Abstract
The purpose of our experiment was to investigate, if apparently healthy, vaccinated chickens may be involved in maintaining and spreading infectious bursal disease virus (IBDV) in poultry environments. We aimed at simultaneous detection and identification of very virulent field strain IBDV (vvIBDV) as well as vaccine strain IBDV in experimentally infected chickens. Two groups of specific pathogen free (SPF) chickens were vaccinated using the intermediate infectious bursal disease (IBD) vaccine D78. Group 1 was vaccinated at the age of one week and group 2 at the age of three weeks. Both groups were challenged with vvIBDV at the age of four weeks. A third, vaccinated, non-challenged group served as negative control. No clinical symptoms were observed in any of these groups. The chickens were euthanised and submitted to autopsy and sample preparation in groups of three at fixed intervals from the age of 28 to 44 days. Gross pathological lesions were not observed. Lymphoid tissues from the bursa of Fabricius, bone marrow, spleen and thymus in addition to cloacal- and bursal swaps were analysed by one-step reverse transcription polymerase chain reaction (RT-PCR). Positive results were confirmed by two-step strain specific duplex (DPX) RT-PCR. The vaccine strain was detected in bursa tissues from all groups, while the challenge strain was detected in few bursal as well as non-bursal tissue samples.The results indicate a possibility of replication of vvIBDV in vaccinated chickens.
Highlights
Gumboro disease or infectious bursal disease (IBD) is associated with reduced production parameters, increased mortality and immunosuppression in young chickens (Jorgensen et al 1995; Lasher & Davis 1997; Saif 1998)
Clinical outbreaks of IBD in vaccinated broiler flocks have caused concern in the Danish poultry industry. The reasons for these outbreaks could be high levels of maternally derived antibodies (MDA) at the time of vaccination that would block responses towards the vaccine, or it could be improper practical handling of the vaccine, decreasing its effect or distribution, or new antigenic variant strains could be emerging. While these factors are most often investigated in connection with each outbreak, a potential reversion of the vaccine strain to virulence or survival of virulent strains in vaccinated chickens remains to be investigated
Serum samples from the experimental chickens documented seroconversion before challenge, and as might be anticipated from previous studies, vaccine virus was detected in most bursa samples, contrary to the other lymphoid tissues (Kabell et al 2005)
Summary
Gumboro disease or infectious bursal disease (IBD) is associated with reduced production parameters, increased mortality and immunosuppression in young chickens (Jorgensen et al 1995; Lasher & Davis 1997; Saif 1998). Extensive virus replication takes place in the bursa of Fabricius of the infected chicken, resulting in lesions in the bursa tissue and viremia followed by damage of other lymphoid organs: spleen, bone marrow, thymus and germinal centres of caecal tonsils (Cheville 1967). The severity of the infection depends on the virus strain and on the susceptibility of the host, regarding age (Allan et al 1972), breed (Nielsen et al 1998) and antibody level (van den Berg 1991). The most virulent IBDV strains cause severe but unspecific clinical symptoms including anorexia, depression, diarrhoea and high mortality rates three to six days after infection in three to six weeks old, susceptible chickens
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
