Evaluation of competitive ELISA for detection of antibodies to Brucella infection in domestic animals

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.

Seropositivity, Comparison Between the Efficiency of Serological Tests and Risk Factors of Brucella Infection in Small Ruminants with History of Abortion in the Afar Region of North-Eastern Ethiopia

Purpose

Brucellosis is one of the most important reproductive diseases that cause abortion and breeding failure in small ruminants in Ethiopia. Therefore, our objective was to detect the seropositivity and risk factors of Brucella infection in small ruminants with history of abortion using modified RBPT, cELISA, and CFT in the Amibara district of the Afar Region, Ethiopia.

Methods

Sera were collected from 226 animals (195 goats and 31ewes) and assessed for seropositivity of Brucella infection using modified RBPT, CFT, and competitive ELISA.

Results

The overall seroprevalence was 12.0% (27 out of 226), 7.5% (17 out of 226), and 26.5% (60 out of 226) by mRBPT, CFT, and cELISA, respectively. Out of 27 sera that were reactive by mRBPT, 17 (63.0%) were also reactive by (CFT). Out of the 17 sera that were reactive by CFT and mRBPT, 14 (82.4%) were reactive by cELISA. Out of the 29 sera that were non-reactive by both mRBPT and CFT, 10 (34.5%) were found reactive by cELISA. Out of the 226 sera that were tested by both mRBPT and cELISA, 20 (8.9%) were reactive by both tests, while 159 (70.4%) were non-reactive by both tests. The percentage of test agreement (79.2%) between mRBPT and cELISA was poor (k=0.353). High seropositivity for Brucella infection was significantly associated with the presence of retained placenta in the studied animals (adjusted OR=2.2, 95% CI, 1.1-4.4, P=0.030) as detected by cELISA.

Conclusion

The current study revealed that a cELISA-based seroepidemiological survey increases the likelihood of detecting individuals with brucellosis and provides reliable evidence for mRBPT. Furthermore, there was a significant association between seropositivity for Brucella infection and retained placenta. These findings emphasize the necessity for proactive measures to reduce the economic impact of brucellosis and mitigate the risk of zoonotic transmission.

Immunoassay-based evaluation of rOmp28 protein as a candidate for the identification of Brucella species

Introduction. Brucellosis is an important bacterial zoonosis, re-emerging as a serious public health concern in developing countries. Two major species, Brucella melitensis and Brucella abortus, cause recurrent facile infection in human. Therefore, rapid and accurate diagnosis for early disease control and prevention is needed in areas with low disease burden.Hypothesis. This study evaluated the sandwich enzyme-linked immunosorbent assay (ELISA) (S-ELISA) immunoassay for potential use of whole-cell (WC) and recombinant outer-membrane protein (rOmp28)-derived IgG polyclonals in sensitive detection of Brucella.Aim. Immunoassay-based WC detection of Brucella species in important sub-clinical matrices at lower limits of detection.Methodology. We purified recombinant rOmp28 with Ni-NTA gel affinity chromatography and produced IgG polyclonal antibodies (pAbs) using BALB/c mice and New Zealand white female rabbits against different antigens (Ags) of Brucella. Checkerboard sandwich ELISA and P/N ratio (optical density of 'P' positive test sample to 'N' negative control) were used for evaluation and optimization of the study. The pAbs were characterized using Western blot analysis and different matrices were spiked with WC Ag of Brucella.Results. Double-antibody S-ELISA was developed using WC Ag-derived rabbit IgG (capture antibody at 10 µg ml^-1) and rOmp28-derived mice IgG (detection antibody at 100 µg ml^-1) with a detection range of 10² to 10⁸ cells ml^-1 and a limit of detection at 10² cells ml^-1. A P/N ratio of 1.1 was obtained with WC pAbs as compared to 0.6 and 0.9 ratios with rOmp28-derived pAbs for detecting B. melitensis 16M and B. abortus S99, respectively. An increased P/N ratio of 4.4 was obtained with WC Ag-derived rabbit IgG as compared to 4.2>4.1>2.4 ratios obtained with rabbit IgGs derived against cell envelope (CE), rOmp28 and sonicated antigen (SA) of Brucella with high affinity for rOmp28 Ag analysed on immunoblots. The rOmp28-derived mice IgG revealed two Brucella species at P/N ratios of 11.8 and 6.3, respectively. Upon validation, S-ELISA detected Brucella WCs in human whole blood and sera samples with no cross-reactivity to other related bacteria.Conclusion. The developed S-ELISA is specific and sensitive in early detection of Brucella from different matrices of clinical and non-clinical disease presentation.

Outer surface protein E (OspE) mediates Borrelia burgdorferi sensu stricto strain-specific complement evasion in the eastern fence lizard, Sceloporus undulatus

In North America, Lyme disease is primarily caused by the spirochetal bacterium Borrelia burgdorferi sensu stricto (Bb), which is transmitted between multiple vertebrate hosts and ixodid ticks, and is a model commonly used to study host-pathogen interactions. While Bb is consistently observed in its mammalian and avian reservoirs, the bacterium is rarely isolated from North American reptiles. Two closely related lizard species, the eastern fence lizard (Sceloporus undulatus) and the western fence lizard (Sceloporus occidentalis), are examples of reptiles parasitized by Ixodes ticks. Vertebrates are known to generate complement as an innate defense mechanism, which can be activated before Bb disseminate to distal tissues. Complement from western fence lizards has proven lethal against one Bb strain, implying the role of complement in making those lizards unable to serve as hosts to Bb. However, Bb DNA is occasionally identified in distal tissues of field-collected eastern fence lizards, suggesting some Bb strains may overcome complement-mediated clearance in these lizards. These findings raise questions regarding the role of complement and its impact on Bb interactions with North American lizards. In this study, we found Bb seropositivity in a small population of wild-caught eastern fence lizards and observed Bb strain-specific survivability in lizard sera. We also found that a Bb outer surface protein, OspE, from Bb strains viable in sera, promotes lizard serum survivability and binds to a complement inhibitor, factor H, from eastern fence lizards. Our data thus identify bacterial and host determinants of eastern fence lizard complement evasion, providing insights into the role of complement influencing Bb interactions with North American lizards.

Latent class evaluation of the performance of serological tests for exposure to Brucella spp. in cattle, sheep, and goats in Tanzania

BACKGROUND

Brucellosis is a neglected zoonosis endemic in many countries, including regions of sub-Saharan Africa. Evaluated diagnostic tools for the detection of exposure to Brucella spp. are important for disease surveillance and guiding prevention and control activities.

METHODS AND FINDINGS

Bayesian latent class analysis was used to evaluate performance of the Rose Bengal plate test (RBT) and a competitive ELISA (cELISA) in detecting Brucella spp. exposure at the individual animal-level for cattle, sheep, and goats in Tanzania. Median posterior estimates of RBT sensitivity were: 0.779 (95% Bayesian credibility interval (BCI): 0.570-0.894), 0.893 (0.636-0.989), and 0.807 (0.575-0.966), and for cELISA were: 0.623 (0.443-0.790), 0.409 (0.241-0.644), and 0.561 (0.376-0.713), for cattle, sheep, and goats, respectively. Sensitivity BCIs were wide, with the widest for cELISA in sheep. RBT and cELISA median posterior estimates of specificity were high across species models: RBT ranged between 0.989 (0.980-0.998) and 0.995 (0.985-0.999), and cELISA between 0.984 (0.974-0.995) and 0.996 (0.988-1). Each species model generated seroprevalence estimates for two livestock subpopulations, pastoralist and non-pastoralist. Pastoralist seroprevalence estimates were: 0.063 (0.045-0.090), 0.033 (0.018-0.049), and 0.051 (0.034-0.076), for cattle, sheep, and goats, respectively. Non-pastoralist seroprevalence estimates were below 0.01 for all species models. Series and parallel diagnostic approaches were evaluated. Parallel outperformed a series approach. Median posterior estimates for parallel testing were ≥0.920 (0.760-0.986) for sensitivity and ≥0.973 (0.955-0.992) for specificity, for all species models.

CONCLUSIONS

Our findings indicate that Brucella spp. surveillance in Tanzania using RBT and cELISA in parallel at the animal-level would give high test performance. There is a need to evaluate strategies for implementing parallel testing at the herd- and flock-level. Our findings can assist in generating robust Brucella spp. exposure estimates for livestock in Tanzania and wider sub-Saharan Africa. The adoption of locally evaluated robust diagnostic tests in setting-specific surveillance is an important step towards brucellosis prevention and control.

Performance characteristics and costs of serological tests for brucellosis in a pastoralist community of northern Tanzania

The control of brucellosis across sub-Saharan Africa is hampered by the lack of standardized testing and the use of tests with poor performance. This study evaluated the performance and costs of serological assays for human brucellosis in a pastoralist community in northern Tanzania. Serum collected from 218 febrile hospital patients was used to evaluate the performance of seven index tests, selected based on international recommendation or current use. We evaluated the Rose Bengal test (RBT) using two protocols, four commercial agglutination tests and a competitive enzyme-linked immunosorbent assay (cELISA). The sensitivity, specificity, positive predictive value, negative predictive value, Youden's index, diagnostic accuracy, and per-sample cost of each index test were estimated. The diagnostic accuracy estimates ranged from 95.9 to 97.7% for the RBT, 55.0 to 72.0% for the commercial plate tests, and 89.4% for the cELISA. The per-sample cost range was $0.69-$0.79 for the RBT, $1.03-$1.14 for the commercial plate tests, and $2.51 for the cELISA. The widely used commercial plate tests performed poorly and cost more than the RBT. These findings provide evidence for the public health value of discontinuing the use of commercial agglutination tests for human brucellosis in Tanzania.

Brucellosis in ruminants and pastoralists in Borena, Southern Ethiopia

Brucellosis is a bacterial zoonotic disease that has important veterinary and public health consequences as well as economic impact in sub Saharan Africa including Ethiopia. A cross-sectional study was conducted in four selected districts of Borena Pastoral setting in Southern Ethiopia from October 2017 to February 2018 to estimate the prevalence of brucellosis and assess associated risk factors in cattle, sheep, goats and occupationally associated humans. A total of 750 cattle, 882 sheep and goats and 341 human subjects were screened for evidence of brucellosis using the Rose Bengal Test (RBT) with positive results confirmed by Competitive-ELISA(c-ELISA). Structured questionnaires were used for collection of metadata from individual animals, herders and animal attendants to test the association between explanatory and outcome variables. The overall animal level prevalence was 2.4% (95% confidence interval, CI: 1.4-3.7) in cattle, 3.2% (95% CI: 2.1-4.6) in sheep and goats, and 2.6% (95% CI: 1.2-5) in humans occupationally linked to livestock production systems. Herd size, parity, and history of abortion were risk factors associated with Brucella seropositivity (P<0.05) in cattle whereas in sheep and goats the results showed that district, age group, flock size, and history of abortion were significantly associated risk factors with Brucella seropositivity (P<0.05). Assisting calving and presence of seropositive animals in a household (P<0.05) were significantly associated with Brucella seropositivity in humans. Evidence of brucellosis in various animal species and the associated human population illustrates the need for a coordinated One Health approach to controlling brucellosis so as to improve public health and livestock productivity.

Characterization of the main immunogenic proteins in Brucella infection for their application in diagnosis of brucellosis

Brucellosis is an important zoonotic bacterial disease widespread in the world. The key step of control this disease is accurate diagnosis and elimination of diseased animals. The classic diagnostic methods, such as tube agglutination test, are inaccurate and nonspecific, because of cross-reaction with Yersinia enterocolitica serotype O:9. Previously, several proteins were reported as Brucella main immunogens. In this study, we used animal infection model to evaluate antibody production against OMP16, BP26, BLS, BCSP31, VirB12, SodC and GroEL proteins and investigated their application in diagnosis of brucellosis. The results showed that the BP26 and BLS are two best immunogenic proteins. In further study, we detected 44 clinical bovine sera using western blot, showing that the BP26 and BLS reacted with 30 Brucella-positive sera, but false-positive results were also shown in 14 Brucella-free sera. In an indirect ELISA assay, compared to lipopolysaccharide-based ELISA, the conformance of the BP26-based ELISA was 92.68 % in Brucella-positive sera, but only 52.94 % in Brucella-free sera. The BLS-based ELISA can hardly differentiate positive sera from negative sera. Besides, truncated fragments of the BP26 protein cannot exclude false-positive results in detection of Brucella-free sera. Altogether, although Brucella main immunogenic proteins have good reaction with Brucella-positive sera, false-positive reaction with Brucella-free sera may lead to misdiagnosis of brucellosis, suggesting that it should be more careful to use these immunogenic proteins as antigen targets to diagnosis of brucellosis.

Diagnosis of canine brucellosis: comparison of various serologic tests and PCR

Canine brucellosis is an infectious and contagious disease associated with reproductive losses in breeding kennels. As a zoonotic disease, it poses a risk to human health, especially for veterinarians and breeders who handle materials potentially contaminated with Brucella canis. However, canine brucellosis is a neglected and underestimated disease given the difficulties in establishing a definitive diagnosis. We evaluated the frequency of detection of B. canis in 5 breeding kennels by using various serologic methods and PCR. Circulation of B. canis in these kennels was confirmed by bacterial isolation. The frequency of positive serologic results varied from 6.3% by AGID to 16.5% by dot-ELISA. There was no positive serology for smooth Brucella. PCR testing was positive in 13.9% of samples. The only detection tests with reasonable agreement were PCR and 2ME-MAT. The diagnosis of canine brucellosis remains challenging. The use of a single laboratory method, or even the use of different laboratory methods, may not be sufficient to reach a definitive diagnosis.

A cross-sectional seroepidemiological study of camel (Camelus dromedarius) brucellosis and associated risk factors in the Sultanate of Oman

Brucellosis is a globally distributed and economically devastating zoonotic disease of multiple species, including camels. Human and livestock brucellosis is prevalent in Oman, especially in southern Dhofar governorates of Oman, where camels share habitat and have close contact with other susceptible species. We conducted a randomized cross-sectional sero-epidemiological study to investigate the seroprevalence of brucellosis in camels of Oman. The sera from 2,250 camels from 552 geographically marked farms were screened through Rose Bengal plate agglutination test and later confirmed by the competitive ELISA (COMPLIZA, VLA, UK). In total, nine [0.4%, confidence interval (CI) 0.4, 0.8] camels from eight (1.5%, CI 0.6, 2.8) herds were tested positive for brucellosis. The highest prevalence was recorded in Dhofar (3.7%, CI 1.4, 7.9) and the lowest in Sharqiyah (1.3%, CI 0.0, 7.2) governorate (p = 0.052). All seropositive camels were of local breed and females. Seroprevalence was higher (0.5%, CI 0.2, 1.0) in adults (>4 yr of age) as compared with young (≤4 yr of age) camels (0.2%, CI 0.0, 0.8). The results of binary logistic regression indicated that camel herds located in south (Dhofar) [odds ratio (OR) 6.39, CI 1.01, 40.67], practice of open replacement system (OR 14.49, CI 1.83, 114.51) and with history of abortions (OR 8.01, CI 1.34, 47.77) were more likely to test positive for brucellosis. We conclude that brucellosis is endemic at a low level in camels of Oman and a control strategy based upon test-and-slaughter/inclusion of camels in the current vaccination program after carefully planned vaccine evaluation studies could be considered to control it.

High sensitive and broad-range detection of cortisol in human saliva using a trap lateral flow immunoassay (trapLFI) sensor

Cortisol, a steroid hormone, is a main biomarker of psychological stress. Early diagnosis and proper treatment of such stress is crucial to prevent the excessive secretion of cortisol. However, cortisol has a low molecular weight and cannot provide sufficient recognition sites for sandwich immunoreaction; it has previously been measured using a competitive immunoassay instead of a general sandwich immunoassay. The disadvantage of this approach is that quantitative measurements are limited because of the narrow measurable range that is key for biosensors. To overcome this limitation, we propose a new detection platform that enables small molecules such as cortisol to be quantified with high detection sensitivity. A trap lateral flow immunoassay (trapLFI) sensor has deletion and detection zones instead of the test and control zones in general lateral flow immunoassay (LFI) sensors. The conjugates used to minimize possible detection targets at low concentration are gold nanoparticles that include an antibody against cortisol and an enzyme for signal generation. Target-bound conjugates are captured in the detection zone, whereas conjugates not binding with targets are trapped in the deletion zone. Using this platform, enzyme-catalyzed color signals increase in the detection zone and decrease in the deletion zone with the concentration of cortisol. The ratio of signal from deletion zone and detection zone supplied a wide analytical range (0.01-100 ng mL-1) with high detection sensitivity (9.9 pg mL-1). Analysis of 15 human saliva samples showed a good correlation with conventional ELISA results (R2 = 0.9432).

Survey of Brucella spp. and Leptospira spp. antibodies in cetaceans and manatees of the Amazon basin and Atlantic Ocean, Brazil

Aquatic mammals can act as sentinels of emerging and resurging pathogens in the environment. Brucella spp. and Leptospira spp. are 2 zoonotic pathogens relevant to aquatic mammals, and their detection can be used to assess pathogen exposure. In this study, serum from 84 individuals-63 cetaceans (families Iniidae, n = 37; Delphinidae, n = 22; and Kogiidae, n = 4) and 21 West Indian manatees Trichechus manatus-was tested by the Rose Bengal Test (RBT) and a commercial competitive enzyme-linked immunosorbent assay (c-ELISA) for detecting Brucella spp. antibodies, and the microscopic agglutination test (MAT) for screening Leptospira spp. exposure. Overall, 4.8% (3/63) of cetaceans were positive by RBT and 15.9% (10/63) by c-ELISA for Brucella spp. Serum from 8 c-ELISA positive cetaceans (with available serum) was further tested via serum agglutination test (SAT) and 1 individual was positive. c-ELISA was more sensitive than RBT. Exposure to Brucella spp. was found in 5 cetacean species: Clymene dolphin Stenella clymene, short-finned pilot whale Globicephala macrorhynchus, pygmy killer whale Feresa attenuata, melon-headed whale Peponocephala electra and Atlantic bottlenose dolphin Tursiops truncatus in the Atlantic Ocean, Brazil, expanding the range of known Brucella seropositive aquatic hosts. No evidence of Brucella spp. exposure was found in Iniidae and Kogiidae odontocetes and manatees. Antibodies against Leptospira spp. were not detected in cetaceans and sirenians by MAT. These results contribute to the evaluation of different Brucella spp. serological methods in cetaceans and manatees and highlight the epidemiology of zoonotic pathogens in aquatic mammals of the southwestern Atlantic Ocean and the Amazon basin.

A competitive lateral flow assay for the detection of tenofovir

Proper management of an HIV infection requires that a patient be at least 80-95% adherent to a prescribed drug regimen to avoid poor health outcomes and the development of drug-resistant HIV strains. Clinicians generally monitor adherence habits indirectly through patient self-reporting, pill counting, and electronic drug monitoring. While direct measurement of patient samples like urine for monitoring drug levels is possible, it requires specialized equipment and training that is not readily available in resource-limited settings where the need is greatest. In this work we report the development of an antibody that binds to tenofovir (TFV), a key small molecule drug for both the treatment and prevention of HIV, and a competitive lateral flow assay that uses that antibody to monitor urine samples for the presence of the drug. TFV was conjugated to an immunogenic protein and injected into rabbits to raise polyclonal antibodies sensitive to the drug. The antibodies were verified for TFV-sensitivity by immunoprecipitation and HPLC. A gold nanoparticle-based competitive assay was developed to detect the presence of TFV in urine samples with a sensitivity of 1 μg mL-1. This TFV assay could be deployed as a point-of-care device for adherence monitoring in resource-limited settings as a low-cost, accurate, and speedy alternative to current methods to better inform changes in treatment.

Exposure of harbour seals Phoca vitulina to Brucella in declining populations across Scotland

Since 2000 there has been a major decline in the abundance of Scottish harbour seals Phoca vitulina. The causes of the decline remain uncertain. The aim of this study was to establish the extent to which the seals in the regions of greatest decline have been exposed to Brucella, a bacterial pathogen that causes reproductive failure in terrestrial mammalian hosts. Tissues from dead seals collected between 1992 and 2013 were cultured for Brucella (n = 150). Serum samples collected from live capture-released seals (n = 343) between 1997 and 2012 were tested for Brucella antibodies using the Rose Bengal plate agglutination test (RBT) and a competitive enzyme-linked immunosorbent assay (cELISA). In total, 16% of seals cultured had Brucella isolated from one or more tissues, but there were no pathological signs of infection. The cELISA results were more sensitive than the RBT results, showing that overall 25.4% of seals were seropositive, with the highest seroprevalence in juveniles. As there was no evidence of either a higher seroprevalence or higher circulating antibody levels in seropositive animals in the areas with the greatest declines, it was concluded that Brucella infection is likely not a major contributing factor to recent declines. However, the consistently high proportion of seals exposed to Brucella indicates possible endemicity in these populations, likely due to B. pinnipedialis, which has demonstrated a preference for pinniped hosts. Importantly, given the close proximity between seals, humans and livestock in many areas, there is the potential for cross-species infections.

An evaluation of serological tests in the diagnosis of bovine brucellosis in naturally infected cattle in KwaZulu-Natal province in South Africa

The diagnostic sensitivity (DSe) of the Rose Bengal test (RBT), the complement fixation test (CFT), the serum agglutination test (SAT), the competitive enzyme-linked immunosorbent assay (cELISA) and the indirect ELISA (iELISA) were determined in naturally infected cattle in KwaZulu-Natal province of South Africa with known infectious status from culture (gold standard). Natural brucellosis infection status of animals was determined by culturing and identification of Brucella abortus biovar 1 from abomasal fluid, milk, hygroma fluid, lymph nodes or uterine discharges samples. The diagnostic specificity (DSp) of the tests mentioned above was determined using samples from known negative herds. There was no statistically significant difference between the tests in their ability to diagnose brucellosis. The RBT and iELISA had the highest DSe of 95.8%, whereas RBT and CFT had the highest DSp of 100%. In South African laboratories, the RBT and CFT serological tests are used, because of the cost efficacy of CFT when compared to the less labour intensive but more expensive iELISA.

Integrating serological and genetic data to quantify cross-species transmission: brucellosis as a case study

Epidemiological data are often fragmented, partial, and/or ambiguous and unable to yield the desired level of understanding of infectious disease dynamics to adequately inform control measures. Here, we show how the information contained in widely available serology data can be enhanced by integration with less common type-specific data, to improve the understanding of the transmission dynamics of complex multi-species pathogens and host communities. Using brucellosis in northern Tanzania as a case study, we developed a latent process model based on serology data obtained from the field, to reconstruct Brucella transmission dynamics. We were able to identify sheep and goats as a more likely source of human and animal infection than cattle; however, the highly cross-reactive nature of Brucella spp. meant that it was not possible to determine which Brucella species (B. abortus or B. melitensis) is responsible for human infection. We extended our model to integrate simulated serology and typing data, and show that although serology alone can identify the host source of human infection under certain restrictive conditions, the integration of even small amounts (5%) of typing data can improve understanding of complex epidemiological dynamics. We show that data integration will often be essential when more than one pathogen is present and when the distinction between exposed and infectious individuals is not clear from serology data. With increasing epidemiological complexity, serology data become less informative. However, we show how this weakness can be mitigated by integrating such data with typing data, thereby enhancing the inference from these data and improving understanding of the underlying dynamics.

Sero-epidemiological survey and risk factors associated with brucellosis in dogs in south-western Nigeria

Introduction

In Nigeria, there is limited information on brucellosis particularly in dogs, despite its public health implications. We undertook a sero-epidemiological survey of brucellosis in dogs to determine the prevalence of the disease and associated risk factors for its occurrence in Nigeria.

Methods

A cross-sectional study was conducted to screen dogs in south-western Nigeria for antibodies to Brucella sp using the rapid slide agglutination test (RSA) and Rose Bengal test (RBT), with positive samples confirmed respectively by serum agglutination test (SAT) and competitive enzyme linked immunosorbent assay (cELISA). Data were analyzed with STATA-12.

Results

From the 739 dog sera tested, 81 (10.96%) were positive by RSA and 94 (12.72%) by RBT; these were corroborated with SAT (4/81; 4.94%) and cELISA (1/94; 1.06%), respectively. Logistic regression identified location (OR=0.04; 95% CI: 0.02-0.09), breed (OR=1.71; 95% CI: 1.34-2.19), age (OR=0.10; 95% CI: 0.04-0.30) and management system (OR=8.51; 95% CI: 1.07-68.05) as risk factors for Brucella infection by RSA. However, location (OR=10.83; 95% CI: 5.48-21.39) and history of infertility (OR=2.62; 95% CI: 1.41-4.84) were identified as risk factors using RBT.

Conclusion

Given the 10.96% to 12.72% seroprevalence of brucellosis recorded in this study, we advocate control of the disease in dogs, and public health education for those at risk of infection. Again, further studies are required to elucidate the role of dogs in the epidemiology of brucellosis in Nigeria considering the conducive human-animal interface and ecological factors responsible for the transmission of the disease.

Limitations of the BP26 protein-based indirect enzyme-linked immunosorbent assay for diagnosis of Brucellosis

Brucellosis is a serious zoonosis that occurs worldwide, and its diagnosis is typically based on the detection of antibodies against Brucella lipopolysaccharide (LPS). However, the specificity of the LPS-based test is compromised by cross-reactivity with Escherichia coli O157:H7 and Yersinia enterocolitica O:9. Also, diagnosis based on the LPS test cannot differentiate between vaccinated and infected individuals. The detection of the 26-kDa cytosoluble protein (BP26) antibody is considered an alternative that circumvents these drawbacks because it is exclusively expressed by infectious Brucella. A BP26-based enzyme-linked immunosorbent assay (ELISA) has been tried for the diagnosis of Brucella-infected animals and humans, but a few results showed that BP26 couldn't react with all Brucella-positive sera. In order to explore whether different animals could produce antibodies against BP26 after being infected with various Brucella species, we infected sheep, goats, and beef cattle with common virulent reference Brucella species. All sera were collected from the experimental animals and tested using both LPS-based ELISAs and BP26-based ELISAs. The results showed that all Brucella-infected individuals could produce high levels of antibodies against LPS, but only B. melitensis 16M- and B. melitensis M28-infected sheep and B. melitensis 16M- and B. abortus 2308-infected goats could produce antibodies against BP26. Therefore, we concluded that the BP26-based indirect ELISA (i-ELISA) showed both Brucella species and host specificity, which obviously limits its reliability as a substitute for the traditional LPS-based ELISA for the detection of brucellosis.

Epidemiology of bovine brucellosis by a combination of rose bengal test and indirect ELISA in the five districts of Uganda

A serological survey on bovine brucellosis was carried out 3 times between 2007 and 2009 in 3 districts (Kiboga, Mpigi and Kiruhura) in western Uganda and 2 (Kumi and Mbale) in the east employing the rose bengal test (RBT) for infected-herd screening and an indirect ELISA (iELISA) for testing the serostatus of individual animals. The animal prevalence was significantly higher in the 3 districts of the west (mean 21.5% in 2009) compared with the 2 districts (mean 3.4% in 2008) in the east (P<0.0001), though a significant difference was not observed between Kumi and Mpigi in 2008. In the west, it was the lowest in Mpigi, but a significant increase was observed between 2008 (5.3%) and 2009 (30.0%), as in Kiruhura, in which the prevalence increased from 8.1% in 2007 to 16.8% in 2009. A similar trend was also observed in Kumi, namely, the seropositivity significantly increased from 2.3% in 2007 to 6.2% in 2008 and became remarkably higher than in Mbale (0.64%). As a result, the farm prevalence was also higher in the west, especially in Kiboga in 2007 (77.8%) and 2008 (65.6%), and Mpigi in 2009 (70.8%). The linear predictor of the fitted generalized linear model proved that the logit of RBT positivity increased linearly over the increase in percent positivity values. This study demonstrated an example of an unaided self-help survey as one of the control measures in Uganda.

An evaluation of the capability of existing and novel serodiagnostic methods for porcine brucellosis to reduce false positive serological reactions

Porcine brucellosis is a zoonotic disease of truly global significance because even in countries without the disease the occurrence of false positive serological reactions (FPSRs) creates significant problems. Statutory diagnostic testing is required in many disease free countries or regions and is often a prerequisite for the movement of live animals. Currently this testing is dependent almost entirely on serological assays and these may result in a significant number of FPSRs. The aim of this study was to examine existing and novel serodiagnostic assays to evaluate their diagnostic sensitivity and resilience to FPSRs. The existing assays evaluated were the RBT, smooth lipopolysaccharide (sLPS) indirect (i) ELISA, sLPS competitive (c) ELISA, and the FPA. The novel assays evaluated were the sLPS TR-FRET assay, a rough (r) LPS iELISA, a recombinant protein BP26 iELISA and a cytoplasmic protein extract (Brucellergene™) iELISA. Four populations of sera were evaluated: those from Brucella suis infected swine (n=34), randomly selected samples from non-infected swine (n=161), sera from non-infected swine within herds exhibiting FPSRs (n=132) and sera from swine experimentally infected with Yersinia enterocolitica O:9 (n=4). The results show that all the assays dependent on the sLPS O-polysaccharide (OPS) for their sensitivity (the RBT, sLPS ELISAs, FPA and the sLPS TR-FRET) had significantly reduced diagnostic specificity when applied to the FPSR population, the RBT being most affected. Of the two rapid homogeneous assays, the TR-FRET was diagnostically superior to the FPA in this study. Neither of the protein based iELISAs demonstrated sufficient diagnostic sensitivity to resolve the FPSRs. The rLPS iELISA showed no cross reaction with the FPSRs and had diagnostic sensitivity similar to that of the OPS based assays.