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Environmental Assessment for Licensing Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector in Canada

For Public Release

July 10, 2008

The information in this environmental assessment was current at the time of its preparation. It is possible that the situation may have changed since that time. If you have any questions, please consult the Veterinary Biologics Section, Terrestrial Animal Health Division.


Table of Contents

  • Summary
  • 1. Introduction
    • 1.1 Proposed Action
    • 1.2 Background
  • 2. Purpose and Need for Proposed Action
    • 2.1 Significance
    • 2.2 Rationale
  • 3. Alternatives
  • 4. Molecular and Biological Characteristics of Parental and Recombinant Organisms
    • 4.1 Identification, Sources, and Strains of Parental Organisms
    • 4.2 Source, Description and Function of Foreign Genetic Material
    • 4.3 Method of Accomplishing Genetic Modification
    • 4.4 Genetic and Phenotypic Stability of the Vaccine Organism
    • 4.5 Horizontal Gene Transfer and Potential for Recombination
    • 4.6 Host Range/Specificity, Tissue Tropism and Shed/Spread Capabilities
    • 4.7 Comparison of the Modified Organisms to Parental Properties
    • 4.8 Route of Administration/Ttransmission
  • 5. Human Safety
    • 5.1 Previous Safe Use
    • 5.2 Probability of Human Exposure
    • 5.3 Possible Outcomes of Human Exposure
    • 5.4 Pathogenicity of Parent Microorganisms in Humans
    • 5.5 Effect of Gene Manipulation on Pathogenicity in Humans
    • 5.6 Risk Associated with Widespread Use of the Vaccine
  • 6. Animal Safety
    • 6.1 Previous Safe Use
    • 6.2 Fate of the Vaccine in Target and Non-Target Species
    • 6.3 Potential of Shed and/or Spread from Vaccinate to Contact Target and Non-Target Animals
    • 6.4 Reversion to Virulence Resulting from Back Passage in Animals
    • 6.5 Effect of Overdose in Target and Potential Non-Target Species
    • 6.6 The Extent of the Host Range and the Degree of Mobility of the Vector
  • 7. Affected Environment
    • 7.1 Extent of Release Into the Environment
    • 7.2 Persistence of the Vector in the Environment / Cumulative Impacts
    • 7.3 Extent of Exposure to Non-Target Species
    • 7.4 Behaviour of Parent Microorganisms and Vector in Non-Target Species
  • 8. Environmental Consequences
    • 8.1 Risks and Benefits
    • 8.2 Relative Safety Compared to Other Vaccines
  • 9. Mitigative Measures
    • 9.1 Worker Safety
    • 9.2 Handling Vaccinated or Exposed Animals
  • 10. Monitoring
    • 10.1 General
    • 10.2 Human
    • 10.3 Animal
  • 11. Consultations and Contacts
  • 12. Conclusions and Actions
  • 13. References

Summary

Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector (Vaxxitek HVT + IBD) consists of a live turkey herpesvirus (also known as Marek's disease virus, serotype 3) modified to express the VP2 antigenic protein of infectious bursal disease virus. This vaccine is administered to healthy chicken embryos at 18 or 19 days of embryonation, or to healthy chicks at one day of age, as an aid in the prevention of Marek's disease and infectious bursal disease. The vaccine was evaluated by the Veterinary Biologics Section of the Canadian Food Inspection Agency for licensing in Canada. As part of the requirements for licensing this product in Canada, an ‘Environmental Assessment' was conducted and a public document containing information on the molecular and biological characteristics of the live genetically modified organism, target animal and non-target animal safety, human safety, environmental considerations and risk mitigating measures was prepared.

1. Introduction

1.1 Proposed Action

Veterinary Biologics Section (VBS), Terrestrial Animal Health Division, Canadian Food Inspection Agency (CFIA) is responsible for licensing veterinary biologics for use in Canada. The legal authority for the regulation of veterinary biologics in Canada is provided under the Health of Animals Act and Regulations. Any veterinary biologic manufactured, sold or represented for use in Canada must comply with the requirements specified by the CFIA regarding the safety, purity, potency, and efficacy of the product. Merial Select Inc. (Gainesville, GA, USA) through Merial Canada Inc. (Baie d'Urfé, QC) has submitted the following vaccine for licensing in Canada:

  • Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector. (Trade Name: Vaxxitek HVT + IBD), USDA Product Code 1A88.R0, CFIA File 800VV/B20.20/S13.1.

This Environmental Assessment was prepared by VBS as part of the overall assessment for licensing the above vaccine in Canada.

1.2 Background

Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector is manufactured by Merial Select Inc. (US Veterinary Biologics Establishment License No 279), and is currently licensed for sale in the US. This avian vaccine consists of a live turkey herpesvirus genetically modified to express the antigenic VP2 protein of infectious bursal disease. The vaccine is intended for use in healthy 18- or 19-day-old chicken embryos and healthy one-day-old chicks as an aid in the prevention of Marek's disease and infectious bursal disease.

Marek's disease (MD) is a highly contagious, ubiquitous disease of chickens caused by a gallid herpesvirus-2 (Marek's disease virus, serotype 1). Chickens predominantly become infected with a MD virus during the first few weeks of life and carry the infection throughout their lives. Clinical MD generally afflicts birds after 4-6 weeks of age, causing paralysis, carcass condemnation at slaughter, and/or mortality. Internally, MD is characterized by lymphoid cell infiltration and proliferation forming tumours (lymphomas) in various organs, including the liver, kidneys, heart, gonads, and spleen, and/or lesions or enlargement of peripheral nerves. Bursal tumours are relatively rare, helping to differentiate MD from avian lymphoid leukosis. The serologically related, non-oncogenic turkey herpesvirus (HVT), also referred to as Marek's disease virus serotype 3, has been used effectively in vaccines against MD for more than 30 years. Vaccination with HVT does not prevent infection with MD viruses, but rather impedes the development of lymphoma.

Infectious bursal disease (IBD), commonly called Gumboro disease, is caused by the extremely stable and contagious IBD virus (IBDV), which targets and destroys the bursa of Fabricius, the organ where B lymphocytes are produced in chickens. Acute, or clinical, IBD typically occurs in birds aged 3-6 weeks and is characterized by a lack of coordination, watery diarrhea, and mortality. Non-acute or subclinical infection, common in birds less than three weeks of age, is associated with immunosuppression causing increased susceptibility to other diseases and decreased response to subsequent vaccination, and culminates into poor performance and/or death of birds. Because of the stability of IBDV in the environment, control by sanitation and isolation has had limited success in commercial poultry production. Consequently, the principal method of control is by vaccination. Current strategies typically involve vaccinating the laying hens to provide passive immunity to chicks, and/or vaccinating the chicks after maternal antibody titres have diminished. Alternatively, one-day-old chicks may be vaccinated with live attenuated strains of IBDV. However, it has been suggested that "mild" live IBDV vaccine strains may show decreased efficacy in the presence of maternal antibodies, and "intermediate" or "hot" live IBD vaccines may retain some pathogenicity (Coletti et al., 2001; Sahar et al., 2004).

2. Purpose and Need for Proposed Action

2.1 Significance

The labelling for Vaxxitek HVT + IBD indicates that the product is recommended for the in ovo vaccination of healthy 18- to 19-day-old embryonated chicken eggs, or for subcutaneous vaccination of healthy one-day-old chickens, as an aid in the prevention of bursal disease and Marek's disease.

2.2 Rationale

VBS evaluates veterinary biologic product submissions for licensure under the Health of Animals Act and Regulations. The general criteria for licensing are: a) the product must be pure, safe, potent and efficacious, b) the product must be licensed in the country of origin, c) vaccine components must be relevant to Canadian disease conditions, and d) the product must be produced and tested in accordance with generally accepted "good manufacturing practices." This U.S. origin vaccine meets these general criteria and presented no unacceptable importation risk, and therefore was evaluated for licensing by VBS.

3. Alternatives

The two alternative options being considered are: a) to issue a Permit to Import Veterinary Biologics to Merial Canada Inc. for the importation of Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector if all licensing requirements are satisfactory, or b) not to issue a Permit to Import Veterinary Biologics if licensing requirements are not met.

4. Molecular and Biological Characteristics of Parental and Recombinant Organisms

4.1 Identification, Sources, and Strains of Parental Organisms

The parental HVT (FC-126 strain) is a double stranded DNA enveloped virus originally isolated from turkey's blood. This strain has been used as a vaccine against Marek's disease since the early 1970s (Purchase et al., 1971).

4.2 Source, Description and Function of Foreign Genetic Material

The foreign genetic material is an expression cassette consisting of: 1) a mammalian virus promoter/enhancer, 2) double stranded DNA encoding the VP2 capsid protein of IBDV, and 3) a mammalian virus polyadenylation signal.

The IBDV genome is composed of two double stranded RNA segments, the larger of which encodes a 110 kilodalton (kD) polyprotein (pVP2-VP4-VP3) in a large open reading frame (ORF), which is cleaved auto-catalytically to yield VP2, VP4 and VP3 proteins (Hudson et al., 1986; Spies et al., 1989).

The VP2 capsid protein appear to be the major, if not sole, antigenic protein of IBDV (Azad et al., 1987; Fahey et al., 1991; Letzel et al., 2007). Double stranded DNA encoding the VP2 structural protein was obtained using the Faragher 52/70 IBDV strain. RNA was isolated from IBDV-infected chicken bursa and used to make complementary DNA (cDNA). The cDNA containing the coding sequences for VP2 was cloned into an intermediate vector. A stop codon was introduced at the end of the VP2 open reading frame at the putative cleavage site between VP2 and VP4 proteins.

The mammalian virus promoter and polyadenylation signal correspond to DNA sequences available on commercially available plasmids.

4.3 Method of Accomplishing Genetic Modification

A fragment of parental HVT was cloned into a plasmid, and subsequently modified by the insertion of linker DNA into an intragenic region of HVT to create the insertion locus. The expression cassette consisting of the mammalian virus promoter, the DNA sequence encoding VP2, and the mammalian virus polyadenylation signal was assembled in a separate plasmid. The expression cassette was then cloned into the HVT fragment. The resulting donor plasmid was linearized and co-transfected along with parental HVT into primary chicken embryo fibroblast (CEF) cells. Recombinants created by homologous recombination were identified based on the expression of the IBDV structural protein and other analyses. The plaque purified cell-associated virus was further amplified in CEF cells to create the Master Seed. Details of the methods used to create the recombinant virus are on file with VBS.

4.4 Genetic and Phenotypic Stability of the Vaccine Organism

Studies provided by the manufacturer indicate that the recombinant HVT + IBD Master Seed is genetically and phenotypically stable when passaged in CEF cells up to and beyond the level used in vaccine production, as well as following repeated passage in live chickens. In particular, it was shown that the sequence of the expression cassette is unaltered following nine passages in chickens plus three passages in CEF cells, and that the expression cassette is not excised from the HVT genome when amplified in CEF cells to three passages beyond the maximum level permitted in production or when isolated following nine passages in chickens.

4.5 Horizontal Gene Transfer and Potential for Recombination

Marek's disease viruses, including HVT, are known to latently infect lymphocytes (Holland et al., 1998). Latently infected cells often harbour multiple copies of the viral genome, which can be found episomally or integrated into host chromosomes (Hirai et al., 1980; Delecluse et al., 1998). Presumably, the recombinant HVT + IBD virus will behave in much the same way as parental HVT regarding the tendency of the virus to recombine with host DNA. The only unparalleled result of such a recombination event would be the introduction of the foreign expression cassette contained within the genetically modified virus. Within the expression cassette, the constitutive mammalian virus promoter is the component most likely to have an effect on the host cell; one could envision that this cis-acting regulatory DNA element could alter the expression of host genes neighbouring the integration site. However, the chances of such aberrant gene expression being deleterious is minimized by the single-cell nature of the effect, and by the short lifespan of most chickens. In addition, it is unlikely that the integration of this particular promoter would be any more detrimental than any other strong viral promoter.

The concern of recombination occurring between the non-pathogenic recombinant HVT + IBD and related viruses within chicken cells to create a new virus that is pathogenic to chickens was addressed in experiments performed by the manufacturer. In these studies, chickens were co-infected with recombinant HVT + IBD virus plus either a serotype 1 or serotype 2 MD virus. No morbidity or mortality was observed, suggesting that the viruses do not routinely recombine to produce pathogenic virus. Moreover, analysis of the DNA recovered from infected lymphocytes showed no evidence of virus recombination. Parental HVT has been widely used as a component of bivalent vaccines with other MD viruses, further suggesting that if recombination does occur between these related viruses, such events are not regularly producing pathogenic virus.

Due to its persistent nature in chickens (and turkeys), the vaccine virus might act as a reservoir of genetic material that could feasibly participate in horizontal gene transfer. The mammalian virus promoter, which in its normal viral context is restricted to its mammalian hosts, will gain exposure to avian pathogens with which horizontal gene transfer could theoretically take place. However, it would not be expected that this rare type of genetic exchange would pose any additional hazard compared to an analogous event involving a strong viral promoter from any other wild type virus. Since the vaccine virus consists of double stranded DNA that presumably replicates in the nucleus like parental HVT, whereas wild type IBDV is double stranded RNA replicating in the cytoplasm (Petek et al., 1973), it is unlikely that a live pathogenic IBDV would swap VP2 alleles with that contained in the vaccine virus. Moreover, even if such a recombination event occurred, the potential for an adverse result is further diminished due to the fact that the VP2 allele in the vaccine originates from a classical strain verses a very virulent strain of IBD virus (Ignjatovic et al., 2004).

4.6 Host Range/Specificity, Tissue Tropism and Shed/Spread Capabilities

Marek's disease viruses replicate exclusively in cells of avian origin (particularly chicken, turkey, duck, and quail) and attempts to infect mammalian cells have repeatedly failed (Sharma, 1998). In exposed birds, MD viruses initially infect and replicate within lymphocytes, where the virus remains cell associated. After about seven days, although lymphocytes continue to harbour the viral genome, the infection becomes latent and viral antigen expression wanes in lymphocytes. Productive infection, producing mature cell-free infectious virus, begins after about a week or more in feather follicle epithelial cells.

Since IBDV also targets chicken lymphocytes, the tissue tropism of the modified HVT virus would not be expected to change. Indeed, studies performed by the manufacturer indicate that the recombinant HVT + IBD virus retains tissue tropism for lymphocytes and feather follicles in vaccinated chickens. Moreover, recombinant HVT + IBD virus could not be recovered following the inoculation of mice, consistent with its presumed avian specific host range.

Parental HVT is shed in feather dander, but it is not known to spread horizontally between chickens (Islam et al., 2007). Data submitted by the manufacturer indicate that the genetic manipulations did not render the HVT + IBD virus capable of spreading from vaccinated chickens to in-contact chickens. However, like parental HVT, recombinant HVT + IBD virus is capable of spreading from vaccinated chickens to in-contact turkeys.

Marek's disease viruses, including the parental HVT, are not known to be transmitted vertically from an infected bird to its egg embryo (Paul et al., 1972).

4.7 Comparison of the Modified Organisms to Parental Properties

The recombinant HVT + IBD virus differs genetically from the parental HVT by the integration of the expression cassette described in section 4.2. The foreign DNA is inserted into what is thought to be a non-coding region of the HVT genome, and hence presumably does not disrupt any endogenous genes. The genetically modified organism does not contain any selectable markers such as antibiotic resistance genes. DNA sequencing of the recombinant HVT + IBD virus by the manufacturer determined that the recombination event between the donor plasmid and wild type parental HVT was perfectly homologous.

4.8 Route of Administration/Transmission

The Vaxxitek HVT + IBD vaccine is to be administered either in ovo to 18- or 19-days-of-embryonation eggs, or subcutaneously in the neck to one-day-old chicks.

5. Human Safety

5.1 Previous Safe Use

The parental HVT strain has been widely used in Marek's disease vaccines for over thirty years. The Vaxxitek HVT + IBD vaccine has been licensed for use in Europe and the U.S. since 2002 and 2004, respectively. Presumably during this time, humans have been exposed to the parental virus, and to a lesser extent, the recombinant organism.

5.2 Probability of Human Exposure

Human exposure to the Vaxxitek HVT + IBD vaccine itself is likely to be limited to employees in the manufacturing facility, veterinarians, animal technicians, and poultry farm operators. However, since HVT is known to persistently infect chickens, and the recombinant HVT + IBD virus has been recovered from chickens at 120 days post-vaccination, there is a chance that individuals working in abattoirs will also be exposed to the recombinant virus. Exposure to humans through the consumption of meat from vaccinated birds will be reduced by the fact that the recombinant HVT + IBD virus is localized to lymphocytes associated with visceral organs and feather follicles, and not the tissues humans predominantly consume as meat. Moreover, even if trace amounts of the recombinant virus were present in chicken meat, studies have shown that the vast majority of ingested nucleic acid is efficiently degraded in the human digestive tract (Jonas et al., 2001).

5.3 Possible Outcomes of Human Exposure

Human exposure to recombinant HVT + IBD is not expected to be of significant health concern. Researchers have repeatedly been unable to infect mammalian cells with MD viruses, including HVT. The inability of the recombinant HVT + IBD virus to proliferate in inoculated mice further supports the expected safety of this virus in humans.

5.4 Pathogenicity of Parent Microorganisms in Humans

The parental HVT organism has not been associated with pathogenicity in humans.

5.5 Effect of Gene Manipulation on Pathogenicity in Humans

The genetic manipulation of the parental HVT has added foreign genetic material encoding a major capsid protein of IBDV. This addition is not expected to cause pathogenicity in humans, since the foreign component is merely one piece (protein) of IBDV, and the intact IBDV itself is only known to produce clinical disease in chickens. Furthermore, an IBDV strain has been safely administered to a few human volunteers as part of an immunotherapy experiment (Csatary et al., 1999). The mammalian virus polyadenylation signal component of the foreign expression cassette is also unlikely to invoke human toxicity, as constructs containing these DNA sequences have been safely administered to human volunteers in various clinical trials (Senzer et al., 2004; Veelken et al., 1997). Although published studies indicating the previous use of the mammalian virus promoter in humans could not be found, this promoter has been used without complication in various animal models, as well as in numerous human cell lines, and is not expected to cause human pathogenicity.

Again, the inability of HVT-based viruses to replicate in mammalian hosts is expected to preclude any adverse effect of these viruses on humans.

5.6 Risk Associated with Widespread use of the Vaccine

No risks to human safety associated with the widespread use of the vaccine have been identified.

6. Animal Ssafety

6.1 Previous Safe Use

A field safety trial was conducted at four geographically distinct farms in the U.S., with 28,700 one-day-old broiler chicks vaccinated subcutaneously, and over 90,000 chickens vaccinated in ovo at 18 days of embryonation. Significant adverse events attributable to vaccination or signs of MD or IBD were not reported. There was no increase in three-week mortality or carcass condemnation at slaughter compared to appropriate controls. These data support the safety of the vaccine in its target population under the conditions of its intended use. Moreover, Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector has been licensed for use in Europe and the U.S. since 2002 and 2004, respectively.

The manufacturer also tested the safety of the vaccine in non-target species by inoculating turkeys (the natural host of the viral backbone), partridges, pheasants, ducks, quail, and pigeons with the recombinant HVT + IBD virus. No sick or dead birds, indicative of vaccine pathogenicity, were observed.

6.2 Fate of the Vaccine in Target and Non-Target Species

The manufacturer has demonstrated that, like parental HVT, the recombinant HVT + IBD virus can be recovered from buffy coat extractions (a method to isolate blood leukocytes including lymphocytes) taken from multiple organs, including the spleen, liver, lung, kidneys, bursa of Fabricius, thymus and gonads, as well as from feather follicles of vaccinated chickens at 27 days post-vaccination.

Recombinant HVT + IBD virus was also detected in leukocyte samples from turkeys housed in contact with vaccinated chickens. Consistent with the notion that HVT does not replicate in mammalian cells, no recombinant HVT + IBD virus could be isolated from buffy coat extractions prepared from inoculated mice.

6.3 Potential of Shed and/or Spread from Vaccinate to Contact Target and Non-Target Animals

MD viruses are shed in feather dander (sloughed skin and feather cells), and since recombinant HVT + IBD virus can be found in feather follicles, it is assumed that the recombinant virus is likewise shed by this route. Similar to parental HVT, data presented by the manufacturer indicate that HVT + IBD is not horizontally transmitted between chickens, but it can spread from vaccinated chickens to in-contact turkeys. The manufacturer has not quantified the duration of virus shedding, but it is presumed that the HVT vectored virus, much like the parental virus, may be shed intermittently or continually throughout the life of the infected bird (Islam and Walkden-Brown, 2007; Witter and Solomon, 1971).

6.4 Reversion to Virulence Resulting from Back Passage in Animals

The manufacturer performed a back passage study with nine passages in chickens. No increase in morbidity or mortality was observed with in vivo passage, demonstrating that the recombinant virus does not acquire pathogenicity when passaged through multiple birds. These results were expected since the parental HVT is a stable, naturally occurring apathogenic virus strain.

6.5 Effect of Overdose in Target and Potential Non-Target Species

The vaccine has been administered in ovo and subcutaneously to chickens at doses approximately 10-fold the dose anticipated in the commercial vaccine without any observed complications.

6.6 The Extent of the Host Range and the Degree of Mobility of the Vector

The HVT backbone is restricted in its host range to avian species, including turkeys, chickens, ducks, and quail.

7. Affected Environment

7.1 Extent of Release into the Environment

The vast majority of vaccinated chickens will be housed indoors in biosecure facilities, and thus will have little direct exposure to the environment. However, limited release of the vaccine organism may occur when barns are cleaned out, or through the vented air. HVT-contaminated litter and air (dust) appear to be capable of infecting turkeys (Witter and Solomon, 1971).

7.2 Persistence of the Vector in the Environment / Cumulative Impacts

The environmental persistence of the recombinant HVT + IBD virus, either cell-associated in lymphocytes, or as mature virus released from feather follicles, was not examined. Herpesviruses are typically inactivated by UV light from the sun (Lytle and Sagripanti, 2005). However, MD viruses in dried feathers and poultry dust have been reported to remain infectious for up to a year (Jurajda and Klimes, 1970; Schat, 1985).

7.3 Extent of Exposure to Non-Target Species

The extent of exposure to non-target species is expected to be curbed by the fact that vaccine administration predominantly occurs in housed domestic poultry without access to the outside. Nonetheless, wild turkeys are a growing population in Canada, increasing the likelihood that the hypothesized limited release of the vaccine virus from the barn could inadvertently be transmitted to turkeys. Moreover, backyard and free range chicken operations are also becoming more prevalent. Even though studies performed by the manufacturer indicate that the recombinant vaccine virus is non-pathogenic to turkeys, precautionary measures should be followed to reduce the potential for spread of the virus to turkey populations. For this reason, the manufacturer has agreed to add a special warning to the labelling of Vaxxitek HVT + IBD indicating that the product should not be administered to chickens with probable direct or indirect exposure to turkeys.

7.4 Behaviour of Parent Microorganisms and Vector in Non-Target Species

The parental HVT virus is not known to be pathogenic to any species.

8. Environmental Consequences

8.1 Risks and Benefits

One of the primary benefits of this genetically modified vaccine is that the vaccine appears to be effective at inducing immunity even when administered to maternal antibody positive chickens (manufacturer's data in licensing dossier; Bublot et al., 2007). Overcoming maternal antibody immunity has been a challenge for many of the currently available IBD vaccines (van den Berg and Meulemans, 1991; Coletti et al., 2001). In addition, the recombinant HVT + IBD virus does not appear to cause the bursal lesions associated with some "hot" live IBD vaccines. It is also possible that the persistence of the recombinant HVT + IBD virus (due to the HVT backbone) in vaccinated chickens might enhance the vaccine's duration of immunity against IBD, and hence reduce the need for booster vaccinations (Tsukamoto et al., 2002). Finally, the HVT backbone has already been established as a safe and effective tool in the protection of chickens against Marek's disease.

The primary risk identified for Vaxxitek HVT + IBD relates to its potential to spread to turkey populations (and potentially other Galliformes) and consequently persist in the environment. It is important to note, however, that no pathogenicity in turkeys is expected for the recombinant HVT + IBD virus, even if it does spread to turkeys. In an experiment performed by the manufacturer, turkeys infected with recombinant HVT + IBD virus (either through direct inoculation or contact with vaccinated chickens) appeared healthy throughout the duration of the study (up to approximately seven weeks of age), akin to turkeys infected with wild type HVT. Moreover, a separate study provided by the manufacturer indicated that the recombinant HVT + IBD virus has a diminished ability to infect turkeys in the context of a wild type HVT infection. Since HVT infection in turkeys is reportedly widespread (Colwell et al., 1972; Witter and Solomon, 1971), this viral exclusion should serve to reduce the likelihood of the recombinant HVT + IBD virus becoming established in turkey populations. The Canadian labelling for Vaxxitek HVT + IBD also carries a precautionary statement that measures should be taken to avoid contact between vaccinated chickens and turkeys, which should further mitigate the proposed risk of spread to turkeys.

In conclusion, even though there is a hypothesized risk that turkeys might inadvertently become infected with the vaccine virus, since there is no evidence to indicate that such an occurrence would be detrimental to turkeys, the benefits of the vaccine in promoting chicken animal health are believed to outweigh the proposed risk of vaccine virus spread to turkeys.

8.2 Relative Safety Compared to other Vaccines

No other HVT-based recombinant vaccines have been licensed for use in Canada. Currently, multivalent vaccines are available combining live parental HVT and live IBDV strains in the same vial. Some current vaccines against IBD contain live "hot" strains of IBDV, which, in order to help the vaccine overcome maternal antibodies, are not fully attenuated. Consequently, live "hot" IBDV strains often possess residual pathogenicity, causing bursal lesions and immunosuppression in vaccinated chickens (Sahar et al., 2004; Mazariegos et al., 1990), leaving some to question the relative safety of these vaccines against IBD.

9. Mitigative Measures

9.1 Worker Safety

The vaccine will be manufactured at Merial Select Inc. (Georgia, U.S.A.), a veterinary biologics establishment licensed by the U.S. Department of Agriculture. Individuals working with the vaccine such as employees in the production facility, as well as veterinarians, animal technicians, and poultry operators can be exposed to the live genetically modified organism. Since recombinant HVT + IBD virus is based on a naturally non-pathogenic virus backbone that is unable to replicate in mammalian cells, human exposure is not anticipated to be of human health concern. The in ovo route of vaccine administration proposed for Vaxxitek HVT + IBD should help reduce the incidence of accidental vaccinator self-injection compared to live bird vaccination. Moreover, since the vaccine does not contain any adjuvant, the risk of clinical problems due to accidental self-injection of oil adjuvant is removed.

9.2 Handling Vaccinated or Exposed Animals

Since chicks reared in a biosecure facility are not often handled directly by humans, and poultry workers typically employ precautionary biosafety measures, exposure through handling vaccinated chicks is not expected to be great. However, poultry workers could become exposed to the vaccine virus through dust and air inside barns that might be contaminated with virus shed through feather dander. Again, the recombinant virus is not believed to be pathogenic to humans.

10. Monitoring

10.1 General

The vaccine licensing regulations in Canada require manufacturers to report all suspected significant adverse reactions to CFIA within 15 days of receiving notice from an owner or a veterinarian. Veterinarians may also report suspected adverse reactions directly to the CFIA. If an adverse reaction complaint is received by VBS, the manufacturer is asked to investigate and prepare a report for the owner's veterinarian and CFIA. If the problem is resolved to the satisfaction of the veterinarian/client, no further action is usually requested by VBS. However, if the outcome of the investigation is not satisfactory, VBS may initiate regulatory action depending on the case, which may include further safety testing, temporarily stopping sales of the product, or product withdrawal from the market.

10.2 Human

No special monitoring of the human safety of the product will be carried out.

10.3 Animal

Veterinarians, vaccinators and producers should report any suspected adverse reactions to VBS as indicated above. For reporting purposes, adverse reactions are divided into Type 1, 2, and 3 reactions. Type 1 reactions are defined as any systemic adverse reaction, anaphylactic or hypersensitivity requiring veterinary treatment including: persistent fever, recumbency, persistent lethargy, decrease in activity, muscle tremors, shivering, hypersalivation, dyspnea and other respiratory problems, cyanosis, diarrhea, vomiting, colic and other gastrointestinal problems, eye problems, abortions and other reproductive problems and neurological signs. Type 2 reactions are defined as death, or an increase in mortality rate, following vaccination. Type 3 reactions are defined as local persistent reactions such as edema, abscess, granuloma, fibrosis, alopecia, hyperpigmentation and excessive pain at the injection site. Suspected adverse reactions should be reported using the form Notification of Adverse Events to Veterinary Biologics (CFIA/ACIA 2205).

11. Consultations and Contacts

Importer

Merial Canada Inc.
20000 Clark-Graham
Baie D'Urfé, Quebec H9X 4B6

Manufacturer

Merial Select Inc.
1158 Airport Parkway
Gainesville, Georgia USA 30503

12. Conclusions and Actions

Based on our assessment of the available information, VBS has concluded that the importation and use of Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector in Canada would not be expected to have any significant adverse effect on the environment, when manufactured and tested as described in the approved Outline of Production, and used according to label directions.

Following this assessment, and the completion of the Canadian veterinary biologics licensing process, the Permit to Import Veterinary Biologics of Merial Canada Inc. may be amended to allow the importation and distribution of the following product in Canada:

  • Bursal Disease - Marek's Disease Vaccine, Serotype 3, Live Marek's Disease Vector. (Trade Name: Vaxxitek HVT + IBD), USDA Product Code 1A88.R0, CFIA File 800VV/B20.20/S13.1.

All serials of this product must be released by the USDA prior to importation into Canada. All conditions described in the Permit to Import Veterinary Biologics must be followed with respect to the importation and sale of this product.

13. References

Azad, A. A., Jagadish, M. N., Brown, M. A. and Hudson, P. J. (1987) Deletion mapping and expression in Escherichia coli of the large genomic segment of a birnavirus. Virology 161(1): 145-152.

Bublot, M., Pritchard, N., Le Gros, F.-X. and Goutebroze, S. (2007) Use of a vectored vaccine against infectious bursal disease of chickens in the face of high-titred maternally derived antibody. Journal Comparative Pathology. 137 (Suppl. 1): S81-S84

Csatary, L. K., Schnabel, R. and Bakács, T. (1999) Successful treatment of decompensated chronic viral hepatitis by bursal disease virus vaccine. Anticancer Research 19(1B): 629-633.

Coletti, M., Del Rossi, E., Franciosini, M. P., Passamonti, F., Tacconi, G. and Marini, C. (2001) Efficacy and safety of an infectious bursal disease virus intermediate vaccine in ovo. Avian Diseases 45(4): 1036-1043.

Colwell, W. M., Simpson, C. F., Williams, L. E. and Forrester, D. J. (1973) Isolation of a herpesvirus from wild turkeys in Florida. Avian Diseases 17(1): 1-11.

Darteil, R., Bublot, M., Laplace, E., Bouquet, J.-F., Audonnet, J.-C. and Rivière, M. (1995) Herpesvirus of turkey recombinant viruses expressing infectious bursal disease virus (IBDV) VP2 immunogen induce protection against an IBDV virulent challenge in chickens. Virology 211(2): 481-490.

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Prepared and revised by:

Veterinary Biologics Section
Terrestrial Animal Health Division
Canadian Food Inspection Agency