Effect of incubation temperature on the diagnostic sensitivity of the glanders complement fixation test

Development and validation of a chemiluminescent western blot assay for glanders (Burkholderia mallei) serodetection

Glanders, caused by Burkholderia mallei, is a zoonotic disease of equids. Serologic testing for glanders is required by disease-free countries before international movement of equids. The World Organisation for Animal Health Terrestrial Manual recommends the complement fixation test (CFT) for clearance of individual animals for movement, but the CFT is prone to false-positive results. A colorimetric western blot (WB) assay was developed and validated to resolve false-positive CFT results; however, that assay is relatively time-consuming, and the interpretation is subjective. We present here a procedurally similar chemiluminescent WB assay that performs comparably to the validated colorimetric WB assay and offers noticeable benefits of decreased time-to-result and greater ease of interpretation.

Protein Microarray-Guided Development of a Highly Sensitive and Specific Dipstick Assay for Glanders Serodiagnostics

Burkholderia mallei, the causative agent of glanders, is a clonal descendant of Burkholderia pseudomallei, the causative agent of melioidosis, which has lost its environmental reservoir and has a restricted host range. Despite limitations in terms of sensitivity and specificity, complement fixation is still the official diagnostic test for glanders. Therefore, new tools are needed for diagnostics and to study the B. mallei epidemiology. We recently developed a highly sensitive serodiagnostic microarray test for human melioidosis based on the multiplex detection of B. pseudomallei proteins. In this study, we modified our array tests by using anti-horse IgG conjugate and tested sera from B. mallei-infected horses (n = 30), negative controls (n = 39), and horses infected with other pathogens (n = 14). Our array results show a sensitivity of 96.7% (confidence interval [CI] 85.5 to 99.6%) and a specificity of 100.0% (CI, 95.4 to 100.0%). The reactivity pattern of the positive sera on our array test allowed us to identify a set of 12 highly reactive proteins of interest for glanders diagnosis. The B. mallei variants of the three best protein candidates were selected for the development of a novel dipstick assay. Our point-of-care test detected glanders cases in less than 15 min with a sensitivity of 90.0% (CI, 75.7 to 97.1%) and a specificity of 100.0% (CI, 95.4 to 100.0%). The microarray and dipstick can easily be adopted for the diagnosis of both B. mallei and B. pseudomallei infections in different animals. Future studies will show whether multiplex serological testing has the potential to differentiate between these pathogens.

Assessment of the control measures of the category A diseases of Animal Health Law: Burkholderia mallei (Glanders)

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for glanders. In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radius of the protection and surveillance zone, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere. Considering the epidemiology and distribution of glanders, it was foreseen that three different situations could lead to a suspicion of the disease. Sampling procedures were defined for each of the three different suspicion types, which can also be applied in most of the other scenarios assessed. The monitoring period (6 months) was assessed as effective in all scenarios. The AHAW Panel of experts considered the minimum radius and duration of the existing protection and surveillance zone, set at the establishment level, effective. Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation, as well as for plausible ad hoc requests in relation to glanders.

Validation of a Commercial Glanders ELISA as an Alternative to the CFT in International Trade of Equidae

Glanders, caused by Burkholderia (B.) mallei is a notifiable zoonotic disease in equidae. For international trade and movement of equids, certificates of negative serological test results for antibodies against B. mallei are required. To date, the complement fixation test (CFT) is the mandatory test to issue these health certificates. The CFT is difficult to standardize and, due to its poor specificity, often leads to false-positive reactions resulting in trade restrictions with considerable financial consequences. In the present study, the new ID Screen Glanders Double Antigen Multispecies ELISA (GLANDA- ELISA) (IDvet, Grabels, France) was evaluated using 400 negative and 370 glanders positive field samples of equidae. The GLANDA-ELISA was significantly more specific (99.8%) than the CFT (97.0%). Considering the comparable sensitivities of CFT (96.5%) and ELISA (98.1%), this new GLANDA-ELISA test appears a suitable confirmatory test and a realistic alternative for serological testing of horses for trade or movement.

Seroprevalence of equine glanders in horses in the central and eastern parts of Mongolia

Glanders is a contagious and fatal equine disease caused by the gram-negative bacterium Burkholderia mallei. B. mallei is prevalent among horse populations in Asia, the Middle East, and South America. More than four million horses have been registered in Mongolia in 2020. However, the recent prevalence of glanders has not been well investigated. In this study, we aimed to investigate the seropositivity of B. mallei in horse populations in Mongolia using the complement fixation test (CFT) and Rose Bengal plate agglutination test (RBT). We randomly collected blood samples from horses in central and eastern Mongolia between 2018 and 2019. Of 337 horses, 26 (7.7%) and 28 (8.3%) were seropositive using RBT and CFT, respectively. Interestingly, seropositivity in horses resulting from crossbreeding of Mongolian native horses with thoroughbred horses was higher than that in Mongolian native horses. Our observations suggest that equine glanders are still endemic to Mongolia.

Serological surveillance and clinical investigation of glanders among indigenous equines in India from 2015 to 2018

Equine glanders is an infectious and notifiable bacterial disease caused by Burkholderia mallei. The disease has been reported in South American, African and Asian countries including India. Here, we present the outcome of glanders serosurveillance carried out between January 2015 and December 2018 to know the status of equine glanders among different states in India. A total of 102,071 equid sera from 299 districts of twenty-one states and one union territory were tested for glanders. Samples were screened with Hcp1 indirect ELISA followed by confirmatory diagnosis by CFT. During this four-year surveillance, a total of 932 glanders-positive cases were detected from 120 districts of 12 states. The study also revealed increasing trend of glanders from 2016 onwards with maximum occurrence in northern India. Overall seroprevalence ranged between 0.62% (95% CI, 0.52-0.72) and 1.145% (95% CI, 1.03-1.25). Seasonal shifting from winter to summer (March to June) coincided with highest number glanders incidence with corresponding seroprevalences of 1.2% (95% CI, 1.09-1.30). The present surveillance unveils territorial ingression of glanders to six states like Jammu & Kashmir, Gujarat, Rajasthan, Madhya Pradesh, Delhi and Tamil Nadu. In addition, re-emerging cases have been reported in Maharashtra, Haryana and Punjab after a gap of 10 years. Lack of awareness, little veterinary care and unrestricted movement of equids across state borders might have led to the introduction and establishment of the infection to these states. We believe that information from this study will provide a baseline data on glanders for devising surveillance and control strategies in India. Being a zoonotic disease, the persistence of glanders poses a potential threat to occupationally exposed humans especially equine handlers and veterinarians. Therefore, targeted surveillance of human population from each glanders outbreak is also recommended.

Evaluation of the comparative accuracy of the complement fixation test, Western blot and five enzyme-linked immunosorbent assays for serodiagnosis of glanders

Glanders is a zoonotic contagious disease of equids caused by Burkholderia (B.) mallei. Serodiagnosis of the disease is challenging because of false-positive and false-negative test results. The accuracy of the complement fixation test (CFT) which is prescribed for international trade by the World Organisation for Animal Health (OIE), five ELISAs and a Western blot (WB) were compared for serodiagnosis of glanders using sera from 3,000 glanders-free and 254 glanderous equids. Four ELISA tests are based on recombinant antigens (TssA, TssB, BimA and Hcp1), the IDVet ELISA is based on a semi-purified fraction of B. mallei and WB makes use of a purified LPS-containing B. mallei-antigen. Sensitivity and specificity of tests were estimated using cut-off values recommended by the test developers. The WB and all ELISAs, except BimA, were significantly more specific than the CFT. ELISAs based on TssA, TssB, and BimA antigens had significantly lower sensitivity compared to CFT while the sensitivities of the Hcp1-ELISA, the IDVet-ELISA and the WB did not differ significantly from that of the CFT. Given their comparable sensitivities and specificities, the CFT (98.0%, 96.4%), the WB (96.8%, 99.4%), the Hcp1-ELISA (95.3%, 99.6%) and the IDVet-ELISA (92.5%, 99.5%) should be further developed to meet OIE requirements.

Spatiotemporal Analysis of Glanders in Brazil

In Brazil, glanders remains a serious problem, with the obligatory sacrifice of disease-positive animals without compensation. Each year, glanders cases are reported in several regions of the country, causing severe economic losses and trade restrictions. The present study describes and discusses the occurrence of glanders foci in Brazil during a 12-year period from 2005 to 2016. The highest frequency of reported affected holdings during the study period was in the northeast region. Moreover, during this period, the disease incidence in Brazil showed an overall increasing tendency. The number of affected holdings significantly increased during the last four years of the period, and more cases were noted during the months of May and June. Spatiotemporally, there are four high-risk glanders clusters: (1) cluster A (relative risk [RR = 6.51, P < .0001) involved the northeast region from March 2008 to February 2014; (2) cluster B (RR = 17.37, P < .0001) involved a southeast region state from March 2013 to June 2015; (3) cluster C (RR = 6.92, P < .0001) involved the states in the midwest, southeast, and south regions of Brazil from March 2015 to May 2016; and (4) cluster D (RR = 19.07, P < .0001) involved a north region state from October 2015 to April 2016. Only two states of the north region (Acre and Amapá) did not experience glanders during the study period.

Seroprevalence and risk factors of glanders in working equines - Findings of a cross-sectional study in Punjab province of Pakistan

Glanders is an infectious and contagious bacterial disease of equines. A little is known about its seroprevalence and risk factors in working equines in countries where the disease is endemic. Also, there are no reports on prevalence of the disease in areas where there is a prior evidence of Burkholderia (B.) mallei detection in soil. A cross-sectional study was conducted in selected districts (n=09) of Punjab province of Pakistan during 2014-2015. A total of 1008 serum samples were screened for detection of antibodies to B. mallei with complement fixation test followed by western blot. The overall seroprevalence was found to be 3.17% (95% CI: 2.25-4.44). The seropositivity was significantly higher from the sampling sites where B. mallei was detected in soil [OR: 10.66 (95% CI: 4.42-31.66), p=0.00]. Other risk factors significantly associated with animal seropositivity were: age group [OR: 1.78 (95% CI: 4.58-15.56), p=0.00], location in urban area [OR: 2.99 (95% CI: 1.46-6.51), p=0.00],body condition [OR: 3.47 (95% CI: 1.64-7.99), p=0.00], presence of farcy lesion[OR: 7.71 (95% CI: 3.47-19.50), p=0.00], proximity to water bodies [OR: 7.71 (95% CI: 3.47-19.50), p=0.00]; domestic animal population [OR: 3.20 (95% CI: 1.24-10.87), p=0.03] and number of households in sampling area [OR: 4.18 (95%CI: 1.82-11.30), p=0.00]. The study provides an estimate of prevalence of glanders and a potential link between animal seropositivity and presence of B. mallei in soil. The risk factors identified in this study can be used in surveillance and disease awareness. The high prevalence of disease in draught horses and contact of infected animals with their care-takers in developing countries signify need to initiate progressive control of the disease using one health approach.

Glanders and the risk for its introduction through the international movement of horses

Glanders is the contagious zoonotic disease caused by infection with Burkholderia mallei. It affects primarily horses, donkeys and mules. The disease was eradicated from large areas of the Western world in the early 20th century, but, over the last 10-20 years, has emerged and re-emerged in areas in which it was previously unknown or had been eradicated. Although glanders was previously thought to manifest in only acute or chronic presentations, it now appears that B. mallei can produce latent infections similar to those caused by Burkholderia pseudomallei. These latent infections may or may not be detectable by current diagnostic tests. The diagnostic test currently recommended by the World Organisation for Animal Health (Office International des Epizooties [OIE]) for international trade in equids is the complement fixation test (CFT). This test has been shown to have varying sensitivities and specificities depending on the antigen and methodology used. False positives are problematic for the horse-owner and veterinary authority, whereas false negatives may allow the reintroduction of B. mallei into B. mallei-free areas. These gaps in knowledge of the epidemiology of glanders, and weaknesses in its diagnosis, coupled with the increased movement of equids, indicate that infection with B. mallei remains a major risk in the context of international movement of equids.

Interlaboratory ring trial to evaluate CFT proficiency of European laboratories for diagnosis of glanders in equids

To evaluate the routine complement fixation test (CFT) used to detect Burkholderia mallei antibodies in equine sera, an interlaboratory proficiency test was held with 24 European laboratories, including 22 National Reference Laboratories for glanders. The panels sent to participants were composed of sera with or without B mallei antibodies. This study confirmed the reliability of CFT and highlighted its intralaboratory reproducibility. However, the sensitivity of glanders serodiagnosis and laboratory proficiency may be improved by standardising critical reagents, including antigens, and by developing a standard B mallei serum.

Versatile microfluidic complement fixation test for disease biomarker detection

The complement fixation test (CFT) is a serological test that can be used to detect the presence of specific antibodies or antigens to diagnose infections, particularly diseases caused by microbes that are not easily detected by standard culture methods. We report here, for the first time, a poly(dimethylsiloxane) (PDMS)/glass slide hybrid microfluidic device that was used to manipulate the solution compartment and communication within the microchannel to establish sampler and indicator systems of CFT. Two types of on-chip CFT, solution-based and solid phase agar-based assays, were successfully demonstrated for biomarker carcinoembryonic antigen (CEA) and recombinant avian influenza A (rH7N9) virus protein detection. In addition, the feasibility of the on-chip CFT in assaying real biopsy was successfully demonstrated by specifically detecting rH7N9 and CEA in human serum. The results demonstrated that the miniaturized assay format significantly reduced the assay time and sample consumption. Exemption from protein immobilization, blocking, complicated washing steps and expensive enzyme/fluorescein conjugates highlights the merits of on-chip CFT over ELISA. Most attractively, the on-chip agar-based CFT results can be imaged and analysed by smartphone, strengthening its point-of-care application potential. We anticipate that the on-chip CFT reported herein will be a useful supplemental or back-up tool for on-chip immunoassays such as ELISA for disease diagnosis and food inspection.

Combining complement fixation and luminol chemiluminescence for ultrasensitive detection of avian influenza A rH7N9

A luminol chemiluminence system was applied in the complement fixation test for detection of rH7N9 in the range of 0.25 fg mL⁻¹–25 ng mL⁻¹.