| Summary |
An Epidemic of Newcastle Disease (ND) occurred in Taiwan in the period from Feb. to May. 1984. Among the 11 counties investigated, there were 245 chicken farms affected, about 2.76 million, or 60%, of the chicken raised in this country were affected, among them about 0.57 Million, or 20% died. The mortality was 12.5% in this epidemic.
In this epidemic, all type of chicken (Breeder, Broiler, layer, Mixer, and Native) and all age groups (1 to 71 week-old) were affected; however, about half of the chicken flocks affected were under 2-month-old.
The most common ND vaccination program in Taiwan was at least 3 vaccination at 4, 14 and 28 days of age, respectively. It was found that most of the chicken flock (78.78%) were affected at the time before 3rd or 4th vaccination. (The time before or just finished the three time's basic im-munization). lt was suspected that improper vaccination method and poor management was the cause of the outbreaks.
Since there were chicken flocks with the proper immunization affected by ND, it is suspected there may be some other causes of the epidemic. The most suspicious cause was the immunosupprcssion effect by Infectious bursa! disease (lBD) virus infection or by improper IBD vaccination program. In this epidemic, about 80% of the affected chicken flock had'nt received any IBO vaccination. Among the chicken flocks previously had received lBD vrccina-
tion. 90% of the tlocks received IBD vaccina-tion younger than 3-week-old. Moreover,the enhancement of the pathogenicity of field strain of ND virus is also suspected.
|