The diagnosis of brucellosis in sheep and goats, old and new tools

Brucellosis in camel, small ruminants, and Somali pastoralists in Eastern Ethiopia: a One Health approach

Brucellosis is a neglected bacterial zoonotic disease with economic and public health importance in pastoral communities of sub-Saharan Africa. A cross-sectional study was conducted from December 2021 to April 2022, to estimate the prevalence and identify the associated risk factors causing brucellosis in animals and associated with occupational diseases in humans from three selected districts of "the Somali Pastoral region," Eastern Ethiopia. In this study, 1,000 serum samples were screened for anti-Brucella spp. antibodies using Rose Bengal Plate Test (RBPT) and further confirmed using a competitive enzyme-linked immunosorbent assay (cELISA). A structured questionnaire was used to collect the biodata of tested animals and animal attendants to test the association between explanatory and outcome variables. The overall animal level prevalence was 5% (95% CI, 6.1-7.2.0) in small ruminants, 2.9% (95% CI, 1.5-4.9) in camels, and 2.0% (95% CI, 0.2-3.7) in occupationally linked humans. Herd size and herd history of retained fetal membranes were risk factors associated with Brucella spp. seropositivity in animals (p < 0.05). Disposing of retained fetal membranes was significantly associated (p < 0.05) with Brucella spp. seropositivity in humans. Evidence of brucellosis in various livestock species and associated seropositivity in humans indicates the need for a coordinated One Health approach, considering sociocultural dynamics of pastoral communities in controlling brucellosis to safe guard public health and increase livestock productivity.

Sero-prevalence and factors associated with anti-Brucella antibodies in slaughter livestock in Uganda

Introduction

Brucellosis is endemic in Uganda and is a major cause of production losses in livestock. Early detection and quantification of the disease is vital for its control and eradication. The aim of this study was to assess the sero-prevalence and factors associated with anti-Brucella antibodies in slaughtered livestock.

Materials and methods

Sera from 886 cattle, 925 small ruminants, and 900 pigs were collected from regional abattoirs in Northern, Eastern and Central Uganda. To estimate sero-prevalence, sera were serially tested using a combination of the Rose Bengal Test (RBT) and Native Hapten (NH) immunoprecipitation test. True sero-prevalence was estimated using the Rogan-Gladden estimator considering the sensitivity and specificity of the NH immunoprecipitation test. Multivariable logistic regression was used to assess factors associated with seropositivity for anti-Brucella antibodies.

Results and discussion

Small ruminants showed the highest seroprevalence (6.7%, 95% CI = 4.2-7.1) followed by cattle (3.8%, 95% CI = 2.4-4.9) and pigs (2.8%, 95% CI = 1.1-2.9). Seropositivity for anti-Brucella antibodies was associated with region of origin (OR = 4.6,95%CI=1.49-17.75, p = 0.013) for cattle; sex (OR = 2.90, 95% C = 1.5-6.34, p = 0.004), age (OR=4.04, 95% CI = 1.07-8.52, p = 0.006) and species (OR = 2.53, 95% CI = 1.08-6.98, p = 0.048) for small ruminants; and finally sex for pigs (OR = 2.88, 95% CI = 1.07-8.52, p = 0.041). Progressive control interventions must include both cattle and small ruminants since they play a bigger role in the maintenance and dissemination of Brucella. The interventions should adopt a risk-based approach with regions at higher risk being given top priority. Bacteriological and molecular studies should be undertaken to clarify the role of pigs and the goat-cattle cross infections in the epidemiological cycle of brucellosis in Uganda.

Rapid discrimination of Brucellosis in sheep using serum Fourier transform infrared spectroscopy combined with PCA-LDA algorithm

Brucellosis in sheep is an infectious disease caused by Brucella melitensis in sheep. The current conventional serological methods for screening Brucella-infected sheep have the disadvantage of time consuming and low accuracy, so a simple, rapid and highly accurate screening method is needed. The aim of this study was to evaluate the feasibility of diagnosing Brucella-infected sheep by serum samples based on the Fourier transform infrared (FTIR) spectroscopy. In this study, FTIR spectroscopy of serum from Brucella-infected sheep (n=102) and healthy sheep (n=125) revealed abnormal protein and lipid metabolism in serum from Brucella-infected sheep compared to healthy sheep. Principal component analysis-Linear discriminant analysis (PCA-LDA) method was used to differentiate the FTIR spectra of serum from Brucella-infected sheep and healthy sheep in the protein band (3700-3090 cm^-1) and lipid band (3000-2800 cm^-1), and its overall diagnostic accuracy was 100% (sensitivity 100%, specificity 100%). In conclusion, our results suggest that serum FTIR spectroscopy combined with PCA-LDA algorithm has great potential for brucellosis in sheep screening.

Evaluation of serological diagnostic tests for bovine brucellosis in dairy cattle herds in an endemic area: a multicenter study

Brucellosis is known as one of the most common zoonotic diseases worldwide affecting both livestock and humans. It causes abortions, reduces milk production, and infertility in infected animals. The disease is routinely diagnosed through three serological techniques, such as rose bengal plate test (RBPT), standard agglutination test (SAT), and indirect enzyme-linked immunosorbent assay (I-ELISA). The aim of this study was to identify and compare the brucellosis seroprevalence among dairy cattle farms through these different serological tests. From 2112 sampled dairy cattle in different parts of Iran, RBPT, SAT, and I-ELISA led to 296 (14.02%), 215 (10.18%), and 297 (14.06%) positive results, respectively. Brucella abortus biovar 3 (62 cases) was identified as the most common cause of brucellosis in tested animals. Our results showed that the specificity and sensitivity of I-ELISA were higher than those obtained by RBPT and SAT. In this study, the overall agreement of RBPT and SAT with I-ELISA reached 95.21% and 94.12% in dairy cattle farms, respectively. Furthermore, Cohen's kappa statistical analysis revealed that the best degree of agreement was seen between RBPT and I-ELISA (0.80), followed by RBPT and SAT (0.78) and finally SAT and I-ELISA (0.72), thereby indicating a strong agreement between RBPT and I-ELISA methods and good agreement between SAT and I-ELISA methods. The McNemar analysis also showed that a significant difference exists between positive and negative results determined by SAT and I-ELISA methods (p < 0.0001). However, the positive and negative results determined by I-ELISA and RBPT did not show a significant difference (p = 0.9207). Therefore, I-ELISA was a more specific and sensitive serological test when compared to RBPT and SAT and could remarkably decrease non-specific reaction by improving the serological screening specificity for an accurate brucellosis diagnosis in endemic areas.

Study on small ruminant brucellosis and owners awareness in two selected districts of southern region, Ethiopia

INTRODUCTION

Brucellosis is one of the infectious diseases that has the greatest impact on the productivity of sheep and goats. A cross-sectional study followed by a simple random sampling technique was used to investigate the seroprevalence of brucellosis (Rose Bengal plate test; RBPT and complement fixation test; CFT) in small ruminants and its related risk variables from November 2019 to June 2020 in Kolme and Abala Abaya districts. A questionnaire was also given to owners to assess their existing knowledge of the disease.

RESULT

Using the RBPT and CFT, 28 (4.1%) and 23 (3.33%) of the 690 animals were found to be seropositive for brucellosis, respectively. In this study, the seroprevalence of brucellosis detected in the Kolme district (5.3%) was greater when compared to Abala Abaya (1.0%). The odds of Brucella infection were greater for goats (odds ratio [OR] 6.0, 95% confidence interval [CI] 16 0.8-44.9) than for sheep. The odds of adult animals (OR 0.05, 95% CI 0.03-0.07) being positive for brucellosis was higher than young animals. A statistically significant difference in the seropositivity of brucellosis was detected in univariate logistic regression among districts, different age groups, herd size, parity number, and reproductive health problems except for species and sex, but in multivariate logistic regression, only reproductive health problems were revealed a statistically significant difference. Out of 138 families, 100% of respondents were unaware of brucellosis, 94.5% drink raw milk, and 74% handle animals with retained fetal membranes with their bare hands.

CONCLUSION

This study showed that brucellosis was a widely spread disease in the study areas and poses a substantial public health danger. To reduce the spread of the disease in small ruminants, public health risks, and economic losses, stringent vaccination application and awareness of personal hygiene are critical.

Investigation of selected bacterial agents causing sheep abortion in the Van Province by RT-PCR and histopathological methods

Abortion causes significant economic losses in the sheep industry. Determination of the aetiology is important in dealing with abortions. The present study was aimed to identify selected important bacterial pathogens in the abortion cases of sheep. A total of 113 samples (105 aborted sheep foetuses, 4 placentas, and 4 vaginal swab samples) from 85 different sheep flocks were examined by real-time PCR (RT-PCR) regarding Chlamydia (C.) spp., C. abortus, Brucella (B.) spp., B. melitensis, Salmonella (S.) spp., S. Abortusovis, Coxiella (C.) burnetii, Listeria (L.) spp., L. monocytogenes, and Campylobacter spp. All cases that were found to be positive for bacterial agents by RT-PCR, were examined pathologically. Tissue samples of foetuses that were found to be positive for B. melitensis and L. monocytogenes by RT-PCR were also investigated immunohistochemically. A total of 35 (30.9%) samples were found to be positive by RT-PCR, with 15 (42.8%), 9 (25.7%), 5 (14.2%), 4 (11.4%), 1 (2.8%), and 1 (2.8%) of them being identified as C. abortus, B. melitensis, S. Abortusovis, C. burnetii, L. monocytogenes and Campylobacter spp., respectively. The presence of the antigen was confirmed also immunohistochemically in the cases with B. melitensis and L. monocytogenes. As a consequence, C. abortus was found to cause the highest rate of sheep abortion cases, which should be taken into account when implementing control measures in epidemiological investigations.

Molecular detection of Brucella spp. in clinical samples of seropositive ruminants in Bosnia and Herzegovina

Brucellosis is one of the most common zoonotic diseases worldwide that is endemic to Bosnia and Herzegovina (B&H) and remains an emerging public and animal health concern in this country. Diagnostic testing of brucellosis in ruminants in B&H relies exclusively on serological methods. The present study was conducted to determine the presence of Brucella spp. in clinical samples of seropositive ruminants by Real-time PCR assay. Of the 135 samples tested, 37% were positive by Real-time PCR. The frequency of detection of Brucella-DNA in the samples collected from aborted animals (n = 20/20; 100%) was significantly higher (P < 0.00001) when compared to asymptomatic animals (n = 30/115; 26%). Among asymptomatic animals, 31.1% of cattle were positive for Brucella-DNA, followed by sheep (23.4%) and goats (16.6%). The results of this research underline the limitations of the current control policy and indicate the need for additional diagnostic methods required for more effective brucellosis control program.

Brucella species circulating in rural and periurban dairy cattle farms: a comparative study in an endemic area

Brucellosis is among the most important zoonotic infectious diseases worldwide affecting both humans and domestic animals. The present study aimed to determine and compare the seroprevalence of brucellosis among rural and periurban dairy cattle farms of four Iranian provinces from 2017 to 2019. We applied different serological tests, including RBT, SAT, and iELISA to evaluate the brucellosis prevalence among 2808 dairy cattle. Species-specific multiplex PCR and biotyping tests were also used to further identify the implicated Brucella species. Serological screening using RBT, SAT, and iELISA led to 157 (5.6%), 112 (3.9%), and 139 (4.9%) positive results among tested cattle, respectively. Brucella abortus biovars 1 (2 cases) and biovars 3 (42 cases) were identified by biotyping experiments and multiplex PCR in all 44 tested lymph node samples. Further, Cohen's kappa statistical analysis revealed that the best degree of agreement was seen between RBT and iELISA (99.4%), followed by SAT/iELISA (98.5%) and finally RBT/SAT (98.4%). Our results also showed a significantly lower seroprevalence of brucellosis in periurban dairy cattle when compared to rural dairy cattle population (p value= 0.01). These results reflect the need for better vaccine coverage using RB51 combined with an appropriate test-and-slaughter program in the rural dairy cattle population.

Acute phase biomarkers, oxidants, antioxidants, and trace minerals of mobile sheep flocks naturally infected with brucellosis

This study assayed the acute phase responses of sheep seropositive to Brucella. Sera collected from ewes (n=160) were subjected to serological tests of Brucella, Rose Bengal plate agglutination test (RBPAT), buffer acidified plate agglutination test (BAPAT), and complement fixation test (CFT). Results revealed that CFT was the most predictive test of brucellosis followed by BAPAT then RBPAT. The moderate predictive blood biochemical parameters were zinc and ascorbic acid. Ewes with low CFT titre (chronic) had low fibrinogen, copper, NO, and GPx. Seropositive animals had high blood concentrations of ascorbic acid and zinc.

Control of Brucella melitensis in endemic settings: A simulation study in the Nile Delta, Egypt

Small ruminant brucellosis remains endemic in many low- and middle-income countries (LMICs), where it poses a major economic and public health burden. Lack of resources to support long-term vaccination, inherent characteristics of small ruminant production systems such as mixing of different flocks for grazing and limitations of the vaccines currently available, which can induce abortion in pregnant animals, have all hindered the effectiveness of control programmes. In the current study, the likely effect of different control scenarios on the seroprevalence of brucellosis among the small ruminant population in a hypothetical area of an endemic region was simulated using compartmental models. The model accounts for variability in transmission rates between villages and also simulates control scenarios that target villages with high seroprevalence. Our results show that vaccination of young replacement animals only can effectively reduce the prevalence of small ruminant brucellosis in endemic settings if a high vaccination coverage is achieved. On the other hand, test-and-slaughter alone is not a promising strategy for control of small ruminant brucellosis under husbandry practices typical of endemic low-resource settings. Furthermore, results show the potential success of some strategies requiring a relatively low overall vaccination coverage such as the vaccination of 50% of young replacements and 25% of adult animals each year. Control strategies selectively targeting high initial seroprevalence villages (p > 10%) did not decrease the overall seroprevalence to acceptable levels in most of the examined scenarios. Scenario analysis showed that the efficacy of the simulated control strategies can be improved mostly by decreasing the proportion of between-village trade and also by improving the performance of the used serological tests and increasing vaccine efficacy.

Soliman H, I. Mohamed H, A. Salem M, A. Ahmed S. Diagnostic performance of RFLP-PCR and sarcosine based indirect ELISA versus immunoassays in Brucella infected and vaccinated small ruminants

This study was carried out for evaluation of the diagnostic performance of different serological assays; buffered acidified plate antigen test (BAPAT), rose bengal plate test (RBPT), immunochromatographic assay (ICA), rivanol test (RivT), indirect ELISA using two types of coating antigens (smooth lipopolysaccharide; S-LPS and N-lauroylsarcosine-extracted antigens; SE) and complement fixation test (CFT). Relative sensitivity and specificity of various techniques were estimated. The traditional serological tests failed to distinguish the vaccinated from naturally infected animals. Using iELISA with extracted antigens (SE) as a coating antigen was a more accurate test to differentiate the naturally infected animals from vaccinated animals. Application of restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) on sera samples from seropositive animals, Rev-1 vaccinated sheep and Brucella field strain infected sheep and goats revealed that there were samples identified as B. melitensis biovar 3 field strain and other samples identified as B. melitensis Rev-1 vaccinal strain. The obtained results established that restriction fragment length polymorphism-polymerase chain reaction can differentiate between animals infected with Brucella field strains from animals vaccinated with the Rev-1 vaccine.

Serological diagnostic potential of recombinant outer membrane proteins (rOMPs) from Brucella melitensis in mouse model using indirect enzyme-linked immunosorbent assay

BACKGROUND

Brucella melitensis is the most important pathogenic species of Brucella spp. which affects goats and sheep and causes caprine and ovine brucellosis, respectively. Serological tests for diagnosis of brucellosis such as Rose Bengal plate test (RBPT) and enzyme-linked immunosorbent assay (ELISA) usually utilize smooth lipopolysaccharides (S-LPS) as a diagnostic antigen which could give false positive serological reactions. Outer membrane proteins (OMP) of B. melitensis have been used as alternative diagnostic antigens rather than S-LPS for differential serological diagnosis of brucellosis, mainly in ELISA with single recombinant OMP (rOMP) as a diagnostic antigen. Nevertheless, the use of single format mainly showed lack of sensitivity against the desired rOMP. Therefore, this study aimed to determine whether a newly developed rOMPs indirect ELISA (rOMPs I-ELISA), based on combination of rOMP25, rOMP28 and rOMP31of B. melitensis, has a potential benefit for use in the serodiagnosis of brucellosis.

METHODS

In this study, omp25, omp28 and omp31 of B. melitensis were cloned and expressed using prokaryotic pET-32 Ek/LIC system and their respective rOMPs were combined as one coating antigen to develop rOMPs I-ELISA. Three groups of BALB/c mice were used to elicit antibody response. Group 1, infected with B. melitensis strain 0331 field strain; group 2, injected with B. melitensis Rev.1 vaccine strain and group 3, infected with Yersinia enterocolitica O:9. Antibody responses in three groups of mice were investigated using Rose Bengal plate test (RBPT) and rOMPs I-ELISA.

RESULTS

The production of rOMP25, rOMP28 and rOMP31 of B. melitensis were achieved and Western immunoblotting analysis demonstrated their reactivity. The RBPT was unable to differentiate the vaccinated mice (group 2) and mice infected with Y. enterocolitica O:9 (group 3) and categorized them wrongly as positive for brucellosis. In contrast, the rOMPs I-ELISA was able to differentiate the mice infected with B. melitensis strain 0331 (group 1) from both of group 2 and group 3, and recorded 100% sensitivity and 100% specificity.

CONCLUSIONS

The results of this study suggested that rOMPs of B. melitensis has potential diagnostic ability to differentiate the FPSR in serological diagnosis of brucellosis.

Evaluation of up-converting phosphor technology-based lateral flow strips for rapid detection of Bacillus anthracis Spore, Brucella spp., and Yersinia pestis

Bacillus anthracis, Brucella spp., and Yersinia pestis are zoonotic pathogens and biowarfare- or bioterrorism-associated agents that must be detected rapidly on-site from various samples (e.g., viscera and powders). An up-converting phosphor technology-based lateral flow (UPT-LF) strip was developed as a point-of-care testing (POCT) to satisfy the requirements of first-level emergency response. We developed UPT-LF POCT to quantitatively detect the three pathogens within 15 min. Sample and operation-error tolerances of the assay were comprehensively evaluated. The sensitivity of UPT-LF assay to bacterial detection reached 10(4) cfu · mL(-1) (100 cfu/test), with a linear quantitative range of 4 to 6 orders of magnitude. Results revealed that the UPT-LF assay exhibited a high specificity with the absence of false-positive results even at 10(9) cfu · mL(-1) of non-specific bacterial contamination. The assay could tolerate samples with a wide pH range (2 to 12), high ion strengths (≥ 4 mol · L(-1) of NaCl), high viscosities (≤ 25 mg · mL(-1) of PEG20000 or ≥ 20% of glycerol), and high concentrations of bio-macromolecule (≤ 200 mg · mL(-1) of bovine serum albumin or ≥ 80 mg · mL(-1) of casein). The influence of various types of powders and viscera (fresh and decomposed) on the performance of UPT-LF assay was determined. The operational error of liquid measurement exhibited few effects on sensitivity and specificity. The developed UPT-LF POCT assay is applicable under field conditions with excellent tolerance to sample complexity and operational error.

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.

A study on seroprevalence of caprine brucellosis under three livestock production systems in southern and central Ethiopia

Caprine brucellosis in Ethiopia is less commonly reported with limited information on the disease status in the country. The objective of this study was therefore to highlight the status of goat brucellosis in three distinctly different livestock production systems of southern and central Ethiopia. A total 3,315 goats of different age and sex, living with other animals in variable flock size, were sampled from 448 flocks raised in sedentary, pastoral and agro-pastoral production systems. Goats were bled aseptically and sera were collected for serial testing using Rose Bengal Plate Test as screening test and subsequently complement fixation test as confirmatory test. Questionnaire and laboratory data were analysed for descriptive, univariable and multivariable logistic regression analysis both at individual and flock level (STATA 11). The study revealed an overall animal level seroprevalence of 1.9 % (95 % CI 1.5, 2.4). In sedentary production system, the observed seroprevalence was 0.6 % (95 % CI 0.2, 0.9) while 1.9 % (95 % CI 1.1, 2.7) and 7.6 % (95 % CI 5.1, 10.1) were the proportion of seroreactors for agro-pastoral and pastoral production systems, respectively. The observed prevalence difference between the three production systems was statistically significant (P < 0.05). At the flock level analysis, 11.2 % (95 % CI 8.2, 14.1) of the flocks sampled had at least one seropositive goat among themselves. Like individual level analysis, the highest prevalence of 32.5 % (95 % CI 21.9, 43.0) was recorded for pastoral production system, followed by agro-pastoral, 13.0 % (95 % CI 7.0, 19.0) and sedentary production system, 3.6 % (95% CI 1.3, 6.0). Accordingly, the odds of Brucella seropositivity were higher (OR = 12.8) in pastoral followed by agro-pastoral (OR = 4.0) in relation to sedentary production system. Large numbers of seroreactors were observed in adult age living in larger flocks with other livestock species. However, no difference was noted between male and female goats. Finally, the need for nationwide survey and subsequent designing and implementation of appropriate control measure is suggested.