| Summary |
An epizootic of infectious bursa! disease (IBO) occurred in Taiwan in 1992. A culmulative total of 294 chicken flocks in 14 counties of cities were affected, as revealed by the results of this present investigation. A culmulative total of 426,709 chickens were estimated to have been affected, among them 192, 497 (45.11 %) died. The number of flocks affected in 1992 was twice of that in 1991, and number of the birds which were lost in 1992 as a result of IBO were 13 times of that in 1991. The epizootic was first observed in February in northern part of Taiwan, then spreading to the central and southern part of Taiwan. The epidemic reached its peak in August and September of 1992, but still had not died out in the first-half year of 1993. Most of the chickens affected by the epizootic were 3 to 7 weeks old (227/267, 85 %). The oldest chickens affected were 12 weeks old. All breeds of chickens were affected, and the country chicken ( native chicken and simulative native chicken) had the highest incidence and mortality rate. Howerer, both the layer and country chicken had a significantly higher mortality rate than broiler (P<0.05), as observed from a considerrstion of vaccine immunization. 45 % (103/229) of the chicken flocks affected never received any IBO vaccination, 42.8 % (98/229) had one IBO vaccination, and 12.2 % (28/229) had two IBO vaccinations. The mortality rate of the flocks which had IBO vaccination was significantly lower than those flocks without IBO vaccination (P<0.01). More than 1/3 of the chicken flocks affected during the epidemic had a mortality rate higher than 10 %. Additionally, above 10 % of the flocks which were affected had a mortality rate higher then 25 %. The highly virulent IBO virus had been isolated during the epizootic. The epizootic in 1992 in Taiwan was suggested in this study as having been caused by the highly virulent IBO virus, similar to those recently reported in many
European countries and neighboring countries such as.Japan and Korea.
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