Comparison of polymerase chain reaction and bacteriological culture for the diagnosis of sheep brucellosis using aborted fetus samples

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.

Scent detection of Brucella abortus by African giant pouched rats (Cricetomys ansorgei)

BACKGROUND

Brucellosis is a contagious zoonosis caused by bacteria of the genus Brucella. While the disease has been eradicated in most developed countries, it remains endemic in sub-Saharan Africa where access to reliable diagnostics is limited. African giant pouched rats (Cricetomys ansorgei) have been trained to detect the scent of Mycobacterium tuberculosis to increase case detection in sub-Saharan Africa. Given the similar diagnostic challenges facing brucellosis and tuberculosis, we explored the feasibility of training African giant pouched rats to detect Brucella.

RESULTS

After 3 months of training, rats reliably identified cultured Brucella, achieving an average sensitivity of 93.56% (SD = 0.650) and specificity of 97.65% (SD = 0.016). Rats readily generalized to novel, younger Brucella cultures that presumably generated a weaker volatile signal and correctly identified at least one out of three fecal samples spiked with Brucella culture during a final test of feasibility.

DISCUSSION

To our knowledge, these experiments are the first to demonstrate Brucella emits a unique odor profile that scent detection animals can be trained to identify. Importantly, cultured E. coli samples were included throughout training and test to ensure the rats learned to specifically identify Brucella bacteria rather than any bacteria in comparison to bacteria-free culture medium. E. coli controls therefore served a crucial function in determining to what extent Brucella abortus emits a unique odor signature. Further research is needed to determine if a Brucella-specific volatile signature is present within clinical samples. If confirmed, the present results suggest trained rats could serve as a valuable, novel method for the detection of Brucella infection.

Comparative Review of Brucellosis in Small Domestic Ruminants

Brucella melitensis and Brucella ovis are the primary etiological agents of brucellosis in small domestic ruminants. B. melitensis was first isolated in 1887 by David Bruce in Malta Island from spleens of four soldiers, while B. ovis was originally isolated in Australia and New Zealand in early 1950's from ovine abortion and rams epididymitis. Today, both agents are distributed worldwide: B. melitensis remains endemic and associated with an extensive negative impact on the productivity of flocks in -some regions, and B. ovis is still present in most sheep-raising regions in the world. Despite being species of the same bacterial genus, B. melitensis and B. ovis have extensive differences in their cultural and biochemical characteristics (smooth vs. rough colonial phases, serum and CO2 dependence for in vitro growth, carbohydrate metabolism), host preference (female goat and sheep vs. rams), the outcome of infection (abortion vs. epididymitis), and their zoonotic potential. Some of these differences can be explained at the bacterial genomic level, but the role of the host genome in promoting or preventing interaction with pathogens is largely unknown. Diagnostic techniques and measures to prevent and control brucellosis in small ruminants vary, with B. melitensis having more available tools for detection and prevention than B. ovis. This review summarizes and analyzes current available information on: (1) the similarities and differences between these two etiological agents of brucellosis in small ruminants, (2) the outcomes after their interaction with different preferred hosts and current diagnostic methodologies, (3) the prevention and control measures, and (4) alerting animal producers about the disease and raise awareness in the research community for future innovative activities.

The Importance of Complementary PCR Analysis in Addition to Serological Testing for the Detection of Transmission Sources of Brucella spp. in Greek Ruminants

The early and accurate diagnosis of brucellosis, a ubiquitous zoonotic infection, is significant in preventing disease transmission. This study aimed to assess the infection rate of Brucella spp. in ruminants and to evaluate the agreement between a serological test and a molecular method for the detection of infected cases. Blood and milk samples of 136 ruminants were analyzed using two laboratory methods: the Rose Bengal plate (RBP) test to detect B. abortus and B. melitensis antibodies and the molecular polymerase chain reaction (PCR) method for the presence of bacterial DNA. The agreement between the methods was assessed using the kappa statistic. Based on the RBP test, there were 12 (8.8%) seropositive animals (10 sheep and 2 cows), while 2 (1.4%) samples were positive on PCR analysis. The positive PCR samples were from seronegative cow samples on RBP testing. There was slight agreement (k = −0.02) between the two methods, which was not statistically significant. Our results indicate that complementary molecular methods are useful to detect the bacteria in infected animals that are seronegative due to an early stage of infection. Therefore, a combination of molecular methods and serological tests can be applied to detect brucellosis in ruminants efficiently.

A one-year descriptive epidemiology of zoonotic abortifacient pathogen bacteria in farm animals in Turkey

This study aimed to investigate the epidemiology of 10 suspicious pathogenic bacteria in 250 stomach contents of aborted calf, lamb, and goat foetuses in 2019. The 155 positive samples obtained from PCR consisted of 53 (58.88 %) bacteria from 90 lamb samples, 10 (43.47 %) bacteria from 23 goat samples, and 92 (67.15 %) bacteria from 137 calf samples. The five most common bacteria associated with abortions were Brucella melitensis, 52 (20.9 %); B. abortus, 13 (5.2 %); Leptospira spp., 34 (13.6 %); Campylobacter fetus, 52 (20.9 %); and Coxiella burnetii, 4 (1.6 %). The highest rate of B. melitensis (65.4 %), B. abortus (69.2 %), Leptospira spp. (67.6 %), and C. fetus (50 %) was detected in the aborted calf samples. The highest individual rate was that of C. fetus (5.2 %). The flock-herd rates of B. melitensis, B. abortus, Leptospira spp., C. fetus, and C. burnetii infections in the 29 farms studied were 34.48 %, 20.69 %, 62.06 %, 82.75 %, and 3.44 %, respectively, with a confidence level and interval of 95 %. The frequency of abortions caused by Leptospira spp. and Campylobacter fetus may be related to increasing in B. melitensis. The rates of aborted calf, lamb, and goat foetuses among the various sampling periods and regions were significantly (P < 0.01) different. In conclusion, precautions should be applied to reduce the spread of these bacterial agents in high-risk areas and to eliminate the risk of harbouring these zoonotic infections in humans. Therefore, these results must be taken into account in the development of control and protection strategies against abortions in animals.

Brucellosis in Iranian livestock: A meta-epidemiological study

Brucellosis is a widespread zoonotic disease affecting human and livestock health. This meta-epidemiological study is aiming to draw a comprehensive picture of the Brucella prevalence in Iranian livestock, trying to estimate most affected subgroups as well as the most appropriate methods and sampling conditions for brucellosis screening programs. A literature search was performed among data published between 1 January 1970 and July 2020. Different subgroups were compared according to animal species, gender, age, sampling season, sampling locations as well as the diagnostic method used for brucellosis screening. To determine heterogeneity of studies, Chi-squared test was used and a random effect model (REM) estimated the pooled prevalence among subgroups. A total of 45 publications, comprising 240 studies/data-reports, were evaluated. A significant increase in the number of studies was found over time (Coefficient = 0.151, p value < 0.001). The most studied species in Iran was cow (n = 75), followed by sheep (n = 63), goat (n = 45), camel (n = 40) and Buffalo (n = 16). The most identified Brucella species in livestock were Brucella melitensis (n = 50), Brucella abortus (n = 39), mix infection of B. melitensis and B. abortus (n = 11) and vaccine strain of B. melitensis Rev1 (n = 4). PCR-based tests were the most common applied diagnostic method (n = 140), while the highest prevalence rate of positive samples was obtained by indirect ELISA (69%). The prevalence of brucellosis was significantly higher in females (10.91%) compared to males (8.23%). The meta-epidemiological study of brucellosis in Iranian livestock would help to strengthen surveillance, control and prevention approaches to counter the spread of this zoonotic disease.

Development of a Genus-Specific Brucella Real-Time PCR Assay Targeting the 16S-23S rDNA Internal Transcribed Spacer from Different Specimen Types

The aim of this study was to develop a 16S-23S ribosomal deoxyribonucleic acid internal transcribed spacer (ITS) quantitative polymerase chain reaction (qPCR) assay for the early diagnosis and rapid screening of brucellosis. Blood, milk, and tissue samples were spiked with B. abortus biovar 1 (B01988-18 strain) to determine the analytical sensitivity and specificity of the assay. The 95% limit of detection of the ITS qPCR assay was highest in tissue, followed by blood, then milk, i.e., 0.48, 4.43, and 15.18 bacteria/PCR reaction, respectively. The diagnostic performance of the assay was compared to the Brucella cell surface protein (BCSP) 31 qPCR assay and bacterial culture. Out of 56 aborted foetal tissue samples from bovine, ovine, and caprine, 33% (19/56) were positive for Brucella spp. The sensitivity and specificity of the ITS qPCR assay was 87% and 95% respectively, compared to 92% and 89% for the BCSP31 qPCR assay and 47% and 55% for bacterial culture, respectively. The assay was efficient, sensitive, and specific, making it a valuable tool in the early detection of the Brucella pathogen.

The global epidemiology of Brucella infections in terrestrial wildlife: A meta-analysis

Brucellosis is a widespread zoonotic disease with serious consequences on human and animal health. Brucella infections were reported in many terrestrial wild animals, from subtropical and temperate regions to arctic regions. In many areas, the epidemiology of brucellosis in wildlife is closely associated with the occurrence of the disease in livestock. Some wild species may contribute to the re-introduction of Brucella infections in livestock (spillback), even in officially brucellosis-free (OBF) regions. Through meta-regression analysis, this study draws a global picture of the prevalence of Brucella spp. in terrestrial wild animals, trying to determine most affected subgroups as well as preferential sampling and screening methods. For this purpose, a literature search was carried out among publications published from 1983 to 2019. Different subgroups were compared according to animal species, feeding, gender, age as well as the method used for sampling and for brucellosis diagnostic. To determine heterogeneity of studies, chi-squared test was used and a random-effects model (REM) estimated the pooled prevalence among subgroups. A total of 68 publications, comprising 229 data reports/studies, were selected. The most-reported Brucella species in wildlife was Brucella abortus, and the highest prevalence rate was found in American bison, Bison bison (39.9%) followed by Alpine ibex, Capra ibex (33%). Serology was the most widely applied diagnostic approach (66%), while PCR appeared to be highly sensitive (36.62% of positive results). The gender of animals showed no significant association with the prevalence of brucellosis (p > .05). Blood samples and visceral organs constituted the great majority of specimen used for the detection of Brucella spp., while lymph nodes showed a high prevalence of positive samples (94.6%). The present study provides insight into the global epidemiology and enzootic potential of brucellosis in wild terrestrial animals worldwide, aiming at helping the appropriate authorities to strengthen prevention, surveillance and control strategies.

Aetiology of livestock fetal mortality in Mazandaran province, Iran

In the farming industry, the productivity of livestock herds depends on the fertility efficiency of animals. The accurate diagnosis of a broad range of aetiological agents causing fetal death is often difficult. Our aim was to assess the prevalence rates of Toxoplasma gondii, Neospora caninum, and Brucella spp. infections in ruminant abortion using bacteriological culture and molecular techniques in Mazandaran Province, northern Iran. Samples were collected from 70 aborted sheep, goat, and cattle fetuses between September 2014 and December 2015. Necropsy was performed on all the received samples, and brain tissue and abomasal content were obtained from the aborted fetuses. Protozoan infections were detected by specific polymerase chain reaction (PCR) and bacterial agents using bacteriological examinations and PCR assay. Infectious pathogens were detected in 22 out of 70 (31.4%) examined fetuses. Moreover, T. gondii, N. caninum, and B. melitensis were verified in 13 (18.6%), four (5.7%), and two (2.85%) samples, respectively. Our results showed that infection with the mentioned pathogenic agents may lead to fetal mortality, which can be a major cause of economic loss. The listed pathogens could be considered important etiological agents of fetal loss in Mazandaran Province, for which appropriate control measures such as vaccination and biosecurity can be implemented to prevent infection and reduce reproductive loss in livestock farms.

Human brucellosis caused by raw dairy products: A review on the occurrence, major risk factors and prevention

Despite considerable efforts made to address the issue of brucellosis worldwide, its prevalence in dairy products remains difficult to estimate and represents an important public health issue in many areas of the globe today. This is partly explained by the increasing tendency for consumption of raw dairy products, making the prevention and control of this zoonosis even more critical. This review summarizes reports published since the early 2000s on human brucellosis caused by contaminated dairy products and the systems of evaluation and assessment which are used to improve the diagnosis, surveillance, control and prevention of the disease. For this purpose, five comprehensive electronic databases were investigated and relevant studies were identified for systematic review. The design and quality of the studies revealed notable variation, especially in the methods used for the detection and characterization of Brucella spp. This report provides helpful information about the health risk associated with the consumption of raw milk and relevant preventive strategies.

Direct diagnosis of Brucella species through multiplex PCR formed by a new method

This study aimed to develop direct PCR methods, which enable the diagnosis of brucellosis agents from ruminant aborted fetus samples at species and genus levels, and determine the applicability of the newly developed methods. For this purpose, 137 lung, 137 liver, and 52 fetal stomach fluid samples belonging to 166 ruminant aborted fetuses (326 samples in total) were examined. Firstly, agent isolation and identification were performed and species-specific multiplex PCR (m-PCR) from the culture was applied to the samples. In addition, the Mayer-Scholl m-PCR method was modified and termed 'modified Mayer-Scholl', and genus specific Bcsp31 PCR was also modified with minor changes. Four different methods were applied to direct examination samples and the obtained results were compared. The conventional culture method was set as the standard method to which sensitivities and specificities of the molecular methods were calculated. According to the assessments on the basis of fetus (n = 166), sensitivity and specificity values for modified Mayer-Scholl m-PCR method were 94.11% and 98.76%, and the same indicators for the modified Bcsp31 PCR were 95.29% and 98.76%, respectively. When all organ samples were taken into account (n = 326), sensitivity and specificity values for the modified Mayer-Scholl m-PCR method were 85.38% and 98.06%, and for the modified Bcsp31 PCR, they were 83.62% and 98.06%, respectively. As a result, it was found that the diagnostic power of the tests were 'high' when results were evaluated at fetus level. On the other hand, it was found to be 'clinically useful' when evaluated at organ level. We concluded that species level identifications can be made through the modified Mayer-Scholl method, which is a direct m-PCR method, with a high diagnostic power by specifying DNAs belonging to Brucella species directly from clinical samples.

Use of serology and real time PCR to control an outbreak of bovine brucellosis at a dairy cattle farm in the Nile Delta region, Egypt

Background

Bovine brucellosis remains one of the most prevalent zoonotic infections affecting dairy cattle in developing countries where the applied control programs often fail. We analyzed the epidemiologic pattern of bovine brucellosis in a dairy cattle herd that showed several cases of abortions after regular vaccination with RB51 (B. abortus vaccine). In 2013 thirty dairy cows, from a Holstein-Friesian dairy herd with a population of 600 cattle, aborted five months post vaccination by a regular RB51 vaccine. Blood samples were drawn from milking cows and growing heifers, as well as heifers and cows pregnant up to 6 months. These samples were collected in June 2013 (n = 257) and May 2014 (n = 263) and were tested by real time (rt)-PCR as well as serological tests, in particular Rose Bengal Test (RBT), Enzyme-Linked Immunosorbent Assays (ELISA) and Fluorescence Polarization Assay. Tissue specimens were also collected from an aborted fetus and cultured. Isolates were subjected to bacteriological typing tests at the genus and species levels.

Results

Five months post vaccination with RB51 vaccine, Brucella (B.) DNA was detected in blood samples of cows by rt-PCR. The serological tests also revealed the spread of Brucella field strains within the herd in 2013. Four Brucella isolates were recovered from specimens collected from the aborted fetus. These isolates were typed as follows: one B. abortus RB51 vaccine strain and three isolates of B. abortus field strain. The seropositive cows with positive rt-PCR might indicate an infection by the Brucella field strain; while the positive rt-PCR results from seronegative animals may either be due to circulating RB51 vaccine DNA in vaccinated animals or to circulating field strain in infected animals before seroconversion.

Conclusion

The results herein suggest that PCR can be a good supplementary tool in an outbreak situation, if an assay is available that can differentiate vaccine and field strains with a high analytical sensitivity. We recommend using RBT and ELISA in parallel in outbreak situations, to identify as many infected animals as possible during the initial screenings. This test procedure should be repeated for at least three successive negative tests, with one month interval.

In vitro activity of Brucella melitensis isolates to various antimicrobials in Turkey

BACKGROUND

Brucellosis is a systemic infectious disease caused by Brucella bacteria. A successful treatment requires antibiotics that can penetrate into the cell at high concentrations. The aim of this study was to assess the biotype and in vitro activity of 80 Brucella isolates obtained from blood against various antimicrobials for human brucellosis in Turkey.

METHODS

Identification of the types of the species designated Brucella species was made using the polymerase chain reaction (PCR), with type-specific primers. Serotyping was performed using mono-specific A and M antisera. The minimum inhibitory concentrations (MICs) of antibiotics known to have good intracellular penetration (doxycycline, rifampicin, ofloxacin, levofloxacin, moxifloxacin, clarithromycin, and azithromycin) were determined by the agar dilution method.

RESULTS

All of the 80 Brucella isolates were determined to be Brucella melitensis: 75 B. melitensis biotype 3 (93.7%) and 5 B. melitensis biotype 1 (6.3%). Doxycycline was the most effective among the tested antibiotics against Brucella species (MIC(50)-MIC(90), 0.25-0.5 μg/ml), and it was followed by levofloxacin (MIC(50)-MIC(90), 0.5-1 μg/ml), moxifloxacin (MIC(50)-MIC(90), 1-1 μg/ml), ofloxacin (MIC(50)-MIC(90), 1-1 μg/ml), rifampicin (MIC(50)-MIC(90), 2-4 μg/ml), azithromycin (MIC(50)-MIC(90), 4-8 μg/ml), and clarithromycin (MIC(50)-MIC(90), 8-32 μg/ml), respectively.

CONCLUSIONS

The in vitro activity of doxycycline and rifampicin, which are used in the classic treatment of brucellosis, was found to be very good. Quinolones were found to have in vitro activity against Brucella isolates. Among the macrolides, azithromycin had a higher level of activity compared with clarithromycin. A combination of quinolones and azithromycin could be an alternative to doxycycline and rifampicin in the treatment of brucellosis.

In vitro antimicrobial susceptibility of Brucella melitensis isolates from sheep in an area endemic for human brucellosis in Turkey

The aim of this study was to assess in vitro antimicrobial susceptibility of Brucella melitensis isolates isolated from naturally infected sheep cases in an area where human brucellosis is endemic, focusing on rifampin (RIF), streptomycin (SM), ciprofloxacin (CPFX), trimethoprim/sulfamethoxazole (TMP/SMZ), gentamicin (GM) and tetracycline (TC) and on 11 other antimicrobials. The identification and typing of Brucella isolates were carried out using standard classification tests and polymerase chain reaction (PCR) methods. Antimicrobial susceptibility testing was carried out on Mueller-Hilton agar. The resistance to SM, CPFX and GM was determined at the rate of 7.3% and to RIF at the rate of 9.7%. The highest (46.3%) resistance was determined against TMP/SMZ. All strains were found to be sensitive to TC at the rate of 100.0%. In conclusion, ovine origin B. melitensis strains evaluated in this study were resistant to at least one antimicrobial (51.2%) that is commonly used in human clinical medicine against brucellosis.

A multiplex real-time polymerase chain reaction assay with two internal controls for the detection of Brucella species in tissues, blood, and feces from marine mammals

Brucellosis has emerged as a disease of concern in marine mammals in the last 2 decades. Molecular detection techniques have the potential to address limitations of other methods for detecting infection with Brucella in these species. Presented herein is a real-time polymerase chain reaction (PCR) method targeting the Brucella genus–specific bcsp31 gene. The method also includes a target to a conserved region of the eukaryotic mitochondrial 16S ribosomal RNA gene to assess suitability of extracted DNA and a plasmid-based internal control to detect failure of PCR due to inhibition. This method was optimized and validated to detect Brucella spp. in multiple sample matrices, including fresh or frozen tissue, blood, and feces. The analytical limit of detection was low, with 95% amplification at 24 fg, or an estimated 7 bacterial genomic copies. When Brucella spp. were experimentally added to tissue or fecal homogenates, the assay detected an estimated 1–5 bacteria/µl. An experiment simulating tissue autolysis showed relative persistence of bacterial DNA compared to host mitochondrial DNA. When used to screen 1,658 field-collected marine mammal tissues in comparison to microbial culture, diagnostic sensitivity and specificity were 70.4% and 98.3%, respectively. In addition to amplification in fresh and frozen tissues, Brucella spp. were detected in feces and formalin-fixed, paraffin-embedded tissues from culture-positive animals. Results indicate the utility of this real-time PCR for the detection of Brucella spp. in marine species, which may have applications in surveillance or epidemiologic investigations.

Rapid immunofiltration assay as a field diagnostic tool for ovine brucellosis

This work describes the development of two rapid immunofiltration assays, enzymatic (ERIFA) and non-enzymatic (NERIFA), for the rapid detection of ovine anti-Brucella antibodies. Brucella abortus lipopolysaccharide and total bacterial extract were dotted separately as diagnostic antigens on a nitrocellulose filter-membrane of the individual assay unit along with a third dot of purified sheep IgG as an internal control. The assay's diagnostic performance was evaluated in comparison with a modified rose bengal test (mRBT) and an indirect enzyme-linked immunosorbent assay (ELISA) through usage of 590 serum samples from healthy, vaccinated, or infected sheep. The ERIFA and indirect ELISA were found to be significantly more sensitive than NERIFA, while mRBT was determined to be statistically equivalent to NERIFA. A perfect agreement (κ = 0.984) and a statistical equivalence to indirect ELISA suggest that the bi-antigenic ERIFA can be used as an "individual rapid ELISA" for screening ovine anti-Brucella antibody both in the field and in limited laboratory conditions.

Diagnosis of brucellosis in livestock and wildlife

AIM

To describe and discuss the merits of various direct and indirect methods applied in vitro (mainly on blood or milk) or in vivo (allergic test) for the diagnosis of brucellosis in animals.

METHODS

The recent literature on brucellosis diagnostic tests was reviewed. These diagnostic tests are applied with different goals, such as national screening, confirmatory diagnosis, certification, and international trade. The validation of such diagnostic tests is still an issue, particularly in wildlife. The choice of the testing strategy depends on the prevailing brucellosis epidemiological situation and the goal of testing.

RESULTS

Measuring the kinetics of antibody production after Brucella spp. infection is essential for analyzing serological results correctly and may help to predict abortion. Indirect ELISAs help to discriminate 1) between false positive serological reactions and true brucellosis and 2) between vaccination and infection. Biotyping of Brucella spp. provides valuable epidemiological information that allows tracing an infection back to the sources in instances where several biotypes of a given Brucella species are circulating. Polymerase chain reaction and new molecular methods are likely to be used as routine typing and fingerprinting methods in the coming years.

CONCLUSION

The diagnosis of brucellosis in livestock and wildlife is complex and serological results need to be carefully analyzed. The B. abortus S19 and B. melitensis Rev. 1 vaccines are the cornerstones of control programs in cattle and small ruminants, respectively. There is no vaccine available for pigs or for wildlife. In the absence of a human brucellosis vaccine, prevention of human brucellosis depends on the control of the disease in animals.

Detection of Brucella abortus in Bovine Milk by Polymerase Chain Reaction

This study compares milk ring test and three different polymerase chain reaction techniques (direct DNA extraction by column purification system, alkaline DNA extraction, and filtrated milk), in order to identifyBrucella abortusinfection in bovine milk. Milk ring test sensitivity and specificity were 72% and 80%, respectively. While specificity of the three polymerase chain reaction techniques was 100%; sensitivity was 92%, 88% and 100%, respectively, for the three polymerase chain reaction procedures. We conclude that the filtered animal’s milk polymerase chain reaction is the best procedure to make the diagnosis ofB. abortusinfections.

IS711-based real-time PCR assay as a tool for detection of Brucella spp. in wild boars and comparison with bacterial isolation and serology

BACKGROUND

Control of brucellosis in livestock, wildlife and humans depends on the reliability of the methods used for detection and identification of bacteria. In the present study, we describe the evaluation of the recently established real-time PCR assay based on the Brucella-specific insertion sequence IS711 with blood samples from 199 wild boars (first group of animals) and tissue samples from 53 wild boars (second group of animals) collected in Switzerland. Results from IS711 real-time PCR were compared to those obtained by bacterial isolation, Rose Bengal Test (RBT), competitive ELISA (c-ELISA) and indirect ELISA (i-ELISA).

RESULTS

In the first group of animals, IS711 real-time PCR detected infection in 11.1% (16/144) of wild boars that were serologically negative. Serological tests showed different sensitivities [RBT 15.6%, c-ELISA 7.5% and i-ELISA 5.5%] and only 2% of blood samples were positive with all three tests, which makes interpretation of the serological results very difficult. Regarding the second group of animals, the IS711 real-time PCR detected infection in 26% of animals, while Brucella spp. could be isolated from tissues of only 9.4% of the animals.

CONCLUSION

The results presented here indicate that IS711 real-time PCR assay is a specific and sensitive tool for detection of Brucella spp. infections in wild boars. For this reason, we propose the employment of IS711 real-time PCR as a complementary tool in brucellosis screening programs and for confirmation of diagnosis in doubtful cases.

Evaluation of three polymerase chain reaction techniques for detection of Brucella DNA in peripheral human blood

Brucellosis is a widespread zoonosis. Currently the diagnosis of this zoonosis is based on microbiological and serological laboratory tests. Polymerase chain reaction (PCR) has been used to detect DNA from Brucella. Different target genes, primer pairs, PCR techniques, and extraction procedures have previously been published for Brucella detection. But only a few of these primers have been used in human samples, and only one study has been carried out to compare sensitivity between them. In the present study, 3 sets of primers and 3 different PCR protocols amplifying 3 different regions of the Brucella genome were compared for detection of Brucella DNA in a peripheral-blood PCR assay to conclude which is most suitable for the clinical diagnostic laboratory. These 3 pairs of primers amplify 3 different fragments included in (i) a gene encoding a 31 kDa Brucella abortus antigen (B4/B5), (ii) a sequence 16S rRNA of B. abortus (F4/R2), and (iii) a gene encoding an outer membrane protein (omp-2) (JPF/JPR). Some modifications on the reported techniques were applied during the present work to improve the outcome. The results showed that the B4/B5 primer pair had the highest sensitivity for detection of positive samples (98%), the JPF/JPR primer pair detected 88.4% of positive samples, whereas F4/R2 primer pair was the least sensitive, being able to detect only 53.1% of positive samples. The specificity of the 3 techniques was 100%. The B4/B5 primer pair was also able to detect the smallest number of bacteria (700 cfu/mL), whereas JPF/JPR was able to detect 7 x 105 cfu/mL and F4/R2 was able to detect 7 x 107 cfu/mL. It is thus concluded that using the B4/B5 primer PCR with the suggested modifications is a robust assay, which meets the sensitivity requirements to be used for testing of human blood samples for brucellosis in the diagnostic laboratory.

Multiple genus-specific markers in PCR assays improve the specificity and sensitivity of diagnosis of brucellosis in field animals

Brucella-specific nucleotide sequences encoding the BCSP 31 kDa protein, Omp2 and the 16S rRNA were employed in three independent diagnostic PCR assays. Results of the three PCR assays on six reference strains of Brucella were in complete agreement. The results of PCR assays based on bcsp and omp2 on 19 Indian field isolates (human, bovine and murine tissues) also agreed completely. However, when the 16S rRNA gene was employed as the diagnostic target in the PCR, only 14 out of these 19 isolates and 2 out of 7 bovine milk isolates were identified as the genus Brucella. The bovine blood samples were insensitive to 16S rRNA PCR. The antibody-detecting ELISA results of field samples (n=87) from a serologically positive herd in India were compared separately with omp2 and bcsp PCRs of blood (n=62). While the bcsp PCR was the most sensitive, the degree of association of ELISA with omp2 blood PCR (kappa=0.37 at P <0.05) was similar to that with the bcsp blood PCR (kappa =0.34 at P <0.05). An improvement in the correlation between ELISA and blood PCR was noticed (kappa =0.5 at P <0.05) when a consensus result of omp2 and bcsp blood PCR was considered for comparison with ELISA. The use of more than one marker-based PCR gave increased sensitivity and higher specificity and appears to be a more reliable molecular diagnostic approach for screening of field animals.

Brucella abortus detection by PCR assay in blood, milk and lymph tissue of serologically positive cows

Brucellosis is a highly infectious disease which is diagnosed using serological and microbiological methods. The objective of this study was to assess the viability of using conventional and real-time PCR assays as potential diagnostic tools for the detection of Brucella abortus in naturally infected cows. PCR assays that amplify various regions of the Brucella genome, IS711 genetic element, 31kDa outer membrane protein and 16S rRNA, were optimised using nine known Brucella strains. Real-time PCR was used to examine the detection efficiency of the IS711 assay which was estimated at 10 gene copies. Milk, blood and lymph tissue samples were collected from naturally infected animals. B. abortus was not detected in blood samples collected from naturally infected cows by conventional or real-time PCR, but was detected in a proportion of the culture-positive milk (44%) and lymph tissue (66% - retropharyngeal, 75% - supramammary) samples by the same methods. There was no difference between PCR and bacteriological detection methods. It is unlikely that conventional or real-time PCR will supersede current diagnostic methods for detection of B. abortus in clinical samples.