Regarding to diagnosis for bovine brucellosis, more than one serological test should be conducted to confirm the infection by Brucella with a reliable result due to various factors including false positive serological reactions. In this study, we compared confirmatory serological tests to determine the appropriate way to detect and confirm the Brucella infection in South Korea. Several serological tests, including serum agglutination test (SAT), indirect (I)- and competitive (C)-ELISA, and fluorescence polarization assay (FPA), for detection of bovine brucellosis were performed with sera from 537 cattle. In addition, comparison of diagnostic efficacy was performed with bacterial isolation represented true positive. Of 537 serum samples, 426 (79.3% of prevalence), 433 (80.6%), 414 (77.1%), and 409 (76.2%) sera were positive for SAT, C-ELISA, I-ELISA, and FPA respectively. Based on the results of serology, the correlation among the serological tests revealed observed agreements of more than 92% with kappa (k) value of more than 0.77. The correlation between serological tests with bacterial isolation appeared observed agreements of between 79.9% and 84.7% with k value of between 0.42 and 0.59. Particularly, FPA recorded almost perfect agreements with C-ELISA and I-ELISA as well as the highest correlation with bacterial isolation. Accordingly, this investigation presented the comparison of correlation and diagnostic efficacy of serological tests for bovine brucellosis in South Korea. We suggest this finding will be a useful data to re-establish the potential serological diagnostic methods that can apply to maintain the low prevalence.

In Korea livestock farms breeding cattle have been suffering from re-emerging problems of Brucella (B.) abortus infection while steady decline of bovine brucellosis. Therefore, this study underscored the identification and association of etiological agent of brucellosis in cattle in South Korea. The incidence of brucellosis in cattle was analyzed by bacteriological and molecular methods in 187 brucellosis-suspicious farms of 11 regions between 2018 and 2020. Brucella isolates from various specimens were identified by Brucella-specific multiplex PCR. Epidemiological data were collected by local official veterinarians through history taking from farmers and animal data systems. In 230 of 560 cattle (40.9%) and 94 of 187 farms (50.3%), a total of 313 B. abortus were isolated from various specimens, the majority of isolates were from supramammary lymph node (41%). In epidemiological findings, the majority of positive cases were mainly caused by resurgence (43.7%) and unknown (37.2%). Of 94 positive cases isolated B. abortus, abortion in cattle infected by B. abortus occurred in 51 farms (54.3%) where led to resurgence in 30 farms and environmental survival of B. abortus in 9 farms. Consequently, these findings revealed the existence of etiological agent of bovine brucellosis in Korea, which still occurred at low levels in distinct regions where are allowed to call for persistent biosecurity. Thus, we highlight that brucellosis in Korea needs to take more effective control strategies with potential evidence. Moreover it is ultimately important to maintain a constant monitoring for eradication of brucellosis.

Fast, cheap and sufficient serodiagnostic tools needs to be developed for the early detectionof brucellosis. Currently the tools cannot differentiate an active infection from vaccinated, norcan it differentiate other bacterial infections with lipopolysaccharides, especially Yersiniainfections. In this study, we purified recombinant outer membrane protein 10 and 28(rOmp10,rOmp28), and a dipstick assay(indirect or sandwich) was constructed with single(rOmp10 orrOmp28) and combined rOmps(rOmp10 and rOmp28) from Brucella(B.) abortus 544 to evaluatebovine Brucella positive serum collected during the beginning of the Korean outbreak from2006 to 2015. In application with single rOmp, rOmp10(70%; indirect, 92.11%; sandwichdipstick) and rOmp28(72.5%; indirect, 86.84%; sandwich dipstick) had comparable results. Inaddition, results indicated that dipstick with combined rOmps(rOmps10 and rOmp28) weresuperior in detecting positive serum samples, at 85% indirect and 100% sandwich dipstick. Surprisingly, the results were the same in detecting negative results at 97.78% for both singleand combined indirect dipsticks. The dipstick tools with rOmp10 and rOmp28 would be usefulfor a rapid screen method for bovine brucellosis.

To date, most serodiagnostic methods for brucellosis screening are based on antibodies against lipopolysaccharides of Brucella spp. However, this approach has the drawback of yielding false-positive results due to cross-reactivity with lipopolysaccharides of other related pathogens, especially Yersinia enterocolitica O:9. In this study, Brucella abortus AspC was cloned and expressed by PCR amplification into a pCold TF expression system to obtain recombinant AspC (rAspC). The immunogenicity of rAspC was confirmed by western blotting of Brucella-positive bovine serum. rAspC-based ELISA was performed to determine whether rAspC could be used in the serodiagnosis of bovine brucellosis. rAspC reacted strongly with anti-Brucella antibodies in positive sera in the tube agglutination test (TAT), but did not show strong reaction with most negative samples. In particular, the average OD492 value at the highest TAT titer showed a 1.4-fold increase with respect to the cutoff value. The accuracy, specificity, and sensitivity of rAspC were 71.88%, 78.33%, and 68%, respectively. These findings suggest that rAspC might be valuable for the serological diagnosis of bovine brucellosis.

The specimens from 32 aborted fetus and 274 aborted cows were collected in 168 farms of Chonnam province from 2005 to 2008 and were tested the brucellosis. The results obtained are summarized as follows. In the 32 aborted fetus, bovine brucellosis was detected in 12 heads (37.5%), bovine viral diarrhea-mucosal disease was detected in 7 heads (19%), ainovirus infection was detected in 1 head (3.1%), and multi-infection of BVD and brucellosis was not detected, respectively. In the 306 cases of aborted fetus and cows, bovine brucellosis was detected in 44 heads (14%). Status of abortion were confirmed in 63 farms (38%) out of 168 farms from June to August. From the point of raising scale, studies found that 128 farms (76%) out of all raised under 20 heads. The incidence of abortion by brucellosis was mainly showed in 30 heads (68.1%) about 151~250 days of gestation. In the result of the 18 farms survey, the causes of infections were detected movement of infected cattle in 5 farms (28%), unknown cause in 12 farms (67%), and recurrence in 1 farm (5%). The results of this study suggest to take an advantage of the prevention and fundamental research for bovine brucellosis in Chonnam province.