA-treated chicks upon challenge infection compared with that of the TK strain. Oocyst output from both SC and TK strains was further decreased by LNMA treatment during challenge infection rather than increased, suggesting minimal involvement of NO production in the immune response to challenge. These results indicate that NO production during primary E. tenella infection may be only one of several immune responses and may not be the main anticoccidial effector.

Effects of combined treatment with recombinant bovine somatotropin and immunization with live oocysts on performance of broiler chicks raised in coccidia-seeded floor pens.

In our laboratory, preliminary studies have indicated that recombinant bovine somatotropin (rbST) can stimulate protective immunity against coccidia infection. A floor pen trial on coccidia-seeded litter was run to further test its activity as an adjuvant during immunization of chicks with a live oocyst vaccine. Five hundred day-old male broiler strain chicks were randomly assigned to five experimental Treatments: 1, medicated controls; 2, unimmunized, not treated with rbST; 3, unimmunized, rbST-treated; 4, immunized, not treated with rbST; 5, immunized, rbST-treated. Each treatment consisted of four pens of 25 chicks each. At the end of the growout period (7 wk), the chicks in Treatment 1 (medicated controls) had the highest mean BW, but mean BW of chickens in Treatment 3 (rbST treatment only) were not significantly less. On the other hand, the mean weights of chicks in Treatments 4 (immunized only) and 5 (immunized plus rbST) were significantly reduced, and not different from those of the untreated chickens (Treatment 2). However, when challenged at 3 wk, the chicks in Treatment 5 had a mean combined total lesion score that was significantly lower than that from Treatment 3, indicating that they had developed a higher degree of specific immunity, but of the expense of weight gain. The results suggest that rbST has a potential for use as an adjuvant with live oocyst vaccination, but that the ratio between rbST dose and numbers of oocysts in the live vaccine needs to be carefully controlled.

Assessment of recombinant bovine somatotropin as an immunomodulator during avian coccidiosis: immunization with living oocysts.

Coccidiosis, a disease of great economic importance to the poultry industry, is generally controlled prophylactically by additions of anticoccidial drugs to the feed. However, increasing development of drug-resistant coccidia species has stimulated searches for alternative control methods, one of which is vaccination. As part of this effort, recombinant bovine growth hormone (rbST) was tested as a possible immune stimulator in combination with live oocyst vaccination. At a dose of 0.045 mg per chick, given by s.c. injection at 1 d of age, rbST did not improve immunity developed by immunization with 500 or 2,500 oocysts of Eimeria maxima as judged by weight gain and lesion scores. At a single dose of 0.09 mg per chick given at 1 d of age in combination with IMMUCOX, rbST provided some protection against challenge infection with Eimeria tenella but not Eimeria acervulina as judged by reduction in lesion scores. Treatment with 0.09 mg rbST per chick alone at 1 and 3 d of age was protective against challenge with E. tenella but not E. acervulina or E. maxima as judged by reduction in lesion scores. These results strongly indicate that rbST can act as an immune modulator in chickens infected with coccidia, and provide a basis for further investigations of its use as a vaccine adjuvant.

Effects of components of Artemisia annua on coccidia infections in chickens.

Four experiments were run to test the anticoccidial activity of dried Artemisia annua leaves and several of their chemical constituents for possible use as prophylactic feed additives. When fed over a period of 3 wk at a level of 5%, a dried leaf supplement of A. annua provided significant protection against lesions due to Eimeria tenella but not Eimeria acervulina or Eimeria maxima. When fed over a period of 5 wk at a level of 1% to chicks undergoing immunization with a live vaccine, it provided significant protection in partially immunized chicks against E. acervulina and E. tenella lesions from a dual species challenge infection. It also afforded lower mean lesion scores in challenged chicks immunized over a period of 5 wk. Artemisinin, an antimalarial component of A. annua, was present at a level of 0.034% in the dried leaf preparation. A 5% supplement thus afforded about 17 ppm artemisin. When the pure compound was fed at that level for a period of 3 wk, it protected weight gains and significantly reduced lesion scores attributable to E. tenella but not E. acervulina. Other components of A. annua, camphor and 1,8-cineole, at 119 ppm also protected weight gains, and reduced E. tenella lesion scores. Camphor reduced E. acervulina lesions. Artemisinin fed for 4 wk at levels of 2, 8.5, and 17 ppm significantly reduced oocyst output from separate E. acervulina and E. tenella infections and a dual species infection. Pure artemisinin thus appears to be effective against at least two coccidia species when used as a feed additive, and its activity may depend, in part, on the length of time it is administered before a challenge infection.