Infectious bursal disease virus (IBDV) has become a major problem in recent years. Conventional vaccines make use of attenuated or inactivated viral strains, but these are gradually losing their effectiveness. We investigated the possibility of using purified VP2, a subunit of IBDV structural protein expressed in insect cells, as a vaccine. The VP2 gene was cloned into pAcYM1. The cloned gene was expressed in a baculovirus system, giving rise to a high quantity of recombinant VP2 (rVP2) protein. The length of the VP2 is 453 amino acids, and it contains two additional amino acids of the baculovirus at the carboxyl terminus. The molecular mass of the protein is about 48 kD. The rVP2 protein reacted with antibodies raised against viral VP2 and had a similar molecular weight. This protein was tested in a controlled vaccination experiment and compared with an inactivated commercial vaccine. High levels of antibodies were raised by the vaccinated birds. The vaccinated birds were challenged with a pathogenic viral strain. rVP2-vaccinated chickens exhibited high resistance to the virus. No mortality or weight changes in the bursa of Fabricius were observed in the vaccinated birds, whereas in the negative control birds, vaccinated with phosphate buffer, up to 50% mortality was found. Higher levels of antibodies were found by enzyme-linked immunosorbent assay in birds vaccinated with rVP2 compared with those vaccinated with the commercial vaccine. This study suggests the potential use of the isolated rVP2 as a subunit vaccine.
We determined the sequence of the coding region of segment A, coding for the viral proteins (VPs) VP2, VP4, and VP3, of a very virulent (vv) infectious bursal disease virus (IBDV) isolated in Israel and named IBDVks. We compared the deduced amino acid sequences of the proteins of the new isolate with those of the same proteins from several IBDV isolates, as published in recent years. The amino acid sequences of VP3 and VP4 of the Israeli isolate were 1.9%-2.3% different from the sequences of their counterparts from classical strains. Thus, the stable region of VP2 of IBDVks was very similar (0-0.68% difference) to the same region of VP2 from vv strains from Europe and Japan but distinct from that of proteins from classical strains from Europe, the United States, and Australia (up to 9.42% divergence), showing that IBDVks is more closely related to the vv strains from Europe and Japan. We found that viruses isolated in recent years resemble each other more than isolates from the same areas isolated a few years earlier. Hence, IBDVks can be categorized in one group with vv new isolates from Europe and Japan. This group has been found to be distinct from new isolates in the United States and strains isolated before the IBDV epidemic during the late 1980s.
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