Estimation of sensitivity and specificity of five serological tests for the diagnosis of porcine brucellosis

While serological tests are essential in surveillance and control programs of animal diseases, to date none of the common serological tests approved in the EU (complement fixation test or Rose-Bengal test) has been shown to be reliable in routine individual diagnosis of porcine brucellosis, and some more recent tests like ELISA have not been fully evaluated yet. In the absence of a gold standard, this study allowed the estimation of sensitivities and specificities of these tests with a Bayesian approach using Markov Chain Monte Carlo algorithms. The pig population that was tested included 6422 animals from Metropolitan France. Serum samples were collected from a large population of pigs, representative of European swine population and tested with five brucellosis serological tests: Rose-Bengal test (RBT), fluorescence polarization assay (FPA), indirect ELISA (I-ELISA) and two competitive ELISAs (C-ELISA). The sensitivity and the specificity of each test were estimated. When doubtful results were excluded, the most sensitive and specific test was C-ELISA(2) (Se C-ELISA(2)=0.964, [0.907; 0.994], 95% credibility interval (CrI); Sp C-ELISA(2)=0.996, [0.982; 1.0], 95% CrI). When doubtful results were considered as negative, C-ELISA(2) was still the most sensitive and specific test (Se C-ELISA(2)=0.960, [0.896; 0.994], 95% CrI and Sp C-ELISA(2)=0.994, [0.977; 0.999], 95% CrI). The same conclusions were reached when doubtful results were considered as positive (Se C-ELISA(2)=0.963, [0.904, 0.994], 95% CrI and Sp C-ELISA(2)=0.996, [0.986; 1.0], 95% CrI).     

Bayesian estimation of the true prevalence,sensitivity and specificity of the Rose Bengal and indirect ELISA tests in the diagnosis of bovine brucellosis

Serology is the most convenient method for detecting brucellosis but the efficient use of such tests in disease control requires evaluation of diagnostic performance and discriminative ability. The objective of this study was to assess the performance of the Rose Bengal test (RBT) and an indirect ELISA (iELISA) in diagnosing brucellosis in 995 serum samples collected from cattle in the Ivory Coast between 2005 and 2009. A Bayesian approach was used to evaluate the two tests by estimating their sensitivities and specificities.The correlation-adjusted sensitivity of the iELISA was estimated to be 96.1% (credibility interval [CrI], 92.7–99.8), whereas that of the RBT was 54.9% (CrI, 23.5–95.1). High correlation-adjusted specificities were found for both tests (95.0%; [CrI, 91.1–99.6] for the iELISA and 97.7%; [CrI, 95.3–99.4] for the RBT, respectively). The true prevalence of brucellosis was estimated from the serum samples to be 4.6% (95%; [CrI, 0.6–9.5]). The level of agreement between the two tests was evaluated using indices of agreement (n = 995). Good agreement was found for negative results (96.6%; confidence interval [CI], 95.7–97.4), a finding supported by an estimated significant correlation of 0.37 (95%; CI, 0.01–0.73) within the sera testing negative. Agreement was lower for sera testing positive (52.2% CI: 41.9–62.5). The findings highlight the importance of using these two tests in combination as part of any brucellosis control programme.     

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).     

Evaluation of sensitivity and specificity of RBT, c-ELISA and fluorescence polarisation assay for diagnosis of brucellosis in cattle using latent class analysis

The sensitivity (Se) and specificity (Sp) of the Rose Bengal test (RBT), competitive ELISA (c-ELISA), serum (sFPA) and blood (bFPA) fluorescence polarisation assay for brucellosis were evaluated using latent class analysis using sera and whole blood collected from infected cattle reared in smallholder dairy farms of Zimbabwe. The latent class model allowed estimation of Se and Sp in the absence of a gold standard test. The c-ELISA had the highest Se (99.0%; 95% credible posterior interval (CPI): 94.8; 100%), while the RBT and sFPA had the highest Sp (99.0%; 95% CPI: 98.0; 99.6%). The bFPA had the lowest Se (71.3%; 95% CPI: 56.2, 83.5%), while its Sp (96.3%; CPI: 93.9; 98.0%) was marginally higher than that of the c-ELISA (95.4% CPI: 93.7; 96.8%). Therefore based on these data, test regimen using the RBT and c-ELISA could be suitable for diagnosis of brucellosis in smallholder dairies in Zimbabwe. Based on cost and ease of performance, the sFPA may be adopted as a confirmatory test, but its performance may be optimised by altering cut-off points to suit the Zimbabwean conditions. Thus, latent class models provide an alternative method for evaluating Se and Sp of diagnostic tests, which could be used to optimise test performance in different cattle populations.     

3种奶牛布鲁氏菌病血清学检测方法的贝叶斯评估

在无"金标准"的情况下,为评估虎红平板凝集试验(RBT)、荧光偏振分析法(FPA)和间接酶联免疫吸附试验(I-ELISA)用于奶牛布鲁氏菌病的抗体检测能力,作者分别以RBT、FPA、I-ELISA3种方法对采自某奶牛场的血清样品进行检测,通过贝叶斯分析法对检测结果进行分析,研究3种方法检测奶牛布鲁氏菌血清抗体的敏感性(Se)和特异性(Sp)。结果显示,RBT、FPA、I-ELISA3种检测方法的敏感性(Se)分别为91.81%、95.92%和95.98%;特异性(Sp)分别为98.80%、86.54%和98.65%。本研究表明,3种血清学检测方法中以I-ELISA的检测能力最好。     

Assessment of performance of selected serological tests for diagnosing brucellosis in pigs

Swine brucellosis due to Brucella suis is considered an emerging zoonotic disease whose control is based on serological testing and the subsequent culling of seropositive animals or the full depopulation of affected flocks. Here we assessed the performance of several serological tests (Rose Bengal Test [RBT], indirect ELISA [i-ELISA], blocking ELISA [b-ELISA], and two competitive ELISAs [c-ELISA]) for diagnosing swine brucellosis caused by B. suis biovar 2. Both frequentistic and Bayesian statistical inference were used. A frequentistic analysis, using sera from known gold standard (GS) populations (i.e., from truly infected or brucellosis free animals), resulted in maximum (100%) diagnostic sensitivity (Se) and specificity (Sp) in the RBT, i-ELISA and b-ELISA tests. However, c-ELISAs resulted in lower diagnostic Se (ranging from 68.5% to 92.6%, according to the different cut-offs selected). A Bayesian analysis of tests yielding the best diagnostic performance with GS sera (RBT, i-ELISA and b-ELISA), but using a large collection of field sera, resulted in similar Se among tests but markedly lower (≈ 80%) than that resulting from the frequentistic analysis using the GS serum populations. By contrast, the estimated Sp in the Bayesian analysis was only slightly lower than 100%, thus similar to that obtained frequentistically. Our results show that adequate diagnostic tests for brucellosis in swine are available, but also emphasize the need for more extensive validation studies before applying these tests under field conditions.     

Bovine and Caprine Brucellosis in Bangladesh: Bayesian evaluation of four serological tests,true prevalence,and associated risk factors in household animals

A cross-sectional study was carried out to estimate the true prevalence of Brucella spp. and identify allied risk factors/indicators associated with brucellosis in the Dinajpur and Mymensingh districts of Bangladesh. A total 320 stratified random blood samples were collected and tested in parallel for Brucella antibodies using Rose Bengal (RBT), slow agglutination (SAT), and indirect and competitive ELISA. In addition, a structured questionnaire was administered to each household herd owner to gather information regarding potential risk factors. Both univariate and multivariate logistic regression analyses were used to identify potential risk factors or indicators at animal level. A Bayesian approach was used to estimate the true prevalence of brucellosis along with the test performances (Se and Sp). The estimated animal level true prevalence in cattle was 9.70 % (95 % CPI 5.0–16 %) and in goat 6.3 % (95 % CPI 2.8–11.0 %). The highest sensitivity was achieved by SAT ranges from 69.6 to 78.9 %, and iELISA was found to be more specific (97.4 to 98.8 %) in comparison with other tests. On the other hand, a significant level of (P?<?0.05) Brucella seropositivity was found in cattle that breed naturally compared with those that undergo artificial insemination. In goats, exotic breeds were significantly associated (P?<?0.05) with Brucella seroprevalence compared with indigenous breeds. Goats with a previous records of abortion and/or retained placenta were also found to have significant levels (P?<?0.05). Cows with previous abortion records showed higher odds (18 times) of being seropositive. None of the evaluated tests can be recommended to apply alone for the diagnosis of bovine and caprine brucellosis.     

Comparison of conventional and non-conventional techniques for the diagnosis of bovine brucellosis in Sudan

The objective of the present study was to detect brucellosis in suspected dairy cattle in Khartoum State, Sudan using the conventional serological tests and tests done on milk in comparison to a PCR-based technique. Milk and blood samples collected simultaneously from suspected brucellosis cows (n = 147) in 12 different dairy farms around Khartoum State were used in the study. Overall, 54 (36.7%) of the total milk samples were positive according to the milk ring test (MRT), while 29 (19.7%) of the serum samples were positive according to the Rose Bengal test (RBT); microscopy on modified Ziehl-Neelsen-stained slides detected 13.6% of the cases, and recovery of Brucella species on both Brucella medium and tryptic soya agar was 7.5%. Thirty-three (22.4%) samples were found positive on PCR-amplified IS711 which were then taken as positive brucellosis cases. The differences of RBT and PCR-IS711 from MRT were highly significant (P < 0.05). MRT detected more cases of bovine brucellosis compared to RBT, PCR, microscopy, and culture. MRT is recommended as a noninvasive test compared to RBT, and it is less expensive compared to PCR and culture.     

Evaluation of a fluorescence polarization assay for the detection of serum antibodies to Brucella abortus in water buffalo (Bubalus bubalis)

The fluorescence polarization assay (FPA) was evaluated for the serological diagnosis of brucellosis in water buffalo (Bubalus bubalis) in southern Italy. This assay uses O-polysaccharide prepared from Brucella abortus lipopolysaccharide conjugated with fluorescein isothiocyanate as a tracer. It has many methodological advantages over older, more established tests and can be performed in a fraction of the time. Sera from 890 buffalos from the Campania Region - 526 positive sera and 364 negative sera according to the complement fixation test (CFT) - were evaluated in this study. All samples were tested with the Rose Bengal test (RBT), CFT, and FPA in parallel and in blind fashion. Sensitivities (Sn) were 84.5% and 92.6%, and specificities (Sp) were 93.1% and 91.2% for RBT and FPA, respectively, relative to CFT. Finally, receiver operating characteristic (ROC) analysis suggested a cut-off value of 117 millipolarization (mP) units. On the whole, these results suggested that FPA might replace RBT in the diagnosis of buffalo brucellosis for its better performance relative to CFT, its adjustable cut-off useful in different epidemiological situations, its reliability, ease of performance, and for its potential application in field and high-throughput laboratories.     

Herd and individual animal prevalence of bovine brucellosis with associated risk factors on dairy farms in Haryana and Punjab in India

Herd and individual animal prevalence along with associated risk factors of bovine brucellosis was assessed on dairy farms located in 22 districts in Haryana and Punjab of India. Examination of 4,580 female animals of 119 dairy farms by Rose Bengal test and enzyme-linked immunosorbent assay revealed that an overall herd prevalence was 65.54 % (78/119) and individual animal prevalence was 26.50 % (1,214/4,580). Herd prevalence in Haryana was 62.79 % which was not significantly different (P?=?0.4208) from Punjab (72.72 %). Individual animal prevalence was 34.15 % in Punjab which was significantly higher (P?<?0.0001) than Haryana (22.34 %). Prevalence of brucellosis on dairy farms was detected in 20 of the 22 districts, of which 12 districts were in Haryana and 8 in Punjab. Risk factors such as species of animals, age of animals, herd size, awareness of dairymen for brucellosis, entry of a purchased animals on the farm, abortion on farm, use of calving pens, type of breeding, and type of farming were analyzed. The study indicated that the odds ratio (OR) was significant with risk factors of species (OR?=?1.63; 95 %CI?=?1.40–1.90; P?<?0.0001), age (OR?=?0.22; 95 %CI?=?0.17–0.29; P?<?0.0001), awareness of brucellosis among dairymen (OR?=?21.65; 95 %CI?=?2.63–178.04; P?=?0.0042), entry of purchased animal on the farm (OR?=?9.16; 95 %CI?=?2.38–35.18; P?=?0.0012), abortion in animals (OR?=?5.57; 95 %CI?=?1.92–16.10; P?=?0.0015) and on cow farm (OR?=?3.43; 95 %CI?=?1.33–8.82; P?=?0.0105). While the OR was insignificant (P?>?0.05) with risk factors of herd size, use of calving pen on farms, type of breeding and on buffalo and mixed type of farms.     

Assessment of milk ring test and some serological tests in the detection of <Emphasis Type="Italic">Brucella melitensis</Emphasis> in Syrian female sheep

Brucella melitensis infection prevalence among Syrian female sheep, to evaluate a number of serological tests and to discuss some epidemiological aspects of brucellosis, was studied. A total of 2,580 unvaccinated Syrian female sheep sera samples were tested for B. melitensis antibodies detection using four serological methods: the Rose Bengal test (RBT), the serum agglutination test (SAT), the complement fixation test (CFT) and an indirect enzyme-linked immunosorbent assay (iELISA). In addition, 2,375 milk samples were collected, then milk ring test (MRT) and bacterial isolation test were employed to evaluate the natural organism shedding. The samples were considered positive in 66%, 64%, and 60% when we employed the RBT, SAT, and iELISA tests, respectively. Whereas, the CFT test revealed the smallest number of positive samples. By using the MRT, the total prevalence of brucellosis was nearly 38% of samples. A large variation was observed concerning the studied areas, ranging from 24% in Tartous to 44% in both Damascus and Damascus rural areas. Brucella was isolated from only 677 samples out of the 2,375 female sheep milk samples.     

Prevalence and risk factors associated with bovine brucellosis in herds under extensive production system in southwestern Nigeria

Using a cross-sectional survey, we determined the prevalence and risk factors associated with bovine brucellosis in herds under extensive production system in southwestern Nigeria. Antibodies to Brucella species in serum samples were tested using the Rose Bengal test (RBT) and competitive enzyme-linked immunosorbent assay (cELISA); for milk, the milk ring test (MRT) and indirect-ELISA (i-ELISA) were used. Questionnaire was administered to cattle herdsmen to determine factors predisposing the animals to bovine brucellosis. Data were analyzed using STATA 12. From 513 serum and 635 milk samples tested among 120 herds, overall animal-level prevalence of 10.1% (95% CI 7.5–12.7%) and 20.2% (95% CI 17.1–23.3%) were recorded by RBT and MRT, respectively; while 9.4% (95% CI 6.9–11.9%) and 17.8% (95% CI 14.8–20.8%) were obtained using cELISA and i-ELISA, respectively. In all, from the 120 herds tested, 29.2% and 43.3% were positive by RBT and MRT, respectively. Multivariable logistic regression revealed that herd location (OR?=?8.12, 95% CI 1.68–38.90) and improper disposal of placenta/fetus (OR?=?17.33, 95% CI 4.81–62.33) were predictors for a seropositive herd using RBT; while herd location (OR?=?5.13, 95% CI 1.27–20.28), large herd size (OR?=?2.62, 95% CI 1.15–5.85), and occurrence of abortion for a year or more (OR?=?4.62, 95% CI 1.53–13.71) were predictors of seropositivity to antibodies to Brucella spp. using MRT. We found high prevalence of brucellosis in cattle herds under extensive management system in southwestern Nigeria. Urgent and coordinated control strategies are required to mitigate this problem.

     

Seroprevalence investigation of bovine brucellosis in Macenta and Yomou,Guinea

Brucellosis is one of the world’s major zoonotic diseases associated with reproductive disorders and a potential infection of human. Brucellosis leads to serious economic losses due to late-term abortion, stillbirth, weak calves, and sterility. In Guinea, the data on brucellosis was only detected as far back as 10 years ago. The purpose of this study was to estimate the prevalence of bovine brucellosis in the provinces of Macenta and Yomou of Guinea. A structured questionnaire was used in the clinical study, and 345 cattle were clinically examined. Three hundred serum samples were initially subjected to the Rose Bengal test (RBT); the positive results of which were confirmed by the complement fixation test (CFT). The investigation indicated that farmers had little information on brucellosis. Hygroma, abortion, sterility, and placental retention were the observed symptoms. Of the 29 RBT-positive samples, 26 were confirmed by CFT. The prevalence of brucellosis in Macenta and Yomou was 12 and 5.33 %, respectively. In both provinces, the prevalence mean was 8.67 %. This study highlighted the immediate necessity to carry out a strengthened surveillance of human and animal brucellosis to obtain as many data as possible in order to establish strategies for prevention and management of brucellosis in Guinea.     

Cross-sectional survey of brucellosis and associated risk factors in the livestock–wildlife interface area of <Emphasis Type="Italic">Nechisar</Emphasis> National Park,Ethiopia

A cross-sectional survey was carried out to investigate the seroprevalence of ovine and bovine brucellosis in the livestock–wildlife interface area of Nechisar National Park, Ethiopia. Furthermore, producer’s knowledge about brucellosis and its zoonotic potential was assessed using a structured questionnaire. A total of 268 cattle and 246 goat sera were collected from 50 herds and 46 flocks and subjected to Rose Bengal test (RBT) and enzyme-linked immunosorbent assay (ELISA) in parallel to detect anti-Brucella species antibodies. Positive reactions were further confirmed with compliment fixation test (CFT). Flock and herd level seroprevalence rate was 12.8% (95% CI 4.8–25.7) and 32.0% (95% CI 19.5–46.7) in goats and cattle, respectively. An overall animal-level seroprevalence of 4.5% (95% CI 2.25–7.86) and 9.7% (95% CI 6.44–13.89) was recorded for goats and cattle, respectively. Seroprevalence showed an increasing trend with age, where adult cattle >?2 years. Goats (>?1 year) recorded relatively higher seroprevalence, but the differences were not statistically significant. Similarly, female cattle and goats recorded a relatively higher seroprevalence, 11 and 5.6%, respectively, compared to males but the difference was not significant. However, a significant (P <?0.01) variation of seroprevalence was noted for parity (bovine), higher in animals in second parity, and abortion history, in both species, higher in animals that experienced abortion. Interviews revealed lack of awareness about brucellosis and food safety related to the zoonotic potential from consuming raw animal products (milk and meat). Ninety-eight percent of respondents did not consider handling abortion material is risky, and only a very low proportion (8%, n?=?50) was able to mention limited zoonotic diseases (anthrax and Taenia cysticercosis) could be transmissible to people. The study indicated that brucellosis is endemic in domestic animals in the interface area and calls for further broad epidemiological investigation of the disease in livestock, human and wildlife following ‘one health’ unified research approaches beside enhancing public awareness.     

An evaluation of the anamnestic test for brucellosis in cattle of the northern pastoral area

SUMMARY An investigation of the anamnestic test for brucellosis using Brucella abortus 45/20 vaccine was carried out in 3 groups of weaner cattle on 2 farms in western Queensland. Each group originally consisted of about 500 cattle. They were bled before and at 6 or 10 weeks after vaccination and again in the following year. The serums were tested by the complement fixation (CFT), Rose Bengal (RBT) and indirect haemolysis tests (IHLT). Most of the cattle reacting to one or more of the tests were killed and selected tissues were subjected to bacteriological examination for B. abortus. B. abortus was isolated from 19 of 30 (63%) pre-vaccinal reactors, 23 (24%) of 96 cattle reacting at 6 or 10 weeks after vaccination (the anamnestic test) and 1 (2%) of 50 cattle reacting one year after vaccination. The reactor found to be infected the year after vaccination had high serological titres in each of the 3 serological tests: RBT of 3, CFT of 128 and IHLT of 256. A subsequent test showed the group to be brucellosis-free. The CFT was the most efficient test. In the pre-vaccination tests 17 of 19 infected animals were positive in the CFT compared with 11 positive in the IHLT and 17 in the RBT. In post vaccination tests 22 of 23 infected animals were positive in the CFT compared with 18 in the IHLT and 19 in the RBT. At the pre-vaccinal and anamnestic tests (6 or 10 weeks after vaccination) 19 of 57 (33%) cattle with CF titre of 4 or 8 yielded B. abortus on culture compared with none of 26 cattle with similar titres in the year after vaccination. The interpretation of CF titres in cattle following 45/20 vaccination needs to be re-examined.     

Effectiveness of Rose Bengal test and fluorescence polarization assay in the diagnosis of <Emphasis Type="Italic">Brucella</Emphasis> spp. infections in free range cattle reared in endemic areas in Zambia

The effectiveness of Rose Bengal test (RBT) and fluorescence polarization assay (FPA) in diagnosing cattle brucellosis in endemic areas was assessed and RBT and FPA test agreement was compared (n = 319). The sensitivity of RBT and FPA in detecting low Brucella titres were evaluated in paired sera (n = 34). A logistic regression model was constructed to predict cattle test result in FPA using RBT as the main predictor and incorporating bio-data and animal history. There was 79.3% agreement between the RBT and FPA (Kappa = 0.59; Std error = 0.05; p = 0.000) and a high correspondence between high RBT scores and positive FPA results suggesting that sera with high RBT score may not require confirmation with tests such as competitive-ELISA or CFT. High FPA cut-off points were more likely to miss animals with low antibody titres. The RBT had a reduced ability in detecting low antibody titres compared to the FPA. FPA test interpretation was improved if a priori information, such as sex and age was used. Under the challenging disease surveillance conditions prevailing in rural Africa, field-testing methods that are sensitive and specific; allow single animal contact, low technical skills in data interpretation are suitable.     

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.     

Evaluation of different enzyme-linked immunosorbent assays for the diagnosis of brucellosis due to Brucella melitensis in sheep

Six serological assays for the diagnosis of ovine brucellosis, due to Brucella melitensis were evaluated. Reference serum samples from sheep of known B. melitensis infection status (n = 118) were assessed using the Rose Bengal test (RBT), complement fixation test (CFT) and four commercial enzyme-linked immunosorbent assays (ELISAs), including two indirect ELISAs (iELISAs), one competitive ELISA (cELISA) and one blocking ELISA (bELISA).The highest differential positive rates (DPR) were obtained with the cELISA and bELISA, while the lowest DPR was estimated using iELISAs. A latent class analysis was performed to estimate the accuracy of the CFT, RBT and bELISA using 1827 sera from sheep undergoing testing as part of a surveillance and control programme. Lower sensitivity and specificity were obtained for the three serological tests when the field samples were used. A higher DPR was achieved by the CFT, compared to bELISA and RBT. The results suggest that ELISAs, and particularly the bELISA, might be suitable for inclusion in the European Union legislation on intra-community trade for diagnosing B. melitensis infection in sheep, as it has a similar test performance compared to the RBT.     

Seroprevalence and risk factors for bovine brucellosis in domestic yaks (<Emphasis Type="Italic">Bos grunniens</Emphasis>) in Tibet,China

A cross-sectional study was conducted in three counties (Damxung, Maizhokunggar and Yadong) in Tibet in April and May 2015. A total of 1,523 yaks owned by 181 herders were randomly selected and blood sampled. Sera were tested using the rose bengal test (RBT) and a competitive immune-enzymatic assay (C-ELISA) and the test results interpreted in parallel. The individual yak prevalence was 2.8% (95% CI 2.0–3.7) with a herd prevalence of 18.2% (95% CI 12.9–24.6). At the individual level, two predictor variables, age and production system, were significantly associated with seropositivity by a binary logistic regression analysis. The odds of Brucella infection were significantly higher in older Yaks (3–5 years old, OR = 4.51; 95% CI 1.53–19.29; ≥6 years old, OR = 3.89; 95% CI 1.23–17.21) compared to those of younger yaks (≤2 years old). The odds of seropositivity for yaks managed under an agro-pastoral production system were 2.9 (95% CI 1.48–5.86) times higher compared to those managed under a pastoral production system. At the herd level, an association between the infection with Brucella and a history of abortions in the herd was observed (OR = 4.98, 95% CI 1.48–16.62). Surprisingly, vaccination was not associated with a lower level of infection (p = 0.49 and p = 0.99 for individual and herd level data, respectively). The results of the survey indicate that bovine brucellosis is endemic among the yak population in the plateau region of China, and the risk factors identified in the study should be considered in the epidemiology of the disease and when developing control programs for the disease.     

Epidemiology of ovine brucellosis in Awassi sheep in Northern Jordan

We used a combined cross-sectional and longitudinal design to estimate seroprevalence of Brucella antibodies in Awassi sheep and the incidence of abortion due to brucellosis during one lambing season, and to test risk factors. The Brucella organisms isolated from aborted fetuses and vaginal swabs were characterized as Brucella melitensis biotype 3. Seventy Awassi sheep flocks were selected randomly from Northern Jordan. Sixty two of the 70 flocks were used in the cross-sectional study and 8 flocks were monitored for three consecutive months to estimate the incidence of abortion. Questionnaire data and 602 serum samples were collected and analyzed. Thirty five flocks (56%) were brucellosis-seropositive by the Rose Bengal plate-agglutination test (RBT) and 28 (45%) by enzyme-linked immunosorbent assay (ELISA). The crude seroprevalence of brucellosis at the individual-animal level was 14.3% by RBT, 7.2% by ELISA and 2.2% using both tests in series. The flock-specific, animal-level abortion risk ranged between 2.5 and 50% (median=22.6%). The flock brucellosis-status was used as the outcome variable in a multivariable logistic regression. Grazing at communal pasture increased odds, but usage of disinfectants, previous vaccination for brucellosis, and tap water were protective. The animal-level incidence of abortion was 20% and the specific incidence risk of abortion due to brucellosis was 13%.