Quantitative anti-PA IgG ELISA; assessment and comparability with the anthrax toxin neutralization assay in goats.

BACKGROUND: Presently, few data exist on the level and duration of anti-protective antigen (PA) IgG in vaccinated livestock. Various adaptation of enzyme-linked immunosorbent assays (ELISAs) have been developed in studies to assess immune response following vaccination, albeit mostly in laboratory rodent models. The quantitative anti-anthrax IgG ELISA in this study describes a method of enumerating the concentration of anti-PA specific IgG present in sera of immunized goats, with the aid of an affinity-purified caprine polyclonal anti-anthrax PA-83 IgG standard. This was compared with the anthrax toxin neutralization assay (TNA) which measures a functional subset of toxin neutralizing anti-PA IgG. RESULTS: The measured concentrations obtained in the standard curve correlated with the known concentration at each dilution. Percentage recovery of the standard concentrations ranged from 89 to 98% (lower and upper asymptote respectively). Mean correlation coefficient (r2) of the standard curve was 0.998. Evaluation of the intra-assay coefficient of variation showed ranges of 0.23-16.90% and 0.40-12.46% for days 28 and 140 sera samples respectively, following vaccination. The mean inter-assay coefficient of variation for triplicate samples repeated on 5 different days was 18.53 and 12.17% for days 28 and 140 sera samples respectively. Spearman's rank correlation of log-transformed IgG concentrations and TNA titres showed strong positive correlation (rs = 0.942; p = 0.01). CONCLUSION: This study provides evidence that an indirect ELISA can be used for the quantification of anti-anthrax PA IgG in goats with the added advantage of using single dilutions to save time and resources. The use of such related immunoassays can serve as potential adjuncts to potency tests for Sterne and other vaccine types under development in ruminant species. This is the first report on the correlation of polyclonal anti-anthrax PA83 antibody with the TNA in goats.

Temporal assessment of seroconversion in response to inactivated foot-and-mouth disease vaccine in Arabian oryx (Oryx leucoryx).

Ten male Arabian oryx (Oryx leucoryx) were vaccinated with a commercially available standard aqueous foot-and-mouth-disease vaccine containing aluminium hydroxide as an adjuvant, and their antibody titres against serotypes O and A were measured using solid-phase blocking elisa and the virus neutralisation test. Mean elisa antibody titres greater than 1.45 log(10) were recorded for serotype A, but low elisa titres were recorded for serotype 0; low titres were recorded by VNT for both serotypes.

Assessment of serum antibody titers against canine distemper virus, canine adenovirus type II, and canine parvovirus in Alaskan sled dogs before and after a long-distance race.

OBJECTIVE: To determine serum antibody titers against canine distemper virus (CDV), canine adenovirus type II (CAV-2), and canine parvovirus (CPV) in trained sled dogs prior to and after completion of a long-distance race. DESIGN: Prospective cohort study. ANIMALS: 195 Alaskan sled dogs (from 18 kennels) that participated in the 2006 Iditarod Trail Race. PROCEDURES: All 1,323 dogs participating in the race had been vaccinated against the 3 viruses at 19 to 286 days prior to initial blood sample collection (obtained within the month preceding the race). Within 12 hours of race completion, blood samples were collected from 195 dogs (convenience sample) and matched with each dog's prerace sample. Serum antibody titers (90% confidence intervals [CIs]) were determined via serum neutralization assays. RESULTS: After racing, geometric mean titers against CDV and CPV were significantly higher (2,495 [90% CI, 321 to 16,384] and 6,323 [90% CI, 512 to 32,768], respectively) than prerace values (82 [90% CI, 11 to 362] and 166 [90% CI, 32 to 1,024], respectively). Sixty-one of 194 (31.4%) dogs had > or = 4-fold increases in anti-CPV antibody titers after racing. Prerace serum antibody titers against CDV, CPV, and CAV-2 varied significantly by sled team but were not associated with time since vaccination. CONCLUSIONS AND CLINICAL RELEVANCE: Postrace increases in serum anti-CDV and anti-CPV antibody titer might reflect exposure of dogs to these agents immediately before or during racing. Dogs had no clinical signs of CDV-, CAV-2-, or CPV-associated disease; therefore, the clinical importance of these titer changes is uncertain.

Assessment of in vitro interferon-gamma responses from peripheral blood mononuclear cells of cattle infected with Mycoplasma mycoides ssp. mycoides small colony type.

Contagious bovine pleuropneumonia (CBPP) is a lung disease caused by the bacterial pathogen Mycoplasma mycoides ssp. mycoides small colony type (MmmSC). It has been spreading due to a number of factors including poor vaccine efficacy and poor sensitivity of current diagnostic tests. The purpose of this study was to assess interferon gamma (IFN-gamma) release after stimulation of peripheral blood mononuclear cells (PBMC) from experimentally infected cattle. PBMC collected from 15 artificially infected animals were incubated with different concentrations of total MmmSC antigen. After 72h of incubation the IFN-gamma release was measured and found to be elevated in 11 animals. We did not observe a correlation between IFN-gamma release of animals with and without pathomorphological gross lesions. Therefore, our data do not confirm a role for CD4 T-lymphocytes in protection, since there is no correlation between IFN-g secretion (supposed to be mainly derived from CD4 T-cells) and disease severity. Additionally, we applied immunocytochemistry on affected lung tissue and detected no build up of T-lymphocytes (CD4 T-cells, CD8 T-cells) but a high presence of myeloid cells.

Assessment of suitability of two serotype A candidate vaccine strains for inclusion in FMD vaccine in India.

The recent type A foot and mouth disease virus field isolates recovered in India are shown to be antigenically quite divergent from the in-use vaccine strain (IND 17/82), warranting the selection of a suitable vaccine strain which can cover this diversity in antigenic spectrum. In earlier studies employing neutralization test with anti-146S rabbit sera raised against eight candidate vaccine strains, IND 81/00 and IND 40/00 belonging to genotype VII were found to offer the best antigenic coverage. In order to assess the credibility of IND 81/00 and IND 40/00 as vaccine strains, 17 recent isolates received during 2005-2006 and representative isolates from older genotypes were subjected to two-dimensional micro-neutralization assay using bovine convalescent serum (against IND 81/00 and IND 40/00) and bovine vaccinate serum (against IND 40/00). From the results it is evident that both the isolates IND 81/00 (antigenic relationship 'r-value' >0.40 with 86% of isolates) and IND 40/00 ('r-value' >0.40 with 78% of isolates) show nearly equal antigenic relatedness with the recent field viruses and hence both of these are effective vaccine candidates in present context. Though very limited in its extent, these useful data obtained with antisera raised in homologous host system are logical extension of the on going quest for the appropriate vaccine strain and circumvents species disparities in the immune recognition of epitopes.

Spatial risk assessment of Rift Valley fever in Senegal.

Rift Valley fever (RVF) is broadening its geographic range and is increasingly becoming a disease of global importance with potentially severe consequences for human and animal health. We conducted a spatial risk assessment of RVF in Senegal using serologic data from 16,738 animals in 211 locations. Bayesian spatial regression models were developed with interpolated seasonal rainfall, land surface temperature, distance to perennial water bodies, and time of year entered as fixed-effect variables. Average total monthly rainfall during December-February was the most important spatial predictor of risk of positive RVF serologic status. Maps derived from the models highlighted the lower Senegal River basin and the southern border regions of Senegal as high-risk areas. These risk maps are suitable for use in planning improved sentinel surveillance systems in Senegal, although further data collection is required in large areas of Senegal to better define the spatial distribution of RVF.

Serological assessment of West Nile fever virus activity in the pastoral system of Ferlo, Senegal.

The Ferlo area (north-central Senegal) is characterized by a system of temporary ponds favorable to arboviruses among which West Nile fever (WNF) was already identified. During the rainy season in 2003, a serological study was undertaken on horses to assess the activity of the WNF virus (WNFV) in Barkedji (Ferlo). The observed serological prevalence rate was 78.3% for neutralizing antibodies, with a 95% confidence interval (CI) of [64.0, 92.7]. This prevalence rate significantly increased with age (P = 10(-5)). This study confirmed that WNF was endemic in the Ferlo. The transmission risks depended on the introduction of the WNFV in the ecosystem--probably with migrating birds, on its amplification in hosts and on the vector-population dynamic. Further studies are needed to investigate how the cycle is initiated in Barkedji at the beginning of the rainy season and the impact of climatic variations on the risk of transmission of WNF. A surveillance system should be implemented: (a) to assess the clinical impact of the WNF on human and equine populations, (b) to provide an early detection of virulent strains, and (c) to assess the risk of WNF transmission to disease-free ecosystems via migrating birds.

Assessment of classical swine fever diagnostics and vaccine performance.

Rapid and accurate diagnosis is of the utmost importance in the control of epizootic diseases such as classical swine fever (CSF), and efficacious vaccination can be used as a supporting tool. While most of the recently developed CSF vaccines and diagnostic kits are mostly validated according to World Organisation for Animal Health (OIE) standards, not all of the well-established traditional vaccines and diagnostic tests were subject to these validation procedures and requirements. In this report, data were compiled on performance and validation of CSF diagnostic tests and vaccines. In addition, current strategies for differentiating infected from vaccinated animals are reviewed, as is information on the control of CSF in wildlife. Evaluation data on diagnostic tests were kindly provided by National Reference Laboratories for CSF in various European countries.

Evaluation of health status of calves and the impact on feedlot performance: assessment of a retained ownership program for postweaning calves.

The objective of this study was to evaluate animal health status at entry to a feedlot against feedlot performance and carcass value. There were 24 herds represented by 417 calves in a retained ownership program. The health status at entry was represented by the levels of serum antibody to infectious bovine rhinotracheitis virus (IBRV), bovine viral diarrhea viruses 1 and 2 (BVDV1a, BVDV2), parainfluenza 3 virus (PI3V), bovine respiratory syncytial virus (BRSV), Mannheimia haemolytica, and Pasteurella multocida, as well as by the presence of virus in nasal swabs and blood leukocytes and the presence of bacteria in nasal swabs. The presence or absence of viruses or bacteria at entry did not predict subsequent illness. However, there were predictors of illness severity (number of treatments) and performance parameters of feedlot performance. Herds with a low morbidity rate had higher levels of BVDV1a antibodies than herds with a high morbidity rate. On both an individual-animal and a herd-average basis, calves with low levels of antibody to BVDV1a and BVDV2 had increased total treatment costs. Also, for individual animals and the herd as a whole, low levels of antibody to P. multocida, BVDV1a, and BVDV2 were related to decreased net value to owner (carcass value minus total feedlot cost). Calves treated twice or more had lower levels of antibody to BVDV1a than those treated once or not at all. Differences in herd morbidity rate and treatment costs were more related to appropriate timing of vaccine (last dose at or near delivery of calf) or lack of a 2nd dose of killed vaccine. This was best illustrated by the levels of antibody to BVDV1a. The results of this study were used to formulate recommendations for the subsequent year.

Epizootics of bovine ephemeral fever on dairy farms in Saudi Arabia.

In 1990 and 1996, field veterinarians suspected the clinical occurrence of bovine ephemeral fever among dairy and conventional cattle in different regions of Saudi Arabia. The disease has a seasonal occurrence; it begins in early summer (May) and ends in late autumn (November). The mortality rate is low: 0.3% to 0.6%. The morbidity rate ranged from 5% to 61% within the different age groups of one affected herd in the 1996 outbreaks and from 3.4% to 19% among four affected herds in the 1990 outbreaks. A sudden sharp drop in milk production occurred in lactating animals, some of which had become dry by the end of the outbreaks. Trials to isolate the causative virus in cell culture and in baby mice were unsuccessful. Serum neutralisation tests, which used a cell culture-adapted vaccine strain of bovine ephemeral fever virus as an antigen, revealed the presence of specific antibodies with significantly increased titres in the convalescent sera of affected animals. In addition, the testing of paired sera from non-affected heifers and from both dry and milking cows, performed twice, with an interval of 21 days, revealed the presence of neutralising antibodies. In the 1990 outbreaks, comparative serological studies indicated a high percentage (67.5%; 27/40) of seropositive animals in herds in which bovine ephemeral fever had been previously suspected. No antibodies were detected in animals of herds which had no recorded clinical history of bovine ephemeral fever. Following serological confirmation of the prevalence of bovine ephemeral fever in Saudi Arabia, some dairy farms started using a live imported vaccine to control the disease. This study discusses the epizootiological findings in regard to bovine ephemeral fever, as well as its economic impact on four affected dairy farms in 1990. In addition, the authors evaluate the efficacy of immunoprophylaxis in another dairy herd during the same outbreaks.

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 naïve 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.

Assessment of safety and protective value of a cell culture modified strain "C" vaccine of hog cholera/classical swine fever virus.

The protective value of a commercial strain "C" vaccine of classical swine fever (CSF) was tested in weaner pigs. Vaccinated animals were challenged intranasally with the virulent hog cholera virus (HCV) strain ALFORT/187 in groups of four pigs each at one to four weeks post vaccination, respectively. Non-vaccinated control animals were challenged in the same manner. Some vaccinated pigs seroconverted as early as one week post vaccination with all pigs yielding neutralizing antibodies (nAb) against the vaccine virus at two weeks post vaccination. After challenge no clinical signs were observed in any of the vaccinated animals whereas non-vaccinated control animals developed fever starting in general on the fourth day post challenge. In vaccinated pigs no challenge virus could be isolated from leucocyte samples taken on days 3 to 7 post challenge while HCV was isolated from buffy coat leucocytes of all non-vaccinated animals. Six out of eight control animals were sacrificed and viral antigen was detected in tonsils, mandibular lymph node and spleen in four animals, exclusively in tonsils in one animal and none in another animal. Two non-vaccinated animals that survived the experiment seroconverted after challenge and developed nAb against the HCV strain ALFORT/187.

Canine parvovirus serum neutralizing antibody assay: assessment of factors responsible for disparity of results between tests.

Canine parvovirus (CPV) serum neutralization (SN) test components were evaluated to determine their effect on antibody titer results. The use of different strains of CPV and different cell substrates had little effect on assay results. Variations in SN antibody titer results were associated with the use of challenge virus preparations that differed in the ratio of hemagglutination units (HAU) to infectivity units (FAID50). Sensitivity and reproducibility can be achieved by using a standardized challenge virus preparation containing a low HAU/FAID50 ratio.