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Pittman Ratterree DC, Chitlapilly Dass S, Ndeffo-Mbah ML. The Reproduction Number of Swine Viral Respiratory Diseases: A Systematic Review. Vet Sci 2024; 11:300. [PMID: 39057984 PMCID: PMC11281358 DOI: 10.3390/vetsci11070300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Revised: 06/26/2024] [Accepted: 06/30/2024] [Indexed: 07/28/2024] Open
Abstract
Diseases in the swine industry can cause significant economic and health impacts. This review examines R0 estimates for respiratory diseases in pigs, assessing variations and comparing transmission risks within and between farms. A literature search of three databases aggregated peer-reviewed research articles on swine viral respiratory diseases' R0 values. The study focused on seven diseases: Aujeszky's disease (AD), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Circovirus, Influenza A (IA), Encephalomyocarditis Virus (EV), Classical Swine Fever (CSF), and African Swine Fever (ASF). R0 values were estimated for transmission within and between herds/farms using various methods, from complex mathematical models to simple calculations. Data primarily came from disease surveillance and laboratory experiments. The median R0 for within-herd and between-herd transmission was 10 and 3.31 for AD, 2.78 and 1.14 for PRRSV, 5.9 and 0.89 for Circovirus, 1.75 and 1.6 for CSF, and 3.94 and 3.15 for ASF. For IA and EV, only within-herd R0 values were estimated at 8.65 and 1.3, respectively. Diseases with high R0 values highlight the need for prompt detection and response to outbreaks. Continuous monitoring and evaluation of pathogen transmissibility are crucial for enhancing disease surveillance and reducing the impact of livestock diseases.
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Affiliation(s)
- Dana C. Pittman Ratterree
- Department of Veterinary Integrative Biosciences, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA;
| | - Sapna Chitlapilly Dass
- Department of Animal Science, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX 77843, USA
| | - Martial L. Ndeffo-Mbah
- Department of Veterinary Integrative Biosciences, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA;
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Nielsen SS, Alvarez J, Bicout DJ, Calistri P, Canali E, Drewe JA, Garin‐Bastuji B, Gonzales Rojas JL, Gortázar Schmidt C, Herskin M, Michel V, Miranda Chueca MÁ, Padalino B, Pasquali P, Sihvonen LH, Spoolder H, Ståhl K, Velarde A, Viltrop A, Winckler C, Gubbins S, Stegeman JA, Antoniou S, Aznar I, Broglia A, Lima E, Van der Stede Y, Zancanaro G, Roberts HC. Assessment of the control measures of the category A diseases of Animal Health Law: Classical Swine Fever. EFSA J 2021; 19:e06707. [PMID: 34306220 PMCID: PMC8294054 DOI: 10.2903/j.efsa.2021.6707] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for Classical swine fever (CSF). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radii of the protection and surveillance zones, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, details of the model used for answering these questions are presented in this opinion as well as the transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones. Several scenarios for which these control measures had to be assessed were designed and agreed prior to the start of the assessment. Here, several recommendations are given on how to increase the effectiveness of some of the sampling procedures. Based on the average length of the period between virus introduction and the reporting of a CSF suspicion, the monitoring period was assessed as non-effective. In a similar way, it was recommended that the length of the measures in the protection and surveillance zones were increased from 15 to 25 days in the protection zone and from 30 to 40 days in the surveillance zone. Finally, the analysis of existing Kernels for CSF suggested that the radius of the protection and the surveillance zones comprise 99% of the infections from an affected establishment if transmission occurred. Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation, as well as for plausible ad hoc requests in relation to CSF.
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Jelsma T, Post J, van den Born E, Segers R, Kortekaas J. Assessing the Protective Dose of a Candidate DIVA Vaccine against Classical Swine Fever. Vaccines (Basel) 2021; 9:vaccines9050483. [PMID: 34068610 PMCID: PMC8151196 DOI: 10.3390/vaccines9050483] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 04/30/2021] [Accepted: 05/04/2021] [Indexed: 11/30/2022] Open
Abstract
Classical swine fever is a highly contagious and deadly disease in swine. The disease can be controlled effectively by vaccination with an attenuated virus known as the “Chinese” (C)-strain. A single vaccination with the C-strain provides complete protection against highly virulent isolates within days after vaccination, making it one of the most efficacious veterinary vaccines ever developed. A disadvantage of the C-strain is that vaccinated animals cannot be serologically differentiated from animals that are infected with wild-type Classical swine fever virus. Previously, a C-strain-based vaccine with a stable deletion in the E2 structural glycoprotein was developed, which allows for differentiation between infected and vaccinated animals (DIVA). The resulting vaccine, which we named C-DIVA, is compatible with a commercial E2 ELISA, modified to render it suitable as a DIVA test. In the present work, three groups of eight piglets were vaccinated with escalating doses of the C-DIVA vaccine and challenged two weeks after vaccination. One group of four unvaccinated piglets served as controls. Piglets were monitored for clinical signs until three weeks after challenge and blood samples were collected to monitor viremia, leukocyte and thrombocyte levels, and antibody responses. The presence of challenge virus RNA in oropharyngeal swabs was investigated to first gain insight into the potential of C-DIVA to prevent shedding. The results demonstrate that a single vaccination with 70 infectious virus particles of C-DIVA protects pigs from the highly virulent Brescia strain.
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Affiliation(s)
- Tinka Jelsma
- Wageningen Bioveterinary Research, 8221 RA Lelystad, The Netherlands; (T.J.); (J.P.)
| | - Jacob Post
- Wageningen Bioveterinary Research, 8221 RA Lelystad, The Netherlands; (T.J.); (J.P.)
| | | | - Ruud Segers
- MSD Animal Health, 5830 AA Boxmeer, The Netherlands; (E.v.d.B.); (R.S.)
| | - Jeroen Kortekaas
- Wageningen Bioveterinary Research, 8221 RA Lelystad, The Netherlands; (T.J.); (J.P.)
- Laboratory of Virology, Wageningen University, 6708 PB Wageningen, The Netherlands
- Correspondence: ; Tel.: +31-6-20919110
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Xie K, Chen H, Peng B, Jin Z, Xiao W, Zhang Z, Huang B, Song Q, Tang Y. On-Site Determination of Classical Swine Fever Virus (CSFV) by a Fluorescent Microsphere-Based Lateral Flow Immunoassay Strip (FM-LFIAs) Based on Monoclonal Antibodies. ANAL LETT 2020. [DOI: 10.1080/00032719.2020.1860998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Kaixin Xie
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Hui Chen
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Bin Peng
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Zhiyuan Jin
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Wei Xiao
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Zhigang Zhang
- State Key Laboratory of Food Safety Technology for Meat Products, Xiamen Yinxiang Group, Xiamen, China
| | - Boyan Huang
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Qifang Song
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
| | - Yong Tang
- Department of Bioengineering, Guangdong Province Engineering Research Center of Antibody Drug and Immunoassay, Jinan University, Guangzhou, China
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5
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Ganges L, Crooke HR, Bohórquez JA, Postel A, Sakoda Y, Becher P, Ruggli N. Classical swine fever virus: the past, present and future. Virus Res 2020; 289:198151. [PMID: 32898613 DOI: 10.1016/j.virusres.2020.198151] [Citation(s) in RCA: 93] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 08/24/2020] [Accepted: 08/28/2020] [Indexed: 12/22/2022]
Abstract
Classical swine fever (CSF) is among the most relevant viral epizootic diseases of swine. Due to its severe economic impact, CSF is notifiable to the world organisation for animal health. Strict control policies, including systematic stamping out of infected herds with and without vaccination, have permitted regional virus eradication. Nevertheless, CSF virus (CSFV) persists in certain areas of the world and has re-emerged regularly. This review summarizes the basic established knowledge in the field and provides a comprehensive and updated overview of the recent advances in fundamental CSFV research, diagnostics and vaccine development. It covers the latest discoveries on the genetic diversity of pestiviruses, with implications for taxonomy, the progress in understanding disease pathogenesis, immunity against acute and persistent infections, and the recent findings in virus-host interactions and virulence determinants. We also review the progress and pitfalls in the improvement of diagnostic tools and the challenges in the development of modern and efficacious marker vaccines compatible with serological tests for disease surveillance. Finally, we highlight the gaps that require research efforts in the future.
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Affiliation(s)
- Llilianne Ganges
- OIE Reference Laboratory for Classical Swine Fever, Institute of Agrifood Research and Technology, Centre de Recerca en Sanitat Animal (CReSA), 08193 Barcelona, Spain.
| | - Helen R Crooke
- Virology Department, Animal and Plant Health Agency, APHA-Weybridge, Woodham Lane, New Haw, Addlestone, KT15 3NB, UK
| | - Jose Alejandro Bohórquez
- OIE Reference Laboratory for Classical Swine Fever, Institute of Agrifood Research and Technology, Centre de Recerca en Sanitat Animal (CReSA), 08193 Barcelona, Spain
| | - Alexander Postel
- EU & OIE Reference Laboratory for Classical Swine Fever, Institute of Virology, University of Veterinary Medicine, Hannover, Buenteweg 17, 30559 Hannover, Germany
| | - Yoshihiro Sakoda
- Laboratory of Microbiology, Faculty of Veterinary Medicine, Hokkaido University, Kita 18 Nishi 9, Kita-ku, Sapporo, 060-0818, Japan
| | - Paul Becher
- EU & OIE Reference Laboratory for Classical Swine Fever, Institute of Virology, University of Veterinary Medicine, Hannover, Buenteweg 17, 30559 Hannover, Germany
| | - Nicolas Ruggli
- The Institute of Virology and Immunology IVI, Mittelhäusern, Switzerland; Department of Infectious Diseases and Pathobiology, University of Bern, Bern, Switzerland
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6
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Jelsma T, Wijnker JJ, Smid B, Verheij E, van der Poel WH, Wisselink HJ. Salt inactivation of classical swine fever virus and African swine fever virus in porcine intestines confirms the existing in vitro casings model. Vet Microbiol 2019; 238:108424. [DOI: 10.1016/j.vetmic.2019.108424] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 09/20/2019] [Accepted: 09/20/2019] [Indexed: 11/25/2022]
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7
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Coronado L, Bohórquez JA, Muñoz-González S, Perez LJ, Rosell R, Fonseca O, Delgado L, Perera CL, Frías MT, Ganges L. Investigation of chronic and persistent classical swine fever infections under field conditions and their impact on vaccine efficacy. BMC Vet Res 2019; 15:247. [PMID: 31307464 PMCID: PMC6632193 DOI: 10.1186/s12917-019-1982-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 06/26/2019] [Indexed: 11/13/2022] Open
Abstract
Background Recent studies have hypothesized that circulation of classical swine fever virus (CSFV) variants when the immunity induced by the vaccine is not sterilizing might favour viral persistence. Likewise, in addition to congenital viral persistence, CSFV has also been proven to generate postnatal viral persistence. Under experimental conditions, postnatal persistently infected pigs were unable to elicit a specific immune response to a CSFV live attenuated vaccine via the mechanism known as superinfection exclusion (SIE). Here, we study whether subclinical forms of classical swine fever (CSF) may be present in a conventional farm in an endemic country and evaluate vaccine efficacy under these types of infections in field conditions. Results Six litters born from CSF-vaccinated gilts were randomly chosen from a commercial Cuban farm at 33 days of age (weaning). At this time, the piglets were vaccinated with a lapinized live attenuated CSFV C-strain vaccine. Virological and immunological analyses were performed before and after vaccination. The piglets were clinically healthy at weaning; however, 82% were viraemic, and the rectal swabs in most of the remaining 18% were positive. Only five piglets from one litter showed a specific antibody response. The tonsils and rectal swabs of five sows were CSFV positive, and only one of the sows showed an antibody response. After vaccination, 98% of the piglets were unable to clear the virus and to seroconvert, and some of the piglets showed polyarthritis and wasting after 36 days post vaccination. The CSFV E2 glycoprotein sequences recovered from one pig per litter were the same. The amino acid positions 72(R), 20(L) and 195(N) of E2 were identified in silico as positions associated with adaptive advantage. Conclusions Circulation of chronic and persistent CSF infections was demonstrated in field conditions under a vaccination programme. Persistent infection was predominant. Here, we provide evidence that, in field conditions, subclinical infections are not detected by clinical diagnosis and, despite being infected with CSFV, the animals are vaccinated, rather than diagnosed and eliminated. These animals are refractory to vaccination, likely due to the SIE phenomenon. Improvement of vaccination strategies and diagnosis of subclinical forms of CSF is imperative for CSF eradication. Electronic supplementary material The online version of this article (10.1186/s12917-019-1982-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Liani Coronado
- National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba
| | - Jose Alejandro Bohórquez
- OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Sara Muñoz-González
- OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Lester Josue Perez
- University of Illinois, College of Veterinary Science, Department of Clinical Veterinary Medicine, Urbana, Illinois, 61802, United States
| | - Rosa Rosell
- OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.,Departament d'Agricultura Ramaderia i Pesca (DARP), Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Osvaldo Fonseca
- National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba
| | - Laiyen Delgado
- National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba
| | - Carmen Laura Perera
- National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba
| | - Maria Teresa Frías
- National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba
| | - Llilianne Ganges
- OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.
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Cabezón O, Muñoz-González S, Colom-Cadena A, Pérez-Simó M, Rosell R, Lavín S, Marco I, Fraile L, de la Riva PM, Rodríguez F, Domínguez J, Ganges L. African swine fever virus infection in Classical swine fever subclinically infected wild boars. BMC Vet Res 2017; 13:227. [PMID: 28764692 PMCID: PMC5540480 DOI: 10.1186/s12917-017-1150-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 07/25/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Recently moderate-virulence classical swine fever virus (CSFV) strains have been proven capable of generating postnatal persistent infection (PI), defined by the maintenance of viremia and the inability to generate CSFV-specific immune responses in animals. These animals also showed a type I interferon blockade in the absence of clinical signs. In this study, we assessed the infection generated in 7-week-old CSFV PI wild boars after infection with the African swine fever virus (ASFV). The wild boars were divided in two groups and were infected with ASFV. Group A comprised boars who were CSFV PI in a subclinical form and Group B comprised pestivirus-free wild boars. Some relevant parameters related to CSFV replication and the immune response of CSFV PI animals were studied. Additionally, serum soluble factors such as IFN-α, TNF-α, IL-6, IL-10, IFN-γ and sCD163 were analysed before and after ASFV infection to assess their role in disease progression. RESULTS After ASFV infection, only the CSFV PI wild boars showed progressive acute haemorrhagic disease; however, the survival rates following ASFV infection was similar in both experimental groups. Notwithstanding, the CSFV RNA load of CSFV PI animals remained unaltered over the study; likewise, the ASFV DNA load detected after infection was similar between groups. Interestingly, systemic type I FN-α and IL-10 levels in sera were almost undetectable in CSFV PI animals, yet detectable in Group B, while detectable levels of IFN-γ were found in both groups. Finally, the flow cytometry analysis showed an increase in myelomonocytic cells (CD172a+) and a decrease in CD4+ T cells in the PBMCs from CSFV PI animals after ASFV infection. CONCLUSIONS Our results showed that the immune response plays a role in the progression of disease in CSFV subclinically infected wild boars after ASFV infection, and the immune response comprised the systemic type I interferon blockade. ASFV does not produce any interference with CSFV replication, or vice versa. ASFV infection could be a trigger factor for the disease progression in CSFV PI animals, as their survival after ASFV was similar to that of the pestivirus-free ASFV-infected group. This fact suggests a high resistance in CSFV PI animals even against a virus like ASFV; this may mean that there are relevant implications for CSF control in endemic countries. The diagnosis of ASFV and CSFV co-infection in endemic countries cannot be ruled out and need to be studied in greater depth.
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Affiliation(s)
- Oscar Cabezón
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.,Servei d'Ecopatologia de Fauna Salvatge, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Sara Muñoz-González
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.,OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Barcelona, Spain
| | - Andreu Colom-Cadena
- Servei d'Ecopatologia de Fauna Salvatge, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Marta Pérez-Simó
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.,OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Barcelona, Spain
| | - Rosa Rosell
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.,OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Barcelona, Spain.,Departament d'Agricultura, Ramaderia, Pesca i Alimentació (DARP), Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Santiago Lavín
- Servei d'Ecopatologia de Fauna Salvatge, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Ignasi Marco
- Servei d'Ecopatologia de Fauna Salvatge, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Lorenzo Fraile
- Departament de Producció Animal, ETSEA, Universidad de Lleida, 25198, Lleida, Spain
| | - Paloma Martínez de la Riva
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), 28040, Madrid, Spain
| | - Fernando Rodríguez
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
| | - Javier Domínguez
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), 28040, Madrid, Spain
| | - Llilianne Ganges
- IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain. .,OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Barcelona, Spain.
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Hadsbjerg J, Friis MB, Fahnøe U, Nielsen J, Belsham GJ, Rasmussen TB. Sequence adaptations during growth of rescued classical swine fever viruses in cell culture and within infected pigs. Vet Microbiol 2016; 192:123-134. [PMID: 27527774 DOI: 10.1016/j.vetmic.2016.07.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 06/24/2016] [Accepted: 07/06/2016] [Indexed: 02/05/2023]
Abstract
Classical swine fever virus (CSFV) causes an economically important disease of swine. Four different viruses were rescued from full-length cloned cDNAs derived from the Paderborn strain of CSFV. Three of these viruses had been modified by mutagenesis (with 7 or 8 nt changes) within stem 2 of the subdomain IIIf of the internal ribosome entry site (IRES) that directs the initiation of protein synthesis. Rescued viruses were inoculated into pigs. The rescued vPader10 virus, without modifications in the IRES, induced clinical disease in pigs that was very similar to that observed previously with the parental field strain and transmission to in-contact pigs occurred. Two sequence reversions, in the NS2 and NS5B coding regions, became dominant within the virus populations in these infected pigs. Rescued viruses, with mutant IRES elements, did not induce disease and only very limited circulation of viral RNA could be detected. However, the animals inoculated with these mutant viruses seroconverted against CSFV. Thus, these mutant viruses were highly attenuated in vivo. All 4 rescued viruses were also passaged up to 20 times in cell culture. Using full genome sequencing, the same two adaptations within each of four independent virus populations were observed that restored the coding sequence to that of the parental field strain. These adaptations occurred with different kinetics. The combination of reverse genetics and in depth, full genome sequencing provides a powerful approach to analyse virus adaptation and to identify key determinants of viral replication efficiency in cells and within host animals.
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Affiliation(s)
- Johanne Hadsbjerg
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark
| | - Martin B Friis
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark
| | - Ulrik Fahnøe
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark
| | - Jens Nielsen
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark
| | - Graham J Belsham
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark.
| | - Thomas Bruun Rasmussen
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, Kalvehave 4771, Denmark
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10
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Cabezón O, Colom-Cadena A, Muñoz-González S, Pérez-Simó M, Bohórquez JA, Rosell R, Marco I, Domingo M, Lavín S, Ganges L. Post-Natal Persistent Infection With Classical Swine Fever Virus in Wild Boar: A Strategy for Viral Maintenance? Transbound Emerg Dis 2015; 64:651-655. [PMID: 26234886 DOI: 10.1111/tbed.12395] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Indexed: 11/29/2022]
Abstract
In this study, fifteen wild boar piglets were intranasally inoculated <10 h after birth with the moderately virulent classical swine fever virus (CSFV) strain Catalonia 01. At 5 days post-inoculation, seven other animals within 48 h of birth were put in contact with them. Viral replication and innate and specific immune responses were evaluated. Of the inoculated animals, 46.67% remained post-natally persistently infected and were apparently healthy with neither humoral nor cellular immunological responses specific to CSFV and with high viral loads in their blood, organs and body secretions. Moreover, the present data extend the time period to 48 h after birth when a moderately virulent CSFV strain could lead to post-natal persistent infection given the generation of persistently infected wild boars in the contact group (33.33%). The innate immune response to the virus, as measured by type I IFN-α in serum, was mostly not impaired in the persistently infected wild boars. Interestingly, a decrease and lack of IFN-γ-producing cells against CSFV and PHA was observed. In endemic countries where wild swine species are increasing and low and moderate virulence CSFV strains are prevalent, the possible generation of this form of disease cannot be ruled out.
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Affiliation(s)
- O Cabezón
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain.,Servei d'Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - A Colom-Cadena
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain.,Servei d'Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - S Muñoz-González
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain
| | - M Pérez-Simó
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain
| | - J A Bohórquez
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain
| | - R Rosell
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain.,Departament d'Agricultura, Ramaderia, Pesca, Alimentació i Medi natural (DAAM), Generalitat de Catalunya, Barcelona, Spain
| | - I Marco
- Servei d'Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - M Domingo
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain.,Departament de Sanitat i Anatomia Animals, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - S Lavín
- Servei d'Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - L Ganges
- Centre de Recerca en Sanitat Animal (CReSA), Institut de Recerca i Tecnologia Agroalimentáries, (IRTA), Bellaterra, Barcelona, Spain
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11
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Summerfield A, Ruggli N. Immune Responses Against Classical Swine Fever Virus: Between Ignorance and Lunacy. Front Vet Sci 2015; 2:10. [PMID: 26664939 PMCID: PMC4672165 DOI: 10.3389/fvets.2015.00010] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 04/20/2015] [Indexed: 11/14/2022] Open
Abstract
Classical swine fever virus infection of pigs causes disease courses from life-threatening to asymptomatic, depending on the virulence of the virus strain and the immunocompetence of the host. The virus targets immune cells, which are central in orchestrating innate and adaptive immune responses such as macrophages and conventional and plasmacytoid dendritic cells. Here, we review current knowledge and concepts aiming to explain the immunopathogenesis of the disease at both the host and the cellular level. We propose that the interferon type I system and in particular the interaction of the virus with plasmacytoid dendritic cells and macrophages is crucial to understand elements governing the induction of protective rather than pathogenic immune responses. The review also concludes that despite the knowledge available many aspects of classical swine fever immunopathogenesis are still puzzling.
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Affiliation(s)
| | - Nicolas Ruggli
- Institute of Virology and Immunology - IVI , Bern , Switzerland
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12
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Postnatal persistent infection with classical Swine Fever virus and its immunological implications. PLoS One 2015; 10:e0125692. [PMID: 25938664 PMCID: PMC4418595 DOI: 10.1371/journal.pone.0125692] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 03/23/2015] [Indexed: 11/19/2022] Open
Abstract
It is well established that trans-placental transmission of classical swine fever virus (CSFV) during mid-gestation can lead to persistently infected offspring. The aim of the present study was to evaluate the ability of CSFV to induce viral persistence upon early postnatal infection. Two litters of 10 piglets each were infected intranasally on the day of birth with low and moderate virulence CSFV isolates, respectively. During six weeks after postnatal infection, most of the piglets remained clinically healthy, despite persistent high virus titres in the serum. Importantly, these animals were unable to mount any detectable humoral and cellular immune response. At necropsy, the most prominent gross pathological lesion was a severe thymus atrophy. Four weeks after infection, PBMCs from the persistently infected seronegative piglets were unresponsive to both, specific CSFV and non-specific PHA stimulation in terms of IFN-γ-producing cells. These results suggested the development of a state of immunosuppression in these postnatally persistently infected pigs. However, IL-10 was undetectable in the sera of the persistently infected animals. Interestingly, CSFV-stimulated PBMCs from the persistently infected piglets produced IL-10. Nevertheless, despite the addition of the anti-IL-10 antibody in the PBMC culture from persistently infected piglets, the response of the IFN-γ producing cells was not restored. Therefore, other factors than IL-10 may be involved in the general suppression of the T-cell responses upon CSFV and mitogen activation. Interestingly, bone marrow immature granulocytes were increased and targeted by the virus in persistently infected piglets. Taken together, we provided the first data demonstrating the feasibility of CSFV in generating a postnatal persistent disease, which has not been shown for other members of the Pestivirus genus yet. Since serological methods are routinely used in CSFV surveillance, persistently infected pigs might go unnoticed. In addition to the epidemiological and economic significance of persistent CSFV infection, this model could be useful for understanding the mechanisms of viral persistence.
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13
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Weesendorp E, Backer J, Loeffen W. Quantification of different classical swine fever virus transmission routes within a single compartment. Vet Microbiol 2014; 174:353-361. [DOI: 10.1016/j.vetmic.2014.10.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 10/24/2014] [Accepted: 10/27/2014] [Indexed: 11/25/2022]
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14
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Tarradas J, de la Torre ME, Rosell R, Perez LJ, Pujols J, Muñoz M, Muñoz I, Muñoz S, Abad X, Domingo M, Fraile L, Ganges L. The impact of CSFV on the immune response to control infection. Virus Res 2014; 185:82-91. [PMID: 24657786 DOI: 10.1016/j.virusres.2014.03.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 03/05/2014] [Accepted: 03/06/2014] [Indexed: 11/19/2022]
Abstract
The severity of the acute form of CSF is responsible for the high mortality rate and has been the subject of many studies. Nevertheless, some animals are likely to develop a mild, chronic, or unapparent form of the disease. Paradoxically, this clinical form of the disease has not been well studied, especially regarding its pathogenesis. In this study, we investigated the infection in domestic pigs that is caused by the CSFV Cat01 strain, which is responsible for the 2001-2002 CSFV outbreak in Catalonia, Spain, and which caused mild and nonspecific clinical signs compared to the infection that is caused by another CSFV strain that is responsible for inducing severe clinical symptoms of disease. We assessed the impact of the CSFV infection in the immune system of domestic pigs, mainly on the kinetics of different cytokines, such as IFN-α (innate immunity) and IFN-γ (adaptive immune response), during the first weeks after infection. In addition, we evaluated the impact on the induction of the humoral response and its relation to the course of infection and the RNA CSFV viral load. The IFN-α levels in the serum samples from the pigs that developed a milder form of the CSF disease (infected with Cat01 strain) were lower than those that were detected in the pig with severe clinical CSF signs (Margarita strain). After infection with Cat01 strain, the IFN-γ levels in response to CSFV were detected in addition to the humoral response. Interestingly, in the serum samples of these animals, we detected the lowest load of CSFV RNA. Similarly, the lowest viral load levels were detected in the tonsils of these pigs. Both the T cells and the humoral response that were generated in most of the pigs that were infected with strain Cat01 may be related to the protection in the symptom progression of CSF against this viral strain. These results explain the antiviral role of IFN-γ in the absence of an antibody response. Likewise, these results corroborate the relevance and relationship that exists between the intensity of the T cell response and the protection against CSFV replication. Additionally, these results also explain how the failure to induce optimal levels of humoral and cellular responses after CSFV infection promotes the spread and persistence of the virus.
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Affiliation(s)
- Joan Tarradas
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Maria Eugenia de la Torre
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Rosa Rosell
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain; Departament d'Agricultura, Ramaderia, Pesca, Alimentació i Medi Natural (DAAM), Generalitat de Catalunya, Spain
| | - Lester Josue Perez
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain; Centro Nacional de Sanidad Agropecuaria (CENSA), La Habana, Cuba
| | - Joan Pujols
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain; Institut de Recerca i Tecnologia Agroalimentàries (IRTA), Barcelona, Spain
| | - Marta Muñoz
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Iván Muñoz
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Sara Muñoz
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Xavier Abad
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain
| | - Mariano Domingo
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain; Departament de Producció Animal, ETSEA, Universidad de Lleida, 25198, Spain
| | - Lorenzo Fraile
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain; Departament de Sanitat i d'Anatomia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra-Barcelona, Spain
| | - Llilianne Ganges
- Centre de Recerca en Sanitat Animal (CReSA), IRTA-UAB, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain.
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15
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Association between transmission rate and disease severity for Actinobacillus pleuropneumoniae infection in pigs. Vet Res 2013; 44:2. [PMID: 23311865 PMCID: PMC3574036 DOI: 10.1186/1297-9716-44-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Accepted: 01/03/2013] [Indexed: 11/22/2022] Open
Abstract
A better understanding of the variation in infectivity and its relation with clinical signs may help to improve measures to control and prevent (clinical) outbreaks of diseases. Here we investigated the role of disease severity on infectivity and transmission of Actinobacillus pleuropneumoniae, a bacterium causing respiratory problems in pig farms. We carried out transmission experiments with 10 pairs of caesarean-derived, colostrum-deprived pigs. In each pair, one pig was inoculated intranasally with 5 × 106 CFUs of A. pleuropneumoniae strain 1536 and housed together with a contact pig. Clinical signs were scored and the course of infection was observed by bacterial examination and qPCR analysis of tonsillar brush and nasal swab samples. In 6 out of 10 pairs transmission to contact pigs was observed, but disease scores in contact infected pigs were low compared to the score in inoculated pigs. Whereas disease score was positively associated with bacterial load in inoculated pigs and bacterial load with the transmission rate, the disease score had a negative association with transmission. These findings indicate that in pigs with equal bacterial load, those with higher clinical scores transmit A. pleuropneumoniae less efficiently. Finally, the correlation between disease score in inoculated pigs and in positive contact pigs was low. Although translation of experimental work towards farm level has limitations, our results suggest that clinical outbreaks of A. pleuropneumoniae are unlikely to be caused only by spread of the pathogen by clinically diseased pigs, but may rather be the result of development of clinical signs in already infected pigs.
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Zhou X, Jiang T, Du X, Zhou P, Jiang Z, Michal JJ, Liu B. Molecular characterization of porcine SARM1 and its role in regulating TLRs signaling during highly pathogenic porcine reproductive and respiratory syndrome virus infection in vivo. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2013; 39:117-126. [PMID: 22366489 DOI: 10.1016/j.dci.2012.02.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Revised: 02/07/2012] [Accepted: 02/08/2012] [Indexed: 05/31/2023]
Abstract
Toll-like receptors (TLRs) are important pattern-recognition receptors (PRRs) that trigger innate immune response and mediate acquired immunity. Evidence has shown that SARM1 (sterile-α and TIR motif containing protein 1) is one of five TIR domain-containing adaptor proteins involved in TLRs signaling transduction. In the present study, a full-length cDNA sequence was cloned for the porcine SARM1 gene, which contains nine exons. Using the radiation hybrid mapping approach, we assigned the porcine gene to SSC12 q13. Under the normal condition, porcine SARM1 was highly expressed in brain and spleen. Polyinosinic-polycytidylic acid (poly (I:C)) weakly induced the porcine SARM1 expression in the early stimulation. We found that porcine SARM1 protein is localized in mitochondria and attenuates NF-κB activation induced by stimulation and infection. The quantitative real-time PCR (Q-PCR) analysis showed that the expression of porcine SARM1 significantly decreased in several tissues of Tongcheng pigs infected with highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV). Gene-interaction network analysis for porcine SARM1 in porcine alveolar macrophages (PAMs) showed that down-regulation of SARM1 gene in infected Tongcheng pig may modulate TRIF-depend TLRs signaling and regulate the expression of disease-resistant genes and inflammatory genes. Our findings provide evidence that porcine SARM1 may play an important role in immune regulation with PRRSV infection.
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Affiliation(s)
- Xiang Zhou
- Key Lab of Agricultural Animal Genetics, Breeding, and Reproduction of Ministry of Education & Key Lab of Swine Genetics and Breeding of Ministry of Agriculture, College of Animal Science and Technology, Huazhong Agricultural University, Wuhan, 430070 Hubei, PR China
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17
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Pathway analysis in blood cells of pigs infected with classical swine fever virus: comparison of pigs that develop a chronic form of infection or recover. Arch Virol 2012; 158:325-39. [DOI: 10.1007/s00705-012-1491-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 08/17/2012] [Indexed: 01/25/2023]
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18
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Graham SP, Everett HE, Haines FJ, Johns HL, Sosan OA, Salguero FJ, Clifford DJ, Steinbach F, Drew TW, Crooke HR. Challenge of pigs with classical swine fever viruses after C-strain vaccination reveals remarkably rapid protection and insights into early immunity. PLoS One 2012; 7:e29310. [PMID: 22235283 PMCID: PMC3250419 DOI: 10.1371/journal.pone.0029310] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Accepted: 11/25/2011] [Indexed: 11/19/2022] Open
Abstract
Pre-emptive culling is becoming increasingly questioned as a means of controlling animal diseases, including classical swine fever (CSF). This has prompted discussions on the use of emergency vaccination to control future CSF outbreaks in domestic pigs. Despite a long history of safe use in endemic areas, there is a paucity of data on aspects important to emergency strategies, such as how rapidly CSFV vaccines would protect against transmission, and if this protection is equivalent for all viral genotypes, including highly divergent genotype 3 strains. To evaluate these questions, pigs were vaccinated with the Riemser® C-strain vaccine at 1, 3 and 5 days prior to challenge with genotype 2.1 and 3.3 challenge strains. The vaccine provided equivalent protection against clinical disease caused by for the two challenge strains and, as expected, protection was complete at 5 days post-vaccination. Substantial protection was achieved after 3 days, which was sufficient to prevent transmission of the 3.3 strain to animals in direct contact. Even by one day post-vaccination approximately half the animals were partially protected, and were able to control the infection, indicating that a reduction of the infectious potential is achieved very rapidly after vaccination. There was a close temporal correlation between T cell IFN-γ responses and protection. Interestingly, compared to responses of animals challenged 5 days after vaccination, challenge of animals 3 or 1 days post-vaccination resulted in impaired vaccine-induced T cell responses. This, together with the failure to detect a T cell IFN-γ response in unprotected and unvaccinated animals, indicates that virulent CSFV can inhibit the potent antiviral host defences primed by C-strain in the early period post vaccination.
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Affiliation(s)
- Simon P. Graham
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Helen E. Everett
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Felicity J. Haines
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Helen L. Johns
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Olubukola A. Sosan
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Francisco J. Salguero
- Pathology and Host Susceptibility Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Derek J. Clifford
- Specialist Scientific Services, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Falko Steinbach
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Trevor W. Drew
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
| | - Helen R. Crooke
- Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, United Kingdom
- * E-mail:
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