Circulating strains of variant infectious bursal disease virus may pose a challenge for antibiotic-free chicken farming in Canada.
Antibiotic-free and safe animal products are most desirable among consumers. However, ensuring safe poultry products is a challenging task when the chicken immune system is compromised. Infectious bursal disease virus (IBDV) causes immunosuppression and predisposes chickens to secondary infections. Breeder vaccination against IBDV is routinely practiced for producing chicks with maternally-derived antibody (MAb) to prevent infection in newly hatched chicks. The majority of IBDV circulating in Canadian farms are variant strains (vIBDV). Whether circulating vIBDV strains are immunosuppressive in chicks or are amenable to current vaccine regimens has not previously been tested through challenge studies. In this study, one-day-old broiler chicks (n=240) carrying MAb were obtained from broiler breeders vaccinated with commercial IBDV vaccines. In the first set of experiments (n=40/group), at six days post-hatch, one group was challenged with a Canadian field isolate, vIBDV (strain-SK09) (3×10(3) EID50). The second and the third groups (controls) were inoculated with non-immunosuppressive IBDV D-78 (10×10(3) TCID50) and saline, respectively. Histopathological examination on days 14 and 30 post-challenge revealed that despite the high level of MAb, vIBDV (SK09) caused severe bursal damage in chicks. Another set of experiments with treatment groups as above, demonstrated that pre-exposure of chicks with vIBDV (SK09) caused immunosuppression resulting in significantly higher mortality and disease severity in chicks challenged with a virulent strain of Escherichia coli (E. coli). Our data provide evidence that IBDV strains circulating in Canada are immunosuppressive, not amenable to current anti-IBDV vaccination strategy, and a potential threat to antibiotic-free chicken farming.
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Shanika
S
Kurukulsuriya
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Khawaja Ashfaque
KA
Ahmed
Animal Health Laboratory, University of Guelph, P.O. Box 3612, Guelph, ON N1H 6R8, Canada.
Davor
D
Ojkic
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Thushari
T
Gunawardana
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Ashish
A
Gupta
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Kalhari
K
Goonewardene
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Ruwani
R
Karunaratne
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada.
Shelly
S
Popowich
Canadian Centre for Health and Safety in Agriculture, University of Saskatchewan, Saskatoon, S7N 5E5, SK, Canada.
Philip
P
Willson
Vaccinology and Immunotherapeutic Program, School of Public Health, University of Saskatchewan, Saskatoon S7N 5E3, SK, Canada; Vaccine and Infectious Disease Organization, 120 Veterinary Road, University of Saskatchewan, Saskatoon S7N 5E3, SK, Canada.
Suresh K
SK
Tikoo
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, SK, Canada. Electronic address: susantha.gomis@usask.ca.
Susantha
S
Gomis
D000822:Animal Husbandry; D000818:Animals; D018175:Birnaviridae Infections / Q000276:immunology / Q000382:microbiology / Q000473:pathology / Q000662:veterinary*; D001835:Body Weight; D002060:Bursa of Fabricius / Q000276:immunology / Q000502:physiology; D002170:Canada / Q000453:epidemiology; D002645:Chickens; D004926:Escherichia coli / Q000502:physiology; D007108:Immune Tolerance; D007243:Infectious bursal disease virus / Q000235:genetics / Q000502:physiology*; D011201:Poultry Diseases / Q000276:immunology* / Q000382:microbiology* / Q000401:mortality / Q000473:pathology
Broiler chickens; Bursal atrophy; Hyper-immunization; Immunosuppression; Maternal antibodies; VP2 hyper-variable domain