Evidence that soilborne wheat mosaic virus moves long distance through the xylem in wheat.

Soilborne wheat mosaic virus (SBWMV) is a member of the genus Furovirus of plant viruses. SBWMV is transmitted to wheat roots by the plasmodiophorid vector Polymyxa graminis. Experiments were conducted to determine the path for SBWMV transport from roots to leaves. The results of immunogold labeling suggest that SBWMV enters and moves long distance through the xylem. SBWMV may enter primary xylem elements before cell death occurs and then move upward in the plant after the xylem has matured into hollow vessels. There is also evidence for lateral movement between adjacent xylem vessels.

Duration of serum antibody responses following vaccination and revaccination of cattle with non-living commercial Pasteurella haemolytica vaccines.

This study was designed to determine the duration of serum antibody responses to Pasteurella haemolytica whole cells (WC) and leukotoxin (LKT) in weanling beef cattle vaccinated with various non-living P. haemolytica vaccines. Serum antibodies to P. haemolytica antigens were determined periodically through day 140 by enzyme-linked immunosorbent assays. At day 140, cattle were revaccinated, and antibody responses periodically determined through day 196. Three vaccines were used in two experiments (A and B), OneShot, Presponse HP/tK, and Septimune PH-K. In general, all three vaccines between 7 and 14 days induced antibody responses to WC after vaccination. Antibodies to LKT were induced with OneShot and Presponse. Revaccination at days 28 and 140 usually stimulated anamnestic responses. Serum antibodies to the various antigens remained significantly increased for up to 84 days after vaccination or revaccination. The intensity and duration of antibody responses were variable depending on the experiment and vaccines used. Vaccination with OneShot usually stimulated the greatest responses to WC. Vaccination with OneShot or Presponse resulted in equivalent primary anti-LKT responses. In experiment B, spontaneous seroconversion was found in numerous calves on day 112. Revaccination of those cattle at day 140 resulted in markedly variable antibody responses such that several groups had no increase in antibody responses.

Serum antibody responses of cattle vaccinated with partially purified native Pasteurella haemolytica leukotoxin.

The objective of these experiments was to study the serum antibody responses of cattle to partially purified, native Pasteurella haemolytica A1 leukotoxin (LKT) formulated with a commercial aluminum hydroxide-DDA-bromide adjuvant. In two experiments, calves received two intramuscular injections 21 days apart and sera were obtained periodically. Serum antibody responses to P. haemolytica outer membrane proteins (OMPs), formalinized P. haemolytica, and LKT were determined. In Experiment A, Holstein calves (140 kg each) were vaccinated with either 10, 1.0 or 0.1 micrograms of LKT, 10(9) c.f.u. of live P. haemolytica, or adjuvanted diluent. In Experiment B, mixed-breed beef calves (200 kg each) were vaccinated with either 100, 50 or 10 micrograms of LKT, 10(9) c.f.u. live P. haemolytica, or adjuvanted diluent. Vaccination of dairy calves with 10 micrograms of partially purified LKT stimulated LKT neutralizing antibody responses similar to those stimulated by vaccination of one calf with live P. haemolytica. In Experiment B, which used larger and different breeds of cattle, two vaccinations 3 weeks apart with 50 micrograms LKT stimulated LKT neutralizing responses equivalent to or greater than those stimulated by vaccination with live P. haemolytica. In both experiments, LKT vaccines stimulated only low antibody responses to formalinized P. haemolytica or to OMPs.