Application of the fluorescence polarization assay for detection of caprine antibodies to Brucella melitensis in areas of high prevalence and widespread vaccination

Research Progress on Brucellosis

Brucellosis is a debilitating febrile illness caused by an intracellular Brucella. The disease is distributed in humans and animals widely, especially in developing countries. Ten species are included in the genus Brucella nowadays; four species of them are pathogenic to humans, which make brucellosis a zoonosis with more than 500,000 new cases reported annually. For human brucellosis, the most pathogenic species is B. melitensis followed by B. suis, while B. abortus is the mildest type of brucellosis. The infection mechanism of Brucella is complicated and mostly relies on its virulence factors. The therapy of the disease contains vaccination and antibiotic. However, there are some defects in currently available vaccines such as the lower protective level and safety. Thus, safe and efficient vaccines for brucellosis are still awaited. The dual therapy of antibacterial is effective in the treatment of brucellosis if a rapid and exact detection method is found.

A systematic review of current immunological tests for the diagnosis of cattle brucellosis

Brucellosis is a worldwide extended zoonosis with a heavy economic and public health impact. Cattle, sheep and goats are infected by smooth Brucella abortus and Brucella melitensis, and represent a common source of the human disease. Brucellosis diagnosis in these animals is largely based on detection of a specific immunoresponse. We review here the immunological tests used for the diagnosis of cattle brucellosis. First, we discuss how the diagnostic sensitivity (DSe) and specificity (DSp), balance should be adjusted for brucellosis diagnosis, and the difficulties that brucellosis tests specifically present for the estimation of DSe/DSp in frequentistic (gold standard) and Bayesian analyses. Then, we present a systematic review (PubMed, GoogleScholar and CABdirect) of works (154 out of 991; years 1960-August 2017) identified (by title and Abstract content) as DSe and DSp studies of smooth lipopolysaccharide, O-polysaccharide-core, native hapten and protein diagnostic tests. We summarize data of gold standard studies (n = 23) complying with strict inclusion and exclusion criteria with regards to test methodology and definition of the animals studied (infected and S19 or RB51 vaccinated cattle, and Brucella-free cattle affected or not by false positive serological reactions). We also discuss some studies (smooth lipopolysaccharide tests, protein antibody and delayed type hypersensitivity [skin] tests) that do not meet the criteria and yet fill some of the gaps in information. We review Bayesian studies (n = 5) and report that in most cases priors and assumptions on conditional dependence/independence are not coherent with the variable serological picture of the disease in different epidemiological scenarios and the bases (antigen, isotype and immunoglobulin properties involved) of brucellosis tests, practical experience and the results of gold standard studies. We conclude that very useful lipopolysaccharide (buffered plate antigen and indirect ELISA) and native hapten polysaccharide and soluble protein tests exist, provided they are applied taking into account the means available and the epidemiological contexts of this disease: i) mass vaccination; ii) elimination based on vaccination combined with test-and-slaughter; and iii) surveillance and existence of false positive serological reactions. We also conclude that the insistence in recent literature on the lack of usefulness of all smooth lipopolysaccharide or native hapten polysaccharide tests in areas where S19 vaccination is implemented is a misinterpretation that overlooks scientific and practical evidence.

How do you get the Rose Bengal Test at the point-of-care to diagnose brucellosis in Africa? The importance of a systems approach

Brucellosis is a major neglected zoonotic disease, whose burden both in animals and humans is severely under-reported. Diagnosis in humans identifies cases in order to treat the disease at the individual level. In animals diagnosis is implemented at the population level in the context of appropriate control or eradication strategies. Molecular and bacteriological diagnosis are rarely undertaken in sub-Saharan Africa, at least outside research projects, due to cost, skills and laboratory infrastructure issues. The brucellosis toolbox contains a wide range of serological tests, but the perfect test for use in animals and humans respectively does not exist. Drug and diagnostic discovery for the neglected zoonoses are notoriously poor, and there is limited investment interest in developing new tools for brucellosis diagnosis. But are current tools being used to their full capacity? The rose Bengal test (RBT) stands out as an efficient, practical and very cheap test adapted for use in the resource-poor context. In this paper, we argue that a social science or system's approach to explore the practicality of improving diagnostic capacity at the point-of care in high-risk brucellosis areas of rural Africa may be a step towards solving the issue of under-diagnosis, but this must go hand-in-hand with implementation of control measures at source in the animal reservoir and capacity to treat human cases.

Cross-sectional study of brucellosis in Jordan: Prevalence, risk factors and spatial distribution in small ruminants and cattle

Brucellosis is considered endemic in many Middle Eastern countries including Jordan. To determine the frequency, risk factors and spatial distribution of ruminant brucellosis in Jordan, a nationwide cross-sectional study was conducted. Small ruminant flocks (n=333) and cattle herds (n=204) were randomly selected, and their disease status was ascertained by testing individual serum samples using the Rose Bengal Test and a competitive ELISA (sheep and goats) and milk samples using an indirect ELISA (cattle). Information on putative risk factors was collected using standardized questionnaires. A logistic model with a binomial outcome was built to identify risk factors for being seropositive. The estimated true seroprevalence values were 18.1% (95% CI: 11-25.3) (cattle-only herds), 22.2% (95% CI: 16.5-28.8) (sheep flocks), 45.4% (95% CI: 30.3-61.6) (goat herds), 70.4% (95% CI: 55.5-84.9) (mixed sheep-goat flocks), 34.3% (95% CI: 28.4, 40.4) (all small ruminant flocks) and 38.5% (95% CI: 24.3-51.8) (mixed herds of cattle and small ruminants). Only 1.5% of small ruminant flocks were vaccinated. The seroprevalence was higher in northern areas, where livestock density is also higher. The logistic model fitted the data well and had a very high predictive ability. In the small ruminant model, five variables were significantly associated with a higher odds of seropositivity: lending/borrowing rams (OR=8.9, 95% CI: 3.0-26.1), feeding aborted material to dogs (OR=8.0, 95% CI: 3.5-18.1) the presence of goats (OR=6.9, 95% CI: 3.1-15.4), introducing new animals to the flock (OR=5.8, 95% CI: 2.5-13.6), and a large flock size (OR=2.2, 95% CI: 1.0-4.6). Conversely, separating newly introduced animals (OR=0.16, 95% CI: 0.05-0.47), separating animals that had aborted (OR=0.19, 95% CI: 0.08-0.46) and using disinfectants to clean pens (OR=0.37, 95% CI: 0.16-0.83) were significantly associated with a lower odds of being seropositive. The main risk factor for cattle herds being seropositive was the introduction of new animals (OR=11.7, 95% CI: 2.8-49.4); while separation of newly introduced animals (OR=0.09, 95% CI: 0.03-0.29), herd disinfection (OR=0.04, 95% CI: 0.01-0.15) and having calving pens (OR=0.14, 95% CI: 0.05-0.43) significantly reduced the odds of infection. Brucellosis is endemic at high levels across Jordan, and the current vaccination programme, which is limited to small ruminants, has very low coverage. A revised brucellosis control programme is required in Jordan. Given the high baseline prevalence, it should be based on vaccination accompanied by measures to promote hygiene and husbandry practices that minimize the risk of introduction and maintenance of Brucella spp., and thereby the risk of human infection.

Ruminant brucellosis in the Kafr El Sheikh Governorate of the Nile Delta, Egypt: prevalence of a neglected zoonosis

Background

Brucellosis is a neglected tropical zoonosis allegedly reemerging in Middle Eastern countries. Infected ruminants are the primary source of human infection; consequently, estimates of the frequency of ruminant brucellosis are useful elements for building effective control strategies. Unfortunately, these estimates are lacking in most Middle East countries including Egypt. Our objectives are to estimate the frequency of ruminant brucellosis and to describe its spatial distribution in Kafr El Sheikh Governorate, Nile Delta, Egypt.

Methodology/Principal Findings

We conducted a cross-sectional study in which 791 sheep, 383 goats, 188 cattle milk tanks and 173 buffalo milk tanks were randomly selected in 40 villages and tested for the presence of antibodies against Brucella spp. The seroprevalence among different species was estimated and visualized using choropleth maps. A spatial scanning method was used to identify areas with significantly higher proportions of seropositive flocks and milk tanks. We estimated that 12.2% of sheep and 11.3% of goats in the study area were seropositive against Brucella spp. and that 12.2% and 12% of cattle and buffalo milk tanks had antibodies against Brucella spp. The southern part of the governorate had the highest seroprevalence with significant spatial clustering of seropositive flocks in the proximity of its capital and around the main animal markets.

Conclusions/ Significance

Our study revealed that brucellosis is endemic at high levels in all ruminant species in the study area and questions the efficacy of the control measures in place. The high intensity of infection transmission among ruminants combined with high livestock and human density and widespread marketing of unpasteurized milk and dairy products may explain why Egypt has one of the highest rates of human brucellosis worldwide. An effective integrated human-animal brucellosis control strategy is urgently needed. If resources are not sufficient for nationwide implementation, high-risk areas could be prioritized.

Brucellosis is a zoonosis of mammals caused by bacteria of the genus Brucella. It is responsible for a vast global burden imposed on human health through disability and on animal productivity. In humans brucellosis causes a range of flu-like symptoms and chronic debilitating illness. In livestock brucellosis causes economic losses as a result of abortion, infertility and decreased milk production. The main routes for human infection are consumption of contaminated dairy products and contact with infected ruminants. The control of brucellosis in humans depends on its control in ruminants, for which accurate estimates of the frequency of infection are very useful, especially in areas with no previous frequency estimates. We studied the seroprevalence of brucellosis and its geographic distribution among domestic ruminants in one governorate of the Nile Delta region, Egypt. In the study area, the seroprevalence of ruminant brucellosis is very high and has probably increased considerably since the early 1990s. The disease is widespread but more concentrated around major animal markets. These findings question the efficacy of the control strategy in place and highlight the high infection risk for the animal and human populations of the area and the urgent need for an improved control strategy.

Use of the Brucella melitensis native hapten to diagnose brucellosis in goats by a rapid, simple, and specific fluorescence polarization assay

The performance of the fluorescence polarization assay (FPA) using the recently described Brucella melitensis native hapten and the Brucella abortus O-polysaccharide tracer was evaluated and compared with those of The World Organization for Animal Health tests related to indirect and competitive enzyme-linked immunosorbent assays as classification variables for goat sera obtained from a high-prevalence area where vaccination was performed; test series were also evaluated to increase the final specificity of the tests. Our results showed that the respective relative sensitivity and specificity were 99.7% and 32.5% for the rose Bengal test with a 3% cell concentration (RBT3), 92.8% and 68.8% for the rose Bengal test with 8% cell concentration (RBT8), 98.4% and 84.9% for the Canadian complement fixation test (CFT), 83.7% and 65.5% for the Mexican CFT, 98.4% and 81.0% for the buffered plate agglutination test (BPAT), and 78.1% and 89.3% for the fluorescence polarization assay (FPA). The use of the FPA as the secondary test significantly increased the final specificities of test combinations; the screening tests BPAT, RBT3, and RBT8 plus FPA resulted in 90%, 91.2%, and 91.3% final specificities, respectively, whereas for the combinations RBT3 plus Mexican CFT, RBT8 plus Mexican CFT, and BPAT plus Canadian CFT, the specificities were 65.5%, 63.2%, and 91.7%, respectively. The results suggested that the FPA may be routinely applied as an adaptable screening test for diagnosis of goat brucellosis, since its cutoff can be adjusted to improve its sensitivity or specificity, it is a rapid and simple test, it can be the test of choice when specificity is relevant or when an alternative confirmatory test is not available, and it is not affected by vaccination, thus reducing the number of goats wrongly slaughtered due to misdiagnosis.

Improved performance of Brucella melitensis native hapten over Brucella abortus OPS tracer on goat antibody detection by the fluorescence polarization assay

The current method for goat brucellosis diagnosis is based on the World Organization for Animal Health (OIE) using the screening card test (CT), with antigen at 8% (CT8) or 3% (CT3) of cell concentrations, and the confirmatory complement fixation test (CFT). However, these tests do not differentiate antibodies induced by vaccination from those derived from field infections by Brucella species or other bacterial agents; in places like Mexico, where the prevalence of brucellosis and the vaccination rates are high, there is a considerable percentage of false positive reactions that causes significant unnecessary slaughter of animals. Furthermore, results of the fluorescence polarization assay (FPA) using the Brucella abortus O-polysaccharide (OPS) tracer in goats are poorer than those with cattle. The present study was undertaken to investigate a tracer prepared from the native hapten (NH) of the Rev. 1 strain of Brucella melitensis to improve FPA performance on goat brucellosis diagnosis. Evaluation of 48 positive samples and 96 negative samples showed that the NH tracer was more accurate (p<0.01) than the OPS tracer (97.2% vs. 93.8% accuracy, respectively). On the diagnostic performance evaluation, the NH tracer performed better (87.5% accuracy, 79.5% sensitivity, 84.3% specificity, and 163.8 performance index) than the OPS tracer (83.5%, 75.9%, 81.0%, and 156.9, respectively) using 1009 positive and 2039 negative Mexican field goat sera samples selected by test series approved by the OIE (card test 3% and CFT). We demonstrated a new application for the NH lipopolysaccharide on detecting antibodies against Brucella using the FPA, which may yield faster results (minutes vs. 24-72h) than the immunodiagnosis assays frequently used in bovine brucellosis. In addition, NH tracer produces similar or better performance results than the conventional OPS tracer, using the FPA in goat sera samples.