Detection of Brucella species DNA in the stomach content of aborted sheep fetuses by PCR

Prevalence of Brucella species in stray cattle, dogs and cats: A systematic review

Stray animals are unowned free roaming, homeless, abandoned, street or sheltered animals, particularly dogs, cats and cattle. They could act as carrier of several zoonotic pathogens such as rabies virus, Mycobacterium and Brucella species. However, comprehensive information on the prevalence of zoonotic pathogens in stray animals is very limited. We conducted a systematic review as per Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) 2020 guidelines to estimate the prevalence of brucellosis in stray dogs, cats and cattle. Eligibility criteria for the study were determined using the PECOS classification (population, exposure, comparison, outcome, study design) as a tool to guide the research and adjust the search strategy. Major bibliographic databases [Web of Science, Medline, Scopus, ScienceDirect, Google Scholar and PubMed] were searched using predefined keywords for published epidemiological studies on brucellosis in stray animals (dogs, cats and cattle). Systematic assessments of all the studies since 1990-2022 were conducted and those reporting the prevalence of brucellosis in stray dogs, cats and cattle using appropriate diagnostic tests (culture, molecular, serological) were included. Studies reporting prevalence of brucellosis (Brucella infection or exposure) in kennel dogs, dairy herds, livestock farms, humans or marine species were excluded. The apparent individual test- wise prevalence along with 95% confidence intervals (CI) was estimated using Epitools. Out of 2689 studies, 37 met the inclusion criteria and were included in the systematic review. Of 37 studies, 28 (75.7%) were conducted in stray dogs, 7 (18.9%) in cattle and 2 (5.4%) in cats. Furthermore, only 21.62% studies (8/37) used probabilistic random sampling approaches and 13.51% studies (5/37) explained and justified the study sample size using appropriate methods for estimation of disease prevalence in the study populations. Higher sero-prevalence in stray dogs has been reported in studies conducted in Jordan (38.0% (95% CI: 24.0-54.0) and Pakistan (38.0% (95% CI: 31.0-45.0) whereas no sero-positivity was recorded in the studies conducted in Brazil, North Colombia, Cyprus, South Korea and USA. All studies on brucellosis (n = 7) in stray cattle were from India; conducted in stray cattle reared in cow-shelters. Sero-prevalence in the range of 4.3%- 64.3% was reported in stray cattle. Differences in diagnostic tests and host species, as well as limited number and non-randomized studies and high statistical heterogeneity did not allow us to determine combined meta-analysed prevalence estimates. Stray animals are likely to pose a zoonotic and disease spillover risk to human and livestock populations.

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 <i>Brucella abortus</i> species specific polymerase chain reaction assay for the diagnosis of bovine brucellosis

Serology is primarily used in the diagnosis of bovine brucellosis. Bacterial culture and isolation is the gold standard in diagnosing brucellosis but, like serology, it does not offer complete (100%) diagnostic sensitivity and specificity. Polymerase chain reaction (PCR) has been suggested to offer better specificity and sensitivity. In this study, we evaluated the performance of Brucella abortus species specific (BaSS) PCR directly from different samples in the diagnosis of bovine brucellosis in naturally infected cattle in KwaZulu-Natal province of South Africa with known infectious status from culture. The BaSS PCR had a low diagnostic sensitivity (DSe) of 70%, but was able to identify vaccine strains using abomasal fluid from aborted foetuses and detect Brucella DNA from decomposing samples. The best sample for the BaSS PCR was abomasal fluid.

Evaluation of PCR methods for detection of Brucella strains from culture and tissues

The genus Brucella causes significant economic losses due to infertility, abortion, stillbirth or weak calves, and neonatal mortality in livestock. Brucellosis is still a zoonosis of public health importance worldwide. The study was aimed to optimize and evaluate PCR assays used for the diagnosis of Brucella infections. For this aim, several primers and PCR protocols were performed and compared with Brucella cultures and biological material inoculated with Brucella. In PCR assays, genus- or species-specific oligonucleotide primers derived from 16S rRNA sequences (F4/R2, Ba148/928, IS711, BruP6-P7) and OMPs (JPF/JPR, 31ter/sd) of Brucella were used. All primers except for BruP6-P7 detected the DNA from reference Brucella strains and field isolates. In spiked blood, milk, and semen samples, F4-R2 primer-oriented PCR assays detected minimal numbers of Brucella. In spiked serum and fetal stomach content, Ba148/928 primer-oriented PCR assays detected minimal numbers of Brucella. Field samples collected from sheep and cattle were examined by bacteriological methods and optimized PCR assays. Overall, sensitivity of PCR assays was found superior to conventional bacteriological isolation. Brucella DNA was detected in 35.1, 1.1, 24.8, 5.0, and 8.0% of aborted fetus, blood, milk, semen, and serum samples by PCR assays, respectively. In conclusion, PCR assay in optimized conditions was found to be valuable in sensitive and specific detection of Brucella infections of animals.

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 Immunomagnetic Separation–Polymerase Chain Reaction in Direct Detection ofBrucella abortusandBrucella melitensisfrom Cheese Samples

The current study was carried out to assess the use of immunomagnetic separation-polymerase chain reaction (IMS-PCR) in direct detection of Brucella abortus and B. melitensis from soft cheese and to examine a relatively small number of field samples for the presence of these species. Two methodologies, one with IMS and the other without IMS, were employed for recovery of the Brucella species from cheese samples. IMS in conjunction with the PCR assay was determined to detect as low as 3x10(2) bacteria/mL, while the limit of detection with the other extraction procedure was 3x10(3) bacteria/mL. In the analysis of 40 cheese samples collected from various markets, only B. abortus was detected by PCR using both DNA extraction procedures in two (5%) samples. No positive results were obtained by culture and B. melitensis was not found in any cheese samples examined. The results suggest that this technique is promising owing to its pace and high sensitivity and should aid in direct detection of Brucella species from complex food samples.

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

PCR assay has been shown to be a promising option for the diagnosis of brucellosis. However, few studies have been performed with field samples in order to evaluate the assay as a diagnostic tool. In this study, routine use of a species-specific PCR assay previously developed for the identification of Brucella cultures was assessed for the detection of Brucella DNA directly from the stomach contents of aborted sheep fetuses. The assay is based on the insertion sequence IS711 in the Brucella chromosome. In the study, during 3 successive lambing seasons (1998-1999, 1999-2000 and 2000-2001) 126 aborted fetus samples each from different flocks and locations were examined. Brucella strains were isolated from 39 (31%) of the samples and all of the strains were identified as Brucella melitensis by biochemical characteristics, agglutination with monospecific A and M sera and PCR. Thirty-seven of 39 B. melitensis isolates were biotyped as biotype 3, and 2 isolates as biotype 1. From 38 of 39 culture positive fetal stomach contents B. melitensis-specific DNA was detected by PCR. PCR was found negative in all of the culture negative samples. Compared with culture, sensitivity and specificity of PCR were determined as 97.4 and 100%, respectively. The results indicate that this PCR procedure has a potential for use in routine diagnosis of sheep brucellosis.

Evaluation of a PCR test for the diagnosis of Brucella ovis infection in semen samples from rams

The sensitivity and specificity of a PCR assay with primers derived from the insertion sequence IS6501 was compared with that of bacteriological culture and serological tests for the diagnosis of Brucella ovis infection in rams. No amplifications were detected with DNAs from the strains phylogenetically related to Brucella and from the seven bacterial species considered as the main etiologic agents of epididymitis in rams. In addition, the specificity of the PCR was 100% when testing semen samples from Brucella-free rams. The comparison of the semen culture and PCR results from 192 semen samples tested, showed a proportion of agreement of 0.91 between both tests. The PCR-based test described has sensitivity similar to that of semen culture and could be used as a complementary test for the direct diagnosis of Brucella ovis in semen samples of rams.

PCR as a diagnostic tool for brucellosis

Numerous PCR-based assays have been developed for the identification of Brucella to improve diagnostic capabilities. Collectively, the repertoire of assays addresses several aspects of the diagnostic process. For some purposes, the simple identification of Brucella is adequate (e.g. diagnosis of human brucellosis or contamination of food products). In these cases, a genus-specific PCR assay is sufficient. Genus-specific assays tend to be simple, robust, and somewhat permissive of environmental influences. The main genetic targets utilized for these applications are the Brucella BCSP31 gene and the 16S-23S rRNA operon. Other instances require identification of the Brucella species involved. For example, most government-sponsored brucellosis eradication programs include regulations that stipulate a species-specific response. For epidemiological trace back, strain-specific identification is helpful. Typically, differential PCR-based assays tend to be more complex and consequently more difficult to perform. Several strategies have been explored to differentiate among Brucella species and strains, including locus specific multiplexing (e.g. AMOS-PCR based on IS711), PCR-RFLP (e.g. the omp2 locus), arbitrary-primed PCR, and ERIC-PCR to name a few. This paper reviews some of the major advancements in molecular diagnostics for Brucella including the development of procedures designed for the direct analysis of a variety of clinical samples. While the progress to date is impressive, there is still room for improvement.

A multiplex PCR for the detection of Brucella spp. and Leptospira spp. DNA from aborted bovine fetuses

Bovine brucellosis and leptospirosis are important causes of bovine abortion around the world. Both diseases can be serologically diagnosed, but many factors may cause false positive and negative results. Direct methods based on bacteriological isolation are usually employed, but they are difficult, time consuming and dangerous. Monoplex polymerase chain reaction (PCR) have been successfully described for the detection of Brucella spp. and Leptospira spp. Aiming at improvement in the direct diagnosis, a multiplex PCR (mPCR) for the detection of these agents in aborted bovine fetuses is described. The detection threshold of the mPCR was evaluated in experimentally contaminated bovine clinical samples using a conventional proteinase K/SDS or a boiling-based extraction protocols. The mPCR was applied to two groups of clinical samples: 63 episodes of bovine abortion and eight hamsters experimentally infected with Leptospira interrogans serovar pomona. Adopting microbiological isolation as reference, the test showed a sensitivity of 100% in both groups of clinical samples. Seven samples collected from bovine fetuses were Brucella spp. culture negative but showed positive results in mPCR. Regarding Leptospira spp. detection, similar results were observed in three bovine clinical samples. All hamsters infected with Leptospira were positive in both microbiological culture and mPCR. The boiling extraction protocol showed better results in some clinical samples, probably by the removal of PCR inhibitors by heat treatment. The high sensitivity, simplicity and the possibility of detection of both bacteria in a single tube reaction support the use of the mPCR described in the routine diagnosis.