Effects of Infectious Bursal Disease Vaccination Strains on the Immune System of Leghorn Chickens

Kulíková L. , V. Jurajda, R. Juranová: Effects of Infectious Bursal Disease Vaccination Strains on the Immune System of Leghorn Chickens. Acta Vet. Brno 2004, 73: 205-209. The detection of infectious bursal disease on chicken farms in the Czech Republic and problems related with it triggered the interest in the immunoprophylaxis of the disease in this country. In the present study, levels of post-vaccination antibodies against infectious bursal disease were monitored by the ELISA test in seven experiments with Leghorn chickens free of maternal antibodies. The chickens were vaccinated with commercial vaccines made of viruses of different virulence (A, B, C – mild; D – intermediate; E, F, G – highly virulent). Effects of vaccination strains on the chickens’ immune system were assessed using the bursa of Fabricius index, and a statistical comparison with results from a control group was made. Of the mild vaccines, only vaccine A produced a sufficiently high antibody titre and 100% positivity in the group. Vaccine C, on the other hand, caused a statistically significant (p < 0.05) atrophy of the bursa of Fabricius. The intermediate vaccine D produced only 80% positivity, with the lowest average post-vaccination antibodies titres and statistically insignificant BF index. The most virulent vaccines E and F demonstrated an almost 100% positivity, high post-vaccination antibodies titres and, as expected, statistically significant (p < 0.01) bursal atrophy. Vaccine G from among the virulent vaccines also produced 100% positivity, but, surprisingly, caused no damage to the bursa of Fabricius. The results of the study point to differences in virulence and immunogenic properties of different vaccination strains within individual groups of vaccines that need to be borne in mind in everyday veterinary practice. Bursa of Fabricius, immunoprophylaxis, ELISA, vaccines, chickens Infectious bursal disease (IBD) is an acute and highly contagious viral disease affecting young chickens and is characterized by massive damage to the bursa of Fabricius (FB) and by immunosuppression (Lukert et al. 1997). The infectious bursal disease virus (IBDV) belongs to the family Birnaviridae (Brown 1986), and it consists of two segments of double-stranded RNA (Jackwood et al. 1984). There are two IBVD serotypes, but only one (serotype 1) is pathogenic for domestic fowl. The expression of serotype 1 pathogenicity, however, varies. While some infected chickens will not even show any clinical symptoms of the disease, other chickens may die: in specific pathogen free (SPF) chickens, IBD mortality ranges between 30% and 70% (Nunoya et al. 1992). The first clinical cases of IBD reported in the mid-1990s from the Czech Republic were preceded by reports of IBD from Slovakia (Pospí‰ i lová 1999). Acute bursal diseases cases were mainly reported from commercial broiler chicken feeding farms and laying broiler pullet farms, and were rare in non-commercial flocks (Juranová et al. 2001).The basis for infectious bursal disease prevention is specific immunoprophylaxis. Inactivated oil vaccines and live apathogenic or attenuated vaccines of various virulence levels are used. There are three types of live vaccines: mild, intermediate (Lukert et al. 1997) and highly virulent. Intermediate vaccines can induce a higher level of immunogenicity in chickens than mild vaccines, but they may differ in virulence and some may even induce atrophy of ACTA VET. BRNO 2004, 73: 205-209 Address for correspondence: MVDr. Libu‰e Kulíková, Ph.D. Klinika ptákÛ, plazÛ a drobn ̆ch savcÛ Veterinární a farmaceutická univerzita Brno Palackého 1-3, 612 42 Brno, âeská republika Phone: + 420 541 562 364 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm the bursa of Fabricius in young chickens (Mazariegos et al. 1990). Virulent vaccines are suitable in areas with a highly pathogenic IBDV. Lack of information on the characteristics of virulent strains makes the monitoring of incidence of the highly virulent IBD virus very difficult (Tsukamoto et al. 1995). The objective of the study presented here was to investigate the degree of virulence of vaccination strains, their inmmunogenicity, their effect on the function of FB and safety and efficacy of their use. Materials and Methods Chickens from a controlled striped Leghorn flock (Czech Academy of Sciences Prague, free of avian leukosis), were used in experiments. The parent flock was IBDV antibodies free. The chickens were housed in experimental units with a slatted floor and were given K1 feed mixture (Biosta s.r.o., Bluãina) and water ad libitum. The seven vaccines representing all the three types of vaccines were chosen at random. The vaccines designated A to G are commonly used vaccines in the Czech Republic. Mild vaccines were vaccines A (strain Z 2037), B (strain OP 23) and C (strain D 78). The intermediate vaccine was vaccine D (strain S 706). Virulent vaccines included vaccines E (strain V 877), F (strain 228 E) and G (strain LC 75). Each commercial vaccine against IBDV was tested in a separate experiment. After hatching, chickens were wing-tagged and housed together. Five out of each batch of 45 chickens were picked at random, bled and euthanized and tested for the level of IBD antibodies. The number of chickens for IBD antibodies tests was considered sufficient in view of their parents’ negative IBDV antibodies titres. The remaining 40 chickens were equally divided into a test group and a control group, i.e. each group consisted of 20 chickens. Vaccines were administered in drinking water according to manufacturers’ recommendations in chicken drinkers (100 vaccination doses per litre of water). At 10 and 17 days after vaccination, ten vaccinated and 5 control chickens from each group were weighed, euthanized and bled. The chickens were autopsied, blood samples were collected for serological tests and the bursa of Fabricius was removed and weighed. Blood serum samples from test and control birds were stored in a freezer at -20 °C and subsequently tested using the commercial IDEXX – Infectious Bursal Disease Antibody Test Kit. Serum samples were tested for IBVD antibodies by the ELISA test. Serum samples with the S:P ratio (S = serum sample, P = positive control) less than or equal to 0.2 were considered negative. Ratios above 0.2 (titres higher than 396) were considered positive. Vaccine efficacy was assessed on the basis of results of serologic assays (titres of post-vaccination antibodies and number of positive chickens) and the relative weight of the bursa of Fabricius calculated as the weight of the bursa of Fabricius (g) / weight of chicken (g) × 1000 (Lucio a Hitchner 1979). Analytical methods of the Excel programme (Microsoft Office Professional, 2000) were used to statistically evaluate the results of experiments.