J APPL POULT RES 2007. 16:187-191
© 2007 Poultry Science Association
Monitoring the Immune Status of Broilers Against Reoviruses Using Challenge and Serologic Data
J. J. Giambrone*,1,
T. Dormitorio*,
K. Cookson
and
K. Burns
* Department of Poultry Science, Auburn University, AL 36849; Fort Dodge Animal Health, Overland Park, KS 66210; and Lohmann Animal Health International, Gainesville, GA 30501
Correspondence: 1 Corresponding author: giambjj{at}auburn.edu
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SUMMARY
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Reoviruses are an important cause of suboptimum performance in commercial broilers worldwide. Integrators use the enzyme-linked immunosorbent assay against the S1133 antigen for monitoring serum of breeders for indicating pullet vaccine success. However, without correlating serology to reovirus challenge, it is difficult to determine whether titers reflect protective immunity. We developed a broiler challenge test against 2 common reovirus isolates (2408 and S1133) to evaluate the efficacy of reovirus pullet vaccine programs. Two reovirus serologic and challenge studies were undertaken using chicks from broiler integrators from the southeastern United States. Breeder flocks, from which the chicks were obtained, received at least 1 live and 2 inactivated reovirus vaccines during their pullet phase. One-day-old progeny were collected from 6 breeder flocks. At 1 d of age, 20 chicks from each broiler flock were bled, and serum was analyzed for antibodies. At 3 to 4 d of age, 20 progeny per flock were challenged with the 2408 reovirus by intratracheal route. At 10 to 14 d of age, another 20 birds per flock were challenged with the S1133 reovirus by footpad. Twenty birds per flock were used as nonchallenged controls. At 3 wk of age, all birds were killed and weighed. Percentage of protection was calculated for each flock based on the absence of gross lesions. Flocks with at least 50% protection were considered well protected. Most flocks were well protected against both viruses. The percentage of protection correlated with day-old enzyme-linked immunosorbent assay titers. Chicks from younger hens had higher titers and the best protection against challenge. Producers, whose hen flocks were monitored herein, were doing a good job of immunizing pullets against reovirus. They are now using reovirus progeny challenge studies along with breeder antibody titers to determine vaccination success of their pullets.
Key Words: reovirus • vaccine • monitoring • immune • hen • challenge • progeny
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DESCRIPTION OF PROBLEM
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Reoviruses are an important cause of suboptimum performance in broilers, resulting in poor feed conversion, lowered BW, higher mortality, and increased condemnation [1, 2].
Maternal immunity derived from breeder pullet vaccination represents the first line of defense against early virus infections [1, 3, 4]. Pullet vaccination success and immune status for breeder hens is based on serologic profiling of hens during egg production. Another means of determining vaccination success of the hens is to determine the susceptibility of their progeny to reovirus challenge infections. Progeny challenge studies for other poultry pathogens such as infectious bursal disease virus (IBDV) are used by the industry to determine the immune status of their hens and efficacy of their breeder pullet vaccine programs [1, 4]. Infectious bursal disease virus percentage of protection scores, derived from progeny challenge studies, above 50% correlate with good broiler flock performance. No such correlation between serum titers of breeders or broilers and field performance exists.
This study implemented a reovirus progeny challenge program and 1-d-old antibody titers as an alternative to breeder hen titers to determine the efficacy of broiler breeder vaccination programs in flocks around the southeastern United States.
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MATERIALS AND METHODS
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Viruses
Chickens were challenged by intratracheal inoculation with mean embryo lethal dose of the 2408 enteric reovirus [5] or by foot pad (FP) with the S1133 arthritic [6] reovirus isolate.
These isolates were chosen because they are commonly included in reovirus vaccines. The 2408 virus must be given intratracheally during the first 5 d of age to cause disease, whereas the S1133 isolate can be given by FP at any time during the first few weeks to cause disease. These viruses, routes, and ages are accepted by the USDA when determining the efficacy of reovirus vaccines.
Chickens
Broilers were obtained from breeder flocks from Arkansas, Alabama, and Georgia.
Breeder flocks ranged in age from 30 to 50 wk when the eggs were taken and hatched. Two studies were done. Each used chicks from different integrators. For each study, progeny were from 6 breeder flocks. Three breeder flocks received the same reovirus pullet vaccine program. Eighty nonvaccinated broiler chicks were obtained from each broiler flock and brought to Auburn University for testing. In each study, flocks 1 to 3 were hens younger than 40 wk of age when the eggs were taken. In contrast, flocks 4 to 6 were hens older than 40 wk of age when the eggs were taken. All breeders from which the broilers were obtained were vaccinated as pullets with at least 1 live embryo attenuated vaccine s.c. during the first week of age and 2 inactivated reovirus vaccines by s.c. injection. Vaccines were from various commercial US manufacturers and contained S1133 (live) and S1133 + 2408 (killed) viruses. Individual vaccine programs for each breeder flock were known but were not revealed to avoid commercialism.
The objectives of this study were not to determine which vaccine was the most efficacious, rather to determine whether current vaccines and programs for pullets, which are commonly used in the industry, would protect progeny against these 2 homologous reoviruses and if a 1-d-old chick antibody using enzyme-linked immunosorbent assay (ELISA) would correlate with resistance to challenge. The study did not attempt to compare hen titers to 1-d-old chick titers, although it is commonly known that the titers of chicks are roughly 50 to 60% of the hens. In addition, individual broiler titers from the same flock are more correlated to resistance, because 1 broiler flock often comes from 2 to 3 houses of breeders. There is titer variability within these hen houses. Therefore, using hen titers instead of broilers would potentially introduce more variables.
All broilers were fed a commercial broiler starter and given feed and water ad libitum. All were held in modified Horsfall-Bauer isolation units maintained with filtered air under negative pressure according to the rules of the Institutional Animal Care and Use Committee of Auburn University.
Serology
Twenty birds per flock were bled at 1 d of age, and sera were analyzed for an antibody against a reovirus (S1133) using a commercial ELISA kit [6].
Reovirus Challenge
For each study, 80 chicks were obtained from each breeder flock and brought to Auburn for testing. At 3 to 4 d of age, 20 chicks from each flock were challenged intratracheally with the 2408 virus [6]. Twenty birds per flock were also challenged by FP with the S1133 [7] virus from 10 to 14 d, and 20 were nonchallenged controls. Twenty chicks from each flock were killed at 1 d of age for serum collection. Challenge date was variable depending on what day of the week the chicks arrived and how long (1 to 2 d) it took for the chicks to be received by mail. A 1- to 2-d difference in challenge time should not have a significant effect on the results.
Each challenge group was kept in a separate unit. At 21 d of age, all birds were killed, weighed, and examined for gross lesions. Gross lesions for the 2408 isolate were found in the visceral area (mainly liver and spleen), whereas FP lesions induced by S1133 were scored from 0 to 4 based on increasing severity of lesions [8]. No histopathologic studies were done.
Statistical Analysis
Body weight means were compared between groups using a statistical analysis system [9]. Percentage of protection was determined based on the percentage of birds within a flock that did not have gross lesions for the 2408 isolate or FP scores that were less than 2 for the S1133 isolate. Flocks with above 50% protection were considered well protected. This figure was derived from previously published work for IBDV [4]. No statistical comparisons were made between titers and percentage of protection scores.
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RESULTS
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Table 1
shows serologic and challenge data for the first study. Protection against both viruses ranged from 15 to 95%. Average protection against both reoviruses was similar. Older breeder flocks 4, 5, and 6 (more than 40 wk of age) produced chicks with significantly lower ELISA geometric mean antibody titers (GMT) and percentage of protection.
Arthritic lesions [7] seen with the FP inoculation and visceral lesions [5] seen after the intratracheal inoculation were similar to those previously described. Body weights were numerically reduced for all reovirus-challenged flocks compared with the nonchallenged groups in both studies. Body weights for control birds from the older breeder flocks were larger at d 1 as well as at 3 wk. No gross lesions were seen in any noninoculated control bird. Individual GMT at 1 d of age for a broiler flock ranged from a low of 300 to a high of 6,000. Average GMT for the 6 flocks, within a trial, ranged from a low of 1,000 to a high of 4,949. Flocks with GMT of above 2,500 were well protected (above 50%) against both viruses. This figure was drawn from prior IBDV progeny challenge results [3, 4]. Titers of chicks derived from younger hen flocks were higher than those from older flocks.
Table 2 shows serologic and challenge data for the second study. Protection against both viruses ranged from 60 to 85%. The average percentage of protection against both reoviruses was similar. Younger breeder flocks (1, 2, and 3) produced chicks that were better protected against both reoviruses than older hen flocks.
Individual ELISA titers for a broiler flock ranged from a low of 600 to a high of 9,632. Average GMT for the 6 flocks within a trial ranged from a low of 3,619 to a high of 7,602. Flocks with the highest titers generally had the best protection.
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DISCUSSION
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Reoviruses cause economic losses in the US broiler industry [1, 2, 3, 10]. Commercial pullets in the United States receive combinations of live and inactivated vaccines containing the 2408, 1703, C08, and S1133 viruses.
Reovirus challenge studies using broiler progeny derived from breeders in the southeastern United States were performed and correlated with 1-d-old chick titers. Results were similar to IBDV progeny challenge studies [4], which showed that producers were doing a good job of hyperimmunizing most breeder flocks against IBDV. This conclusion was reached because all broiler flocks, except flock 6 in trial 1, had percentage of protection scores of 30 or better. As expected, protection against both reoviruses was similar, because both isolates were present in the killed (S1133 + 2408) vaccines, which the breeders received, and both isolates are in the same serologic subtype [3]. Although no statistical comparisons were done comparing antibody titers and percentage of protection score, flocks with the highest 1-d-old ELISA titers generally had the highest percentage of protection scores.
As with prior IBDV data [4], older breeder flocks produce chicks with lower titers and less protection. Therefore, integrators with flocks over 40 wk of age that are producing chicks with day-of-age ELISA titers near 1,000 and have progeny with less than 50% protection should provide these breeder flocks another inactivated reovirus vaccine. In the long term, efforts to enhance breeder reovirus titer levels and duration of immunity are the most cost-effective way to reduce reovirus-related losses in the broiler progeny.
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CONCLUSIONS AND APPLICATIONS
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- Progeny challenge results for reovirus can be used as a successful adjunct to ELISA testing of hens to determine the success of vaccination of the breeder pullets.
- As hens age, they pass less antibody and protection to their progeny.
- Low 1-d-old chick ELISA titers (1,000) will not provide adequate resistance to challenge infection.
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ACKNOWLEDGMENTS
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We thank Fort Dodge Animal Health and Lohmann Animal Health Inc. for sending the day-old chicks and helping with the cost of the studies. We also thank the Alabama Agricultural Experiment Station for their financial support and integrators around the United States for supplying the day-old birds.
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REFERENCES AND NOTES
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- Giambrone, J. J., and R. P. Clay. 1986. Evaluation of broiler breeder pullet vaccination programs for preventing clinical reovirus infections in the progeny. Poult. Sci. 65:457–461.[ISI][Medline]
- Giambrone, J. J., and W. Solano. 1988. Serologic comparison of reovirus isolates using virus neutralization and enzyme linked immunosorbent assay. Avian Dis. 32:678–680.[ISI][Medline]
- Cookson, K. C., J. J. Giambrone, and J. H. Rodenberg. 2005. A reovirus progeny challenge study comparing breeder flocks on two different IBDV/reovirus programs. Poult. Sci. 84(Suppl.1):112. (Abstr.)
- Giambrone, J. J., T. V. Dormitorio, T. Brown, and K. Takeshita. 1999. Monitoring of the immune status of broiler breeders against infectious bursal disease virus using progeny challenge and serological data. J. Appl. Poult. Res. 8:362–367.[Abstract/Free Full Text]
- Rosenberger, J. K., F. J. Sterner, K. P. Botts, K. P. Lee, and A. Margolin. 1989. In vitro and in vivo characterization of avian reoviruses. I. Pathogenicity and antigenic relatedness of several avian reovirus isolates. Avian Dis. 33:535–544.[ISI][Medline]
- IDEXX Inc., Westbrook, ME.
- Van der Heide, L., M. Kalbac, and W. C. Hall. 1976. Infection tenosynovitis (viral arthritis): Influence of maternal antibodies on the development of tenosynovitis lesions after experimental infection by day-old chickens with tenosynovitis virus. Avian Dis. 20:641–648.[ISI][Medline]
- Van der Heide, L., M. Kalbac, and M. Brustolon. 1983. Development of an attenuated apathogenic reovirus vaccine against viral arthritis. Avian Dis. 27:698–706.[ISI][Medline]
- Zar, J. H. 1984. The analysis of variance. Multiple sample hypothesis. Page 162 in Biostatistical Analysis. Prentice-Hall, Englewood Cliffs, NJ.
- Guo, Z., J. J. Giambrone, T. V. Dormitorio, and Wu Hongzhuan. 2003. Influence of a reovirus antibody complex vaccine on the efficacy of Marek’s disease vaccine administered in ovo. Avian Dis. 47:1362–1368.[ISI][Medline]
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SUMMARY
DESCRIPTION OF PROBLEM
