A comparative assessment of culture and serology in the diagnosis of brucellosis in dairy cattle

Reproductive Fate of Brucellosis-Seropositive Elk (Cervus canadensis): Implications for Disease Transmission Risk

Brucellosis is a disease caused by the bacterium Brucella abortus that infects elk (Cervus canadensis) and cattle (Bos taurus). There is the potential for transmission from wildlife to livestock through contact with infected material shed during abortions or live births. To understand the impact of exposure on pregnancy rates we captured 30-100 elk per year from 2011 through 2020, testing their blood for serologic exposure to B. abortus. Predicted pregnancy rates for seropositive animals were 9.6% lower in prime-age (2.5-15.5 yr; 85%, 95% confidence interval [CI]: 74-91%) and 37.7% lower in old (>15.5 yr; 43%, 95% CI: 19-71%) elk as compared with seronegative animals. To understand the risk of seropositive elk shedding B. abortus bacteria and the effects of exposure on elk reproductive performance, we conducted a 5-yr longitudinal study monitoring 30 seropositive elk. We estimated the annual probability of a seropositive elk having an abortion as 0.06 (95% CI: 0.02-0.15). We detected B. abortus at three abortions and two live births, using a combination of culture and PCR testing. The predicted probability of a pregnant seropositive elk shedding B. abortus during an abortion or live birth was 0.08 (95% CI: 0.04-0.19). To understand what proportion of seropositive elk harbored live B. abortus bacteria in their tissues, we euthanized seropositive elk at the end of 5 yr of monitoring and sampled tissues for B. abortus. Assuming perfect detection, the predicted probability of a seropositive elk having B. abortus in at least one tissue was 0.18 (95% CI: 0.06-0.43). The transmission risk seropositive elk pose is mitigated by decreased pregnancy rates, low probability of abortion events, low probability of shedding at live birth events, and reasonably low probability of B. abortus in tissues.

Prevalence of brucellosis in livestock of African and Asian continents: A systematic review and meta-analysis

Brucellosis is a highly contagious bacterial disease that mainly affects ruminants, but it may affect equines, canines, and felines. The disease is of utmost significance from an economic standpoint in countries where there is no national brucellosis prevention and eradication policy in operation. A systematic review was done to estimate disease burden, incidences, prevalence, and geographical distribution critical in planning appropriate intervention strategies for the control and prevention of Brucellosis. Research articles that were published during the period 2000–2020 were considered for this study after reinforced scrutiny by two independent authors. Meta-regression was used to examine heterogeneity, and subgroup and sensitivity analyses were used to calculate residual heterogeneity and the pooled prevalence of Brucellosis in livestock. Confounders such as geography, a diagnostic test, and species had the greatest R2 values of 17.8, 8.8, and 2.3%, respectively, indicating the presence of heterogeneity and necessitating more research into sensitivity and subgroup analysis. The combined pooled prevalence of brucellosis in both Asia and African countries was 8% when compared to 12% in the Indian livestock population. The findings of our systematic review and meta-analysis indicate that brucellosis continues to be an important animal and public health concern in developing countries of Asia and Africa, as evidenced by the prevalence rate of brucellosis in these regions. Our findings suggested that well-planned epidemiological surveillance studies in different geographic settings are needed to generate reliable data on disease burden including the economic loss in Asian and African countries.

Evaluation of diagnostic tests' sensitivity, specificity and predictive values in bovine carcasses showing brucellosis suggestive lesions, condemned by Brazilian Federal Meat Inspection Service in the Amazon Region of Brazil

Cervical bursitis is a suggestive lesion of bovine brucellosis. Diagnostic sensitivity and specificity of two brucellosis serological tests, Rose Bengal (RB) and serum agglutination test with 2-mercaptoethanol (SAT/2-ME), and of isolation and identification (bacteriology) were evaluated through Bayesian latent class analysis (BLCA). A total of 165 paired serum and cervical bursitis samples detected at inspection by Brazilian federal meat inspection services were analyzed. The best model fit to the data occurred when accounting for the conditional dependence between serological tests. According to this model, RB and SAT/2-ME had almost the same sensitivity, 0.960 [0.903 - 0.992] and 0.963 [0.906 - 0.994] with 95 % Credible Interval (95 %CrI), respectively. Specificities were 0.9068 [0.562 - 0.997] and 0.875 [0.546 - 0.990] for RB and SAT/2-ME, respectively, also with 95 %CrI. Bacteriology had lower sensitivity than serological tests, 0.594 (95 %CrI: [0.525 - 0.794]) and the highest specificity of all evaluated tests, 0.992 (95 %CrI: [0.961-1.00]). Prevalence of infected animals was 0.829 (95 %CrI: [0.700-0.900]). BLCA showed that both RB and SAT/2-ME fitted to the purpose of initial screening the brucellosis suspect in carcasses with cervical bursitis in a reliable way. The results of RB or SAT/2-ME can guide the sanitary actions for brucellosis control and help the implementation of a risk-based surveillance system in the meat production chain. This strategy is especially true in remote areas with large beef cattle herds, raised extensively, where in vivo tests are rarely performed due to logistic and management constraints, as in the Northern region of Brazil.

Bovine brucellosis - a comprehensive review

Brucellosis is a zoonotic disease of great animal welfare and economic implications worldwide known since ancient times. The emergence of brucellosis in new areas as well as transmission of brucellosis from wild and domestic animals is of great significance in terms of new epidemiological dimensions. Brucellosis poses a major public health threat by the consumption of non-pasteurized milk and milk products produced by unhygienic dairy farms in endemic areas. Regular and meticulous surveillance is essentially required to determine the true picture of brucellosis especially in areas with continuous high prevalence. Additionally, international migration of humans, animals and trade of animal products has created a challenge for disease spread and diagnosis in non-endemic areas. Isolation and identification remain the gold standard test, which requires expertise. The advancement in diagnostic strategies coupled with screening of newly introduced animals is warranted to control the disease. Of note, the diagnostic value of miRNAs for appropriate detection of B. abortus infection has been shown. The most widely used vaccine strains to protect against Brucella infection and related abortions in cattle are strain 19 and RB51. Moreover, it is very important to note that no vaccine, which is highly protective, safe and effective is available either for bovines or human beings. Research results encourage the use of bacteriophage lysates in treatment of bovine brucellosis. One Health approach can aid in control of this disease, both in animals and man.

Evaluation of the English bovine brucellosis surveillance system considering probability of disease introduction and non-random sampling

The English surveillance system for bovine brucellosis was evaluated. The confidence in detecting at least one infected herd in the local population (surveillance system sensitivity or SSe), and the confidence in freedom from disease (PFree) adjusted (PFreeAdj) for the probability of disease introduction from abroad by imported animals (PIntro), were estimated for quarterly surveillance periods of 2016; because dairy herds were tested quarterly on bulk tank milk (BTM) with an antibody indirect ELISA. A stochastic model was developed and six surveillance components (representing also the local population strata), were evaluated. All English herds and their relative risk (RRs) of infection within each stratum were considered. The importance of each component was assessed using actual national data, which reflected non-random sampling. The contribution of the abortions testing was assessed with particular focus, because a decline in statutory submissions was observed in recent years. Beef herds without submissions (B-NoTest herds) at the laboratories were still considered as a population stratum, where infected cattle could be imported. Additionally, we evaluated the importance of different hypothetical design between-herds prevalence (Ph) values, at which the country could be classified as "infected". The potential negative effect on SSe due to the dilution of antibodies when individual samples are pooled within BTM and tested by the milk iELISA, was also investigated. The quarterly median SSe and PFreeAdj were both ≥ 95 % if at least four (0.008 %) herds were infected in the country due to independent import events. The system appeared able to substantiate Official Brucellosis Free (OBF) status frequently (on quarterly basis) using Ph=0.2 % (EU legislation). The component based only on BTM testing (M herds) showed the highest sensitivity; while the surveillance components based on abortions or post import calving (PIC) testing, had very low sensitivity at the (considered) Ph values lower than 0.2 %. In contrast, at Ph = 0.2 %, components based on abortion testing had median sensitivity between 91.3 % and 99.9 %, and the dilution effect on BTM testing did not change remarkably the SSe and PFreeAdj. When Ph was set to 1-2 infected herds (0.002-0.004 %), these were usually allocated by the model within the B-NoTest stratum (the largest stratum) and SSe reduced. Thus, if policy considers necessary increasing the SSe for low Phs (system's optimization as an early warning system); the cost efficiency of active risk based surveillance in beef herds (considering imports) could be investigated in the future.

Comparative evaluation of fluorescence polarization assay and competitive ELISA for the diagnosis of bovine brucellosis vis-a-vis sero-monitoring

Brucellosis is an important zoonosis that constitutes a serious public health hazard which is caused by a bacterium belonging to the genus Brucella. In the present study, two highly specific serological tests for brucellosis diagnosis, fluorescence polarization assay (FPA) and competitive ELISA (cELISA) were standardized in the laboratory, evaluated and compared with rose bengal plate test (RBPT), indirect ELISA (iELISA) and commercial cELISA kit. For test evaluation, 1386 serum samples [apparently healthy animals (n = 260), samples from Brucella infected farms (n = 701) and B. abortus S19 vaccinated animals (n = 425)] were analyzed to assess suitable diagnostic test in B. abortus S19 post vaccinated bovine population. In apparently healthy brucellosis free farms, RBPT, iELISA, in-house FPA and cELISA were found to be highly specific than commercial cELISA. Commercial cELISA kit was comparatively more sensitive than other serological tests in samples collected from infected farms. The FPA showed sensitivity nearly equal to RBPT and in-house cELISA showed greater sensitivity than RBPT in infected farms. In animals with persistent vaccinal antibodies, only in-house FPA and cELISA recorded higher specificity of 87.64 and 90.27%, respectively. The other tests, RBPT and iELISA displayed similar reactivity with vaccine antibodies to that of infection antibodies whereas commercial cELISA kit showed an intermediate specificity of 47.69%. With these findings, RBPT, iELISA and cELISA are suggested for screening infected herds, and in-house developed FPA and cELISA tests with a proven specificity can be used for confirmatory diagnosis of brucellosis in B. abortus S19 post vaccinated animal populations.

Screening and identification of a human domain antibody against Brucella abortus VirB5

Brucellosis is caused by the genus Brucella. Brucella is widely distributed in cattle, swine, sheep, goat and other mammals including human. Animal brucellosis causes severe economic losses and affects related international transportation and trade. Human brucellosis causes both acute and chronic symptoms of multi-organ dysfunction. Brucella type IV secretion system (T4SS) VirB5 was required for macrophages infection and essential for virulence in mice. VirB5 is located on the cell surface and serves as a specific adhesin targeting host cell receptors. The aim of this study was to isolate and characterize a specific human domain antibody against Brucella abortus (B. abortus) VirB5 from human single domain antibody (sdAb or VHH) phage display library. Following five rounds of screening, an sdAb named as BaV5VH4 showed the highest affinity by enzyme-linked immunosorbent assay (ELISA). Its interaction with B. abortus VirB5 was verified by binding assay, dot blot and molecular docking. These findings in this paper could greatly help elucidate the molecular mechanisms of Brucella infection, and accelerate the development of sdAbs-based vaccines and neutralizing therapeutics of brucellosis.

Risk factors for new bovine brucellosis infections in Colombian herds

BACKGROUND

Bovine brucellosis is a zoonotic disease that causes substantial economic losses and has a strong impact on public health. The main objective of this paper is to determine the risk factors for new infections of Brucella abortus on Colombian cattle farms previously certified as being free of brucellosis. A case-control study was conducted by comparing 98 cases (farms certified as brucellosis-free for three or more years but became infected) with 93 controls (farms that remained brucellosis-free during at least the previous three years). The farms were matched by herd size and geographical location (municipality). Information was obtained via a questionnaire completed by veterinary officers through a personal interview with the herd owners.

RESULTS

Two-thirds of the herds (67%) were dairy herds, 16% were beef herds, and 17% were dual-purpose (beef and milk) herds. After exploratory univariate analysis, all explanatory variables with a p-value of ≤0.20 were included in a logistic regression model using the forward stepwise method to select the model with the best goodness of fit. The significant risk factors were the replacement of animals from farms not certified as brucellosis-free compared to replacement from certified brucellosis-free farms (OR = 4.84, p-value < 0.001) and beef cattle farms compared to dairy cattle farms (OR = 3.61, p-value = 0.017). When herds with and without artificial insemination were compared, it was observed that farms that used natural breeding with bulls from non-certified herds had a higher risk than farms using artificial insemination (OR = 2.45, p-value = 0.037), but when the bulls came from brucellosis-free farms, farms with natural breeding were less affected (OR = 0.30, p-value = 0.004) than farms using artificial insemination, whether with frozen semen from certified brucellosis-free herds or fresh semen from uncontrolled herds. The latter is commonly sold to neighbouring farms.

CONCLUSIONS

The government should make efforts to inform farmers about the risks involved in the introduction of semen and replacement heifers from farms that are not certified as brucellosis-free and to establish measures to control these practices.

Characterization of circulating miRNA signature in water buffaloes (Bubalus bubalis) during Brucella abortus infection and evaluation as potential biomarkers for non-invasive diagnosis in vaginal fluid

Brucellosis is an infectious disease caused by bacteria from the Brucella genus that can be transmitted to humans through contact with infected animals or contaminated animal products. Brucellosis also causes financial losses in animal production. Ruminants are highly susceptible to brucellosis, and the causative agent water buffaloes (Bubalus bubalis) is Brucella abortus. Circulating microRNAs (miRNAs) are cropping up as promising biomarkers for several infectious diseases. The goals of this study were to characterize the serum miRNA signature associated with brucellosis in water buffaloes and investigate the miRNAs’ potential use as biomarkers in vaginal fluids. Next Generation Sequencing was used to assess miRNA expression profiles in Brucella-positive and Brucella-negative blood sera; dysregulated miRNAs in blood serum and vaginal fluids were validated using RT-qPCR. ROC curves were generated to evaluate the diagnostic value of miRNAs for Brucella. GO and KEGG pathway enrichment analyses were exploited to investigate the biological functions of dysregulated miRNAs. The results showed that 20 miRNAs were modulated, of which, 12 were upregulated and 8 were downregulated. These findings were corroborated by RT-qPCR, and ROC curves indicated that the miRNAs can serve as potential biomarkers for Brucella. GO and KEGG pathway analyses pointed out that some of these miRNAs are related to immune response and apoptosis. These results provided an overview of miRNA expression profiles and highlighted potential biomarkers for Brucella infection in water buffaloes. We also demonstrated the potential of vaginal fluids in studies involving microRNA detection. Further functional and mechanistic studies of these miRNAs may improve our understanding of the biological processes involved in Brucella infection and host immune response.

Development of an indirect ELISA based on whole cell Brucella abortus S99 lysates for detection of IgM anti-Brucella antibodies in human serum

BACKGROUND

Brucellosis is the most common zoonotic diseases worldwide. The aim of this study was to develop and evaluate the diagnostic performance of an indirect-ELISA (I-ELISA) method based on whole cell Brucella abortus S99 lysates for detection of IgM anti-Brucella antibodies in a human serum.

MATERIALS AND METHODS

The study was conducted in two species-rich endemic areas of Iran (Tehran and Lorestan provinces). Serum samples of 102 patients and 150 healthy individuals were tested by the new kit and the commercial Vircell kit for the presence of anti-Brucella IgM antibodies. The disease status was confirmed by Wright agglutination test. The difference in the mean optical densities (OD) recorded by the new and the Vircell kits for patients and healthy individuals were tested using Two-tailed Student t-test. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the new kit were informed using Receiver operating curve analysis. The results were used to guide the choice of cutoff. Agreements in ODs recorded by the new and the Vircell kit was visually inspected using Bland-Altman plot.

RESULTS

The new I-ELISA showed excellent diagnostic performance (sensitivity and PPV = 95.7%, specificity and NPV = 97.8%) for the diagnosis of brucellosis. The cut-off area for the antibody index (AI) was determined to be 8-10, where AIs less than 8 and greater than 10 were considered Brucella-negative and -positive, respectively. AIs of 8-10 show equivocal results, requiring re-testing. The Vircell kit showed low (36.8%) sensitivity and perfect (100%) specificity on the same samples. The Bland-Altman plot showed low agreement between both tests in recording the OD values for the same individuals.

CONCLUSION

The new I-ELISA based on whole cell Brucella abortus S99 showed a good performance for the detection of Brucella spp. Lack of agreement between the new and the Vircell kit suggest that the performance of ELISA kits might be dependent on the geographical area under study. Hence, validation of the new and the Vircell kits is recommended prior to their implementation in other geographical areas.

The Evaluation of Brucella Spp. Isolation Rates in Ruminant Abortion Cases by Using Different Selective Media

The aim of this study is to evaluate the success of Brucella spp. isolation in ruminant abortion cases by using different selective media. To this end, 58 samples from ruminant abortion cases were utilized. 4 selective media; namely, Farrell Medium (FM), CITA Medium (CM), Modified Thayer Martin (MTM) and Jones & Morgan (JM) were preferred for isolation. In addition to these, one medium with antibiotics was used to extend the range of the results. Suspensions prepared from organ and fetal stomach contents were inoculated to media plates and incubated at 37C° for 5-8 days in 5-10% CO2 condition. Conventional biotyping method was used to identify Brucella isolates within the level of species and biovar. MTM (67.2%) and Farrell (65.5%) outperformed the other media with regards to isolation rate. However, regarding the inhibition ability against contaminant microrganisms, Farrell (86.2%) and CITA (72%) have the highest and second highest percentages respectively. The media’s inhibition ability was examined in the samples in which Brucella spp. isolation occurred to be able to investigate the correlations between isolation and inhibition. Lower isolation percentage was observed in the samples in which the media displayed the lowest inhibition ability against contaminants. In this context, using two different selective media with high inhibition ability against contaminants may be recommended to enhance the isolation rate. Moreover, the components stimulating the growth of Brucella strains might be added to the media to obtain better results.

Isolation of Brucella abortus and Brucella melitensis from Seronegative Cows is a Serious Impediment in Brucellosis Control

Brucellosis is a zoonosis occurring worldwide, with economic and public health impacts. Its diagnosis remains a challenge in endemic countries and basically relies on serology. The present study was carried out on two dairy cattle farms allegedly free from brucellosis, but with sporadic cases of abortion. The aim of this study was to investigate the presence of Brucella (B.) spp. in uterine discharge of seronegative cows after abortion. In farm I, B. melitensis biovar (bv) 3 was cultured from two of five cows after abortion, while in farm II, B. abortus bv 1 was cultured from three of eleven cows after abortion. These cows had been intrauterinely infected but remained seronegative until abortion and seroconverted only thereafter. Shedding of brucellae in uterine discharge of culture positive/seronegative aborting cows is a serious problem resulting in maintenance and further spread of infection. Thus, serosurveys in endemic countries have to be accompanied by molecular detection and/or culture of aborted material to close the diagnostic window and to hinder uncontrolled spread.

A systematic review of current immunological tests for the diagnosis of cattle brucellosis

Brucellosis is a worldwide extended zoonosis with a heavy economic and public health impact. Cattle, sheep and goats are infected by smooth Brucella abortus and Brucella melitensis, and represent a common source of the human disease. Brucellosis diagnosis in these animals is largely based on detection of a specific immunoresponse. We review here the immunological tests used for the diagnosis of cattle brucellosis. First, we discuss how the diagnostic sensitivity (DSe) and specificity (DSp), balance should be adjusted for brucellosis diagnosis, and the difficulties that brucellosis tests specifically present for the estimation of DSe/DSp in frequentistic (gold standard) and Bayesian analyses. Then, we present a systematic review (PubMed, GoogleScholar and CABdirect) of works (154 out of 991; years 1960-August 2017) identified (by title and Abstract content) as DSe and DSp studies of smooth lipopolysaccharide, O-polysaccharide-core, native hapten and protein diagnostic tests. We summarize data of gold standard studies (n = 23) complying with strict inclusion and exclusion criteria with regards to test methodology and definition of the animals studied (infected and S19 or RB51 vaccinated cattle, and Brucella-free cattle affected or not by false positive serological reactions). We also discuss some studies (smooth lipopolysaccharide tests, protein antibody and delayed type hypersensitivity [skin] tests) that do not meet the criteria and yet fill some of the gaps in information. We review Bayesian studies (n = 5) and report that in most cases priors and assumptions on conditional dependence/independence are not coherent with the variable serological picture of the disease in different epidemiological scenarios and the bases (antigen, isotype and immunoglobulin properties involved) of brucellosis tests, practical experience and the results of gold standard studies. We conclude that very useful lipopolysaccharide (buffered plate antigen and indirect ELISA) and native hapten polysaccharide and soluble protein tests exist, provided they are applied taking into account the means available and the epidemiological contexts of this disease: i) mass vaccination; ii) elimination based on vaccination combined with test-and-slaughter; and iii) surveillance and existence of false positive serological reactions. We also conclude that the insistence in recent literature on the lack of usefulness of all smooth lipopolysaccharide or native hapten polysaccharide tests in areas where S19 vaccination is implemented is a misinterpretation that overlooks scientific and practical evidence.

Narrative overview of animal and human brucellosis in Morocco: intensification of livestock production as a driver for emergence?

Brucellosis is one of the most widespread zoonoses in the world caused by several species of the genus Brucella. The disease, eradicated in many developed countries, is a re-emerging neglected zoonosis endemic in several zones especially in the Mediterranean region, impacting on human health and livestock production. A One Health approach could address brucellosis control in Morocco but scarcity of reliable epidemiological data, as well as underreporting, hinders the implementation of sustainable control strategies. Surveillance and control policies implemented by the Moroccan government in domestic animals (cattle and small ruminants) in the last few decades are assessed for disease impact. This study considers the origins of animal brucellosis in Morocco and the potential for emergence of brucellosis during a shift from extensive to intensive livestock production.

Development of an improved competitive ELISA based on a monoclonal antibody against lipopolysaccharide for the detection of bovine brucellosis

Background

Brucellosis is the most common bacterial zoonosis, and serological tests are routinely used in brucellosis control and eradication programs. In order to improve the accuracy of serological diagnostic method used in bovine brucellosis detection, this study developed an improved competitive ELISA with higher specificity and good sensitivity.

Results

This study prepared 12 monoclonal antibodies against smooth Brucella lipopolysaccharide. One monoclonal antibody 3 F9, presented C epitope specificity, was used to develop a competitive ELISA for the serological detection of bovine brucellosis. The competitive ELISA, a commercial competitive ELISA kit, the rose-bengal plate agglutination test, and a microplate agglutination test were all used in the detection of 6 hyperimmune antisera against other commonly cross-reacted bacterial pathogens and 110 clinical bovine serum samples. The results of the test comparisons indicated that the competitive ELISA had higher specificity than the commercial competitive ELISA kit and RBT, and comparable sensitivity with the commercial ELISA kit.

Conclusions

This study provided a valuable detection tool with high specificity and good sensitivity, which prevent the wrong-culling of bovines in the eradication campaigns of bovine brucellosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0436-3) contains supplementary material, which is available to authorized users.