Immunogenicity of a Moraxella bovis bacterin containing attachment and cornea-degrading enzyme antigens.

An adjuvanted Moraxella bovis bacterin containing attachment antigens and cornea-degrading enzyme antigens protected cattle from infectious bovine keratoconjunctivitis (IBK) when experimentally challenged with homologous and heterologous challenge cultures of M. bovis. This bacterin also protected cattle against field exposure to M. bovis. Transmission electron microscopy and fluorescein labeled anti-M. bovis pili antiserum showed pili on the M. bovis bacterin strain. Scanning electron microscopy demonstrated a fibrillar glycocalyx. The bacterin strain of M. bovis, but not all strains of M. bovis, destroyed bovine corneal cell monolayers in vitro. Bovine corneal cells began to separate from each other within 5 min after M. bovis organisms were added and adhered to the cell monolayers. Moraxella bovis organisms remained attached to the disintegrating cells as the cell membrane separated and was digested. Vaccination stimulated bacterial agglutination antibodies. However, protection against experimental challenge was more closely related to the cornea-degrading enzyme content of the experimental bacterins. Twenty-two of 29 cattle (76%) vaccinated with bacterins containing a relative enzyme activity (REA) greater than 0.4 were protected in a rigorous challenge of immunity test. Only 1 of 21 non-vaccinated calves (5%) was free of IBK. Ninety-two percent (24/26) of calves vaccinated with a bacterin containing a REA greater than 0.29 remained free of IBK following field exposure, whereas 47% (8/17) non-vaccinated calves developed IBK. Only 8 of 12 calves (67%) vaccinated with a bacterin containing a REA of 0.09 remained free of IBK. In a larger field efficacy test consisting of 32 herds in six states, the incidence of IBK in individual herds ranged from 0% to 55%. The overall rate of infection was 11.2%. Vaccination of calves with an M. bovis bacterin that contained a REA of 0.63 reduced the incidence of IBK from 11.2% (217/1931) in the non-vaccinated controls to 4.3% (66/1520) in cattle vaccinated once and to 3.1% (48/1536) in cattle vaccinated twice.

Cell-mediated immune response to rabies virus in dogs following vaccination and challenge.

Peripheral blood lymphocytes (PBL) from non-vaccinated dogs and from dogs either vaccinated intramuscularly (IM) or subcutaneously (SC) with an inactivated rabies virus vaccine (Rabguard-TC, Norden Laboratories, Lincoln, NE) or intramuscularly with an attenuated rabies virus vaccine (Endurall-R, Norden Laboratories, Lincoln, NE) were exposed in vitro to rabies virus. Blastogenesis of PBL was measured by incorporation of 3H-thymidine into the DNA of proliferating cells in the presence of a suboptimal concentration of phytohemagglutinin (PHA). Following the first vaccination, there was no difference in the blastogenic response of lymphocytes from dogs vaccinated IM with either the inactivated or attenuated rabies virus vaccines. The inactivated rabies vaccine stimulated as great or greater blastogenic response when it was given SC. The PBL from non-vaccinated control dogs were not stimulated by rabies virus. Dogs vaccinated with the inactivated vaccine developed a lymphocyte blastogenic response to rabies virus following challenge with virulent street rabies virus. Nonvaccinated control dogs did not develop a lymphocyte blastogenic response to rabies virus following challenge with virulent street rabies virus.

Characterization of an attenuated temperature sensitive feline infectious peritonitis vaccine virus.

Intranasal administration of a ts-FIPV vaccine protected cats against two rigorous challenges of immunity. Investigations showed that ts-FIP viral RNA synthesis was normal at 39 degrees C and structural proteins were synthesized, but not expressed at the cell surface. Lack of surface expression combined with decreased virus titer indicate that, although structural viral proteins were initially synthesized, they were not packaged into intact virions at the nonpermissive temperature. The ts-FIP vaccine virus was shown to replicate exclusively in the upper respiratory tract, where lower temperatures allow maturation of the virus. Viral proteins expressed on cells in the upper respiratory tract probably stimulate the development of local IgA and CMI responses and a systemic CMI response which in turn may stop the dissemination of virulent FIPV if it crosses the mucosal barrier. Investigations are ongoing to study the protective mechanism of ts-FIPV induced immunity.

Vaccination of cattle and sheep with a combined Clostridium perfringens types C and D toxoid.

Cattle and sheep (30 each) were vaccinated with a combined Clostridium perfringens type C and C perfringens type D toxoid. Vaccination and blood sample collections were made every 2 weeks over a period of 8 weeks. Increases in antitoxin titers occurred after the 2nd administration of the 2.0-ml combined product. Highest titers were recorded when the 2nd vaccinal dose was given 2 weeks after the first. This confirms reports that response to clostridial antigens is greater when the 2nd immunizing dose is delayed 2 to 6 weeks after the initial dose.

Development of a modified live, canine origin parvovirus vaccine.

A modified live, canine origin parvovirus vaccine was tested for safety, efficacy, and clinical performance. The vaccine protected dogs from challenge of immunity with canine parvovirus (CPV) that caused clinical illness in all nonvaccinated dogs. Vaccinates all developed CPV serum neutralization antibody titers, with a mean value of 1,664. Challenge virus was not isolated from vaccinates, but feces from nonvaccinated dogs were CPV-positive for up to 4 days following challenge. In a pathogenicity test, dogs inoculated orally with 10 times the label dose remained clinically normal. In a reversion-to-virulence test, the vaccine strain remained nonpathogenic through 6 passages in seronegative test dogs. An immunologic interference test demonstrated that test dogs developed antibodies for all antigens in a combined canine distemper virus-adenovirus 2-parainfluenza virus-parvovirus vaccine and a Leptospira interrogans serovars canicola and icterohaemorrhagiae bacterin. A total of 1,796 doses of the multivalent preparation was administered in a field study, with veterinary practitioners reporting 36 local and 5 generalized reactions.

Efficacy of viral components of a nonabortigenic combination vaccine for prevention of respiratory and reproductive system diseases in cattle.

Efficacy and safety of components of an IM-administered vaccine for prevention of infectious bovine rhinotracheitis virus (IBRV), parainfluenza type-3 (PI-3) virus, bovine viral diarrhea virus (BVDV), and respiratory syncytial virus (RSV) infections and campylobacteriosis and leptospirosis were evaluated in cattle, including calves and pregnant cows. Challenge of immunity tests were conducted in calves for IBRV, PI-3 virus, or BVDV vaccinal components. All inoculated calves developed serum-neutralizing antibodies and had substantially greater protection (as measured by clinical rating systems) than did controls after challenge exposure to virulent strains of IBRV, PI-3 virus, BVDV, or RSV. In in utero tests, IBRV or bovine RSV vaccinal strains were inoculated into fetuses of pregnant cows. Histologic changes or abortions did not occur after fetal inoculation of the RSV vaccinal strain, and 10 of 14 fetuses responded serologically. Of 9 fetuses, one responded serologically to the IBRV vaccinal strain after in utero inoculation and was aborted 3 weeks later. In an immunologic interference test, 10 calves vaccinated with 2 doses of the multivalent vaccine, containing the 4 viral components and a Campylobacter-Leptospira bacterin, developed serum-neutralizing antibodies to IBRV, PI-3 virus, BVDV, and RSV without evidence of serologic interference. Under field conditions, 10,771 cattle, including 4,543 pregnant cows, were vaccinated. Vaccine-related abortions did not occur.

Studies on the antigenicity of an inactivated, aluminum hydroxide adjuvant equine influenza vaccine.

An inactivated, aluminum hydroxide adjuvant equine influenza vaccine was tested in horses and guinea pigs to determine the levels of antigen that would elicit maximum serological responses. Vaccine containing serial twofold increments of A/Equi-1/Prague and A/Equi-2/Miami strains of equine influenza virus was administered to random groupings of both types of test animals. The hemagglutination inhibition antibody response for each group was then measured. Results in horses and guinea pigs were compared to determine if the equine serological values could be related to a potency test in laboratory animals. The highest mean hemagglutination inhibition antibody response in horses occurred in groups vaccinated, respectively, with 128 or 256 hemagglutination units of A/Equi-1 and 512 or 1024 hemagglutination units of A/Equi-2 antigen. Groups vaccinated with further two- or fourfold increases in these antigens had mean hemagglutination inhibition titers that were somewhat lower than the maximum levels. When graded doses of vaccine were given to guinea pigs, their hemagglutination inhibition antibody titers reached a plateau of maximum values, similar to the serological response in vaccinated horses. Test horses remained clinically free from signs of equine influenza during the year following vaccination and no untoward post-vaccination reactions were observed.

Field trial evaluation of a reo-coronavirus calf diarrhea vaccine.

Field trials were conducted using an experimental, modified live virus, oral vaccine for prevention of reo- and coronavirus calf diarrhea. Prior to the trials, one or both of the specific causative agents were identified from affected calves in each participating herd. In 21 herds, sequential trials were conducted in which results of uninterrupted vaccination were compared with disease rates during a preceding or subsequent control period. In these herds there was a statistically significant reduction in the morbidity and mortality from disease in 1,598 vaccinates compared with the rates in 829 prevaccination control calves. Morbidity and mortality in 206 post-vaccination control calves rose marginally above the rates in the same vaccinates. In 26 other herds, where double blind trials were conducted, rates of morbidity and mortality from disease were virtually the same for 1,080 vaccinated calves and 355 placebo calves. Vaccinates in the sequential trials had the lowest morbidity and mortality rates of any test group in either field trial format. In a selected dairy herd, both field trial formats were implemented and the results compared. In the double blind trial, vaccinates and placebo calves had comparable rates of morbidity and mortality from disease. When a sequential trial was later implemented, a statistically significant reduction in morbidity and mortality occurred in vaccinates compared with rates in control calves.

Feline leukaemia vaccine protection against viral latency.

Seventeen cats, which were previously vaccinated with a subunit, feline leukaemia vaccine (Leukocell) and subsequently challenged with virulent feline leukaemia virus (FeLV), were tested at 2 to 4 years postchallenge for reactivation of latent FeLV infections. Administration of weekly doses of methylprednisolone induced significant decreases in lymphocyte numbers, but did not reactivate virus in bone marrow cultures from 15 cats in vivo or in vitro. These cats were observed to be neither persistently or latently viraemic prior to corticosteroid administration. The results of this study indicate that the vaccine is effective in affording significant protection against latent FeLV infections, even after severe immunosuppression. This finding, coupled with previously published results indicating protection against persistent viraemia and tumour formation, makes this vaccine highly effective in protecting against FeLV infections and associated disease.

Evaluation of immunosuppressive effect and efficacy of an improved-potency feline leukaemia vaccine.

An inactivated feline leukaemia vaccine was tested to determine if process improvements would permit it to be effectively used in a two-dose primary regimen versus the three-dose regimen required for a previous vaccine. Twenty-five cats were vaccinated with two subcutaneous doses given 3 weeks apart. Vaccinates and controls were artificially immunosuppressed to enhance susceptibility to challenge, and inoculated with virulent feline leukaemia virus (FeLV) 2 weeks after the second dose. Following challenge, seven (28%) vaccinates became persistently viraemic, versus six (60%) controls. Nine (36%) other vaccinates became transiently viraemic and nine were aviraemic. The mean postvaccination ELISA gp70 antibody value was 0.796 for aviraemic vaccinates, 0.575 for transiently viraemic vaccinates, and 0.350 for persistently viraemic vaccinates. Eighteen of 25 vaccinates had a postvaccination antibody response greater than or equal to 32 to feline oncornavirus associated cell membrane antigen. Seven of 25 (28%) vaccinates developed postvaccination virus neutralization (VN) antibody titres, and 16 of 25 (64%) developed postchallenge VN antibody titres. One of 10 controls developed postchallenge VN antibody titres. An in vitro lymphocyte blastogenesis assay to evaluate immunosuppressive effects of vaccination revealed no significant difference in the mean stimulation index for vaccinates versus controls. Results indicated that vaccination with two doses was an effective immunoprophylactic regimen in the face of FeLV challenge severe enough to produce persistent viraemia in 60% of non-vaccinated controls.

Effect of age and pregnancy on the antibody and cell-mediated immune responses of horses to equine herpesvirus 1.

The cell-mediated immune response and antibody response of horses of varying ages and of pregnant horses to equine herpesvirus 1 antigen were examined. Six to eight month old horses showed either no increase or slight increases in anti-equine herpesvirus 1 serum neutralizing antibody following vaccination and revaccination with a modified live equine herpesvirus 1 vaccine. However, these same horses showed a marked increase in the cell-mediated immune response to equine herpesvirus 1 as measured by the lymphocyte transformation test. Eighteen to 21 month old horses showed four to 64-fold increases in anti-equine herpesvirus 1 serum neutralizing antibody titer following vaccination, but the cell-mediated immune response to equine herpesvirus 1 was low or absent. Only after revaccination did they show an increased cell-mediated immune response to equine herpesvirus 1. The cell-mediated immune response of mares in the latter stages of pregnancy to equine herpesivurs 1 was suppressed although antibody titers increased as much as 16-fold following exposure to virulent equine herpesvirus 1.

An enzyme immunoassay for measuring Escherichia coli pilus antigens.

Quantitative enzyme-linked antibody centrifuge (ELAC) assays have been developed for measuring Escherichia coli adhesion pilus antigens K99, K88, 987P and F41 in E. coli bacterins used for protecting newborn animals against neonatal enteric colibacillosis. The test consists of reacting an alkaline phosphatase conjugate of specific pilus antigen antibody directly with dilutions of the bacterin on test and a standard reference bacterin. Following incubation the unbound conjugate is removed by two centrifugation steps and the bacteria with bound conjugate are reacted with substrate. The optical density is measured at 405 nm. Unknown samples are compared to a standard bacterin known to develop sufficient immunity in sows to provide protective levels of passive maternal immunity to their piglets. A relative potency (RP) value is calculated and used for standardizing bacterial concentrates and for final potency testing. The advantages to be realized are: shortening of the test period, specificity, and reduction in test animal usage.