| Riemerella anatipestifer infection is a contagious disease of ducks, goose, turkeys and variousother birds, and has caused the highest mortality among duck diseases. It is a major disease confrontingthe duck industry all over the world, duck farm upon the occurrence of the disease is difficult toeradicate infection. It usually brings lots of economic losses to the duck industry because of highmortality (5%~75%) and loss of weight. The disease, variously known as new duck disease, ducksepticaemia and infectious serositis, occurs in acute form in ducks under about8weeks of age (althoughducklings up to10-35days of age are the most susceptible), and in chronic form in older birds. Controlof the disease mainly depend on antibiotic treatment, as the bacteria to multiple antibiotic resistancecontinues to increase and needs of food security, vaccine development will be very urgent.At present, there are21serotypes of R. anatipestifer which have been identified throughout theworld, and there is very little or no cross-protection amongst each serotype. Hundreds of R. anatipestiferisolates were isolated and identificated from duck farms all over the country, by serological studyresults show that serotype1,2and10are the most prevalent serotype of R. anatipestifer infection. Tobetter control the infection, we developed the inactivated oil-emulsion vaccines of serotype1,2and10R. anatipestifer in this study.Serotype1,2and10R. anatipestifer strains were recovered and identified for the study afterrejuvenation in vivo. Strains CH3、WJ4, NJ-3、Yb2, HXb2and YXL1were selected for the virulenceassay. The results showed that all strains had a strong virulence and the median lethal dose was2×108CFU,3.25×108CFU;5.62×107CFU,1.07×105CFU;82CFU,2.8×108CFU respectively. WJ4, Yb2and HXb2was selected as the challenge strains, and the challenge dose was5×108CFU、1×106CFU、800CFU respectively. Five isolates of each serotype R. anatipestifer were used as the vaccinecandidates to develop inactivated oil-emulsion vaccines respectively. After two injectionssubcutaneously on5days and18days, all the ducklings generated high ELISA titers of specificantibodies against respective R. anatipestifer isolates. However, there are large differences in theprotection from challenge with same serotype challenge strains. The results of antibody production andprotection from challenge indicated that CH3﹑NJ-3and HXb2were ideal candidates for the productionof inactivated oil-emulsion vaccine.On the basis of the inactivated oil-emulsion vaccines of serotype1,2and10R. anatipestifer, theoptimal immune dosage for different serotype vaccine were determined. The results showed thatoptimal immune dose of serotype1,2and10R. anatipestifer was109、5×108、5×108CFU/doserespectively. The trivalent inactivated oil emulsion vaccine of R. anatipestifer was developed withstrains CH3、NJ-3and HXb2and used to immunize Cherry Valley ducklings. Immunization assayindicated that all the duckling immunized with the vaccine mentioned above generated high ELISAtiters of antibodies against R. anatipestifer. A comparative study of different adjuvant vaccine immune protection can be found that the trivalent inactivated oil-emulsion vaccine of R. anatipestifer preparedwith Montanide ISA VG has better immune protection than others. The protection rate was greater than90%after the first immunization, and the ducklings after two immunizations were100%protected fromthe challenges of WJ4, Yb2or HXb2.The protection period of the trivalent inactivated oil-emulsion vaccine of R. anatipestifer wasdetermined. The results showed that the specific antibody could be detected in serum of duckling afterthe first immunization, and antibody titer lasted for more than10weeks. To establish immunizationschedule, we monitored the antibody production of the ducklings which were immunized at day1,2,3,4,5,6and7. The results showed that the ducklings were immunized at day3~7generated higher andmore stable levels of antibodies than those immunized at day1~2. |
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