Serologic responses of young colostrum fed dairy calves to antigens of Pasteurella haemolytica A1

The potential and limitations of early calfhood vaccination to induce active immunity to Pasteurella haemolytica A1 in conventional colostrum fed calves were investigated. Holstein dairy calves (n = 29) were vaccinated at 2 and 4 weeks of age, or at 6 and 8 weeks of age with a commercial culture supernatant vaccine (Presponse, Langford Inc., Guelph, Ont., Canada), or remained unvaccinated as controls. Serum antibody titres were measured using an indirect bacterial agglutination assay, a leukotoxin neutralization assay, and enzyme immunoassays for antibodies of the IgM, IgG1, and IgG2 isotypes binding purified capsular polysaccharide of P. haemolytica A1. Seroconversion (fourfold or greater increase in serum antibody titre) rates were compared using Fisher's exact test. The effects of passive antibody titres and age on response to vaccination were assessed by linear modelling. Vaccination at 2 and 4 weeks of age was associated with 40%, and 0% of calves seroconverting on the basis of agglutinating antibody titres, and leukotoxin neutralizing titres respectively, and 50%, 0%, and 0% seroconverting on the basis of IgM, IgG1 and IgG2 antibodies to capsular polysaccharide, respectively. Agglutinating antibody responses were not related to prevaccination antibody titres, or to age at vaccination. Higher responses (p = 0.08) to leukotoxin were observed in older calves (after taking differences in prevaccination titres into account). Statistical analyses of responses to capsular polysaccharide among calves with comparable prevaccination IgG1 antibody titres revealed significantly higher IgM, IgG1 and IgG2 responses in older calves. Rising titres of IgM antibodies in nonvaccinated calves after 5 weeks of age suggest natural exposure to P. haemolytica A1 or antigens which result in serologic cross-reactions as a means of priming immune responses.     

A study of maternally derived measles antibody in infants born to naturally infected and vaccinated women

Maternal, cord and infant measles antibody levels were measured and compared in a group of 411 vaccinated mothers and 240 unvaccinated mothers, and their babies, between 1983 and 1991. Maternal and cord sera were tested by haemagglutination inhibition and/or enzyme-linked immunosorbent assay, and plaque reduction neutralization tests were also used to test infant sera. Geometric mean titres were significantly higher in the unvaccinated than in the vaccinated mothers (P < 0.001). Infants born to mothers with a history of measles had higher antibody levels at birth than infants of vaccinated mothers and, although the difference narrowed over time, continued to have higher levels up to 30 weeks of age. Between 5 and 7 months of age significantly more of the children of vaccinated mothers had plaque reduction neutralization antibody levels below that which would interfere with vaccination. As the boosting effect of circulating natural measles disappears, earlier measles vaccination may need to be considered, perhaps as part of a two-dose policy.     

Assessment using ELISA of the herd immunity levels induced in cattle by foot-and-mouth disease oil vaccines

The development of a liquid-phase blocking sandwich ELISA (LPBE) to measure antibodies (Ab) produced in cattle with the O, A and C foot-and-mouth disease virus (FMDV) types of commercial vaccines used in Argentina is described. The test was specific: 99% of na?ve cattle sera (n = 130) gave titres below log10 = 1.2, and none had a titre above log10 = 1.5. Comparative studies with serum neutralization test (SNT) using sera from cattle which received one or more vaccine doses is reported. The overall rank correlation coefficient (Spearman's rho, rs) between SNT and LPBE were highly significant (rs > 0.67, P < 0.0001) for all vaccine strains. LBPE Ab titres on sera collected 90 days post vaccination were compared with results of cattle protection tests by applying a logistic regression. The minimum Ab titres at which 85% and 75% of the cattle were protected for each FMDV type were determined in order to interpret field Ab data in terms of protection. Application of this method allows large scale serological examinations to monitor antibody levels in vaccinated animals as an indirect indicator of the FMD control program status in the field. Its use in the evaluation of commercial batches of FMD vaccine is discussed.     

Effect of levodopa therapy on visual evoked potentials and visual acuity in amblyopia

Between 10 and 11 years after children were vaccinated with Vi capsular polysaccharide of Salmonella typhi or meningococcal A + C control vaccine in a double blind randomized trial, we traced 83 subjects, aged 16-20 years. A blood sample was taken for determination of Vi antibody titres in both groups by radioimmunoassay. TO and TH titres were also done to assess if the participants had had recent exposure to typhoid fever. Fifty-eight percent of subjects in both groups had protective levels of Vi antibody against Salmonella typhi (a titre greater than 1 microgram ml-1). There was no significant difference in the levels of Vi antibodies in the cases versus the controls (p = 0.5). Two of the children who had received meningococcal A + C vaccine had recently had typhoid fever. Our data show that adolescents in typhoid endemic areas have high levels of Vi antibodies regardless of previous vaccination status, suggesting that Vi antibodies are acquired in adolescence by a large percentage of the population in this area. Moreover, Vi vaccination has led to ongoing antibody production in greater than 50% of Vi vaccinated children in an endemic area for a period of 10 years. Ongoing antigenic exposure may have contributed to these antibody levels.     

Effect of passive immunization or maternally transferred immunity on the antibody response to a genetic vaccine to rabies virus

A plasmid vector, termed pSG5rab.gp, expressing the glycoprotein of rabies virus was tested in young adult or neonatal mice in the presence of maternally transferred immunity or passively administered antibodies to rabies virus for induction of an antibody response. Mice born to rabies virus-immune dams developed an impaired antibody response to genetic immunization at 6 weeks of age, as had been previously observed upon vaccination with an inactivated viral vaccine. Similarly, mice passively immunized with hyperimmune serum showed an inhibited B-cell response upon vaccination with the pSG5rab.gp vector, resulting in both cases in vaccine failures upon challenge with a virulent strain of rabies virus. In contrast, the immune responses of mice vaccinated as neonates in the presence of maternal immunity or upon passive immunization to rabies virus with the pSG5rab.gp construct were only marginally affected.     

The effects of IFN-gamma activated mouse peritoneal and alveolar macrophages on Cryptosporidium parvum development

Three hundred and forty-seven serum samples from 22 Iowa swine herds were screened for TGEV/PRCV neutralizing antibody. Ninety-one percent of the sera and all 22 herds were positive. These sera were then tested by the blocking ELISA test to distinguish TGEV and PRCV antibody. The ELISA test confirmed the high percentage of TGEV/PRCV positive sera. By the blocking ELISA test, 12 herds were PRCV positive, 6 herds were TGEV positive and 4 herds were mixed with sera either positive for TGEV or PRCV antibody. The results suggest a recent increase in TGEV/PRCV seroprevalence in Iowa swine most likely due to subclinical PRCV infections.     

Oropharyngeal airway dimensions and functional-orthopedic treatment in skeletal Class II cases

Lambs sucking non-immunised ewes or ewes immunised 4-5 weeks before lambing with live attenuated, aromatic-dependent (aroA) Salmonella typhimurium (strain CS 332) were challenged orally at either 2, 4 or 7 days of age with virulent S. typhimurium (strain CS 94) at doses ranging from 10(9) to 10(13) colony forming units. No lambs displayed signs of clinical salmonellosis and all survived challenge but those sucking immunised ewes had organisms of the challenge strain in their faeces for much shorter periods of time than lambs of the control ewes. High titres of specific antibodies were measured in colostrum and milk of immunised ewes in comparison with very low titres measured in samples from control ewes; these differences were reflected by the titres of antibodies in the sera of corresponding lambs. At 2 days after lambing, the major antibody isotype in the colostrum of immunised ewes and sera of their lambs was IgM whereas at 7 days IgG1 was the predominant isotype. While it was clear that vaccination of pregnant ewes with the live attenuated vaccination conferred protection against experimentally-induced salmonellosis in their lambs, considerable protection was observed in control lambs in spite of there being very low titres of antibodies in the mammary secretion of their dams. The latter observation could be related to the presence of contain non-antibody potent bactericidal factors previously described in colostrum and milk.     

Therapeutic periocular vaccination with a subunit vaccine induces higher levels of herpes simplex virus-specific tear secretory immunoglobulin A than systemic vaccination and provides protection against recurrent spontaneous ocular shedding of virus in latently infected rabbits

Rabbits latently infected with herpes simplex virus type 1 (HSV-1) were vaccinated either periocularly or systemically with a subunit vaccine (gB2 + gD2) plus adjuvant or adjuvant alone. Tear films were collected daily to measure recurrent infectious HSV-1 shedding. After systemic vaccination, the latently infected rabbits were not protected against recurrent ocular viral shedding (HSV-1-positive tear film cultures/total cultures) compared with either the systemic or periocular adjuvant controls (systemic vaccination = 49 of 972, 5.0%; systemic control = 46 of 972, 4.7%; periocular control = 43 of 930, 4.6%; P > 0.8). In contrast, latently infected rabbits vaccinated periocularly with the same vaccine had significantly reduced recurrent shedding (20 of 1026, 2.0%) compared with controls (P < 0.001) or systemic vaccination (P = 0.0002). Thus, recurrent HSV-1 shedding was significantly reduced by therapeutic local periocular subunit vaccination but not by therapeutic systemic subunit vaccination. Neutralizing antibody titers in the serum of systemically and ocularly vaccinated rabbits was similar. In contrast, HSV-specific tear secretory immunoglobulin A was significantly higher in the ocularly vaccinated group (P < 0.01). These results strongly suggest that in the rabbit, and presumably in humans, the local ocular (mucosal) immune response is much more important than the systemic immune response for therapeutic protection against recurrent ocular HSV-1. Thus development of a therapeutic vaccine against recurrent ocular HSV-1 should be directed at enhancing the local ocular (mucosal) immune response.     

Age-dependent Neisseria meningitidis serogroup C class-specific antibody concentrations and bactericidal titers in sera from young children from Montana immunized with a licensed polysaccharide vaccine

Neisseria meningitidis serogroup C bactericidal titers and class-specific enzyme-linked immunosorbent assay (ELISA) antibody concentrations were measured in sera from 173 children (1 to 5 years old) before and 6 weeks and 7 months following vaccination with a quadrivalent (A/C/Y/W-135) polysaccharide vaccine. The immune responses of the children were compared with those of 40 adults 6 weeks postvaccination. Both bactericidal titers and ELISA antibody concentrations were significantly higher in the adults than in the children (P < 0.05). In addition, the ratio of immunoglobulin G (IgG) to IgM was higher in the children than in the adults. With an ELISA total antibody concentration of >/=2 microg/ml used as a measure of seroconversion, >/=84% of the individuals from each age group responded to the serogroup C polysaccharide. However, with a >/=4-fold-increase in bactericidal titer used, only 18% of 1-year-olds, 32% of 2-year-olds, and 50 to 60% of 3-, 4-, and 5-year-olds seroconverted. The ELISA results suggest that >50% of all children retained >/=2 microg of total antibody per ml at 7 months postimmunization. However, the bactericidal titers suggest that <10% of children <4 years old retained a >/=4-fold increase at 7 months following vaccination. Of particular note, 59 of 79 sera (75%) from the 1- and 2-year-olds had high ELISA antibody concentrations (2 to 20 microg/ml) with no associated bactericidal titer (<1:8). Discordant results between bactericidal titers and ELISA antibody concentrations were not explained by the presence of IgA blocking antibody or relative levels of IgG and IgM. The bactericidal results show age-dependent differences in the production and retention of antibody in young children immunized with serogroup C polysaccharide; these differences are not evident with the ELISA data.     

Evaluation of antigens of Fasciola gigantica as vaccines against tropical fasciolosis in cattle

Vaccine trials were conducted in Brahman cross cattle evaluating the efficacy of 4 native antigens purified from adult Fasciola gigantica flukes, and 1 recombinant F. gigantica antigen, as vaccines against tropical fasciolosis. The antigens tested were native glutathione S-transferase, cathepsin L, paramyosin, fatty acid binding protein (FABP), and a recombinant FABP expressed in E. coli, and were formulated in 1 or more of several adjuvants (Quil A, Squalene Montanide 80, MF59-100, Auspharm, NAGO, polylactoglycolide microspheres, Algammulin, DEAE, Freund's). Vaccination induced low, moderate or high antibody titres to the various antigens which were dependent on the adjuvant. Low but significant reductions in fluke burdens (31%, P < 0.026) and fluke wet weight (36%, P < 0.041) were only observed in cattle vaccinated with the native FABP in Freund's adjuvant. There was no correlation between total antibody titres to FABP and protection. The protection observed in cattle vaccinated with native FABP of F. gigantica supports the notion that this class of proteins is a useful target for protection of animals against Fasciola and extends the efficacy of FABPs to the tropical liver fluke. This is the first report of vaccination of cattle against F. gigantica with a purified protein.     

Mechanomyography and oxygen consumption during incremental cycle ergometry

Brucella abortus strain RB51 was recently approved as an official brucellosis calfhood vaccine for cattle by the Animal and Plant Health Inspection Service branch of the United States Department of Agriculture. Currently available serologic surveillance tests for B. abortus do not detect seroconversion following SRB51 vaccination. The purpose of this study was to evaluate a dot-blot assay using gamma-irradiated strain RB51 bacteria for its specificity and sensitivity to detect antibody responses of cattle vaccinated with strain RB51. Dot-blot titers of sera at a recommended dosage (10(10) colony-forming units) were similar to those of sera from cattle vaccinated with similar numbers of B. abortus strain 19 and greater (P < 0.05) than titers of nonvaccinated cattle. In the first 12 weeks after vaccination with 10(10) colony-forming units of strain RB51, the RB51 dot-blot assay had 100% specificity for titers of 80 or less and a 53% sensitivity for titers of 160 or greater. Sensitivity of the RB51 dot-blot assay peaked at 4 weeks after vaccination with 10(10) colony-forming units of strain RB51. Dot-blot responses of sera from cattle vaccinated with a reduced dosage of strain RB51 (10(9) colony-forming units) did not differ (P > 0.05) from titers of sera from nonvaccinated cattle. Following intraconjunctival challenge with B. abortus strain 2308, titers on the RB51 dot-blot assay did not differ (P > 0.05) between nonvaccinated cattle and cattle vaccinated at calfhood with strain 19 or strain RB51.     

Induction of immunologic refractoriness in adults by meningococcal C polysaccharide vaccination

Thirty-four adults were vaccinated with 1/50 of the usual dose of meningococcal polysaccharide vaccine (1 microg of A, C, Y, and W135 polysaccharides, given intramuscularly). This dose was selected as a probe to assess B cell memory. The probe elicited meningococcal C bactericidal antibody responses in all 18 adults who had been vaccinated 4 years earlier with an investigational meningococcal A and C oligosaccharide-protein conjugate vaccine and in the majority of the 11 subjects vaccinated for the first time. In contrast, the responses of the 5 adults given a full dose of licensed polysaccharide vaccine 4 years earlier were <1/10 of those of the other 2 groups. Thus, adults previously given a full dose of meningococcal polysaccharide vaccine show evidence of immunologic refractoriness to group C polysaccharide, whereas refractoriness is not observed after conjugate vaccination. These findings have implications for the use of meningococcal polysaccharide vaccine when the risk of disease is low.     

Vaccination with glutaraldehyde-fixed bovine respiratory syncytial virus (BRSV)-infected cells stimulates a better immune response in lambs than vaccination with heat-inactivated cell-free BRSV

The lamb model was used to investigate the possible protective effects of vaccination with inactivated viral antigens against experimental infection with bovine respiratory syncytial virus. Two groups of eight lambs were vaccinated with either glutaraldehyde-inactivated cell-associated virus or heat-inactivated cell-free virus and subsequently challenged with live virus, along with a group of naive lambs. The virus was shed for significantly longer periods, and the virus titres in nasal secretions were significantly higher in the group of naive lambs than in the two groups of vaccinated lambs. The period of virus-shedding in nasal secretions and virus titres was significantly lower (p < 0.01) in the group of lambs immunized with the cell-associated preparation. The same antigen stimulated better cellular immune responses as measured by virus-specific cytotoxicity or by virus-specific lymphocyte proliferation. However, priming with inactivated vaccines had no significant effect on lymphocyte responses to phytohaemagglutinin, which was found to be significantly reduced (p < 0.01) following challenge with live virus.     

Antibody responses of three Haemophilus influenzae type b conjugate vaccines after one, two and three doses in Filipino children

Differences in the magnitude of antibody response after one, two or three doses of Haemophilus influenzae type b conjugate vaccines have been reported which may influence decision-making regarding which vaccine should be used. This is of particular importance in developing countries where children may not receive a full immunization series and the vaccination schedule may be delayed. Serum antibody responses to three Hib capsular polysaccharide protein conjugate vaccines (PRP-OMP, HbOC and PRP-T) were evaluated in 102 Filipino infants. Vaccination was carried out at 6, 10 and 14 weeks of age based on the national Expanded Programme on Immunization (EPI) schedule together with diphtheria-tetanus-pertussis, hepatitis B and oral poliomyelitis vaccines. Sera were collected at 6 weeks and 1 month after each vaccination. Anti-Hib polysaccharide antibody concentrations were determined by Farrtype radioimmunoassay (RIA) and enzymeimmunoassay (EIA), Following the first dose, the geometric mean concentrations (GMC, micrograms ml-1) for PRP-OMP, HbOC and PRP-T were 0.69, 0.27 and 0.38, respectively. After two doses, there was a significant response (P < 0.05) to PRP-OMP and PRP-T (0.89 and 1.47) but not for HbOC (0.37). Differences in the GMC after the primary series were significant (pairwise P < 0.05): GMC was highest for PRP-T (4.0), followed by HbOC (1.6) and PRP-OMP (1.1). All three Hib vaccines were immunogenic when given in the local EPI schedule in Filipino infants although significant differences in the kinetics and magnitude of antibody responses were noted. The anti-Hib antibody concentrations determined by RIA and EIA were also compared in order to validate the latter for use in laboratories where it is feasible. There was a good correlation (r2 = 76%; P = 0.0001) in the Hib antibody titres obtained by both assays.     

Immunoprophylaxis of Rhodococcus equi pneumonia in foals

An immunoprophylaxis program for R. equi infection of foals has been established on a number of thoroughbred breeding farms in Argentina over the past 4 years. Nearly 800 mares annually were immunized subcutaneously during the last 2 months of pregnancy with 2-3 doses of a vaccine containing soluble antigens of R. equi, including the virulence associated protein (VapA) and 'equi factors' exoenzymes. The mortality from R. equi pneumonia in the foals from vaccinated dams dropped from an average of 3% in the 5 years before the vaccination program was initiated to an average of 1.2% in the 4 years during which the program was applied (P < 0.02). On 3 farms, an additional 380 foals of vaccinated dams annually over 3 years also received at 25 days of age 600-1200 ml of hyperimmune plasma from donors immunized with this vaccine, and as well at 4 days of age in foals with poor transfer of R. equi antibodies from their dams. The average foal mortality because of R. equi in the 380 foals annually to which hyperimmune plasma was administered dropped from 5.8% on these 3 farms to 0.2% (P < 0.05). Active vaccination of foals of unvaccinated mares on an enzootic farm at 20, 30, and 40 days of age did not protect them from mortality due to R. equi pneumonia. Serology was done by complement fixation and an agar gel immunodiffusion (AGID) tests using antigens prepared in the same manner as the vaccine antigens. The immune responses among hyperimmune plasma donors varied considerably as did the responses of vaccinated mares. Of 1117 serum samples with normal post suckling gammaglobulin levels (> 600 mg%) collected at 2 days of age from foals of vaccinated mares, 36% showed a negative or weak positive AGID reaction, while the remainder had positive to strongly positive reactions.     

Immune reaction to tetanus in the elderly: what is the duration of vaccine protection?

Infectious diseases represent one of the most frequent causes of morbidity and mortality in the elderly. Little information is yet available on the state of immunization against well-known antigens such as tetanus toxoid (TT) in old age. It was, therefore, the aim of this study to analyze antibody titres and peripheral blood mononuclear cell (PBMC) reactivity to TT in healthy SENIEUR compatible young (< 30 years, n = 25) and old (> 65 years, n = 32) blood donors. TT-specific antibodies were measured by the ELISA technique; PBMC proliferation was assessed by 3H-thymidine incorporation analysis. In the young group TT antibody titres were detectable in all but two individuals, whereas 60% of the old persons had no detectable TT antibodies. This seemed partly to be due to a shortened immunological memory in old age, since 32% of the aged persons without TT antibodies had been vaccinated within the past 10 years, 21% even 3 to 6 years prior to investigation. TT antibody concentrations were normal in aged individuals vaccinated within the past two years. Peripheral blood lymphocytes from all but two persons without antibody titres did not proliferate when stimulated with TT in vitro, indicating that no memory T cells were available to reinduce an efficient immune response. Our results suggest that the tetanus vaccination strategy practised in Austria does not guarantee full protection in the elderly.     

Failure of colostral immunoglobulin transfer in calves dying from infectious disease

Serum IgG1 concentrations of calves less than 3 weeks old and dying from infectious disease were significantly lower (P less than 0.01) than those of clinically normal calves. Fifty percent of the dead calves had serum IgG1 concentrations that were more than 2 standard deviations below the normal mean, and an additional 35% had IgG1 concentrations that were more than 1 standard deviation below the normal mean. Low IgG1 concentrations were attributed to failures in passive transfer of colostral immunoglobulin. The few calves dying of noninfectious causes generally had normal serum immunoglobulin concentrations. The results of this study emphasize the importance of adequate colostral intake and absorption to the neonatal calf. In view of the large numbers of calves that die from neonatal infection each year, it may be assumed that failure in passive transfer, as reflected by low serum immunoglobulin concentrations, is one of the most important factors influencing neonatal calf mortality.     

Randomized controlled trial of ipratropium bromide and frequent low doses of salbutamol in the management of mild and moderate acute pediatric asthma

The standardized enzyme-linked immunosorbent assay (ELISA) for measurement of serum immunoglobulin G (IgG) antibody responses to meningococcal C polysaccharide has been modified to employ assay conditions that ensure specificity and favor detection primarily of high-avidity antibodies. The modified and standard assays were used to measure IgG antibody concentrations in sera of toddlers vaccinated with meningococcal polysaccharide vaccine or a meningococcal C conjugate vaccine. The results were compared to the respective complement-mediated bactericidal antibody titers. In sera obtained after one or two doses of vaccine, the correlation coefficients, r, for the results of the standard assay and bactericidal antibody titers were 0.45 and 0.29, compared to 0.85 and 0.87, respectively, for the modified assay. With the standard assay, there were no significant differences between the geometric mean antibody responses of the two vaccine groups. In contrast, with the modified assay, 5- to 20-fold higher postvaccination antibody concentrations were measured in the conjugate than in the polysaccharide group. Importantly, the results of the modified assay, but not the standard ELISA, paralleled the respective geometric mean bactericidal antibody titers. Thus, by employing conditions that favor detection of higher-avidity IgG antibody, the modified ELISA provides results that correlate closely with measurements of antibody functional activity that are thought to be important in protection against meningococcal disease.     

Invasive infection with Haemophilus influenzae type b in spite of complete vaccination

Five patients, 4 boys and 1 girl aged 13-41 months, developed invasive Haemophilus influenzae type b (Hib) disease (2 epiglottitis, 3 meningitis) despite full (or at least 3 times) vaccination. At admission as well during convalescence, 3 out of 5 had IgG anti Hib antibody levels < or = 5 U/ml. Serum immunoglobulin levels, including IgG subclasses, as well as complement were normal in all cases. In 2 of the 3, booster vaccinations with Hib conjugate vaccine elicited adequate antibody titres. Since the incorporation of the conjugated Hib polysaccharide tetanus toxoid vaccine (HibTT) in the National Vaccination Programme in the Netherlands, the number of invasive infections caused by Hib has dropped significantly. Causes of Hib conjugate vaccine failures are mostly unknown. In about one-third of the cases serum immunoglobulin levels are deficient, most often IgG2 or IgM. Susceptibility to Hib infection is in part also genetically determined. In the follow-up of Hib vaccine failures, anti Hib antibody titres should be determined. Booster vaccinations may be necessary.     

Isotype-specific antibody responses to foot-and-mouth disease virus in sera and secretions of "carrier' and "non-carrier' cattle

Isotype-specific antibody responses to foot-and-mouth disease virus (FMDV) were measured in the sera and upper respiratory tract secretions of vaccinated and susceptible cattle challenged with FMDV by direct contact or by intranasal inoculation. A comparison was made between cattle that eliminated FMDV and those that developed and maintained a persistent infection. Serological and mucosal antibody responses were detected in all animals after challenge. IgA and IgM were detected before the development of IgG1 and IgG2 responses. IgM was not detected in vaccinated cattle. Challenge with FMDV elicited a prolonged biphasic secretory antibody response in FMDV "carrier' animals only. The response was detected as FMDV-specific IgA in both mucosal secretions and serum samples, which gained statistical significance (P < 0.05) by 5 weeks after challenge. This observation could represent the basis of a test to differentiate vaccinated and/or recovered convalescent cattle from FMDV "carriers'.