Abstract Coccidiosis control for breeding and laying chickens requires the development of immunity against multiple Eimeria species. Vaccines approved for use in Europe are precocious (attenuated) strains. Only one precocious vaccine (Paracox® 8) was widely available to breeder and layer producers in the European Union (EU) from 1991 until 2015, with registration in all EU member states except Luxembourg. Recently, 2 new products have been introduced to the market: Hipra Evalon® and a 2 part product originally designated as Huveguard® Start (now designated Mmat) and Huveguard® Plus (now designated NB). Nonattenuated (nonprecocious) vaccines, by contrast, are used in other parts of the world, but are not available in the EU. Three precocious vaccines (Paracox® 8, Evalon® and the combined Huveguard vaccines) were compared to each other and to a nonattenuated vaccine from North America (Coccivac®D2) with respect to precocity and pathogenicity. All 3 precocious vaccines demonstrated significantly reduced oocyst output compared to the nonattenuated breeder/layer coccidiosis vaccine. One vaccine (Paracox® 8) demonstrated oocyst output for all species at 96 h (more precocious), while the other 2 vaccines did not have output until 24 or even 48 h later for individual species (less precocious). When tested at 40X the manufacturer's recommended dose (attempting to simulate the field effect of uneven application), all 3 precocious vaccines demonstrated lower lesion scores and better weight gain over the 7 d post challenge compared to the nonattenuated vaccine. DESCRIPTION OF PROBLEM Coccidiosis, caused by various species of the genus Eimeria, is a ubiquitous problem of floor-reared chickens, including replacement broiler breeders and replacement layer pullets. The common pathogenic species, E. acervulina, E. maxima, E. necatrix, E. tenella, and E. brunetti cause intestinal lesions within the host that can result in reduced weight gain of individual birds, reduced uniformity of flock weights, and mortality . While coccidiosis is often controlled with chemoprophylaxis in broilers, the poultry industry depends upon acquired immunity to protect long-lived breeder and layer flocks against these parasites . Immunity is species- and sometimes strain-specific [3, 4] and is developed via exposure to coccidia, including repeated exposure to low numbers of oocysts  created either by vaccination with live sporulated oocysts (either attenuated or nonattenuated) , or by controlled natural exposure with step-down doses of an anticoccidial drug to control field infection until immunity develops . One method of stimulating immunity is to use an attenuated, live, sporulated oocyst vaccine developed with precocious Eimeria species. Precocious strains are missing one or more secondary schizogony stages compared to the normal life cycle of the parent Eimeria strain, and thus have a shortened pre-patent period and a significantly reduced oocyst output. The development of precocious Eimeria isolates through serial selection of the earliest oocysts shed by infected birds has been described by researchers Jeffers, McDonald, Shirley, and Long in the mid-1970s through mid-1980s [8–15]. The more precocious an isolate is, the less pathology is induced by asexual stages, and the fewer oocysts are shed. The precocious strains are still capable of inducing a protective immune response to challenge with the parent strains under laboratory and field conditions. The immune response to vaccination with live coccidiosis vaccines under field conditions depends upon repeated reinfection through ingestion of sporulated oocysts shed through the feces of the vaccinates into the poultry house environment . Excessive reduction of oocyst output through precocity or reduced sporulation due to dry environmental conditions may hinder this process and delay the onset of immunity [16, 17]. Uneven hatchery or field application or uneven uptake of the fecal oocysts in the field environment can occasionally result in naïve or partially immune birds that can become exposed to wild Eimeria spp. in the house, or to higher doses of oocysts shed by properly vaccinated hatch-mates after the first Eimeria life cycle has been completed . Until 2015, most of the European Union had only one live Eimeria vaccine for the vaccination of replacement birds (Paracox®, MSD Animal Health, Madison, NJ, USA). Paracox® (P) contains precocious strains of Eimeria acervulina, E. maxima (2 strains, CP and MFP), E. mitis, E. praecox, E. tenella, E. necatrix, and E. brunetti, for a total of 8 strains . Two biological companies have recently introduced new live Eimeria vaccines to Europe. Evalon® (E) (Hipra, Amer, Girona, Spain) contains precocious strains of E. acervulina, E. maxima, E. tenella, E. necatrix, and E. brunetti for a total of 5 strains . Huveguard® Start (Huvepharma, Sophia, Bulgaria) contains 4 precocious strains, E. acervulina, E. maxima, E. mitis, and E. tenella for administration at 1 d of age , while Huveguard® Plus is a separate product containing 2 precocious strains E. necatrix and E. brunetti, to be given at 14 d of age . At the time of the study, the Huveguard trade names were not fully established. They have since been registered in some countries as Huveguard® Mmat and Huveguard® NB, respectively. Together the Huveguard® products provide protection for the common challenge species of breeder and layer replacements. In this study, both Huveguard products are given simultaneously (HSP) to inoculate birds with the full complement of Eimeria species for comparison with the other vaccines. The aim of this study was to compare Paracox® (P), Evalon® (E) and Huveguard® Start plus Huveguard® Plus (HSP) with respect to precocity and pathogenicity with a nonattenuated vaccine Coccivac®-D2 (Merck Animal Health, Madison, NJ, USA). Coccivac®-D2 contains nonattenuated strains of E. acervulina, E. mivati, E. maxima, E. tenella, E. necatrix, and E. brunetti for a total of 6 strains . Vaccines P, E, and D2 are all approved for application at 1 d of age. MATERIALS AND METHODS In each of the studies, the guidelines presented in the Guide for the Care and Use of Agricultural Animals in Research and Teaching, 3rd Edition, 2010  were followed. The guidelines are approved by the institutional animal care and use committee (IACUC—Southern Poultry Research, Athens, GA, USA). Part A: Precocity Fifty male Cobb 500 broiler chicks were placed into 5 groups of 10 birds in isolation units. At 3 d of age, the birds in each group were inoculated via oral gavage with 5 times (5×) the manufacturer's recommended dose of one of the 4 test vaccines, P, E, HSP, or D2. One group remained un-inoculated, as negative controls. The authors chose 5× dose to increase the oocyst output and the opportunity to capture oocysts at their earliest shedding point. Pooled fecal samples from each group were collected via hand collection of fresh feces, with clean gloves used between each sample, at 5 24-h intervals beginning at 72 h (72, 96, 120, 144, and 168 h). Fecal samples were subjected to a salt solution for flotation and samples were enumerated using a McMaster counting chamber using techniques described in Holdsworth et al. (2004) . Morphological identification of oocysts was based upon the descriptions by Reid , but for vaccine D2, E. acervulina and E. mivati were counted together as one species. Part B: Pathogenicity Five hundred one-day-old male Cobb 500 broilers were separated into 10 birds per cage × 10 cages per treatment group. Five treatment groups were included: 3 attenuated vaccines (P, E, HSP), one nonattenuated vaccine group (D2), as well as uninoculated controls. At 7 d of age, a start weight (birds weighed as a group per cage) was determined, and then each vaccine group received 40× of the manufacturer's recommended dose of the respective vaccine via gavage, while uninoculated controls were housed in a separate location to avoid cross-contamination. The 40× level was selected to induce pathology without mortality in the nonattenuated vaccine group based upon a prior dose titration. At 7 d postinoculation, the birds from all treatment groups and the negative controls were weighed by cage. One bird per cage was humanely sacrificed by cervical dislocation for lesion scoring. Lesion scoring was done for E. acervulina, E. maxima, E. tenella, E. necatrix, and E. brunetti as described in Johnson and Reid , with E acervulina and E. mivati scored together for vaccine D2. Data was analyzed as described [27, 28]. All statements of statistical significance are based upon probability ≤0.01. RESULTS AND DISCUSSION Part A: Precocity None of the vaccines had detectable oocyst output prior to 96 h postinoculation. Vaccine P was the most precocious: it yielded oocysts at 96 h for all species, and produced higher counts for each species at that time point compared to the other vaccines. Vaccine E yielded 96-h oocyst output for 4 of the 5 species at lower numbers, and vaccine HSP yielded low-level 96-h oocyst output for 2 of the 5 species. The nonattenuated vaccine D2 had low oocyst output at 96 h for E. acervulina and E. maxima, and no oocysts could be detected at 96 h for E. tenella, E. necatrix, or E. brunetti. Vaccine D2 induced the highest overall oocyst output from 96 h through 192 h at a magnitude ranging from 4× (E. necatrix) to 115× (E. tenella) compared to the attenuated vaccines. Vaccine P produced the highest oocyst output of the attenuated vaccines over the same time period. (Table 1) Table 1. Precocity and Fecundity: Oocyst output1 at 96 h and total oocyst output2 from 96 to 192 h. Eimeria species Vaccine P Vaccine E Vaccine HSP Vaccine D2 Oocyst output at 96 h (precocity) E. acervulina 634 100 133 33 E. maxima 133 0 0 67 E. tenella 400 100 0 0 E. necatrix 133 67 33 0 E. brunetti 334 67 0 0 Total oocyst output from 96 to 192 h (fecundity) E. acervulina 1468 567 1733 44,1553 E. maxima 566 501 1033 9739 E. tenella 834 533 234 26,914 E. necatrix 1134 367 366 4102 E. brunetti 601 300 600 13,540 Eimeria species Vaccine P Vaccine E Vaccine HSP Vaccine D2 Oocyst output at 96 h (precocity) E. acervulina 634 100 133 33 E. maxima 133 0 0 67 E. tenella 400 100 0 0 E. necatrix 133 67 33 0 E. brunetti 334 67 0 0 Total oocyst output from 96 to 192 h (fecundity) E. acervulina 1468 567 1733 44,1553 E. maxima 566 501 1033 9739 E. tenella 834 533 234 26,914 E. necatrix 1134 367 366 4102 E. brunetti 601 300 600 13,540 1Oocysts per gram of feces (OPG). 2OPG sum of collections at 96 + 120 + 144 + 168 + 192 h. 3The authors counted E. acervulina and E. mivati together as “E. acervulina” due to the difficulty of morphological distinction. View Large Part 2: Pathogenicity The authors chose a 40× manufacturer's recommended dose in an attempt to simulate what can happen to naïve birds when they are missed by initial vaccination, and then become exposed to oocysts shed following initial vaccination, or subsequent oocyst shedding by vaccinated hatch-mates. The results for lesion scores and average daily gain are presented in Table 2. At a 40× dose, the lesion scores of the nonattenuated vaccine (D2) were significantly higher compared to the controls for all species. Vaccine HSP was not significantly different from vaccine D2 with respect to E. acervulina and E. maxima. Vaccine P and vaccine E lesion scores did not differ significantly from uninoculated controls for any of the 5 Eimeria species. The average daily weight gain during the 7 d postinoculation was significantly less in all of the vaccine groups compared to uninoculated controls. Average daily weight gains for the 3 attenuated vaccines were significantly better than the nonattenuated vaccine D2 group. It is important to note, however, that even at a 40× manufacturer recommended dose, the nonattenuated D2 vaccine produced an average lesion score of 1.7 for E. tenella, with only one bird out of 10 exhibiting a score of 3 on the Johnson and Reid scale . Despite a lack of attenuation, the vaccine is not highly pathogenic. Table 2. Pathogenicity: Average lesion Scores1 and average daily gain (g) following 40X inoculation.2 Uninoculated Eimeria species Control Vaccine P Vaccine E Vaccine HSP Vaccine D23 E. acervulina 0.0b 0.2b 0.3b 0.6a,b 2.6a E. maxima 0.0b 0.5b 0.9b 1.0a,b 2.1a E. tenella 0.0b 0.1b 0.0b 0.0b 1.7a E. necatrix 0.0b 0.0b 0.0b 0.0b 0.6a E. brunetti 0.0b 0.1b 0.1b 0.1b 0.9a Weight gain (g) 0.183a 0.156b 0.136b 0.141b 0.115c Uninoculated Eimeria species Control Vaccine P Vaccine E Vaccine HSP Vaccine D23 E. acervulina 0.0b 0.2b 0.3b 0.6a,b 2.6a E. maxima 0.0b 0.5b 0.9b 1.0a,b 2.1a E. tenella 0.0b 0.1b 0.0b 0.0b 1.7a E. necatrix 0.0b 0.0b 0.0b 0.0b 0.6a E. brunetti 0.0b 0.1b 0.1b 0.1b 0.9a Weight gain (g) 0.183a 0.156b 0.136b 0.141b 0.115c 1Johnson and Reid Lesion Score 2Differing superscripts indicate significant difference between treatment groups (P < 0.01) 3Lesion score represents combined E. acervulina and E. mivati due to the similarity of the lesions in location and appearance. View Large CONCLUSIONS AND APPLICATIONS The results of the study show that there are marked differences between the attenuated vaccines and the nonattenuated vaccine with respect to precocity, fecundity and pathogenicity. The nonattenuated vaccine induced higher lesion scores and induced greater oocyst output compared to the attenuated vaccines. Higher oocyst output increases the opportunity under field conditions for every bird in a flock to find and recycle sporulated vaccinal oocysts, which contributes to a rapid development of immunity . Higher oocyst output, however, can also result in greater pathogenicity when a nonattenuated vaccine completes successive life cycles in a flock, particularly if some of the birds remain naïve following the initial vaccination. The attenuated vaccines themselves demonstrated numerical differences in precocity and fecundity. Of the attenuated strains, vaccine P demonstrated the highest level of precocity, vaccine HSP the lowest level of precocity and vaccine E was intermediate. Greater precocity implies a reduction in pathogenicity due to loss of more secondary schizogony stages. The pathogenicity study demonstrated significantly better weight gain in the face of 40× manufacturer's recommended dose for the attenuated vaccines compared to the nonattenuated D2; however, with respect to lesion scores, vaccine HSP did not differ from vaccine D2. The lower oocyst output of the attenuated strains implies that the onset of immunity under field conditions may be slower, with implications on flock uniformity as well as protection against challenge. Further investigation into the comparative onset of immunity of the 3 attenuated vaccines is needed. Footnotes Primary Audience: Breeder/Layer Pullet Producers, Veterinarians, Biologics Producers REFERENCES AND NOTES 1. McDougald L. R., Fitz-Coy S. H., 2013. 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This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact email@example.com
Journal of Applied Poultry Research – Oxford University Press
Published: Mar 1, 2018
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