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Wei F, Jiang X, He D, Diao Y, Tang Y. The isolation and characterizations of a duck adenovirus 1 causing Egg Drop Syndrome in ducks, China. Vet Microbiol 2023; 285:109873. [PMID: 37703613 DOI: 10.1016/j.vetmic.2023.109873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 09/03/2023] [Accepted: 09/08/2023] [Indexed: 09/15/2023]
Abstract
A fowl adenovirus variant designated as DAdV-JSXZ strain was isolated from the tissue specimen of fallopian tubes of a duck case, which was submitted from a 276-day-old Cherry valley breeding duck flock experienced egg-dropping syndromes in March 2022. Full-genome sequence of the DAdV-I JSXZ strain by next-generation sequencing revealed that the complete genome length of DAdV-JSXZ strain was 33,213 nucleotides and shared a high degree of nucleotide identity (97.0-99.4 %) with other DAdV-I reference strains. In pathogenicity studies, this isolated duck JSXZ strain reproduced similar egg-dropping symptoms in healthy breeding ducks, pathologic lesions of follicular hemorrhage, and the laid eggs in low fertilization and hatchability rates. Our research findings demonstrated that DAdV-I JSXZ strain was one of the causative agents of duck egg dropping syndrome in egg-laying ducks and could cause acute respiratory symptoms in ducklings.
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Affiliation(s)
- Feng Wei
- College of Animal Science and Technology, Shandong Agricultural University, 61 Daizong Street, Tai'an, Shandong Province 271018, China; Shandong Provincial Key Laboratory of Animal Biotechnology and Disease Control and Prevention, Tai'an, Shandong 271018, China; Shandong Provincial Engineering Technology Research Center of Animal Disease Control and Prevention, Tai'an, Shandong 271018, China
| | - Xiaoning Jiang
- College of Animal Science and Technology, Shandong Agricultural University, 61 Daizong Street, Tai'an, Shandong Province 271018, China; Shandong Provincial Key Laboratory of Animal Biotechnology and Disease Control and Prevention, Tai'an, Shandong 271018, China; Shandong Provincial Engineering Technology Research Center of Animal Disease Control and Prevention, Tai'an, Shandong 271018, China
| | - Dalin He
- College of Animal Science and Technology, Shandong Agricultural University, 61 Daizong Street, Tai'an, Shandong Province 271018, China; Shandong Provincial Key Laboratory of Animal Biotechnology and Disease Control and Prevention, Tai'an, Shandong 271018, China; Shandong Provincial Engineering Technology Research Center of Animal Disease Control and Prevention, Tai'an, Shandong 271018, China
| | - Youxiang Diao
- College of Animal Science and Technology, Shandong Agricultural University, 61 Daizong Street, Tai'an, Shandong Province 271018, China; Shandong Provincial Key Laboratory of Animal Biotechnology and Disease Control and Prevention, Tai'an, Shandong 271018, China; Shandong Provincial Engineering Technology Research Center of Animal Disease Control and Prevention, Tai'an, Shandong 271018, China.
| | - Yi Tang
- College of Animal Science and Technology, Shandong Agricultural University, 61 Daizong Street, Tai'an, Shandong Province 271018, China; Shandong Provincial Key Laboratory of Animal Biotechnology and Disease Control and Prevention, Tai'an, Shandong 271018, China; Shandong Provincial Engineering Technology Research Center of Animal Disease Control and Prevention, Tai'an, Shandong 271018, China.
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2
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Wang L, Zhang P, Huang B, Wang M, Tian H, Liu P, Liu W, Tian K. Fiber Protein Produced in Escherichia coli as a Subunit Vaccine Candidate Against Egg-Drop Syndrome 76. Front Vet Sci 2022; 9:819217. [PMID: 35280142 PMCID: PMC8913573 DOI: 10.3389/fvets.2022.819217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Accepted: 01/13/2022] [Indexed: 11/28/2022] Open
Abstract
The egg-drop syndrome ‘76 (EDS ‘76) caused by duck atadenovirus A (DAdV-1) infection in laying hens leads to the decrease in egg production, causing heavy economic losses in the poultry industry; thus, vaccines with high safety and immunogenicity are needed. In this study, the DAdV-1 fiber protein expressed in Escherichia coli with codon optimization showed the hemagglutination (HA) titer of 13 log2 after purification (0.6 mg/mL). Compared with inactivated EDS ‘76 vaccine, the specific pathogen-free chickens immunized with 0.4 mL fiber protein (HA titer of 11 log2) induced an equal level of HA inhibition (HI) titer and neutralizing antibodies. Meanwhile, after immunization with fiber protein, the lowest HI titer that could provide the effect to reduce egg production rate in laying hens after the challenge was 7 log2. Moreover, fiber protein with an HA titer of 7 log2 could induce an HI titer no <7 log2 in laying hens, which was equal to or higher than the lowest HI titer (7 log2) that could reduce egg production against DAdV-1 infection significantly, indicating that it is economically feasible for vaccine development. Importantly, the HI antibodies maintained at a high level up to 180 days postimmunization contribute to the clinical application of the vaccine candidate. Overall, the fiber protein produced in E. coli is an effective subunit vaccine candidate in EDS ‘76 control for its high immunogenicity and protection in chickens.
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Affiliation(s)
- Linguo Wang
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, China
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Pantao Zhang
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Baicheng Huang
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Mengyue Wang
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Hui Tian
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Peng Liu
- National Research Center for Veterinary Medicine, Luoyang, China
| | - Wujie Liu
- National Research Center for Veterinary Medicine, Luoyang, China
- *Correspondence: Wujie Liu
| | - Kegong Tian
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, China
- National Research Center for Veterinary Medicine, Luoyang, China
- Kegong Tian
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3
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MÉSzÁRos JF. Control of Infectious Diseases in Large-Scale Poultry Breeding and Production. WORLD POULTRY SCI J 2019. [DOI: 10.1079/wps19830013] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- J. F. MÉSzÁRos
- Veterinary Medical Research Institute, Hungarian Academy of Sciences, Budapest 1581 P. O. Box 18, Hungary
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Cha SY, Kang M, Park CK, Choi KS, Jang HK. Epidemiology of egg drop syndrome virus in ducks from South Korea. Poult Sci 2013; 92:1783-9. [PMID: 23776265 DOI: 10.3382/ps.2013-03067] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Egg drop syndrome virus (EDSV) is an important pathogen of poultry that decreases egg production in chickens and causes respiratory disease in goslings. In 2011, we obtained serum samples from 139 domestic Pekin ducks, 416 one-day-old Pekin ducklings, and 75 wild ducks (67 mallards and 8 pintails) to survey their exposure to EDSV. A total of 123 of 139 sera (88.5%) from Pekin ducks, 396 of the ducklings (95.2%), and 16 of 67 mallards (23.9%) were positive. Field cases of EDSV in wild and domestic ducks were investigated. Six cases from domestic Pekin ducks were identified by PCR detection and were used for virus isolation and molecular analysis. Phylogenetic analyses of the partial hexon and full fiber genes showed that the D11-JW-012 and D11-JW-017 strains among 6 isolates belonged to different clusters compared with other known strains including the 127 strain. We assessed cell growth efficiency by hemagglutination (HA) titers and cytopathic effects in duck embryo liver cells and chicken embryo liver (CEL) cells to investigate host adaptation. The D11-JW-017 strain propagated more in chicken embryo liver than the D11-JW-012 strain and the field isolate from chickens. Our results demonstrate the high prevalence of EDSV in wild and domestic ducks in South Korea and provide information on EDSV from ducks that showed variable adaptability in chickens.
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Affiliation(s)
- S-Y Cha
- Department of Infectious Diseases & Avian Diseases, Chonbuk National University, Chonbuk, Jeonju, South Korea
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Raj GD, Sivakumar S, Sudharsan S, Mohan AC, Nachimuthu K. Genomic characterization of Indian isolates of egg drop syndrome 1976 virus. Avian Pathol 2012; 30:21-6. [PMID: 19184869 DOI: 10.1080/03079450020023159] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Abstract
Five Indian isolates of egg drop syndrome (EDS) 1976 virus and the reference strain 127 were compared by restriction enzyme analysis of viral DNA, and the hexon gene amplified by polymerase chain reaction. Using these techniques, no differences were seen among these viruses. However, partial sequencing of the hexon gene revealed major differences (4.6%) in one of the isolates sequenced, EDS Kerala. Phylogenetic analysis also placed this isolate in a different lineage compared with the other isolates. The need for constant monitoring of the genetic nature of the field isolates of EDS viruses is emphasized.
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Affiliation(s)
- G D Raj
- Department of Animal Biotechnology, Madras Veterinary College, Chennai 600 007, India
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Heffels U, Khalaf SE, Kaleta EF. Studies on the persistence and excretion of egg drop syndrome 1976 virus in chickens. Avian Pathol 2008; 11:441-52. [PMID: 18770207 DOI: 10.1080/03079458208436116] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
EDS virus strain 127 did not induce clinical signs or gross lesions in susceptible chicks of various age groups and in adult cocks. Virus persistence in various internal organs and the rate of excretion of virus by experimentally-infected chicken declined rapidly with increasing age. Virus 127 was detectable in organs of young chicks up to 5 weeks post-infection and in their faeces up to 2 weeks post-infection. In adult birds virus 127 persisted in tissues for about 3 weeks and was excreted with faeces for only 1 week post-infection. Vaccination of adult cocks with an inactivated vaccine resulted in intermittent shedding of virus only within the first 4 days post-challenge; thus, in comparison to non-vaccinated chickens, vaccination reduced virus excretion in faeces to a major extent.
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Affiliation(s)
- U Heffels
- Klinik fur Geflügel der Tierärztlichen Hochschule Hannover,Bischofsholer Damm 15, D-3000 Hannover 1, W. Germany
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Smyth JA, Adair B. Lateral transmission of egg drop syndrome‐76 virus by the egg. Avian Pathol 2008; 17:193-200. [DOI: 10.1080/03079458808436438] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Joan A. Smyth
- a Department of Agriculture , Veterinary Research Laboratories , Stoney Road, Stormont, Belfast, BT4 3SD, Northern Ireland
| | - B.M. Adair
- a Department of Agriculture , Veterinary Research Laboratories , Stoney Road, Stormont, Belfast, BT4 3SD, Northern Ireland
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8
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Raj GD, Thiagarajan V, Nachimuthu K. Detection of antibodies to egg drop syndrome virus in chicken serum using a field-based immunofiltration (flow-through) test. Avian Dis 2007; 51:788-90. [PMID: 17992943 DOI: 10.1637/0005-2086(2007)51[788:doated]2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A simple, user-friendly, and rapid method to detect the presence of antibodies to egg drop syndrome 76 (EDS) virus in chicken sera based on an immunofiltration (flow-through) test was developed. Purified EDS virus antigen was coated onto nitrocellulose membranes housed in a plastic module with layers of absorbent filter pads underneath. Following addition of serum to be tested and washing, monoclonal antibodies or polyclonal serum to chicken immunoglobulin G (IgG) was used as a bridge antibody to mediate binding between EDS virus-specific IgG and protein A gold conjugate. The appearance of a pink dot indicated the presence of antibodies to EDS virus in the sample tested. The results could be obtained within 5-10 min. The developed immunofiltration test could detect antibodies in the sera of experimentally vaccinated chickens from 2 wk postvaccination. With field sera samples, this test was positive in samples having hemagglutination inhibition titers of 8 and above. This test has the potential to be used as a field-based kit to assess seroconversion in EDS-vaccinated flocks.
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Affiliation(s)
- G Dhinakar Raj
- Department of Animal Biotechnology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai, India.
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9
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Cook JK, Darbyshire J. Epidemiological studies with egg drop syndrome‐1976 (eds‐76) virus. Avian Pathol 2007; 9:437-43. [DOI: 10.1080/03079458008418427] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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10
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Senthilkumar N, Kataria JM, Koti M, Dhama K, Dash BB. Restriction enzyme analysis of Indian isolates of egg drop syndrome 1976 virus recovered from chicken, duck and quail. Vet Res Commun 2004; 28:447-53. [PMID: 15379439 DOI: 10.1023/b:verc.0000035002.23065.d0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Egg drop syndrome 1976 (EDS-76) is caused by a haemagglutinating adenovirus belonging to group III of the genus Aviadenovirus in the family Adenoviridae. All isolates are serologically identical, but have been divided into three groups based on restriction endonuclease (RE) analysis. In this study the viral DNA of various Indian EDS-76 viral isolates (CEDS-A, CEDS-B, EDS-M, EDS-ML, EDS-1/AD/86, EDS-KC and QEDS) obtained from different avian species and different geographical regions were digested with restriction endonucleases viz., EcoRI, BamHI, HindIII and PstI. The results showed that one Indian isolate obtained from duck (DEDS-KC) was different from all other chicken and quail counterparts. All other isolates were identical to the reference viral strain BC-14, which belong to group I of EDS-76 viruses. The duck isolate EDS-KC could not be placed in any of the three groups reported earlier.
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Affiliation(s)
- N Senthilkumar
- Division of Avian Diseases, Indian Veterinary Research Institute, Izatnagar 243 122, UP, India
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Tsukamoto K, Kuwabara M, Kaneko M, Mase M, Imai K. No evidence for adaptation of current egg drop syndrome 1976 viruses to chickens. Avian Dis 2004; 48:220-3. [PMID: 15077820 DOI: 10.1637/7084] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In order to determine whether the current field strains of egg drop syndrome (EDS) 1976 viruses adapt to chickens, we compared the growth efficiency of three Japanese field strains (PA-1/79, AWI/98, Gifu/01) in chicken and duck embryo liver cells. The growth efficiency in chicken or duck embryo liver cells was almost similar in these strains. The fiber protein may carry the type-specific antigen and the hemagglutination activity, and hexon protein may contain the subgroup-specific antigenic determinants. Therefore, the fiber head and hexon loop 1 DNA domain sequences of the six Japanese field strains UPA-1/79, ME/80, 44/81, Kyoto/91, AWI/98, Gifu/01) were compared, but these DNA domains were identical among the six field strains. Our data suggested that the EDS virus was maintained without discernible changes for the last two decades in the field.
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Affiliation(s)
- K Tsukamoto
- Department of Infectious Diseases, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
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Adair B, Todd D, McFerran J, McKillop E. Comparative serological studies with egg drop syndrome virus. Avian Pathol 1986; 15:677-85. [DOI: 10.1080/03079458608436330] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Mockett AP, Brown TD, Davis PJ. A hybridoma secreting a neutralising monoclonal antibody to egg drop syndrome 1976 virus. Avian Pathol 1984; 13:333-7. [PMID: 18766848 DOI: 10.1080/03079458408418535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
A hybridoma (HPRS/AM/1) secreting neutralising antibody to Egg drop syndrome 1976 virus strain D61 was established. This monoclonal antibody also neutralised two other strains tested thereby showing that all the strains possess at least one common antigenic determinant which is important in infection. However, this epitope was not involved in haemagglutination. The antigen was identified in the nuclei of infected chick kidney cells by an indirect fluorescent antibody test.
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Affiliation(s)
- A P Mockett
- Houghton Poultry Research Station, Houghton, Huntingdon, Cambridgeshire, England
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14
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Reid GG, Grimes TM, Eaves FW, Blackall PJ. A survey of disease in five commercial flocks of meat breeder chickens. Aust Vet J 1984; 61:13-6. [PMID: 6704066 DOI: 10.1111/j.1751-0813.1984.tb07122.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Causes of sickness and death in approximately 30,000 chickens in 5 meat breeder flocks were investigated between May 1979 and April 1980. Approximately 23% of disease was due to neoplasms; 81% of these were Marek's disease despite vaccination against this infection. Other frequent diagnoses included cellulitis (15%), respiratory disease (14%), lesions of the reproductive tract (11%) and tenosynovitis/arthritis (9%). Antibodies to Mycoplasma gallisepticium, avian adenovirus, infectious bursal disease virus and reticuloendotheliosis virus were present in all flocks. Antibody to Newcastle disease virus (NDV) was found in 2 flocks but titres were not considered protective against a virulent NDV challenge. Antibody to egg drop syndrome 1976 virus was found in 2 flocks comprised of the same breed of bird.
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van Eck JH. Effects of experimental infection of fowl with EDS'76 virus, infectious bronchitis virus and/or fowl adenovirus on laying performance. Vet Q 1983; 5:11-25. [PMID: 6302974 DOI: 10.1080/01652176.1983.9693868] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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Cook JK. Egg drop syndrome 1976 (EDS-76) virus infection in inadequately vaccinated chickens. Avian Pathol 1983; 12:9-16. [PMID: 18766758 DOI: 10.1080/03079458308436144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Experiments were carried out to study the epizootiology of the egg drop syndrome 1976 virus infection in chickens that were not adequately protected by vaccination. Virus excretion was demonstrated when chickens vaccinated at the recommended level were challenged within 10 days of vaccination and when chickens were challenged 6 weeks after administration of low doses of vaccine. In the latter experiment, those chickens which shed virus had all shown a poor haemagglutination inhibition antibody response to vaccination but had high serum neutralisation antibody titres when challenged.
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Affiliation(s)
- J K Cook
- Houghton Poultry Research Station, Houghton, Huntingdon, U.K
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van Eck JH. Serological examination and egg production of progeny of fowl experimentally infected with egg drop syndrome 1976 virus. Vet Q 1982; 4:117-23. [PMID: 6293156 DOI: 10.1080/01652176.1982.9693851] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Following EDS'76 virus (BC14 virus) infection of breeder chickens by the conjunctival route, vertical transmission occurred in the first week after infection. In the progeny which had been infected with EDS'76 virus by the vertical route, increasing haemagglutination inhibiting (HI) titres to BC14 virus and increasing numbers of birds with HI titres were observed from 3 weeks to 15 weeks of age. Sixty-one per cent of the hens and 77 per cent of the cocks had 2 log HI BC14 virus titres exceeding 4 at an age of 15 weeks. Some birds which han been serologically negative throughout the rearing period, seroconverted between 25 and 28 weeks of age. This phenomenon occurred in hens as well as in cocks. Simulation of stress twice during the laying period by injection of corticosteroid hormone did not increase the number of birds serologically positive to EDS'76 virus. EDS'76 was observed in the group of hens that was vertically infected, since egg production was significantly depressed between 28 and 34 weeks of age. Probably this was mainly the results of a production drop in the hens showing serconversion at 27 or 28 weeks of age. In this group of fowl vertically infected with EDs'76 virus, serologically positive birds appeared to be protected for the greater part to BC14 virus challenge at 50 weeks of age, while negative birds seemed to be fully susceptible. Chicks hatched from eggs collected in the third and fourth week after infection of the dams had maternal antibodies. Fertility and hatchability of apparently normally shelled eggs seemed not to be affected after BC14 virus infection of the dams. Intensive contact with contaminated faeces is probably an indispensable condition for lateral transmission of the virus.
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Cook JK, Darbyshire J. Longitudinal studies on the egg drop syndrome 1976 (eds‐76) in the fowl following experimental infection at 1‐day‐old. Avian Pathol 1981; 10:449-59. [DOI: 10.1080/03079458108418495] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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van Eck JH. Incidence of EDS'76 virus infection in fowl in 1980 in the Netherlands in comparison with the incidence in 1976-1978. Vet Q 1981; 3:150-2. [PMID: 6267729 DOI: 10.1080/01652176.1981.9693817] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Serological examinations demonstrated that Egg Drop Syndrome 1976 (EDS'76) virus infection was of no significance in the Dutch poultry industry in 1980, in contrast to the situation in 1976-1978 when this infection was of widespread occurrence. The conclusion was reached that the sharp decrease in the incidence of EDS'76 virus infection was due to large scale vaccination in 1978 and 1979. The results of this study show that there is no further need for general EDS'76 vaccinations. However, continuous serological monitoring is necessary to detect flocks for which vaccination is indicated.
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