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KMID : 0359320000400010110
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Korean Journal of Veterinary Research
2000 Volume.40 No. 1 p.110 ~ p.116
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Development of a live vaccine strain of duck viral hepatitis using a Korean isolate
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김재홍/Kim, Jae Hong
한명국/모인필/김기석/성환우/송창선/이윤정/Han, Myung Guk/Mo, In Pil/Kim, Ki Seuk/Sung, Haan Woo/Song, Chang Seon/Lee, Youn Jeong
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Abstract
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Duck viral hepatitis is an acutic, highly infectious viral disease of young ducklings. The most practical means for controlling duck viral hepatitis is the vaccination of ducklings or of a breeding stock.
We attempted to develop a vaccine strain of duck hepatitis virus (DHV) using a Korean isolate by serial chicken embryo passages. The propagation of DHV in chicken embryos was carried 140 passages.
After the 50^(th) passage, of which the virus was non-pathogenic for ducklings, approximately every 20^(th) passage of the virus was tested for vaccinal efficacy. Both the 70^(th) and 90^(th) passage of the virus gave good protection against challenge infection to a DHV-DRL reference strain(type 1) and a virulent Korean isolate. The 110^(th), 125^(th) and 140^(th) passage of the virus were less protective than the 70^(th) and 90^(th) passage, which means that more than 110^(th) passage may lead to over-attenuation of the virus.
Ducklings vaccinated with the chicken-embryo-adapted virus by oral, intramuscular or eye drop administration showed earlier rosistance to challenge infection from 3 to 7 days postvaccination. Of the above methods, ducklings vaccinated intramuscularly presented the most rapid resistance against challenge.
The minimum immune dose of the chicken-embryo-adapted virus in ducklings was also studied. Ducklings inoculated with a dose of 10^(2.0) ELD_(50) and below were not fully protected against challenge with a virulent DHV, showing a protection rate of 67% to 73%, but ducklings inoculated with a dose of 10^(3.0) ELD_(50) and over were completely protected.
The virus yield of the chicken-embryo-adapted DHV was examined at 24hrs and 48hrs of the incubation time in the allantoic fluid, embryo head and embryo minus head of the embryonating egg. In all three components, the titer of the virus was higher at 48 hours than that at 24 hours after incubation. And the titer of the virus was higher in the embryo minus head, embryo head and the allantoic fluid, in order.
Field trials for evaluating the efficacy of the attenuated DHV as a live vaccine were done in duck farms with about 25% mortality of flocks resulting from duck viral hepatitis. After the use of the experimental vaccine, the mortality due to duck viral hepatitis was dramatically reduced in the farms.
These results indicated that the attenuated DHV using a Korean isolate could be a good candidate as a live vaccine strain of DHV in Korea.
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