BACKGROUND: Infectious bursal disease (IBD) is a highly contagious disease of young birds. Differentiation between classical virulent and very virulent IBDV (vvIBDV) isolate is very important for the poultry industry to choose the right vaccination program. Molecular and serological tests are time consuming and have variable sensitivity. However, the melting curve analysis is relatively fast method with high precision. OBJECTIVES: This study was designed to evaluate the efficacy of the melting curve analysis for differentiation of some Iranian IBDVs which their identity had been previously determined by RT-PCR/RFLP analysis. METHODS: In this study, after RNA extraction and reverse transcription and Real Time RT- PCR of IBDVs, high melting resolution at temperatures ranging from 81 to 92°C were performed. RESULTS: The findings of this study showed that in the high resolution melting curve analysis, the viruses were classified from A to D. Three vaccine strains of D78, Gumbokal, Bursa CE; IBD L; Bursine 2; and all field viruses were placed in groups A, B, C, and D, respectively. High resolution melting curve analysis after normalization also showed all viruses of this study were placed in 4 HRM genotypic group. Three strains, D78, Gumbokal, Bursa CE, produced similar and non-differentiable curve but were different from other vaccine and field strains. Two other vaccine strains, IBD L and Bursine 2, were different from each other and other viruses. CONCLUSIONS: We concluded that the real-time RT-PCR HRM technique is cost-effective and reliable among the currently used methods and can be used for differentiation of IBDV isolates.

T-cell-mediated and humoral immune responses were measured in chickens infected with standard and variant strains of infectious bursal disease virus. One-day-old and 3-week-old chickens were infected with these viruses and then given sheep RBC, killed Brucella abortus strain 19, and Newcastle disease virus. Appropriate serologic tests were used to monitor the primary and secondary responses to the antigens. Lymphoblast transformation assays were performed weekly. The response to the infectious bursal disease virus was determined by virus neutralization tests, microscopic examination of bursas, and bursal to body weight ratios. One-day-old chickens had T-cell-mediated and humoral immune suppression with both strains of virus, compared with controls. The lymphoblast transformation responses indicated that the variant strain was significantly (P < 0.05) more suppressive than the standard strain. Three-week-old chickens had humoral immune suppression with the standard strain, but not with the variant strain. The lymphoblast transformation response was transiently suppressed at this age by the variant strain only. During the first week of infection, 1-day-old and 3-week-old chickens had lower neutralizing antibody titers to the variant strain than to the standard strain.

Ever since infectious bursal disease (IBD) was recognised in Nigeria over forty years ago, it continues to pose a threat to poultry production with limited information on the likely role of other avian species especially those raised in close proximity with chickens. For this study, blood samples were obtained from184 unvaccinated apparently healthy birds comprised of Japanese quails (63) andindigenous chickens (60) on smallholdings as well as pigeons (61) in a live-bird market in Osun and Oyo states, southwest Nigeria.Sera from these birds were analysed for IBD virus antibodies using a commercial ELISA kit. Overall, 69 (37.5%) sera were positive for IBDV with 52.8% (65/184) and 6.6% (4/184)from birds on smallholdings and live-bird market, respectively. These findings indicate that these birds were sub-clinically infected and could serve as reservoirs shedding the virus into the environment and perhaps, corroborate the suggestion that the inability to effectively control or eradicate the disease from poultry flocks in Nigeria may be due to limited information on the contributions of other avian species other than chicken in the spread of IBD virus.