Isolation and characterization of infectious bursal disease virus (IBDV) field strains and pathotypes in Ghana

English

Isolation and characterisation of Ghanaian field IBD virus were undertaken as part of a comprehensive study to establish an efficacious vaccination programme against the disease in the country. Bursal homogenates were prepared from chickens that died of IBD in five different locations of the country. Batches of 11-day-old Specific Antibody Negative (SAN) embryonating eggs were inoculated with 0.2 ml of homogenate each on the chorioallantoic membrane. The eggs were incubated and candled daily, and all embryonic deaths were examined for gross IBD lesions. In addition, batches of 3-week-old SAN chickens were inoculated intra-occularly with 10 μl of the bursal homogenate and observed over 10 days for clinical signs and gross lesions of IBD. Pathotyping of the virus isolates was done by the biological method, using groups of 10, 6-week-old SAN chickens and confirmed by the reverse transcriptase-polymerase chain reaction-restriction fragment length polymorphism (RTPCR- RFLP) technique. Embryos inoculated with homogenates from all five locations died 3 to 5 days pest inoculation (PI), showing characteristic IBD lesions of extensive haemorrhages, congestion of limbs and stunted growth. Inoculated 3-week-old SAN chickens showed 100 per cent cumulative mortality, enlarged haemorrhagic and oedematous bursae, and haemorrhages in the breast and thigh muscles. Six-week-old SAN chickens inoculated with bursal homogenates showed similar lesions. One isolate LV/G19 selected and standardized for viral challenge studies had an ELD50 value of 106.3. The SAN chickens challenged with this isolate were more susceptible between the ages of 3 and 6 weeks, but morbidity and mortality were seen up to 10 weeks of age. This study confirms the presence of the very virulent Infectious Bursal Disease Virus (vvIBDV) in Ghana and the urgent need for its control.

Amakye-Anim, J.; Otsyina, H. R.; Osei-Somuah, A.; Aning, K. G.