Seroprevalence of Q fever in naturally infected dairy cattle herds

Coxiella burnetii is the causal agent of Q fever, a worldwide spread zoonosis. Prevention of C. burnetii shedding in cattle is critical to control the spread of the pathogen between animals, and from animals to humans. Vaccination with a phase 1 vaccine has been shown to be effective in preventing shedding when implemented in still susceptible animals, even in infected cattle herds. The identification of these animals (dairy cows and nulliparous females) as targets for vaccination consequently is crucial. Hygiene measures conventionally also are implemented, but their relative impact on C. burnetii diffusion remains unknown. The objectives of this study therefore were to (i) describe the distribution of the within-herd apparent seroprevalence among cows and nulliparous females and (ii) to explore the association between management practices and herd characteristics on the one hand, and these seroprevalences on the other. In a sample of 100 naturally and clinically infected dairy herds, blood samples were taken systematically from all nulliparous females (older than 12 months) and cows, and serologically tested. Information on herd characteristics and management practices were collected through a questionnaire filled in by each farmer. The variation in within-herd seroprevalence among cows and the risk for a herd of having at least one seropositive nulliparous female were investigated using multivariate (linear and logistic respectively) regression models. Median within-herd seroprevalence was 0.32 (Q1=0.22; Q3=0.43). We observed a low to null (median=0.01; Q1=0; Q3=0.10) within-herd seroprevalence in nulliparous females contrary to a high value (median=0.42) and variability (Q1=0.28; Q3=0.56) in cows. Only a few herd characteristics and management practices were found to be related to seroprevalence. Within-herd seroprevalence in cows was found to be significantly (P<0.10) higher in herds (i) with a number of cows<46, (ii) with seasonal calving, and (iii) with grazing or contact through the fence with other ruminant herds. The risk of having at least one seropositive nulliparous female was increased in herds (i) with seasonal calving and (ii) where the foetus and/or the placenta of aborted cows were not systematically removed. Our findings support, in addition to the implementation of high level of hygiene measures, the relevance of vaccination (at least in nulliparous females) as a method to control the spread of C. burnetii within an infected herd, as vaccination is effective in susceptible animals and given that nulliparous females are mostly not infected even in infected herds.     

Old and new diagnostic approaches for Q fever diagnosis: correlation among serological (CFT, ELISA) and molecular analyses

The objective of this study was to evaluate the performance of the complement fixation test (CFT) with respect to ELISA for the serological diagnosis of Q fever and to assess the role of serology as a tool for the identification of the shedder status. During 2009-2010, sera from 9635 bovines and 3872 small ruminants (3057 goats and 815 sheep) were collected and analyzed with CFT and ELISA. In addition, 2256 bovine, 139 caprine and 72 ovine samples (individual and bulk tank milk samples, fetuses, vaginal swabs and placentae) were analyzed with a real-time PCR kit. The relative sensitivity (Se) and specificity (Sp) of CFT with respect to ELISA were Se 26.56% and Sp 99.71% for cattle and Se 9.96% and Sp 99.94% for small ruminants. To evaluate the correlation between serum-positive status and shedder status, the ELISA, CFT and real-time PCR results were compared. Due to the sampling method and the data storage system, the analysis of individual associations between the serological and molecular tests was possible only for some of the bovine samples. From a statistical point of view, no agreement was observed between the serological and molecular results obtained for fetus and vaginal swab samples. Slightly better agreement was observed between the serological and molecular results obtained for the individual milk samples and between the serological (at least one positive in the examined group) and molecular results for the bulk tank milk (BTM) samples. The CFT results exhibited a better correlation with the shedder status than did the ELISA results.     

Agreement between three serological tests for Neospora caninum in beef cattle.

During 1999, serum samples were collected from beef cows on pastures in western Canada. Some of the herds had a history of confirmed abortions associated with Neospora caninum infection. All these samples were initially analyzed using a single application of 1 common commercial enzyme-linked immunosorbent assay (ELISA) for antibodies to N. caninum. From these initial results, 239 positive and 250 negative samples were randomly selected for further testing. This group of samples was retested using the 3 commercially available ELISA tests for N. caninum as per the manufacturer's recommendations. The agreement between 2 of the ELISAs was good (K = 0.76); agreement of these 2 tests with the third test was much lower (K = 0.46 and 0.60). Quantitative agreement between tests measured by intraclass correlation coefficients was also acceptable between the first 2 tests but was almost zero when the first 2 tests were compared with the third. This information is necessary to understand the differences in seroprevalence reported in different regions from laboratories using different methods.     

An evaluation of three serological tests for antibody to Brucella suis in pigs

The Rose Bengal Plate Agglutination test (RBT), the complement fixation text (CFT) and the tube agglutination test (TAT) were applied to serums from 345 feral and 80 domestic pigs sampled at slaughter. At least 2 of the 3 serological tests were applied to each serum. Tissues from all pigs were cultured for Brucella suis and the degree of culture effort was categorised from 1 to 4 in decreasing order. Fifty-eight feral and 35 domestic pigs were culture-positive. A greater proportion of culture-positive pigs was obtained for category 1 and 2 culture effort. Tissues yielding B. suis most often were mandibular, gastrohepatic and external iliac lymph nodes, spleen and various abdominal organs. Infection in domestic pigs was associated with exposure to feral pigs. The sensitivity (Se) in culture-positive pigs of the RBT (79.1%) was significantly greater than that of either the CFT (49.1%) or TAT (51.1%). The specificities (Sp) in culture-negative pigs were 81.2% for the RBT, 90.8% for the CFT and 81.0% for the TAT. A more realistic estimate of Sp for the RBT was considered to be 97.6%, based on serological results from 31,326 domestic pigs routinely tested for regulatory purposes. The RBT was clearly superior to the other 2 tests in this study. However, a more sensitive screening test would be preferable for use in a test and slaughter eradication program. The RBT would be a suitable confirmatory test.     

Occurrence of Coxiella burnetii in Polish dairy cattle herds based on serological and PCR tests

The aim of the research was to assess the prevalence of antibodies to Coxiella burnetii in dairy cattle herds in Poland and to compare the results of real-time PCR and ELISA tests performed on bulk tank milk (BTM) samples. In total, 2635 serum samples collected from 969 dairy cattle herds from all provinces were tested using ELISA. Additionally, BTM specimens from 101 herds were analysed by ELISA and real-time PCR targeting IS1111 element. Presence of anti-C. burnetii antibodies was confirmed in 25.39% of serum samples in 237 herds (24.46%) and the herd-level seroprevalence in Voivodeships varied from 2.5% to 61.4%. Moreover, 46 (45.5%) of analysed bulk tank milk samples gave postive result in ELISA and microbial DNA was detected in 40 (39.6%) of tested herds. The comparative analysis of ELISA and real-time PCR results obtained for BTM samples using the chi-square test showed statistically significant relationship between results of both methods.     

A field evaluation of serological and cellular diagnostic tests for bovine tuberculosis.

This paper describes the field evaluation of a serological test and a new in vitro assay for cell-mediated reactivity for the diagnosis of bovine tuberculosis. The use of a Mycobacterium bovis-specific antigen (MPB-70) in an ELISA to test the serological response to tuberculosis infection resulted in a specificity of 96.4% and a sensitivity of 18.1%. The most favourable results were obtained with the interferon gamma (IFN-gamma) assay which had a sensitivity of 81.8% and a specificity of 99.1%. Respective figures for the single intradermal tuberculin test were 68.1% and 96.7%. The use of MPB-70 as the antigen in the IFN-gamma assay reduced the sensitivity of this assay, without producing any useful increase in specificity. The IFN-gamma assay was also demonstrated to be a practical diagnostic test for use with large groups of cattle.     

Evaluation of cellular and serological diagnostic tests for the detection of Mycobacterium bovis-infected goats

We have evaluated the comparative intradermal skin (CID) test, the interferon gamma (IFN-γ) assay, two ELISAs with bovine PPD antigen, the standard and the anamnestic using sera obtained, respectively, at the time of the tuberculin injection and 15 days later, for the diagnosis of caprine tuberculosis (TB). The sensitivity and specificity results were high for the CID test (83.7%, 100%), the IFN-γ assay (83.7%, 96%) and the anamnestic ELISA (88.6%, 95.8%). In contrast, they were comparatively low for the standard ELISA (54.9%, 88%). However, test results with the standard ELISA were positive in a group of goats with cavitating TB (100%). A combination of the CID test and the IFN-γ assay offered the highest sensitivity, 95.8%, and also high specificity, 96%. In spite of this, the evidence that the serological tests were most sensitive for the detection of goats with severe lesions (100% positivity) suggested that a combination of CID test and anamnestic ELISA may be most useful as part of an eradication campaign against caprine TB.     

Preparation and evaluation of antigens used in serological tests for caprine syncytial retrovirus antibody in sheep and goat sera

Methods used to prepare antigens from caprine syncytial retrovirus (CSR) for use in the agarose gel immunodiffusion test (AGID) or an indirect enzyme-linked immunosorbent assay (ELISA) are described. Caprine and ovine sera were tested for antibody to CSR using the AGID test and ELISA incorporating a caprine system (CSR antigen and rabbit anti-goat IgG) or an ovine system (maedi-visna virus antigen and rabbit anti-sheep IgG). Good correlation was achieved in the results of the 3 tests when sera were devoid of antibody or were strongly positive. Variations in the results on weakly positive sera were considered to be more a matter of interpretation than due to basic differences in the reagents employed.     

Evaluation of three serological tests for brucellosis in naturally infected cattle using latent class analysis

Serological methods are traditionally used in diagnosis of brucellosis. However, the comparative performance of these tests and their accuracy under the local environment in Zambia has not been assessed. Thus, the objective of our study was to evaluate the diagnostic performance of three serological tests for brucellosis; Rose Bengal Test (RBT), competitive ELISA (c-ELISA) and Fluorescence Polarisation Assay (FPA) in naturally infected cattle in Zambia without an appropriate reference test to classify animals into truly infected and non-infected. Serological test results from a study to determine sero-prevalence were used to compare the performance of RBT, c-ELISA and FPA in diagnosing brucellosis in traditional cattle. Since none of the tests can be seen as a perfect reference test or gold standard, their performance in a population of naturally infected cattle was evaluated using latent class analysis which allows the sensitivity (Se) and specificity (Sp) to be estimated in the absence of a gold standard. The highest Se was achieved by the c-ELISA (97%; Credible Posterior Interval (CPI)=93-100%) and the highest Sp by the FPA (93%; CPI=85-99%), conversely these tests also had the lowest Sp and Se, respectively, with the RBT performing well in both the Se (93%; CPI=84-98%) and Sp (81%; CPI=61-97).     

A comparison of three serological tests in the diagnosis of caprine brucellosis.

The serum agglutination test (SAT), the Rose Bengal plate test (RBPT) and the milk ring test (MRT) were used in the diagnosis of caprine brucellosis. There was a close correlation between the SAT and RBPT when both tests were negative but the RBPT failed to detect 79.82 per cent of sera in excess of 50 iu. Also, owing to the relatively poor milking potential of the Nigerian goat and the false positive results with the MRT, it is concluded that the SAT offers a better serological diagnostic tool for caprine brucellosis in this locality.     

A comparison of three serological tests for the diagnosis of B. ovis infection in rams

The complement fixation test (CFT), the enzyme labelled immunosorbent assay (ELISA) and the gel diffusion precipitin test (GD) were compared, for the diagnosis of Brucella ovis infection in rams. The sensitivities of the tests in 109 rams which were shedding B. ovis in their semen were: CFT 96.3%; ELISA 97.2%; GD 91.7%. The specificities of the tests in 141 rams from non-infected flocks were: CFI 99.3%; ELISA 98.6%; GD 100%. Predictive values of the three tests were measured in 285 rams from infected flocks. Thirty-eight percent of these rams were shedding B. ovis in their semen. Predictive values of positive tests were: CFT 75.5%; ELISA 66.7%; GD 72.5%. Predictive values of negative tests were: CFI 97.1%; ELISA 97.6%; GD 93.8%.     

Corynebacterium pseudotuberculosis infection in goats. I. Evaluation of two serological diagnostic tests

The bacterial agglutination test (BAT) and the hemolysis inhibition test (HIT) were employed and evaluated.The threshold value between positive and negative antibody titres in BAT and HIT was determined on the basis of titration results for sera from 25 adult goats infected with Corynebacterium pseudotuber-culosis (positive), and sera from 25 adult goats from a herd in which caseous lymphadenitis did not occur (negative).Antibody titres were expressed as logio to the reciprocal value of the highest positive serum dilution in both tests. Positive titre (T) in BAT was stipulated as T ≥ 2.1 and in HIT as T > 0.6. The sensitivity and specificity was 0.96 in both tests in the material used. Twenty-three of the 25 goats infected with G. pseudotuberculosis were positive in both BAT and HIT.The reproducibility in both tests was described by the use of correlation coefficient and coefficient of variation. The values were estimated using duplicate determination of titres of 155 serum samples. Correlation coefficients were 0.87 for BAT and 0.95 for HIT. Coef-ficients of variation were 26.4 % for BAT and 14.1 % for HIT. The coefficient of variation was related to titres. It was highest for BAT at low titres.It was concluded that both tests can be used for seroepidemio-logical investigations of C. pseudotuberculosis infection in goats.