Evaluation of field and laboratory protocols used to detect avian influenza viruses in wild aquatic birds

Careful selection and observance of standard field and laboratory protocols are critical for successful detection and characterization of avian influenza viruses (AIV) from wild birds. Cloacal swabs were collected from hunter-killed or nesting waterfowl and shorebirds from wildlife refuges in Alabama, Georgia, and Florida during 2006 to 2008. Swab samples were inoculated into embryonated eggs followed by hemagglutination (HA) test to determine the presence of hemagglutinating agents. Antigen capture-ELISA (AC-ELISA) and real-time reverse transcription-PCR (RRT-PCR) were used to detect AIV from both allantoic fluids (AF) and swab specimens of HA-positive samples. Hemagglutination inhibition test was used to detect Newcastle disease virus, another hemagglutinating virus common in wild birds. The HA-positive AF were sent to the National Veterinary Services Laboratory for subtyping of the isolates. Out of 825 samples tested, 19 AIV and 3 avian paramyxovirus subtypes were identified by the National Veterinary Services Laboratory. Without egg passage, AC-ELISA did not detect virus, whereas matrix gene of 13 AIV were detected using RRT-PCR. When testing was done on AF, 14 were positive for influenza A by AC-ELISA and 20 by RRT-PCR. Antigen capture-ELISA did not detect influenza A when the HA titer was lower than 125, whereas RRT-PCR detected AIV from AF with HA titer as low as 4. The highest isolation rate was from Florida, where out of 109 samples analyzed, 14 AIV were detected by RRT-PCR from AF. Real-time reverse transcription-PCR was more sensitive, specific, and cost-effective than AC-ELISA. However, to avoid false-negative results, testing should be performed on AF and not directly from cloacal swabs. Our procedures to detect AIV directly from cloacal swabs need further optimization for improved sensitivity.

Detection and characterization of avian influenza and other avian paramyxoviruses from wild waterfowl in parts of the southeastern United States

Cloacal swabs were taken from migratory hunter-killed, nonmigratory, nesting waterfowl and migratory shorebirds from wildlife refuges in Alabama, Georgia, and Florida during 2006 to 2008. Samples were processed in embryonated eggs followed by hemagglutination (HA), Directigen, and real-time reverse transcription-PCR tests. Sequence analysis of the hemagglutinin (H) gene of the H10N7 Alabama isolate revealed that it was closely related (98%) to recent isolates from Delaware and Canada, but only 90% related to an H10N7 isolated 30 yr ago. Four isolates had 94 to 97% similarity to published H1N1 isolates including one from swine. No H5 or H7 isolates were found. One sample was highly pathogenic in embryos, produced a high HA titer, and was positive for both avian influenza (AIV) and Newcastle disease virus or avian paramyxovirus (APMV)-1. In recent (2008) sampling, more (14%) AIV, APMV, or both were isolated than in 2006 to 2007 (1% isolation rate). The higher isolation rate during 2008 may be attributed to optimized sample collection, storage in dry ice, new egg incubator, healthier eggs, time or habitat for isolation, species sampled, migratory status of birds, and more experience with detection procedures. An additional egg passage resulted in increased viral titer; however, no HA-negative samples became HA positive. The chance of transmission of APMV or low-nonpathogenic AIV from wild waterfowl to commercial poultry is possible. However, the chance of transmission of H5 or H7 AIV isolates from waterfowl to commercial farms in Alabama, Georgia, or Florida is unlikely. Therefore, continual testing of these birds is justified to ensure that H5 or H7 AIV are not transmitted to commercial poultry.

Molecular and phenotypic characterization of infectious bursal disease virus isolates

Two infectious bursal disease viruses (IBDVs 1174 and V1) were isolated from IBDV-vaccinated broiler flocks in California and Georgia. These flocks had a history of subclinical immunosuppression. These isolates are commonly used in IBDV progeny challenge studies at Auburn, AL, as well as vaccine manufacturer's vaccine efficacy studies, because they come from populated poultry-producing states, and are requested by poultry veterinarians from those states. Nested polymerase chain reaction (PCR) generated viral genome products for sequencing. A 491-bp segment from the VP2 gene, covering the hypervariable region, from each isolate was analyzed and compared with previously sequenced isolates. Sequence analysis showed that they were more closely related to the Delaware (Del) E antigenic variant than they are to the Animal Health Plant Inspection Service (APHIS) standard, both at the nucleotide level (96%, 97%) and at the amino acid level (94%, 97%). Both isolates had the glutamine to lysine shift in amino acid 249 which has been reported to be critical in binding the virus neutralizing Mab B69. Phenotypic studies showed that both isolates produced rapid atrophy of the bursae and weight loss, without the edematous bursal phase, in 2-wk-old commercial broilers having antibody against IBDV. A progeny challenge study showed both isolates produced more atrophy of the bursae (less percentage of protection) than the Del E isolate. Molecular and phenotypic data of these important IBDV isolates help in the improved detection and control of this continually changing and important viral pathogen of chickens.

Transmissible proventriculitis in broilers

This article reviews transmissible proventriculitis in poultry from 1971 to 2006. The disease is important in commercial broilers worldwide, resulting in reduced profits. The aetiology of this disease is unknown and different clinical presentations often result in a confused or complicated diagnosis. The lesion of enlarged proventriculus is often referred to as proventriculitis. However, the term proventriculitis can only be used correctly when there is microscopic evidence of inflammation of the proventriculus glands. Infectious and non-infectious causes of proventriculitis, with major emphasis on the infectious or transmissible causes, are reviewed.

Yeast-derived sigma C protein-induced immunity against avian reovirus

Avian reoviruses (ARVs) can result in disease and economic losses in the poultry industry. Vaccines against ARV may not provide full protection and can cause adverse reactions. The coding sequence of the sigma C protein from strain S1133 of avian reovirus was expressed in Schizasaccharomyces pombe. Sigma C protein expression was demonstrated by Western blotting, and the protein was evaluated for its ability to protect specific-pathogen-free (SPF) chickens against challenge with the virulent S1133 strain. Serologic and challenge-infection data showed the efficacy of the recombinant vaccine administered orally each week for 3 consecutive wk. Sigma C protein induced antibody, as determined by enzyme-linked immunosorbent assay. Percentage (%) protection induced by the low dose (125 microg purified yeast-expressed sigma C protein/chicken) or the high dose (250 microg purified yeast-expressed sigma C protein/chicken) was 64 and 91, respectively. The commercial vaccine administered once or twice provided 82% protection. Results supported the feasibility of a plant-derived vaccine for use in poultry immunization schemes.

Expression of immunogenic VP2 protein of infectious bursal disease virus in Arabidopsis thaliana

VP2 protein is the major host-protective immunogen of infectious bursal disease virus (IBDV) of chickens. Transgenic lines of Arabidopsisthaliana expressing recombinant VP2 were developed. The VP2 gene of an IBDV antigenic variant E strain was isolated, amplified by RT-PCR and introduced into a plant expression vector, pE1857, having a strong promoter for plant expression. A resulting construct with a Bar gene cassette for bialaphos selection in plant (rpE-VP2) was introduced into Agrobacterium tumefaciensby electroporation. Agrobacterium containing the rpE-VP2 construct was used to transform Ar. thaliana and transgenic plants were selected using bialaphos. The presence of VP2 transgene in plants was confirmed by PCR and Southern blot analysis and its expression was confirmed by RT-PCR. Western blot analysis and antigen-capture ELISA assay using monoclonal anti-VP2 were used to determine the expression of VP2 protein in transgenic plants. The level of VP2 protein in the leaf extracts of selected transgenic plants varied from 0.5% to 4.8% of the total soluble protein. Recombinant VP2 protein produced in plants induced antibody response against IBDV in orally-fed chickens.

Safety and efficacy of an experimental reovirus vaccine for in ovo administration

A commercial reovirus vaccine alone or experimental reovirus vaccine plus antibody complex were inoculated into 18-day-old specific pathogen free (SPF) broiler embryos at 0.1 of the recommended chick dose. The following groups were used: group 1A was not vaccinated or challenged; group 1B was not vaccinated, but was challenged with virulent reovirus; group 2 received the vaccine complexed with 1/4 dilution of antiserum; group 3 received the vaccine with 1/8 dilution of antiserum; group 4 received the vaccine with 1/16 dilution of antiserum, and group 5 received vaccine alone. At 1, 3, 6, 9, and 12 days of age, serum was collected and antibody against avian reovirus was analyzed by enzyme-linked immunosorbent assay (ELISA). At the same times, spleens were collected and vaccine virus detected by inoculating chicken embryo fibroblasts (CEFs) and examining for cytopathic effect. At 15 days of age, chickens in groups 2-5 were challenged with reovirus. At 22 days of age, birds were euthanatized and weighed. Efficacy of the vaccines was based on safety, percent protection, and antibody response. In ovo vaccination with the commercial or experimental vaccines did not adversely affect hatchability of SPF chickens. The vaccine complexed with antibody resulted in significantly less posthatch mortality (3.7%) when compared to mortality of chickens that received vaccine alone (17%). Both vaccine virus recovery and antibody response were delayed at least 3 days in birds receiving the experimental vaccines. In evo administration of reovirus antibody complex vaccines provided at least 70% protection. The experimental reovirus-antibody complex vaccines were safe and efficacious when given in ovo to SPF broiler embryos.

Effect of In Ovo Administered Reovirus Vaccines on Immune Responses of Specific-Pathogen-Free Chickens

We investigated the effect of in ovo administered reovirus vaccines on the immune responses of specific-pathogen-free chickens. T-cell mitogenic responses to concanavalin A were numerically lower at 9 and 12 days of age and significantly lower at 6 days of age in birds vaccinated with a commercial reovirus vaccine compared with unvaccinated birds or birds vaccinated with an experimental reovirus-antibody complex vaccine. There were no significant differences in proportions of subpopulations of helper (CD4+CD8-) or cytotoxic (CD4-CD8+) T cells except at 12 days of age, when the percentages of CD4-CD8+ cells in the two vaccinated groups were statistically higher than in the nonvaccinated group. B-cell populations were not different among vaccine groups except at 9 days of age, when the vaccinated groups had the highest level of B cells. This commercial reovirus vaccine should not be given in ovo to embryos having little or no maternal antibody, otherwise immunosuppression may occur in the chicks. The addition of the antibody complex to the vaccine prevented this T-cell immunosuppression.

Influence of a Reovirus-Antibody Complex Vaccine on Efficacy of Marek's Disease Vaccine Administered In Ovo

Two experiments determined the influence of an experimental reovirus-antibody complex vaccine on Mareks disease virus (MDV) vaccine when used in ovo. Designs were the same except that specific-pathogen-free (SPF) broiler eggs were used in Experiment 1 and commercial broiler eggs with maternal antibodies against reovirus were used in Experiment 2. At 18 days of incubation, embryos were separated into four groups and inoculated with either diluent, MDV vaccine, reovirus-antibody complex vaccine, or a combination of reovirus-antibody complex and MDV vaccine. At 5 days of age, half the chickens in each group were challenged with MDV. At 7 wk old, all were euthanatized, weighed, and examined. At 7 days of age, remaining chickens in each group were challenged with reovirus. At 21 days old, chickens were euthanatized and weighed. No vaccine adversely affected hatchability or posthatch mortality in SPF or commercial chickens. There were no significant differences in protection against reovirus challenge when vaccines were used separately or in combination, and lesion scores were nearly identical in all vaccinated groups in both experiments. However, percentage of protection against reovirus was lower in Experiment 2, indicating an adverse effect of maternal immunity on efficacy of the reovirus vaccine. There were no significant differences in protection against MDV when the vaccines were used separately or combined. Severity of MDV lesions was nearly identical in all vaccinated groups in both experiments. However, the combination of vaccines gave numerically lower protection against MDV than MDV vaccine alone. Use of a larger number of birds, as in field conditions, may result in statistically lower protection for the vaccine combination. Large field trials are needed to determine the potential of the reovirus-antibody complex vaccine.

Detection of infectious bursal disease vaccine viruses in lymphoid tissues after in ovo vaccination of specific-pathogen-free embryos

Control of infectious bursal disease virus (IBDV) by vaccination is important for poultry production worldwide. Two vaccines, an IBDV immune complex (ICX) vaccine and an IBDV-2512 vaccine, were administered at 100 mean embryo infectious dose to specific-pathogen-free 18-day-old broiler embryos in ovo. At 3, 6, 9, 15, and 21 days post in ovo vaccination (PIOV), bursa, spleen, and thymus tissues were collected and analyzed for virus protein by antigen capture chemiluminescent enzyme-linked immunosorbent assay (ELISA). Chicks were bled and antibody titers were determined by the antibody ELISA. At 21 days PIOV, chickens were challenged with a 1:500 dilution of an antigenic standard IBDV strain. At 28 days PIOV, birds were euthanatized and bursa weight:body weight ratios were determined. Embryos vaccinated with either vaccine exhibited 92% hatchability; however, within 1 wk of hatch, birds vaccinated with IBDV-2512 showed 56% mortality, whereas those given IBDV-ICX had only 3.2% mortality. Both IBDV-ICX and IBDV-2512 vaccines were detected in bursa, spleen, and thymus at day 3 PIOV. A 5-day delay in virus replication was observed with IBDV-ICX vaccine. By day 15 PIOV, the IBDV-ICX was no longer detectable in the bursa and spleen but persisted in the thymus. The IBDV-2512 vaccine persisted in the spleen and thymus on day 15 PIOV. By day 21 PIOV, neither vaccine virus was detected in any lymphoid organ. This assay can be useful in the early detection of vaccine virus in the tissues of chickens vaccinated via the in ovo route. Both vaccines caused bursal atrophy at all times PIOV. The IBDV-2512 caused splenomegaly at day 6 PIOV, whereas splenomegaly was not seen in IBDV-ICX-vaccinated birds until day 9 PIOV. Thymus atrophy was observed in IBDV-2512-vaccinated chicks from day 3 PIOV, whereas this occurred on day 15 PIOV in IBDV-ICX-vaccinated birds. Bursa weight: body weight ratios in IBDV-ICX-vaccinated unchallenged and vaccinated challenged birds were not different (P < 0.05).

Safety and efficacy of in ovo administration of infectious bursal disease viral vaccines

In ovo vaccination against Marek's disease virus and infectious bursal disease virus (IBDV) in commercial broilers in the United States is common. Little information exists as to the safety and efficacy of intermediate IBDV vaccines given in ovo. Experiments were initiated to determine the safety and efficacy of three commercially available live intermediate IBDV vaccines by in ovo route. Commonly used vaccines were given at 18 days of embryonation to specific-pathogen-free (SPF) broiler embryos (first and second study) or to commercial broiler embryos (third study) that had maternal antibody against IBDV. When any of the antigenic standard vaccines was given at full dose to SPF embryos, embryonic and 3-wk posthatch mortality increased. Vaccines also caused significant microscopic lesions in the bursa of Fabricius at 1 and 3 wk posthatch. In contrast, there was no adverse effect on embryonic or posthatch mortality when vaccines were given at half dose to SPF or commercial broiler embryos. However, significant microscopic lesions were evident at 1 and 3 wk posthatch in the bursae of SPF embryos given the vaccines at half dose. When vaccines were given at half dose to commercial broiler embryos, lesions were evident at 1 but not 3 wk of age. In the third study, in ovo vaccinated chickens were challenged with either a virulent standard (APHIS) or antigenic variant (variant E) IBDV virus at 3 wk of age. All vaccines produced at least 87% protection against the standard and 60% protection against the variant challenge IBDV, as measured by bursal weight to body weight ratios. This study was the first to examine the safety and efficacy of the three commonly used intermediate IBDV vaccines given in ovo in protection against standard and antigenic variant IBDV challenge viruses.

The use of monoclonal antibody probes for the detection of avian reovirus antigens

Two monoclonal antibodies (MAb), E9 and H3, prepared against avian reovirus (ARV) S1133, were used in an immuno-dot assay to detect ARV antigens from cell culture and from tendon tissue samples of chickens. The limit of viral antigens detected was 8 ng using both MAb probes. The probes detected 10 ARV isolates representing at least two serotypes or pathotypes. The results indicated that these probes had broad specificity. The probes, however, did not cross-react with viral antigens prepared from six unrelated avian viruses. The ARV antigens in tendon tissue samples were detected by both probes, and it is possible, therefore, to use either of the two MAb probes for detection of ARV infections.

In situ hybridization, immunohistochemistry, and in situ reverse transcription-polymerase chain reaction for detection of infectious bursal disease virus

Development of molecular techniques for the detection of infectious bursal disease virus (IBCV) is an important area of research. An in situ hybridization (ISH) test was developed with a 491-bp cDNA fragment derived from the VP2 gene of IBDV. The fragment was amplified and simultaneously labeled with incorporation of digoxigenin-11-dUTP in a nested polymerase chain reaction (PCR) assay. The resulting digoxigenin-labeled 491-bp nested PCR product was used as probe for ISH to detect and localize IBDV RNA in formalin-fixed, paraffin-embedded bursae of Fabricius from chickens both experimentally infected as well as commercially reared. Bursae from six clinically ill commercial broilers suspected to be IBDV infected were examined by ISH and immunohistochemistry. In two samples, IBDV infection was detected by both ISH and immunohistochemistry, whereas in the other two histologically normal bursae, IBDV was detected only by ISH. Two commercial chickens with atrophied bursae were negative by both ISH and immunohistochemistry. No positive IBDV stained cells were in RNase treated sections from infected birds, uninfected chickens, or reovirus-infected chickens. The ISH test developed herein resulted in important modifications, which makes it superior to other previously published procedures. We also described a direct in situ reverse transcription-polymerase chain reaction method for the amplification and detection of IBDV genome in formalin fixed, paraffin-embedded bursae of Fabricius with a single primer pair with direct incorporation of digoxigenin-11-deoxyuraciltriphosphate (dUTP) into the amplicon. Both molecular tests with their important modifications represent improved detection of IBDV.

Sequence analysis of the VP2 hypervariable region of nine infectious bursal disease virus isolates from mainland China

The VP2 hypervariable region of infectious bursal disease virus (IBDV) from nine Mainland Chinese strains was amplified by reverse transcriptase/nested polymerase chain reaction and cloned into pGEM-T vector. The nine isolates, which were from the center (HN3), the north (Bj-1, B2/28, HD96), the east (JS-18 and AH-2), the northeast (D11-2, C4-2), and the west (Ts) of China, were sequenced and compared with each other and with six reference IBDV sequences. Clustering analysis separated the nine isolate into two groups. The six virulent isolates, propagated in bursae, formed the first group. They revealed only one to three amino acid changes from the very virulent (vv) European and Japanese isolates, suggesting that they might have the same origin as European and Japanese vvIBDV strains. On the basis of their distinct geographic origins, extensive dissemination of vvIBDV in China was indicated. (The other three chicken embryo fibroblast cell cultured isolates with mild pathogenicity were placed in the second group.) Their sequences correlated closely with those of the culture-adapted strains (Cu-1 (4) and Cj-801). None of the nine isolates showed very close sequence relationship with the antigenic variant strains from the USA. Although antigenic variants have been reported in China, the reverse transcriptase/polymerase chain reaction-restriction endonuclease analyses of the nine viruses tested herein were not similar to any U.S.A. variant strains on the basis of computer software analysis. Our results and conclusions agree with a previous molecular study of IBDV isolates from the south of China.

Simplified sample processing combined with a sensitive nested polymerase chain reaction assay for detection of infectious bursal disease virus in the bursa of Fabricus

A rapid and sensitive protocol for the detection and amplification of infectious bursal disease virus (IBDV) RNA in the bursa of Fabricius was developed. By digestion with proteinase K and subsequent extraction with phenol and chloroform, IBDV RNA was efficiently released from a single bursa. IBDV RNA extraction time was shortened to 4 hr, compared with 24 hr with the traditional method, and only one bursa was needed instead of five. This more simplified procedure resulted in a significant reduction in costs due to less labor and the reduction in expensive chemicals and reagents. Four primers were selected from the sequence of a hypervariable region in VP2 genes. For the amplification of genomic IBDV RNA, the product (643 bp) of reverse transcriptase-polymerase chain reaction (RT-PCR) was reamplified and double checked by a nested PCR amplifying a 491-bp cDNA. The sensitivity of nested PCR was at least 100 times greater than RT-PCR as determined by dilution of the bursal homogenate. The fidelity of the nested PCR product was confirmed by Southern blotting, demonstrating specificity to the VP2 gene of IBDV. The simplified sample processing, shortened procedure time, and technical ease of this nested PCR render it more suitable for implementation in routine RT-PCR with restriction fragment length polymorphism testing for the detection and differentiation of IBDV RNA, especially for studies of IBDV infections of individual chickens.

Molecular characterization of avian reoviruses using nested PCR and nucleotide sequence analysis

A nested polymerase chain reaction (PCR) with subsequent nucleotide sequence analysis identified and differentiated avian reoviruses (ARVs). PCR products amplified from the S1 gene segment of ARV of USA isolates were 738 and 342 bp, respectively. PCR products were conformed by Southern and dot blot hybridizations. The amplified cDNA fragments were cloned into the pUC18 vector and subjected to DNA sequencing. The nucleotide and deduced amino acid sequences of four USA (S1133, 1733, 2408, and CO8) and two Australian isolates (RAM-1 and SOM-4) were compared. Results of paired difference analysis and a predicted dendrogram revealed that USA isolates were closely related, but different from, Australian isolates. The deduced amino acid sequences of the N-terminal region of ARV sigma C showed a heptapeptide repeat of hydrophobic residues in all ARV isolates.

Characterization of a nonradioactive cloned cDNA probe for detecting avian reoviruses

Avian reoviruses (ARVs) cause important losses in the poultry industry. Improved tests are needed for diagnosis of ARV infections. A cDNA library was prepared from the S1133 isolate of ARV. EcoRI-adaptored cDNA molecules were ligated into the plasmid pUC19 and used to transform Escherichia coli strain DH5 alpha MCR. One cDNA clone was selected and designated HJp1. The HJp1 was labeled by random priming with digoxigenin-dUTP. This cDNA probe hybridized with the S1 gene fragment of the ARV S1133 strain in northern blot hybridization. The probe detected ARV isolates in dot-blot hybridization assays. The probe did not cross-hybridize with nucleic acids extracted from mock-infected chicken embryo fibroblast cells or unrelated avian viruses. Probe HJp1 detected as little as 0.78 ng of ARV RNA.

Comparison of several enzymes between normal physeal and tibial dyschondroplastic cartilage of broiler chickens

Normal physeal and dyschondroplastic cartilage of broiler chickens was examined for six enzymes by isoelectric focusing in thin-layer polyacrylamide slab gels. Acid phosphatase (ACP), esterase (EST), malate dehydrogenase (MDH), and peroxidase (PRX) were present in the normal physeal cartilage but not in the dyschondroplastic cartilage. Staining intensity of glucose-6-phosphate isomerase (GPI) and triose-phosphate isomerase (TPI) was reduced in the dyschondroplastic cartilage compared with that of the physeal cartilage. Differences in the presence of these enzymes possibly demonstrated their roles in processes of bone formation, cartilage resorption, and calcification. ACP could be involved in calcification. Lack of EST and PRX may be related to the failure of vascular invasion in dyschondroplastic cartilage of afflicted birds. A deficiency of MDH and reduced GPI and TPI in dyschondroplastic cartilage may reflect a reduction in the activity of energetic metabolism, causing the dissipation of energy and necrotic cells.

In situ detection of reovirus in formalin-fixed, paraffin-embedded chicken tissues using a digoxigenin-labeled cDNA probe

An in situ hybridization (ISH) technique using a digoxigenin (DIG)-labeled cDNA probe detected avian reovirus (ARV) RNA in formalin-fixed, paraffin-embedded chicken tissues. Tissues were collected 3 and 10 days following inoculation with the R-2 or the S1133 strain of ARV. The cDNA clone HJp1, located on the S1 gene segment of the ARV S1133 strain, was used to prepare a nonradioactive probe. The ISH assay localized ARV RNA in infected tissues including heart, liver, intestine, pancreas, and tendon. No positive-stained cells occurred in sections from uninfected chickens.

Amplification, cloning and sequencing of the sigmaC-encoded gene of avian reovirus

The sigmaC-encoding cDNA of avian reovirus (ARV) 1733 strain was amplified, cloned and sequenced using double nested polymerase chain reaction (PCR). The ARV sigmaC protein is a minor component of the outer capsid that induces type-specific neutralization antibodies. Four overlapping sigmaC-encoding cDNA fragments were obtained. Together, the four fragments represented the whole coding sequence. The nucleotide and deduced amino acid sequences of sigmaC-encoded gene of U.S. (S1133 and 1733) and Australian isolates (RAM-1 and SOM-4) were compared. The U.S. isolates were closely related, but different from Australian isolates. The degree of differences between the U.S. and Australian isolates was over 44.89% at both the nucleotide and deduced amino acid levels and suggested that the virus is evolving separately in different continents. The deduced amino acid sequences of ARV sigmaC indicated a heptapeptide repeat in the N-terminal region of ARV sigmaC existed in all ARVs. The results suggested that ARV sigmaC is structurally related to mammalian reovirus (MRV) sigma1.

Sequence comparisons of the variable VP2 region of eight infectious bursal disease virus isolates

The VP2 gene is part of the genomic segment A of infectious bursal disease virus (IBDV). It has been identified as the major host-protective antigen of IBDV and is known to contain conformationally dependent protective epitopes. A 643-base pair segment covering the hypervariable region of this gene from three recent serologic variant IBDV isolates from the southeastern United States, two variants from the Delmarva Peninsula, and three serologic standard viruses were amplified and sequenced using the reverse transcription polymerase chain reaction and cycle sequencing techniques. This was done to determine the molecular similarity among isolates that differ antigenically and pathologically. Sequence analysis suggested that the Arkansas (Ark) and Mississippi (Miss) isolates evolved closely and separately from the Delmarva variants (GLS and DELE), in contrast to the other southeastern variant Georgia (Ga), which is more closely related (98.32%) to Delaware E (DELE). All variants, except for Miss, underwent a shift in amino acid number 222 from proline to threonine. The sequence of Univax BD virus, a commercially available intermediate vaccine, was markedly different, evolving from a separate lineage than the others. Restriction enzyme sites could differentiate most isolates. Except for Miss, variants do not have EcoRII site at the larger hydrophilic domain. All variants lost their HaeIII, StuI, and StyI cutting sites with a change in base number 856. The TaqI site is in DELE, whereas the SpeI site is absent in the standard vaccine viruses. The SWASASGS heptapeptide is conserved in all virulent viruses, including APHIS, but not in the attenuated (Univax BD and Bursa Vac 3) and published (D78 and PBG98) vaccines.

Promoter and transcription of type X collagen gene in broiler chickens with tibial dyschondroplasia

Type X collagen is produced exclusively in hypertrophic chondrocytes of the growth plate of the proximal tibiotarsus and is believed to play an important role during normal development from chondrogenesis to osteogenesis. Chondrocytes of chickens with tibial dyschondroplasia (TD) fail to attain full hypertrophy and the amount of type X collagen, being a marker of hypertrophy, is likely to be reduced. It is not clear whether transcriptional regulation is functional for expression of the type X collagen gene in TD birds. Nucleotide sequence of the type X collagen gene promoter was determined by sequencing PCR-based DNA clones. Nucleotide identity of this fragment between the normal and TD carriers was 97.6%. Both normal and TD birds were similar in a putative transcription start site, the site of TATAA box, and neither had a CCAAT box. However, there were two gaps in TD carriers, four gaps in normals, and five nucleotide substitution sites. By rapid amplification of cDNA ends by PCR (RACE-PCR), transcription of the gene was assessed using total RNA and mRNA from both normal chondrocytes and TD lesions at 3 and 4 wk of age. The RACE-PCR product for type X collagen mRNA was detectable in both normal and TD birds at two stages. No difference was found between them. This result does not support the hypothesis that transcriptional regulation of type X collagen gene is important in TD development of chickens. Variations in the promoter region did not affect transcription of type X collagen gene in TD carrier chickens.

Production and characterization of monoclonal antibodies against avian reovirus strain S1133

Monoclonal antibodies (MAbs) were produced against the avian reovirus strain S1133. MAbs were isotyped and used to develop diagnostic tests. Splenocytes from immunized mice were screened by enzyme-linked immunosorbent assay (ELISA). Two hybridomas secreted MAbs against avian reovirus S1133. One MAb secreted IgG1 and the other secreted IgG2a. All MAb light chains were kappa Specificity of MAbs was tested against four avian reovirus strains: S1133, 1733, CO8, and 2408. Strains S1133, 1733, and 2408 viruses were in the same subtype; the CO8 virus belonged to a different subtype. The MAbs reacted with all reovirus strains by ELISA, dot blot, immunofluorescence assay, and immunoblotting. No MAb had neutralizing activity against the tested reoviruses. Immunoblot analysis showed the one MAb bound to protein sigma A with molecular weight of 39,000 Daltons for all reovirus strains. Another MAb bound to the protein sigma C with an approximate molecular mass of 32,000 Daltons. An indirect immunoperoxidase (IP) procedure was developed using a MAb to detect reovirus in formalin-fixed, paraffin-embedded tissues from infected chickens and chicken embryo fibroblast cell cultures. The IP test was simple, fast, and economical and enabled simultaneous evaluation of viral antigen-producing cells with tissue pathologic changes confirming that the reovirus caused the lesions.

Random amplified polymorphic DNA comparisons among broiler lines selected for incidence of tibial dyschondroplasia

Lines selected for high (H) and low (L) incidence of tibial dyschondroplasia (TD) for eight generations and a randombred control (C) line of broiler chickens were fingerprinted by random amplification of genomic DNA mixed from 20 individuals of each line with 20 oligonucleotide primers. Among these 20 primers, 15 could distinguish the H from the L line, 14 the H from the C line, and 13 the L from the C line. Band sharing (BS), on the average over 20 primers, was .7 for the H vs L comparison and .8 for both H vs C and L vs C comparisons. The levels of BS calculated from individuals was .6 between the H and L line, .7 between the H and C line, and .7 between the L and C line. The ranking of BS values obtained from individual DNA samples was consistent with that obtained from the mixed DNA samples. Genomic distance between divergently selected lines (H vs L) was larger than that between the divergently selected lines and randombred line (H vs C and L vs C). Individual variation within lines was detected in spite of eight generations of selection. Results showed that eight generations of divergent selection for TD incidence in broiler chickens had resulted in genetic variation among lines. The procedure of random amplified polymorphic DNA assay using mixed DNA samples could be used to evaluate genetic distance among lines of chickens.

Detection of genetic variations in serotype I isolates of infectious bursal disease virus using polymerase chain reaction and restriction endonuclease analysis

Reverse transcription with polymerase chain reaction (PCR) followed by restriction endonuclease analysis detected genetic variations among serotype I isolates of infectious bursal disease virus (IBDV). Using a set of synthetic primers derived from the large genome segment of APHIS-IBDV, the hypervariable region (AccI-SpeI fragment) located in the VP2 gene was amplified. With all strains, a cDNA fragment of approximately 643 bp was amplified, indicating that there were no apparent deletions or insertions in this region among isolates. Fragments amplified from 9 isolates were digested with 14 restriction enzymes. Restriction fragment profiles generated by restriction enzymes NaeI, StuI, TaqI, and SacI, showed genetic variations among isolates. This study provided a simple and sensitive method for detection of genetic variations among isolates that are closely related serologically and could not be differentiated using current serologic methods.

Correlation of circulating antibody and cellular immunity with resistance against Cryptosporidium baileyi in broiler chickens

The correlation of circulating antibody and cell-mediated immunity (CMI) with resistance to Cryptosporidium baileyi was studied using hormonal and chemical bursectomy in the one experiment and cyclosporin A in a second experiment. In Expt. 1, there was no correlation between antibody (confirmed by enzyme-linked immunosorbent assay) and resistance to infection as measured by body weight, gross lesions, morbidity, and mortality. Bursectomy altered antibody production, but not CMI, as measured by the delayed-type hypersensitivity skin reaction. In Expt. 2, cyclosporin A reduced CMI, but not antibody production. Chicks treated with cyclosporin A were more susceptible to C. baileyi (more severe respiratory disease) than untreated controls. Results suggested that CMI is more important in resistance to C. baileyi than circulating antibody.

Production and characterization of monoclonal antibodies against variant A infectious bursal disease virus

Monoclonal antibodies (MAbs) were produced against a variant subtype of infectious bursal disease virus (IBDV) from Delaware variant isolate A (Var-A). Splenocytes from immunized mice were fused to myeloma cells, and antibody-producing hybridomas were screened by dot-blot enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence (IF) against the homologous isolate. Specificity of the MAbs was tested against viral isolates representing all six serologic subtypes of IBDV and three untyped IBDVs--GLS, Ark, and Miss--found in serotype 1 by dot-blot ELISA and IF. The MAb G11 recognized all isolates, whereas H7 did not recognize two viruses in subtype 1, the Lukert strain and APHIS. MAbs G11 and H7 were not neutralizing and identified both the precursor proteins (VP2a) and protein product (VP2b of VP2) in Western immunoblots. Results showed an antigenic determinant in IBDV isolates and antigenic variation between subtype 1 viruses and other subtypes. This confirms and extends previous work that showed that IBDVs evolved from subtype 1 by alteration or substitution of antigenic sites.

Immunohistochemical detection of infectious bursal disease virus in formalin-fixed, paraffin-embedded chicken tissues using monoclonal antibody

Immunoperoxidase and immunofluorescence techniques detected and localized infectious bursal disease virus (IBDV) in formalin-fixed paraffin-embedded sections of the bursa of Fabricius of experimentally and naturally infected chickens. The primary antibody was a monoclonal antibody that bound all IBDV serologic subtypes, including the GLS isolate. Both techniques were valuable in detecting IBDV. The presence and severity of microscopic lesions in the bursa correlated with the location and number of positive IBDV-infected cells as measured by either test. Mild vaccine strains induced minimal microscopic lesions and resulted in a few cells positive by either test. In contrast, virulent IBDV produced widespread lymphoid necrosis and numerous cells positive by both assays. The immunoperoxidase test was more useful than the immunofluorescence test, since the same section could be stained and examined by immunoperoxidase and then restained and examined for microscopic pathology. The presence of immunoperoxidase-positive stained cells associated with areas of microscopic pathology suggested that microscopic lesions were induced by IBDV.

Digoxigenin-labeled nucleic acid probe for the detection of infectious bursal disease virus in infected cells

A cDNA probe was synthesized from the VP-4 region of a virulent field isolate of infectious bursal disease virus (IBDV). The probe was labeled during synthesis with a non-radioactive steroid hapten, digoxigenin. The probe was used to develop a hybridization assay to detect the presence of IBDV in infected cell-culture and tissue suspensions from the bursa of Fabricius of infected chickens. The test was rapid, reproducible, and sensitive, and it could detect four serologic subtypes of IBDV, including the GLS-5 isolate.

Coarse-spray immunization of one-day-old broilers against enteric reovirus infections

Coarse-spray (CS) administration of a commercial S1133 reovirus vaccine was evaluated in 1-day-old specific-pathogen-free broilers for prevention of clinical infection induced by intratracheal challenge with two enteric reovirus isolates. In Expt. 1, chickens were challenged at 4 days of age with either the 2408 or CO8 isolate. In Expt. 2, chickens were challenged at 7 days of age with either isolate. In Expt. 3, chickens were challenged at 3, 5, or 7 days of age with the 2408 isolate. In Expt. 1, vaccinated birds showed significant protection against challenge with either isolate at 4 days of age as measured by morbidity, mortality, gross lesions, and body weight. In Expt. 2, vaccinated birds showed greater protection against challenge at 7 days of age. In Expt. 3, resistance in vaccinated birds increased with time between vaccination and challenge. Vaccinated birds challenged at 3 days of age showed no significant protection, whereas vaccinated birds challenged at 5 or 7 days of age had increased resistance. This vaccine did not induce a drop in weight gain, morbidity, mortality, or microscopic lesions in the tendons.

Tissue-print hybridization using a non-radioactive probe for the detection of infectious bursal disease virus

Tissue-print hybridization was evaluated as a simplified means for detection of infectious bursal disease virus (IBDV) in the bursa of Fabricius from infected chickens. The assay employed a biotin-labeled synthetic oligonucleotide as a probe. The bound probe was detected using a color assay consisting of streptavidin conjugated to alkaline phosphatase. Bursae were imprinted onto nitrocellulose and then hybridized with the biotinylated probe. Bursal prints from IBDV-infected chickens were readily distinguished from control prints by color development and differences in signal intensity.

Pathobiology of cryptosporidiosis (C. baileyi) in broiler chickens

Pathologic and clinicopathologic changes were examined in broiler chickens inoculated with Cryptosporidium baileyi (Cb) alone or in combination with infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV) or Escherichia coli (Ec). Concurrent infections with Cb and either IBV or Ec resulted in a greater respiratory inflammatory response than either agent given alone. Concurrent Cb, IBV or Ec infections resulted in a decreased density of respiratory cryptosporidial stages. No interactions between Cb and IBDV were observed. Clinicopathologic results in broiler chicks exhibiting signs of respiratory cryptosporidiosis indicated that pO2 decreased, pCO2 increased, HCO3 increased and CO2 increased. Changes in blood gases and serum electrolyte values correlated with signs of acute respiratory disease. Blood gases and serum electrolyte values were unchanged in birds with bursal and cloacal infections only. Results of these studies clarified pathogenetic events associated with avian respiratory cryptosporidiosis, and demonstrated that cryptosporidiosis may enhance the severity of respiratory disease caused by other avian pathogens.

Effect of a live reovirus vaccine on reproductive performance of broiler breeder hens and development of viral tenosynovitis in progeny

A live commercial reovirus vaccine, Enterovax, was administered to adult broiler breeder hens via the drinking water to determine its efficacy in stimulation of circulating antibody. This vaccine was compared with a commercial inactivated reovirus vaccine. Only the inactivated product resulted in increased antibody as measured by a commercial enzyme-linked immunosorbent assay. However, the live reovirus vaccine caused diarrhea in the hens and decreased eggshell quality, fertility, and hatchability. In addition, the live vaccine virus was vertically transmitted from hens to their progeny, resulting in increased embryonic mortality and viral tenosynovitis.

Efficacy of coarse-spray administration of a reovirus vaccine in young chickens

Coarse-spray (CS) administration of a commercial S1133 reovirus vaccine in chickens for prevention of clinical viral tenosynovitis (VT) infection was evaluated. In Expt. 1, one-day-old specific-pathogen-free (SPF) white leghorns were vaccinated with a combination of reovirus, Newcastle disease (ND), and infectious bronchitis (IB) vaccines by CS and infectious bursal disease vaccine by the subcutaneous (SQ) route. In Expt. 2, one-day-old commercial broilers were vaccinated by CS with reovirus vaccine and Marek's disease (MD) vaccine by SQ. In Expt. 3, one-day-old commercial broilers received reovirus vaccine in combination with ND-IB vaccines at 1 day of age by CS and MD vaccine by SQ. Some birds received an initial or second vaccination at 7 days of age by CS or the drinking-water (DW) route. Birds vaccinated by CS at 1 day of age with reovirus vaccine did not produce circulating virus-neutralizing antibody against reovirus, although they had resistance to VT infection. In contrast, initial or booster vaccination at 7 days of age by CS or DW resulted in an antibody response and greater resistance to challenge than did CS vaccination at 1 day of age. There was no difference in efficacy between CS and DW routes at 7 days of age. The reovirus vaccine did not interfere with other vaccines as measured by serologic (ND-IB-IBD) or challenge (MD) studies.