Comparison of reproductive protection against bovine viral diarrhea virus provided by multivalent viral vaccines containing inactivated fractions of bovine viral diarrhea virus 1 and 2.

Bovine viral diarrhea virus (BVDV) is an important viral cause of reproductive disease, immune suppression and clinical disease in cattle. The objective of this study was to compare reproductive protection in cattle against the impacts of bovine viral diarrhea virus (BVDV) provided by three different multivalent vaccines containing inactivated BVDV. BVDV negative beef heifers and cows (n = 122) were randomly assigned to one of four groups. Groups A-C (n = 34/group) received two pre-breeding doses of one of three commercially available multivalent vaccines containing inactivated fractions of BVDV 1 and BVDV 2, and Group D (n = 20) served as negative control and received two doses of saline prior to breeding. Animals were bred, and following pregnancy diagnosis, 110 cattle [Group A (n = 31); Group B (n = 32); Group C (n = 31); Group D (n = 16)] were subjected to a 28-day exposure to cattle persistently infected (PI) with BVDV (1a, 1b and 2a). Of the 110 pregnancies, 6 pregnancies resulted in fetal resorption with no material for testing. From the resultant 104 pregnancies, BVDV transplacental infections were demonstrated in 73 pregnancies. The BVDV fetal infection rate (FI) was calculated at 13/30 (43%) for Group A cows, 27/29 (93%) for Group B cows, 18/30 (60%) for Group C cows, and 15/15 (100%) for Group D cows. Statistical differences were observed between groups with respect to post-vaccination antibody titers, presence and duration of viremia in pregnant cattle, and fetal infection rates in offspring from BVDV-exposed cows. Group A vaccination resulted in significant protection against BVDV infection as compared to all other groups based upon outcome measurements, while Group B vaccination did not differ in protection against BVDV infection from control Group D. Ability of inactivated BVDV vaccines to provide protection against BVDV fetal infection varies significantly among commercially available products; however, in this challenge model, the inactivated vaccines provided unacceptable levels of BVDV FI protection.

Virus detection by PCR following vaccination of naive calves with intranasal or injectable multivalent modified-live viral vaccines.

We evaluated duration of PCR-positive results following administration of modified-live viral (MLV) vaccines to beef calves. Twenty beef calves were randomly assigned to either group 1 and vaccinated intranasally with a MLV vaccine containing bovine alphaherpesvirus 1 (BoHV-1), bovine respiratory syncytial virus (BRSV), and bovine parainfluenza virus 3 (BPIV-3), or to group 2 and vaccinated subcutaneously with a MLV vaccine containing bovine viral diarrhea virus 1 and 2 (BVDV-1, -2), BoHV-1, BRSV, and BPIV-3. Deep nasopharyngeal swabs (NPS) and transtracheal washes (TTW) were collected from all calves, and whole blood was collected from group 2 calves and tested by PCR. In group 1, the proportions of calves that tested PCR-positive to BVDV, BoHV-1, BRSV, and BPIV-3 on any sample at any time were 0%, 100%, 100%, and 10%, respectively. In group 1 calves, 100% of calves became PCR-positive for BoHV-1 by day 3 post-vaccination and 100% of calves became PCR-positive for BRSV by day 7 post-vaccination. In group 2, the proportions of calves that tested positive to BVDV, BoHV-1, BRSV, and BPIV-3 on any sample at any time were 50%, 40%, 10%, and 0%, respectively. All threshold cycle (Ct) values were >30 in group 2 calves, irrespective of virus; however, Ct values <25 were observed in group 1 calves from PCR-positive results for BoHV-1 and BRSV. All calves were PCR-negative for all viruses after day 28. Following intranasal MLV viral vaccination, PCR results and Ct values for BRSV and BoHV-1 suggest that attempts to differentiate vaccine virus from natural infection is unreliable.

Evaluation of reproductive protection against bovine viral diarrhea virus and bovine herpesvirus-1 afforded by annual revaccination with modified-live viral or combination modified-live/killed viral vaccines after primary vaccination with modified-live viral vaccine.

The objective of this study was to compare reproductive protection in cattle against bovine viral diarrhea virus (BVDV) and bovine herpesvirus 1 (BoHV-1) provided by annual revaccination with multivalent modified-live viral (MLV) vaccine or multivalent combination viral (CV) vaccine containing temperature-sensitive modified-live BoHV-1 and killed BVDV when MLV vaccines were given pre-breeding to nulliparous heifers. Seventy-five beef heifers were allocated into treatment groups A (n=30; two MLV doses pre-breeding, annual revaccination with MLV vaccine), B (n=30; two MLV doses pre-breeding, annual revaccination with CV vaccine) and C (n=15; saline in lieu of vaccine). Heifers were administered treatments on days 0 (weaning), 183 (pre-breeding), 366 (first gestation), and 738 (second gestation). After first calving, primiparous cows were bred, with pregnancy assessment on day 715. At that time, 24 group A heifers (23 pregnancies), 23 group B heifers (22 pregnancies), and 15 group C heifers (15 pregnancies) were commingled with six persistently infected (PI) cattle for 16days. Ninety-nine days after PI removal, cows were intravenously inoculated with BoHV-1. All fetuses and live offspring were assessed for BVDV and BoHV-1. Abortions occurred in 3/23 group A cows, 1/22 group B cows, and 11/15 group C cows. Fetal infection with BVDV or BoHV-1 occurred in 4/23 group A offspring, 0/22 group B offspring, and 15/15 group C offspring. This research demonstrates efficacy of administering two pre-breeding doses of MLV vaccine with annual revaccination using CV vaccine to prevent fetal loss due to exposure to BVDV and BoHV-1.

Effects of sub-minimum inhibitory concentration antibiotic levels and temperature on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus.

The objective of this study was to determine the effects of sub-minimum inhibitory concentrations (sub-MICs) of 2 veterinary antibiotic preparations, chlortetracycline (CTC) and chlortetracycline-sulfamethazine (CTC + SMZ), on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus at normal and febrile body temperatures. Sub-minimum inhibitory concentrations of both antibiotics reduced the growth rates of M. haemolytica and H. somnus. Growth of both species was not inhibited when grown at 41 degrees C compared to 37 degrees C. There was no detectable consistent effect of antibiotic or temperature on outer membrane protein expression for either species. Our study indicates that sub-MIC levels of CTC and CTC + SMZ markedly impair growth of clinical M. haemolytica and H. somnus isolates, potentially allowing more effective host clearance during infection.

Issues and challenges in developing long-acting veterinary antibiotic formulations.

Antibiotics are an important class of therapeutic agents, which are used for the treatment of bacterial infectious diseases in a variety of animal species. Antibiotic therapy varies from treatment period to administration routes, depending on the animal species or the type of the disease being treated. Despite the fact that there are a wide variety of commercially available antibiotics, difficulties and problems associated with the administration of antibiotics to animals still exist. Thus, there is a great need and tremendous opportunity to develop long-acting antibiotic formulations for veterinary applications. In this review article, common approaches used to develop long-acting antibiotic formulations are summarized. The challenges and issues related to the development of these long-acting formulations are also discussed.

Alteration of DNA adenine methylase (Dam) activity in Pasteurella multocida causes increased spontaneous mutation frequency and attenuation in mice.

Pasteurella multocida is one of the primary bacterial pathogens associated with bovine respiratory disease (BRD) complex. Relatively few virulence factors of P. multocida have been characterized, and there is a need for improved vaccines for prevention of BRD. In other Gram-negative species, DNA adenine methylase (Dam) regulates the expression of virulence genes, and appropriate expression of Dam is required for virulence. In this study, the authors cloned and sequenced the P. multocida A1 dam gene and demonstrated that it is able to restore Dam function in an Escherichia coli dam mutant. When P. multocida dam was placed under the control of a constitutively expressed promoter on a plasmid, it caused an increased spontaneous mutation rate in P. multocida. In addition, the plasmid-mediated alteration of Dam production in P. multocida caused it to be highly attenuated in mice. These findings indicate that appropriate expression of Dam is required for virulence of P. multocida, which is believed to be the first report that Dam is required for virulence of a species in the Pasteurellaceae. Therefore, Dam may function as a virulence gene regulator in the Pasteurellaceae, similar to previously reported findings from other Gram-negative species.

Controlled release of oxytetracycline in sheep.

A novel biodegradable injectable formulation of oxytetracycline (OTC) was administered subcutaneously to sheep at a dose of 40 mg/kg. Blood samples were collected from the jugular vein at predetermined time intervals. The concentration of OTC in plasma was analyzed by an HPLC method. The concentrations of OTC in plasma were maintained at or above 0.5 microg/ml (minimum inhibitory concentration) for approximately 6 days. The pharmacokinetic parameters of OTC in sheep were also determined by monitoring the plasma concentration of OTC after a single intravenous injection of a commercially available OTC formulation at 10 mg/kg body weight. The in vivo release profiles of OTC from the biodegradable injectable formulations in sheep were determined from the plasma concentration time profiles by the deconvolution method using PCDCON software. The in vitro release of OTC from the biodegradable injectable formulation was tested in phosphate buffer (pH 7.4), containing 0.686% w/v of sodium sulfite as antioxidant. The correlation between the in vitro and in vivo release of OTC from the injectable formulation was also evaluated. The results of the in vivo evaluation of the formulation in sheep indicated that a controlled release biodegradable injectable dosage form of OTC for food animals is feasible.