engleski

Highly Virulent Infectious Bursal Disease in Broilers with No or Low Mortality but with Reduced Body Masses and Immunosuppression

Highly virulent infectious bursal disease (IBD) viruses, in contrast to classical and variant IBD viruses, cause usually 10% mortality of susceptible broiler chickens but sometimes it may reach 25%. An outbreak of IBD in vaccinated broiler chickens in Croatia is generally described with no increased mortality but significantlyreduced body weight gain. Experimental infection of fully susceptible 30-day-old birds with IBD virus isolated from affected chickens resulted in no mortality and mild clinical signs, but body weight gains were significantly reduced (52.9 grams and 83.6 grams per day in susceptible and immune birds, respectively) during the two weeks following contact infection. Rapid seroconversion was noted in unvaccinated birds. Induced transcription of inteferon alpha and gamma of susceptible broilers was significantly reduced on the 7^th and 14^th day after exposure to the isolated virus, whereas induction in broilers vaccinated against IBDV was not reduced. Infection of 4-week-old Leghorn type SPF chickens with the virus resulted in severe disease with 60% mortality, which implicated that the isolated IBD virus was highly virulent although it did not cause high mortality of susceptible broiler chickens. Nucleotide sequencing of the hypervariable region of the VP2 gene confirmed thet the virus was genetically similar to highly virulent IBD viruses.

highly virulent IBD; broilers; reduced body mass; immunosuppression; vaccination

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