Lah Usa Newsletter May 09

avianinsight A L O H M A N N A N I M A L H E A LT H N E W S B R I E F

Vol u m e 2

|

2009

Infectious Bursal Disease Virus Strains for Vaccination and Inactivated Bursal Tissue Origin Vaccines

Alejandro Banda DVM., Ph.D., Dipl. ACPV., Dipl. ACVM, Associate Clinical Professor Poultry Research and Diagnostic Laboratories College of Veterinary Medicine Mississippi State University

Introduction Immunosuppression continues to be a major concern for the poultry industry. This condition is characterized by dysfunction of the immune system, with a suboptimal response either by the humoral or the cellular compartments. Infectious bursal disease virus (IBDV) is one of the most common immunosuppressive agents in poultry. IBDV targets primarily the bursa of Fabricious. The bursa is committed to differentiation and proliferation of B-lymphocytes into antibody producing plasma cells. In the bursa, IBDV produces severe destruction of B-lymphocytes by either necrosis or apoptosis, and consequently the antibody-mediated response (humoral) is affected. However, recent studies have demonstrated that this virus can also hinder some of the mechanisms of cellular

inside

immunity. Immunosuppressed chickens are more susceptible to viral respiratory infections and elevated mortality due to airsacculitis or colisepticaemia. In broilers, the rate of condemnation post-slaughter due to septicaemia-toxaemia syndrome may be increased in affected flocks. Moreover, the immune response to vaccines is frequently impaired and the overall productive performance may be significantly decreased in all types of chickens. Methods for controlling IBDV infections include biosecurity and vaccination using live attenuated and/or inactivated vaccines. A key practice for controlling IBDV is the vaccination of breeders with inactivated vaccines to boost and prolong their humoral immune response. Once passively transferred to the progeny, antibodies will provide an early protection against challenge in the field. Two of the factors to consider in the selection of an inactivated IBDV vaccine are the knowledge of the type of IBDV antigen(s) and their method of propagation.

Types of IBDV Strains There are numerous reports regarding antigenic and pathogenic variations of IBDV strains. Two different serotypes have been identified and designated as serotype 1 and 2. Only serotype 1 has been associated with clinical problems in chickens. Within serotype 1, classic (also known as standard) and variant strains

have been isolated and identified. Over time, some classic strains have evolved into a more aggressive pathotype called very virulent IBDV (v vIBDV), which is present in many countries in Europe, Africa and Latin America. The antigenic variant strains evolved from the standard viruses through a major antigenic shift. Variant strains hold the ability to infect chickens in the first five days of life, causing rapid bursa atrophy and subsequent immunosuppression. Variant strains are negative performance factors for broilers produced in areas where these viruses are prevalent, such as in the USA. The strategy to protect against v vIBDV challenge includes a precise timing of vaccination of young growing birds with live attenuated IBD vaccines to achieve immunization before the v vIBDV gains enough critical mass in the chicken house to cause a flock challenge. The strategy used to protect against the variant strains challenge includes an aggressive vaccination program in replacement breeder flocks using inactivated vaccines that include both classic and variant strains. The objective is to provide the offspring with sufficient maternally derived antibodies to protect them through the early days, when variants are known to infect and cause bursal atrophy.

Infectious Bursal Disease Virus Strains for Vaccination and Inactivated Bursal Tissue Origin Vaccines

p.1

Notes from the CEO

p.4

Effect of the Attenuation and Propagation Methods For vaccine production, the IBDV strains should be adapted to and propagated in a host system. The host systems currently used to produce live attenuated and killed vaccines include chicken embryonated eggs, cell cultures and bursal tissue. A number of scientific investigations have addressed the effect of the host system used for the attenuation and propagation on the antigenic and pathogenic properties of IBDV strains. Several reports indicate that multiple passages in chicken embryos may reduce the pathogenicity of IBDV strains, whereas the adaptation in cell cultures has consistently reduced their pathogenicity. On the other hand, depending on the host system used to replicate the virus, the attenuation may also modify the antigenic properties of the viruses. Laboratory studies have demonstrated that antibodies from birds immunized with inactivated vaccines made from viruses adapted to cell cultures or chicken embryos generally have lower capability to neutralize (blocking) variant viruses when compared with antibodies from birds immunized with inactivated bursal derived pathogenic IBDV strains (Sharma and Rosenberger, 1987). In recent studies conducted by RodriguezChavez and Rosenberger in 2002, it was demonstrated that after the adaptation in embryos or cell cultures, changes occurred in the major antigenic sites (neutralizing epitopes) of the virus that induce the formation of protective antibodies. Serological evaluations by virus neutralization assays showed that sera prepared from inactivated bursa-derived IBDV strongly neutralized strains from the same origin regardless of the propagation method. Sera prepared from inactivated embryo-derived IBDV strains did not neutralize some of the bursa-derived strains (1084 E and STC) as effectively as sera prepared against bursa-derived IBDV strains. Likewise, sera prepared from inactivated cell culture-derived strains poorly

neutralized bursa-derived IBDV strains. Furthermore, inactivated bursa-derived IBD strains, using either variant or standard strains, induced the highest neutralizing antibody titers at six days post inoculation when compared with the inactivated viruses propagated in embryos or cell cultures. Inactivated embryo and cell culture-derived strains induced lower neutralizing antibodies and the onset of antibody production was delayed. Furthermore, the inactivated strains propagated in bursas or embryos induced higher antibodies by ELISA in comparison with the titers induced by cell culture-derived strains. Changes in the pathogenicity, and antigenicity of IBDV derived from different host systems have been partially explained by alterations of the viral genome and epitopes. Different nucleotides and amino acids have been associated with attenuation and with modification of the antigenic properties. Recently, with the use of molecular techniques, it has been determined that the viral populations of some RNA viruses are not homogeneous, with the presence of viral subpopulations whose genomes differ in one or more nucleotides from the consensus sequence of the population. This condition has been denominated as quasi-species. These subpopulations are originated by high mutation rate during the genome replication, with the identification by real-time RT-PCR of wild and vaccine quasi-species. The clinical significance of these quasi-species in the infection by IBDV is still unknown. However, it is likely that this is the type of IBDV challenge that the birds could be exposed to in the field. During adaptation, it is possible that a selection process takes place where some viral subpopulations are more capable to infect and replicate in chicken embryos or in cell cultures in comparison with others, and it is possible that other viral subpopulations are lost. This is an important issue since this diversity of viral subpopulations may represent diversity in antigenic epitopes with a consequent increase in

immunologic cross-reactions among the strains. It seems that the populations found in the bursa-derived antigens are more diverse, therefore, these antigens may induce a wider immunological response.

Bursal Tissue Origin Vaccines Bursa-derived inactivated vaccines (also known as bursa tissue origin vaccines) are commercially available. Inactivated bursa tissue origin (BTO) vaccines are elaborated by infecting chickens with an IBDV isolate that will replicate in the bursa tissue (tropic tissue target organ). Several days after infection of SPF birds, the infected bursa tissues are harvested, processed and inactivated to elaborate the emulsion vaccine. The idea of commercial BTO vaccines originated as a simple and effective manner to increase the antigenic content in inactivated vaccines and to provide the virus natural conditions for replication. With the identification of variant IBD strains affecting poultry, these strains were produced on bursa tissue to retain their original structures. Although this concept started in the 1980s by Dr. Box in the UK to obtain higher protection in progeny via higher levels of maternal antibodies, the concept was later adapted in the USA to produce variant strain inactivated vaccines for breadth of protection. Since the original product was commercially developed by a vaccine company, most of the research studies associated with the original technique remained proprietary. There are very few reports on BTO inactivated vaccines in the scientific literature, including the vaccines developed via this technique in the USA. Wyeth and Chettle (1982) compared four inactivated oil emulsion vaccines under field conditions. Pullets were primed with a live mild IBD vaccine in drinking water at 6 weeks of age. Oil emulsion vaccines were administered at 21 weeks by the intramuscular route. The BTO vaccine induced higher levels of maternal antibodies, which also persisted longer (20 days) when compared with maternal antibodies in chicks from parents vaccinated with

embryo origin vaccine (9 to 14 days). In 1988, Box documented that the progeny from breeders vaccinated with a BTO vaccine at 18 weeks of age achieved 50% susceptibility at 38 days compared with 30 days for chicks derived from parents vaccinated with an embryo-propagated product. An unpublished trial conducted by a large integrator in the USA demonstrated that progeny of breeders receiving a BTO product were 95% protected against standard type 1 IBDV challenge (based on bursa: body weight ratio). The comparable value for commercial embryo origin vaccine was 91%. When the variant E strain was used to challenge the progeny, the levels of protection for the two vaccines attained 83% and 54%, respectively. In terms of broiler production, the producer demonstrated 1% less mortality and a 1.4% improvement in feed conversion in broiler flocks from breeders vaccinated with the BTO vaccine. As mentioned above, the different attenuation and propagation methods for IBDV vaccine strains induce antigenic modifications in the virus that may have influence on the immunity elicited in the birds. The complete or partial inclusion of bursaderived antigens may be a good alternative to provide wider antigenic spectrum and protection against some field strains of IBDV. However, one major issue related to the production of BTO inactivated vaccines for IBDV is the cost associated to housing and feeding of the specific pathogen free (SPF) chickens to be used to replicate the IBDV strains. The Animal and Plant Health Inspection Service (APHIS) has established standard regulations that require that inactivated vaccines for IBDV should be elaborated from virus derived from cell cultures or embryonated chicken eggs (9 CFR 113.212). However, since some isolates present difficulties to replicate in traditional chicken embryo or tissue culture methods, APHIS has granted an exemption under 9 CFR 113.4(a), to elaborate vaccines from virus derived from bursal tissue.

These are some of the USDA requirements to produce vaccines containing bursa-derived antigens: a) The master seed viruses should be tested for the presence of extraneous chicken anemia virus (CAV). b) Laboratories should use only IBD susceptible chickens derived from an SPF source flock for vaccine production. c) The chickens used for vaccine production should be housed and handled in isolation to maintain their pathogen-free status and to prevent exposure to avian pathogens. d) In some cases, the laboratories should document the capacity of their IBDV inactivation procedure to inactivate extraneous CAV, or alternately, the firm should test the bulks of antigen prior to inactivation for the presence of CAV by a test acceptable to APHIS.

Conclusions • The antigenic diversity of IBDV used to immunize birds with the goal of protection against field challenge is highly advantageous. • Bursa-derived antigens provide a wider antigenic spectrum and protection against field IBDV challenge. • BTO vaccines elicit antibodies with an increased capability to neutralize IBDV strains. • Progenies from breeders vaccinated with BTO products exhibit higher and more persistent maternal antibody levels when compared with progenies from breeders vaccinated with chicken embryo or tissue culture origin products. • The technologies to guarantee the purity and quality of BTO vaccines are currently available and under regulation by USDA.

References APHIS-USDA. Bursal disease vaccine of chicken bursa origin. Veterinary Services Memorandum No. 800.81. http://www. aphis.usda.gov/animal_health/vet_biologics/ publications/memo_800_81.pdf. March 30, 2001.

Abdel-Alim, G.A. Y M Saif. Pathogenicity of cell culture-derived and bursa-derived infectious bursal disease viruses in specific-pathogen-free chickens. Avian diseases.;45:844-852.(2001). Box, P. Antibody profile of broiler breeder hens and their progeny immunized with bursal-derived or embryo-origin killed infectious bursal disease vaccine. Proceedings of the 37th Western Poultry Disease Conference, Davis, California pp. 21-24. (1988). Jackwood, D.J. and S. Summer. Identification of infectious bursal disease virus quasispecies in commercial vaccines and field isolates of this double-stranded RNA virus. Virology 304, 105–113 (2002). Lasher, H., and S. Shane. Infectious bursal disease. World’s Poultry Science 50:133166. (1994). Rodriguez-Chavez, I.R., J.K. Rosenberger, and S. Cloud. Characterization of the antigenic, immunogenic, and pathogenic variation of infectious bursal disease due to propagation in different host systems (bursa, embryo and cell culture). I Antigenicity and immunogenicity. Avian Pathol. 31:463-471. (2002). Rodriguez-Chavez, I.R., J.K. Rosenberger, and S. Cloud. Characterization of the antigenic, immunogenic, and pathogenic variation of infectious bursal disease due to propagation in different host systems (bursa, embryo and cell culture). II Antigenicity and the epitope level. Avian Pathol. 31:473-483. (2002). Rodriguez-Chavez, I.R., J.K. Rosenberger, and S. Cloud. Characterization of the antigenic, immunogenic, and pathogenic variation of infectious bursal disease due to propagation in different host systems (bursa, embryo and cell culture). III Pathogenicity. Avian Pathol. 31:485-492. (2002). Wyeth, P.J. and N. Chettle, N. Comparison of the efficacy of four inactivated infectious bursal disease oil emulsion vaccines. Vet. Record 110:359-361. (1982).

Notes from the CEO The economy is in an unusual situation globally. A number of poultry companies have suffered as a result of the ultra-high feed ingredient prices of the last half of 2008, causing some of them to reduce placements, though none have ceased production completely. Lohmann Animal Health International (LAHI), however, is enjoying increased Dave Zacek CEO, sales, both domestically and Lohmann Animal Health internationally. Because many of our customers have reduced placements, this indicates LAHI has gained new customers and/or gained new products with existing customers. Additionally, more and more firms have

taken up our bursa-derived inactivated line for broiler breeders. Progeny performance compared to other brands has been the determining factor in these changes. If you have yet to take a serious run at AviPro® 226 BTO2-REO and AviPro® 442 ND-IB2-BTO2-REO, please take the opportunity now. The sooner you begin using these products in your breeder program, the sooner you will experience the rewards of the improved performance result. In addition, construction continues at our Winslow, Maine location as we expand and upgrade many of our facilities. We are in this for the duration and are committed to providing the industry with the products and services you need and can count on. Get to know our Avian Professionals today.

375 China Road Winslow, Maine 04901

avianinsight

207.873.3989

800.655.1342

for more information:

www.lahinternational.com