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Current knowledge and future research needed on PCV2 vaccines T. Opriessnig, Dr med. vet., PhD Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, Iowa Porcine circovirus type 2 (PCV2) was first described in 1998 and associated with a newly described sporadic wasting disease in weaned pigs observed almost simultaneously in Canada, California, and France (Allan and Ellis, 2000). As of January 1, 2008, ten years after its initial discovery, PCV2 is known as one of the most important viruses in the global pig industry. The acronym PCVAD (porcine circovirus associated disease) was introduced in March 2006 to summarize the different manifestations of PCV2-associated disease in fetal, growing and mature pigs. The current understanding is that PCVAD includes systemic infection or postweaning multisystemic disease (PMWS), PCV2-associated pneumonia, PCV2-associated enteritis, PCV2-associated reproductive failure, and PCV2-associated dermatitis and nephropathy syndrome (PDNS) (Opriessnig et al., 2007). All of these manifestations vary in severity from mild lesions to severe PCV2-associated lesions and disease. In the last few years, PCV2 has triggered tremendous interest from scientists across the globe and this has resulted in an increasing number of publications and perspectives on the epidemiology, pathogenesis and control of PCV2 (Table 1). Methods used to control PCVAD 1. Serotherapy Serotherapy for PCV2 had been utilized extensively by some European practitioners to control and prevent PCVAD prior to availability of commercial vaccines and was first described in the literature by Ferreira et al. (2001) and Waddilove and Marco (2002). PCV2 serotherapy utilizes injection of convalescent serum by either subcutaneous or intraperitoneal routes. Significant reduction of clinical disease and overall herd mortality rate was observed in herds that used serotherapy. However, when this technique was investigated under controlled experimental conditions, it was not possible to achieve significant differences between treated and untreated pigs (Thomas et al., 2007) and the apparent success of serotherapy reported in European field trials remains unexplained. 2. Autogenous vaccines Autogenous vaccines prepared from lung or lymphoid tissue homogenates obtained from PCVAD pigs and inactivated with 2% formaldehyde have been utilized by some practitioners facing severe losses associated with PCVAD and the inability to attain commercial vaccine due to limited supplies. Those practitioners generally reported marked reduction of mortality (i.e. from 20% to 3%) and limited to no adverse side effects with this regimen (Wagner, 2007). When 3 different autogenous products were tested under experimental conditions it was found that PCV2 was not sufficiently inactivated by the formalin treatment (unpublished data). In addition, although autogenous vaccines improved mortality in severely affected farms, concurrent use of commercial PCV2 vaccine products was found to work significantly better. As soon as the commercial PCV2 vaccines became widely available, the use of autogenous PCV2 vaccines was eliminated. 3. Current commercially available inactivated vaccines Four commercial killed PCV2 vaccines are available in different regions of the world including North America (Table 2). Table 1: Trend of numbers of scientific presentations on the topic PCV2 at International Pig Veterinary Society (IPVS) meetings. 2000 2002 2004 2006 2008 Australia USA Germany Denmark South Africa Number of abstracts on PCV2 23 38 50 59 124 Total number of abstracts 605 688 872 934 918 Percentage of abstracts on PCV2 3.8% 5.5% 5.7% 6.3% 13.5% 2008 Allen D. Leman Swine Conference 63
T. Opriessnig Table 2: PCV2 vaccines Company Name Antigen Dose Licensed for Ingelvac CircoFLEX PCV2 expressed in inactivated Baculovirus 1 ml IM Single dose Healthy pigs 3 weeks and older Suvaxyn PCV2 One Dose Inactivated PCV1-2 Chimera 2 ml IM Single dose Healthy pigs 4 weeks and older After introduction of commercial vaccines in the United States in 2006, available supplies could not keep up with demand. Practitioners and producers faced with insufficient doses of PCV2 vaccines started to decrease the recommended dose per pig in order to increase the number of vaccinated pigs. This led to numerous uncontrolled field trials on half and quarter dose regimens administered once or twice. Occasionally, even different products were used in the same pig and off-label usage mainly in breeding animals started to occur more and more frequently. With rising feed costs and decreased profits in pork production, some of these practices are likely to be continued in the future. It needs to be kept in mind that vaccines are approved by demonstrating efficacy per label instructions and use of the vaccine in other ways cannot and should not be supported by the manufacturers since appropriate trials have not been done with reduced doses. The amount of PCV2 antigen/protein within a dose was determined by following federal regulations required to obtain vaccine license. Despite all the initial problems with producing sufficient doses of PCV2 vaccines, today PCV2 vaccines are among the most commonly used vaccines in swine production (Table 3). Research on the use of PCV2 vaccines started almost 10 years ago. PCV2 vaccines became initially available in Europe followed by North America. Today, several products are available in all major swine producing regions worldwide (Table 4). Circumvent PCV2 expressed in inactivated Baculovirus 2 ml IM Two injections 3 weeks apart Healthy pigs 3 weeks and older Circovac Inactivated PCV2 2 ml IM Primary vaccination: Two injections 3-4 weeks apart, at least 2 weeks before mating Revaccination: One injection at each gestation, at least 2-4 weeks before farrowing Healthy female breeding age pigs Frequently asked questions regarding PCV2 vaccines 1. What can be expected from a PCV2 vaccine? In general, the goal of using PCV2 vaccination is to protect a pig and/or a group of pigs against one or more of the following: (1) Clinical manifestations of PCVAD; (2) extensive shedding of PCV2 into the environment via fecal samples, nasal and oral secretions, and/or semen; and (3) the effects of subclinical PCV2 infection. The following has been attributed to the usage of PCV2 vaccines: a. Under experimental conditions (Fenaux et al., 2004; Fort et al., 2008; Opriessnig et al., 2008a; Opriessnig et al., 2008b) Reduced PCV2 viremia in serum after PCV2- challenge Reduced PCV2-associated lymphoid lesions Reduced amount of PCV2 DNA/antigen in tissues Reduced nasal shedding of PCV2 DNA Reduced fecal shedding of PCV2 DNA Induction of anti-pcv2-igm antibodies 64 2008 Allen D. Leman Swine Conference
Current knowledge and future research needed on PCV2 vaccines Table 3: Pig vaccination trend in the United States (top 3 selling products; Klaas Okkinga; personal communication) Agent Number of pigs vaccinated in 2007 PCV2 73 million M. hyopneumoniae 70-80 million Lawsonia intracellularis 25 million Table 4: PCV2 vaccine facts Company Location and time of first introduction to customers 2004, Germany and France under temporary license October 2006, USA Full license April 2006, USA Full license Commercially available in the following countries (July 1, 2008) Full license: Europe, Brazil, parts of Latin America, Japan, Thailand, Malaysia Under special import permit: Canada, the Philippines, China USA, Canada, Mexico, Colombia, Europe, the Philippines, Japan, Korea, New Zealand USA, Canada, Brazil, parts of Latin America, Europe, Australia, Thailand, New Zealand March 2006, USA Conditional license December 2007, USA Full license USA, Canada, Parts of Latin America, parts of Europe (separate product license) Induction of anti-pcv2-igg antibodies Induction of anti-pcv2-neutralizing antibodies Cross-protection between PCV2a and PCV2b b. Under field conditions growing pigs (Fachiner et al., 2008; Horlen et al., 2008; Kixmöller et al., 2008) Improved average daily gain Increased percentage lean meat yield Improved feed conversion Decreased mortality rate Decreased back fat depth Increased numbers of closeouts Reduced medication cost c. Under field conditions breeding animals (Vila, 2008) Reduced numbers of mummies Increased numbers of live born pigs Increased numbers of pigs per sow per year Reduced numbers of open days per sow per litter Due to their remarkable efficacy in the field, PCV2 vaccines have been referred to as miracle vaccines by some producers and practitioners; however, it must be kept in mind that a PCV2 vaccine will not protect against the effects of infections with other pathogens or lack of common sense husbandry, management and disinfection practices. It also needs to be considered that vaccine efficacy in general can not be expected to be 100% in every instance. 2. Can vaccine compliance be measured and if yes, how is it done? Due to the fact that most if not all pigs have varying levels of anti-pcv2-antibodies, care must be taken by using serology for measuring vaccine compliance. Pigs with low amounts of anti-pcv2 antibodies at the time of vaccination will likely show a response to vaccination (i.e. increase of anti-pcv2-igg levels) within 2 3 weeks post vaccination (Opriessnig et al., 2008a) and paired serum samples is one way to measure vaccine administration. However, as discussed below, a lack of anti-pcv2-igg response after vaccination does not rule out compliance with vaccine administration. Two of the four currently available products are based on ORF2 protein expressed in the baculovirus system. This can be used when interpreting PCV2 ELISA results 2008 Allen D. Leman Swine Conference 65
T. Opriessnig on baculovirus based assays. Research under controlled experimental conditions has shown that pigs will develop anti-baculovirus-antibodies and this can be measured in this particular type of PCV2 ELISA (Patterson et al., 2008). However, it is currently unknown how long antibaculovirus antibodies are present and if anti-baculovirus antibodies are transferred to piglets via the colostrum (in the case the dam was exposed to a baculovirus-based vaccine at some point in her life). 3. Is a serological response to PCV2 vaccination always seen and necessary for vaccine efficacy? As mentioned above, care must be taken by using serology for measuring vaccine compliance as well as vaccine efficacy. Pigs with a low amount of anti-pcv2 antibodies at the time of vaccination will likely show a response to vaccination (i.e. increase of anti-pcv2-igg levels) within 2 3 weeks post vaccination (Opriessnig et al., 2008a). However, a lack of anti-pcv2-igg response after vaccination does not always rule out effective vaccination. It has been shown that pigs that didn t respond to PCV2 vaccination as determined by serology (Fenaux et al., 2004) were protected from developing PCV2-associated lesions and disease following natural or experimental PCV2 exposure. It is generally believed that the success of PCV2 vaccines is due to induction of a strong cellular immune response and experiments to further examine this are underway. 4. Do maternal anti-pcv2 antibodies interfere with PCV2 vaccine efficacy? At least two controlled research trials have shown that maternal anti-pcv2 antibodies do not interfere with PCV2 vaccine efficacy (Fort et al., 2008; Opriessnig et al., 2008c). In addition, the field efficacy of PCV2 vaccines would support this fact as most if not all pigs have passively derived anti-pcv2-antibodies and PCV2 vaccines are effective under these conditions. However, recently an immunofluoresence titer of 1:320 was determined by one group (Henry et al., 2008) to be sufficient to interfere with successful PCV2 vaccination under field conditions based solely on serology data. Experimental proof of this is lacking to date. 5. Do maternal vaccine derived anti-pcv2 antibodies interfere with PCV2 vaccine efficacy? In general, it is assumed that this is not the case; however, experimental confirmation is lacking to date. Studies on this topic are currently underway at Iowa State University and results will be presented. 6. When is the appropriate timing of PCV2 vaccine administration? PCV2 vaccines should be administered as early as possible and at least 3-4 weeks ahead of anticipated exposure. This may mean vaccinating pigs at 2 3 weeks of age in herds where PCVAD occurs in the nursery. Later administration may coincide with circulation of field PCV2 strains and is not always successful (Wagner, 2007). 7. Are two-dose products more efficacious compared to one-dose products? Is there a difference in duration of immunity between products? Studies on these topics are currently underway at Iowa State University and results will be presented. 8. Can PCV2 vaccines be administered in PCV2 viremic pigs and what can be expected in such a situation in terms of PCV2 vaccine efficacy? This is one of the most frequent questions asked by practitioners and the answer is not known to date. With the widespread prevalence of PCV2 infection, the high percentage of subclinically infected pigs, and the high success rate of PCV2 vaccination it can be speculated that PCV2 viremia (as determined by the presence of PCV2 DNA in serum by PCR) does not interfere with vaccine efficacy. 9. Can PCV2 vaccines be expected to be effective in pigs concurrently infected by several pathogens? Under experimental conditions, PCV2 vaccines are effective when administered prior to concurrent PCV2 and PRRSV infection (Opriessnig et al., 2008b). Data from the field are in support of the experimental findings as most growing pigs are infected with several pathogens. Future perspectives/next generation vaccines 1. Combination vaccines Combination vaccines have the main advantage that they reduce labor and material cost by reducing the total number of injections for an individual pig. Especially the combination of PCV2 and Mycoplasma hyopneumoniae appears to be promising since both vaccines are given at approximately the same age. It remains to be further evaluated if a combination should be packaged as one-dose combination (preferred by some costumers for PCV2) or as two-dose combination (preferred by some costumers for Mycoplasma hyopneumoniae). 2. Multivalent PCV2 vaccines PCV2b was introduced during 2005 and 2006 in North America and is now the dominant PCV2 strain worldwide. All commercially available PCV2 vaccines today are based on genotype PCV2a and all have been shown to be effective in preventing lesions and disease associated with either PCV2a or PCV2b. There may or may not be 66 2008 Allen D. Leman Swine Conference
Current knowledge and future research needed on PCV2 vaccines some benefit in adding a PCV2b strain to current killed vaccine preparations. 3. PCV2 live vaccines PCV2 live vaccines would offer the benefit that they would not need to be administered intramuscularly. Therefore the cost and labor would be markedly reduced. In addition, PCV2 live vaccines might be more effective when trying to overcome high levels of maternal antibodies or concurrent infection with immunosuppressive viruses such as PRRSV. A chimeric PCV1 2 live vaccine was tested under experimental conditions and offered protection against PCV2-associated lesions and viremia following PCV2 challenge (Fenaux et al., 2002; 2004) Summary PCVAD is a good example of a disease syndrome caused by PCV2 and other factors which can lead to significant losses in growing pigs but which can be controlled well by recently developed killed vaccines. References 1. Allan GM, Ellis JA. Porcine circoviruses: a review. J Vet Diagn Invest. 12:3 14, 2000. 2. Fachinger V, Bischoff R, Jedidia SB, Saalmüller A, Elbers K. The effect of vaccination against porcine circovirus type 2 in pigs suffering from porcine respiratory disease complex. Vaccine. 26:1488 1499, 2008. 3. Fenaux M, Halbur PG, Haqshenas G, Royer R, Thomas P, Nawagitgul P, Gill M, Toth TE, Meng XJ. Cloned genomic DNA of type 2 porcine circovirus is infectious when injected directly into the liver and lymph nodes of pigs: characterization of clinical disease, virus distribution, and pathologic lesions. J Virol. 76:541 551, 2002 4. Fenaux M, Opriessnig T, Halbur PG, Elvinger F, Meng XJ. A chimeric porcine circovirus (PCV) with the immunogenic capsid gene of the pathogenic PCV type 2 (PCV2) cloned into the genomic backbone of the nonpathogenic PCV1 induces protective immunity against PCV2 infection in pigs. J Virol. 78:6297 6303, 2004. 5. Ferreira D, Sansot B, Laval A. Attempt to use serotherapy to control mortality in PMWS. In: Proc Conf ssdna Viruses, St. Malo, France. p. 144, 2001 6. Fort M, Sibila M, Allepuz A, Mateu E, Roerink F, Segalés J. Porcine circovirus type 2 (PCV2) vaccination of conventional pigs prevents viremia against PCV2 isolates of different genotypes and geographic origins. Vaccine. 26:1063 1071, 2008. 7. Henry S, Tokach L, Dritz S, Nietfield J, Rowland R, Hesse H. PCV2 studies: Research from the K-State PCV2 team. Proc Annual Am Assoc Swine Vet Meeting, 39: 463 467, 2008 8. Horlen KP, Dritz SS, Nietfeld JC, Henry SC, Hesse RA, Oberst R, Hays M, Anderson J, Rowland RR. A field evaluation of mortality rate and growth performance in pigs vaccinated against porcine circovirus type 2. J Am Vet Med Assoc. 232:906 912, 2008. 9. Kixmöller M, Ritzmann M, Eddicks M, Saalmüller A, Elbers K, Fachinger V. Reduction of PMWS-associated clinical signs and co-infections by vaccination against PCV2. Vaccine. 26:3443 3451, 2008. 10. Opriessnig T, Meng XJ, Halbur PG. Porcine circovirus type 2 associated disease: update on current terminology, clinical manifestations, pathogenesis, diagnosis, and intervention strategies. J Vet Diagn Invest. 19:591 615, 2007. 11. Opriessnig T, Patterson AR, Elsener J, Meng XJ, Halbur PG. Influence of maternal antibodies on efficacy of porcine circovirus type 2 (PCV2) vaccination to protect pigs from experimental infection with PCV2. Clin Vaccine Immunol. 15:397 401, 2008a. 12. Opriessnig T, Madson DM, Prickett JR, Kuhar D, Lunney JK, Elsener J, Halbur PG. Effect of porcine circovirus type 2 (PCV2) vaccination on porcine reproductive and respiratory syndrome virus (PRRSV) and PCV2 coinfection. Veterinary Microbiology. In press; available online, 2008b. 13. Opriessnig T, Ramamoorthy S, Madson DM, Patterson AR, Pal N, Carman S, Meng XJ, Halbur PG. Differences in virulence among porcine circovirus type 2 isolates are unrelated to cluster type 2a or 2b and prior infection provides heterologous protection. Journal of General Virology. Accepted for publication, 2008c. 14. Patterson AR, Johnson J, Ramamoorthy S, Meng XJ, Halbur PG, Opriessnig T. Comparison of the ability of three ELISAs to detect porcine circovirus-2 (PCV2)-specific antibodies after vaccination or inoculation with genetically distinct PCV1 or PCV2 isolates. Journal of Veterinary Diagnostic Investigation. Accepted for publication, 2008. 15. Thomas PJ, Opriessnig T, Juhan NE, Meng XJ, Halbur PG. Planned exposure to porcine circovirus type 2 by serum injection is not effective at preventing porcine circovirus associated disease. Journal of Swine Health and Production 15:330 338, 2007. 16. Villa T. PCV2 and reproductive performance: facts and figures for the disbelievers. Merial Symposium. Intern Pig Vet Soc Conf, Durban, South Africa, 2008. 17. Waddilove AEJ, Marco E. Assessing serotherapeutic control of PMWS in the field. In: Proc Intern Pig Vet Soc Conf, Ames, Iowa, USA, 17:204, 2002. 18. Wagner M. Porcine circovirus associated disease: A practitioner s perspective on clinical observations and control with vaccination. Proc Annual Swine Disease Conf, Ames, Iowa, 15:56 59, 2007. 2008 Allen D. Leman Swine Conference 67