Bioassay of Clostera anastomosis Granulosis virus

The second-instar healthy larvae of Clostera. anastomosis were collected in the artificial woodland of poplar in Shuangcheng Town, Heilongjiang Province, China. The dead larvae of C. anastomosis infected by granulosis virus （GV） of Clostera anastomosis were grinded to obtain GV. The GV viral pesticide was diluted to seven concentrations, 1.58×10^3PIB·mL^-1, 1,58×10^4PIB·mL^-1, 1.58×10^5PIB·mL^-1 1.58×10^6PIB·mL^-1, 1,58×10^7PIB·mL^-1; 1.58×10^8PIB·mL^-1 and 1.58×10^9PIB·mL^-1 and the fresh poplar leaves were dipped in the seven concentrations liquids to feed the larvae. After nine days the mortality of larvae was investigated. The minimum corrected mortality （7.32%） of larvae was observed at concentrations of 1.58×10^3PIB·mL^-1 and the maximal mortality （97,36%） was observed at concentration of 1.58×10^9PIB·mL^-1. The regression equation between the logarithm of the virus concentration and the mortality was y= 1.946＋0.558x The LC50 was 2.97×10^5PIB·mL^-1. The LT50 for the virus concentration of 1.58×10^5, 1.58×10^6, 1.58×10^7, 1,58×10^58, 1.58×10^9 PIB·mL^-1 were 8.55d, 6.89d, 5.9d, 4.65d, and 4.08d, respectively, shorting gradually with the concentration increasing, It is concluded that the toxicity of Clostera anastomosis GV is very strong and as a kind of insecticides it has big potential in practical application.

Analysis of the function of D279N mutation of VP2 of infectious bursal disease virus

Infectious bursal disease virus（IBDV）is responsible for the highly contagious infectious bursal disease of chickens.Further understanding the gene-function is necessary to design the tailored vaccine.The amino acid residue 279,located on strand P_F of VP2,is one of the three residues that have been reported to be involved in cell-tropism but with some inconsistency.In this study,to further clarify the amino acids involved in the cell tropism of IBDV,a series of mutations about residue 279were introduced into the VP2 of vv IBDV Gx strain.With the reverse genetic system,we found single mutation of D279N,double mutations of D279N/A284T or Q253H/D279N were not enough to adapt IBDV to chicken embryo fibroblast（CEF）cell.To evaluate whether residue 279 could influence the replication and virulence of IBDV,the virus r Gx HT-279 with three mutations（Q253H/D279N/A284T）was rescued and evaluated.Results showed that the mutation of residue 279 in VP2had no efficient effects on both the replication efficiency in vitro and the virulence to SPF chickens of IBDV.In summary,the results demonstrated that residue 279 of VP2 did not contribute efficiently to cell tropism,replication efficiency,and virulence of IBDV at least in some strains.These findings provided further information for understanding the gene function of IBDV.

Immunological Changes of Chicks Immunized with March＇s Disease Vaccines and Challenged with Virulent MD Virus

The experiment was conducted to inoculate one-day old chicks with March's disease (MD) trivalent and herpesvirus of turkey (HVT) vaccines separately, and then to challenge them with virulent MD virus (vMDV) at the age of 15 days. and 5, 25, 45 and 75 days after the challenge with vMDV, comparing with the control-challenged chicks without immunization, to detect the immunoprotetive efficacy and dynamic changes of the inductive activity of interleukin-2(IL-2), expression of IL-2 receptor and proliferative function of T cells in thymus and spleen; the number of ANAE+T, AP+T cells and IgG, IgM, IgA antibody-producing cells in Bursa Fabricius, spleen,thymus, cecal tonsil and Harder gland; as the amount of T cells and IgG, IgM, IgA in peripheral blood as well as the content of IgG, IgM and IgA in the tear, trachea washings, bile and intestinal fluids of the experimental chicks. The experimental results firstly demonstrate that the immunorcgulation of IL-2, and IL-2 receptor, the cellualr and humoral immune responses were significantly enhanced in the central and peripheral immune organs; the local mucosal immune function were markedly amplified in the respiratory and digestive tracts of the immunized-challenged,chicks, which were closely correlated with the immunoprotection against MD; the immune response and immunoprotective effect of the trivalent vaccine-immunized chicks were much better than those of HVT vaccine-immunized chicks:

N-terminal domain of the RNA polymerase of very virulent infectious bursal disease virus contributes to viral replication and virulence

Dear Editor,Infectious bursal disease virus （IBDV） causes an economically significant disease of chickens worldwide （Berg,2000）. The molecular basis for the virulence of very virulent IBDV （vvIBDV） is not fully understood. Previous studies have shown that genome segment A, especically VP2 protein, plays the most important role in the tropism and pathogenicity of serotype 1 IBDV （Brandt et al., 2001）. VP2 is,however, unlikely to be the only factor for the virulence of vvIBDV （Boot et al., 2000）.