Comparative assay of fluorescent antibody test results among twelve European National Reference Laboratories using various anti-rabies conjugates

Fatal Sarcoptes scabiei and Demodex sp. co-infestation in wolves (Canis lupus) at the Białowieża National Park, Poland - is it a consequence of climate change?

Introduction

In winter 2021/2022, a wolf population in the primeval Białowieża Forest in Poland was struck by an outbreak of severe mange caused by mixed infestations of Sarcoptes and Demodex mites. We present an epidemiological analysis of this mange which caused significant morbidity and mortality.

Material and Methods

Ten sites known for wolf activity were monitored by camera trapping. A diagnostic necropsy and testing of a young wolf was performed to determine the causes of death.

Results

Five young wolves with severe alopecia of the entire body and some other individuals with minor to medium mange lesions were identified by the camera surveillance. The necropsy of the carcass revealed emaciation, dehydration and anaemia with starvation as the cause of death, likely attributable to severe infestation with Sarcoptes scabiei and Demodex sp. mites. Rabies and infections with Borreliella sp., Anaplasma sp., Ehrlichia sp., Francisella tularensis, Babesia sp. and tick-borne encephalitis virus were excluded by specific tests.

Conclusions

The described analysis is the first documented co-infestation of this kind in wolves. The outbreak coincided with very mild winter conditions with a high average minimum temperature, which may have favoured mite survival outside the host, and light snowfall, which may have influenced the wolves' ability to hunt. Other potential drivers of the outbreak could be the large proportion of wetland terrain, increasing number of wolves in the area and anthropogenic pressure on their habitats including the migration crisis at the Polish-Belarusian border and the increased presence of military and border forces, even despite the relief from the anthropogenic pressure from tourism due to the COVID-19 lockdown.

Comparison of Pan-Lyssavirus RT-PCRs and Development of an Improved Protocol for Surveillance of Non-RABV Lyssaviruses

Rabies is a zoonotic and fatal encephalitis caused by members of the Lyssavirus genus. Among them, the most relevant species is Lyssavirus rabies, which is estimated to cause 60,000 human and most mammal rabies deaths annually worldwide. Nevertheless, all lyssaviruses can invariably cause rabies, and therefore their impact on animal and public health should not be neglected. For accurate and reliable surveillance, diagnosis should rely on broad-spectrum tests able to detect all known lyssaviruses, including the most divergent ones. In the present study, we evaluated four different pan-lyssavirus protocols widely used at an international level, including two real-time RT-PCR assays (namely LN34 and JW12/N165-146), a hemi-nested RT-PCR and a one-step RT-PCR. Additionally, an improved version of the LN34 assay ((n) LN34) was developed to increase primer–template complementarity with respect to all lyssavirus species. All protocols were evaluated in silico, and their performance was compared in vitro employing 18 lyssavirus RNAs (encompassing 15 species). The (n) LN34 assay showed enhanced sensitivity in detecting most lyssavirus species, with limits of detection ranging from 10 to 100 RNA copies/µL depending on the strain, while retaining high sensitivity against Lyssavirus rabies. The development of this protocol represents a step forward towards improved surveillance of the entire Lyssavirus genus.

Dual-Mode Immunosensor for Electrochemiluminescence Resonance Energy Transfer and Electrochemical Detection of Rabies Virus Glycoprotein Based on Ru(bpy)32+-Loaded Dendritic Mesoporous Silica Nanoparticles

Rabies is a serious zoonotic disease in almost all warm-blooded animals and causes fatal encephalitis. The detection of rabies virus (RABV) is critical and remains a significant challenge. Herein, an electrochemiluminescence resonance energy transfer (ECL-RET) and electrochemical (EC) dual-mode immunosensor was developed for highly sensitive detection of RABV glycoprotein. Dendritic mesoporous silica nanoparticles (DMSNs) were employed to load Ru(bpy)₃²⁺ and to obtain ECL probes (Ru@DMSNs). Ru@DMSNs were decorated on the electrode surface, followed by the modification of the RABV antibody (Ab₁). RABV was specifically recognized and captured by Ab₁, causing the decline of the ECL signal due to the obstruction of electron transfer. Additionally, manganese oxide nanoparticles (MnO_x) modified with Ab₂ can further quench the ECL signal of Ru@DMSNs via the RET between Ru@DMSNs and MnO_x. Meanwhile, MnO_x can catalyze the oxidation of o-phenylenediamine (o-PD), generating a significant differential pulse voltammetry (DPV) signal as a second signal to monitor RABV glycoprotein concentration. Consequently, an immunosensor was developed to achieve dual-signal detection of RABV and improve reliability. Under the optimal conditions, detection ranges of 0.10 pg·mL^-1 to 10 ng·mL^-1 for ECL (with an 88 fg·mL^-1 detection limit) and 1 pg·mL^-1 to 2 ng·mL^-1 for EC (with a 0.1 pg·mL^-1 detection limit) were obtained for RABV detection. The reliability of this immunoassay was validated by eight brain tissue samples. The results were found to be compatible with the results of the real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, indicating the potential applicability of this method for RABV diagnosis.

Detection of rabies virus antigen by the indirect rapid immunohistochemistry test in equines and comparisons with other diagnostic techniques

Laboratory diagnosis of rabies in equines is essential for distinguishing the disease from other sources of encephalitis. Diagnosis by conventional techniques such as a direct fluorescent antibody test (dFAT) or viral isolation in mice or cell culture can be difficult, and the application of molecular biological methods may be necessary. We performed an indirect rapid immunohistochemistry test (iRIT) for the detection of the rabies virus (RABV) antigen in the central nervous system (CNS) of equines and compared the results with those of other diagnostic techniques. We reviewed result records from the Rabies Diagnosis Laboratory at Instituto Pasteur, São Paulo, Brazil, of 174 samples of equine CNS from July 2014 to June 2016, which were investigated by dFAT, rabies tissue culture infection test (RTCIT), mouse inoculation test (MIT) and reverse transcription-polymerase chain reaction (RT-PCR) followed by genetic sequencing. These samples, 29 presented divergent results among techniques and were selected for the performed in the iRIT. The detected positivity rate was 4/29 (14%) by dFAT, 5/28 (18%) by RTCIT, 10/29 (35%) by MIT and 26/27 (96%) by RT-PCR. We analysed 29 samples through imprints of the cortex, hippocampus, cerebellum and brainstem in slides fixed in 10% buffered formaldehyde. Eighteen samples were identified as positive (62%) by iRIT assay, representing a greater number of positive cases than that detected by dFAT, MIT and RTCIT but not by RT-PCR. Among the brain regions, the brainstem presented the highest positivity (78%), followed by the hippocampus (69%), cerebellum (67%) and cortex (67%). Our results provide evidence that iRIT can contribute to a rapid diagnosis of rabies in equines and that complementary tests should be used to improve diagnostic accuracy in this species.

Evaluation of polyclonal anti-RNP IgG antibody for rabies diagnosis by indirect rapid immunohistochemistry test

Rabies still represents a major public health threat and estimated to cause 60,000 human deaths annually, particularly in developing countries. Thus, adequate surveillance based on rapid and reliable rabies diagnosis for both humans and animals is essential. The WHO and OIE recommended gold standard diagnostic technique for rabies is the direct immunofluorescence assay (dFAT). However, dFAT is expensive and requires a high level of expertise. As an alternative, the rapid immunohistochemistry technique is a promise to be a simple and cost effective diagnostic tool for rabies, and can be performed on field conditions prevalent in developing countries. However, no validated commercial conjugate antibody for rabies is available to meet the laboratory demand. Here, we evaluated the polyclonal anti-rabies virus ribonucleoprotein (RNP) IgG antibody for Rabies lyssavirus (RABV) detection by indirect rapid immunohistochemistry test (iRIT). We tested polyclonal anti-RNP IgG antibody against a batch of 100 brain specimens representing a wide phylogenetic origin in the State of São Paulo, Brazil. The purified IgG obtained 100% of diagnostic specificity and sensibility for RABV antigen detection in iRIT compared with the gold standard dFAT. In conclusion, our results demonstrate that the polyclonal anti-RNP IgG antibody may be used as a diagnostic reagent for rabies using iRIT, with the expectation of increase in availability and cost reduction of the epidemiological surveillance for developing countries.

Performance evaluation of the polyclonal anti-rabies virus ribonucleoprotein IgG antibodies produced in-house for use in direct fluorescent antibody test

Fluorescein isothiocyanate (FITC) labelled anti-rabies virus ribonucleoprotein (RNP) antibodies can be used as immunoreagents in direct fluorescent antibody testing (dFAT) for rabies diagnoses. While in-house products are occasionally used by laboratories, most conjugates are commercial reagents. Commercial anti-RNP antibodies are only available for research purposes in Brazil, however, which contributes to the increasing use of in-house produced antibodies. Considering that conjugate quality may influence the results obtained during rabies diagnosis, we sought to analyze the performance requirements of in-house produced polyclonal anti-RNP IgG-FITC for application in dFAT. To that end, their reproducibility, diagnostic sensitivity, and specificity were evaluated. The titer of polyclonal anti-RNP IgG-FITC was initially determined and evaluated by dFAT, using central nervous system (CNS) samples of different animal species (dogs, cats, bovines, equines, bats, and non-human primates). As our main result, the polyclonal anti-RNP IgG-FITC reached a titer of 1:30/1:40 in dFAT, with 100% of diagnostic sensitivity and specificity. In terms of reproducibility, the antibodies, regardless the production batch, presented the same performances. In conclusion, the in-house produced polyclonal anti-RNP IgG-FITC proved suitable for rabies virus antigen detection by dFAT.

Economic and feasibility comparison of the dRIT and DFA for decentralized rabies diagnosis in resource-limited settings: The use of Nigerian dog meat markets as a case study

BACKGROUND

Rabies lyssavirus (RABV) is the aetiologic agent of rabies, a disease that is severely underreported in Nigeria as well as elsewhere in Africa and Asia. Despite the role that rabies diagnosis plays towards elucidating the true burden of the disease, Nigeria-a country of 180 million inhabitants-has a limited number of diagnostic facilities. In this study, we sought to investigate two of the World Organization for Animal Health (OIE)-recommended diagnostic assays for rabies-viz; the direct fluorescent antibody test (DFA) and the direct rapid immunohistochemical test (dRIT) in terms of their relative suitability in resource-limited settings. Our primary considerations were (1) the financial feasibility for implementation and (2) the diagnostic efficacy. As a case study, we used suspect rabies samples from dog meat markets in Nigeria.

METHODS/PRINCIPAL FINDINGS

By developing a simple simulation framework, we suggested that the assay with the lowest cost to implement and routinely use was the dRIT assay. The costs associated with the dRIT were lower in all simulated scenarios, irrespective of the number of samples tested per year. In addition to the cost analysis, the diagnostic efficacies of the two assays were evaluated. To do this, a cohort of DFA-positive and -negative samples collected from dog meat markets in Nigeria were initially diagnosed using the DFA in Nigeria and subsequently sent to South Africa for diagnostic confirmation. In South Africa, all the specimens were re-tested with the DFA, the dRIT and a quantitative real-time polymerase chain reaction (qRT-PCR). In our investigation, discrepancies were observed between the three diagnostic assays; with the incongruent results being resolved by means of confirmatory testing using the heminested reverse transcription polymerase reaction and sequencing to confirm that they were not contamination.

CONCLUSIONS/SIGNIFICANCE

The data obtained from this study suggested that the dRIT was not only an effective diagnostic assay that could be used to routinely diagnose rabies, but that the assay was also the most cost-effective option among all of the OIE recommended methods. In addition, the results of our investigation confirmed that some of the dogs slaughtered in dog markets were rabies-positive and that the markets posed a potential public health threat. Lastly, our data showed that the DFA, although regarded as the gold standard test for rabies, has some limitations-particularly at low antigen levels. Based on the results reported here and the current challenges faced in Nigeria, we believe that the dRIT assay would be the most suitable laboratory test for decentralized or confirmatory rabies diagnosis in Nigeria, given its relative speed, accuracy, cost and ease of use.

An inter-laboratory trial as a tool to increase rabies diagnostic capabilities of Sub-Saharan African Veterinary laboratories

To achieve the goal of eliminating dog-mediated human rabies deaths by 2030, many African countries have agreed to list rabies as a priority zoonotic disease and to undertake both short and long-term control programs. Within this context, reliable local diagnosis is essential for the success of field surveillance systems. However, a harmonized, sustainable and supportive diagnostic offer has yet to be achieved in the continent. We herewith describe the organization and outcome of a proficiency test (PT) for the post-mortem diagnosis of rabies in animals, involving thirteen veterinary laboratories and one public health laboratory in Africa. Participants were invited to assess both the performance of the Direct Fluorescent Antibody (DFA) test and of a conventional RT-PCR. From the submitted results, while thirteen laboratories proved to be able to test the samples through DFA test, eleven performed the RT-PCR method; ten applied both techniques. Of note, the number of laboratories able to apply rabies RT-PCR had increased from four to ten after the exercise. Importantly, results showed a higher proficiency in applying the molecular test compared to the DFA test (concordance, sensitivity and specificity: 98.2%, 96.97% and 100% for RT-PCR; 87.69%, 89.23% and 86.15% for DFA test), indicating the feasibility of molecular methods to diagnose animal pathogens in Africa. Another positive outcome of this approach was that negative and positive controls were made available for further in-house validation of new techniques; in addition, a detailed questionnaire was provided to collect useful and relevant information on the diagnostic procedures and biosafety measures applied at laboratory level.

Zero Endemic Cases of Wildlife Rabies (Classical Rabies Virus, RABV) in the European Union by 2020: An Achievable Goal

The elimination of rabies transmitted by Classical Rabies Virus (RABV) in the European Union (EU) is now in sight. Scientific advances have made it possible to develop oral vaccination for wildlife by incorporating rabies vaccines in baits for foxes. At the start of the 1980s, aerial distribution of vaccine baits was tested and found to be a promising tool. The EU identified rabies elimination as a priority, and provided considerable financial and technical resources to the infected EU Member States, allowing regular and large-scale rabies eradication programs based on aerial vaccination. The EU also provides support to non-EU countries in its eastern and south eastern borders. The key elements of the rabies eradication programs are oral rabies vaccination (ORV), quality control of vaccines and control of their distribution, rabies surveillance and monitoring of the vaccination effectiveness. EU Member States and non-EU countries with EU funded eradication programs counted on the technical support of the rabies subgroup of the Task Force for monitoring disease eradication and of the EU Reference Laboratory (EURL) for rabies. In 2018, eight rabies cases induced by classical rabies virus RABV (six in wild animals and two in domestic animals) were detected in three EU Member States, representing a sharp decrease compared to the situation in 2010, where there were more than 1500 cases in nine EU Member States. The goal is to reach zero cases in wildlife and domestic animals in the EU by 2020, a target that now seems achievable.

Additional Progress in the Development and Application of a Direct, Rapid Immunohistochemical Test for Rabies Diagnosis

Laboratory-based surveillance is fundamental to effective rabies prevention and control. The direct fluorescent antibody (AB) test (FAT) is the gold standard for rabies diagnosis. Recently, additional tests besides the FAT have been developed, such as the direct rapid immunohistochemical test (DRIT). In this study, our objective was to further refine technical aspects of the DRIT using a combination of two monoclonal ABs (MABs), 502 and 802, conduct additional testing among rabies reference laboratories using a diversity of animal species and rabies virus (RV) variants and compare the potential utility of the DRIT for end users via proficiency testing (PT) against the FAT. Considering the ideal molar ratios of biotin to AB in formulation of the DRIT conjugate, 3.9 was found to be superior to 7.4, for detection of RV antigens in the brain of a naturally infected raccoon. Optimization of the DRIT conjugate may also be dependent upon the apparent choice of specific viral antigens for testing, as a gray fox RV variant reacted less strongly than a raccoon RV variant in determining the working dilution of the MAB cocktail. Using the same MABs and protocol, the DRIT was compared to the FAT using more than 800 samples of mammalian brains, representative of more than 25 taxa, including in excess of 250 animal rabies cases from Europe and North America. Sensitivity was determined at 98% (96⁻100%, 95% CI) and specificity was calculated at 95% (92⁻96%, 95% CI). In a comparison among end users, PT of laboratory personnel resulted in values of 77⁻100% sensitivity and 86-100% specificity. Based upon these and previously reported results, the DRIT appears to be a suitable alternative to the FAT for use in lyssavirus diagnosis.

Evaluation of Enzyme Linked Immuno-Sorbent Assay and Rapid Immuno-Diagnostic Test for Rabies Antigen Detection in Archived Dog Brain Tissues

Rabies urgently requires strengthening of new and existing diagnostic methodology in order to overcome the threat it poses. We evaluated the Enzyme Linked Immuno-Sorbent Assay (ELISA) and the Rapid Immunodiagnostic Test (RIDT) in detecting rabies viral antigens, comparing both tests with the Direct Fluorescent Antibody Test (DFAT) which is the gold standard in rabies diagnosis. Fifty dog brain tissues collected from the archives of the Central Diagnostic Laboratory, National Veterinary Research Institute, Vom, Nigeria, were utilized for this study. ELISA performed better than RIDT and recorded equivalent result with DFAT as compared with RIDT. There was a 96 % agreement between ELISA and DFAT for rabies antigen detection (concordance coefficient 78 % : 95 % C. I. 0.6366 to 0.8654) while there was a 54 % agreement between RIDT and DFAT (concordance coefficient 17 % : 95 % C. I. 0.05138—0.2752). Compared to DFAT, the sensitivities of ELISA and RIDT were 95.5 % and 47.6 %, respectively, and the specificities of ELISA and RIDT were 100 % and 87.5 % respectively. The simple Cohen’s kappa coefficient for ELISA related to the DFAT was found to be 0.834 (95 % C. I. 0.613—1.0). For RIDT, the Kappa value was 0.170 (95 % C. I. 0.003—0.337). The ELISA is as reliable a diagnostic method as the DFAT which is the gold standard for rabies diagnosis. It has an advantage of being able to analyse large number of samples at the same time, making it more suitable for epidemiological studies and for laboratories that cannot perform the DFAT. The unsatisfactory result of RIDT in this study reiterates the need to perform an adequate test validation before it can be used in the laboratory for rabies diagnosis.

Application and Comparative Evaluation of Fluorescent Antibody, Immunohistochemistry and Reverse Transcription Polymerase Chain Reaction Tests for the Detection of Rabies Virus Antigen or Nucleic Acid in Brain Samples of Animals Suspected of Rabies in India

Accurate and early diagnosis of animal rabies is critical for undertaking public health measures. Whereas the direct fluorescent antibody (DFA) technique is the recommended test, the more convenient, direct rapid immunochemistry test (dRIT), as well as the more sensitive, reverse transcription polymerase chain reaction (RT-PCR), have recently been employed for the laboratory diagnosis of rabies. We compared the three methods on brain samples from domestic (dog, cat, cattle, buffalo, horse, pig and goat) and wild (leopard, wolf and jackal) animals from various parts of India. Of the 257 samples tested, 167 were positive by all the three tests; in addition, 35 of the 36 decomposed samples were positive by RT-PCR. This is the first study in which such large number of animal samples have been subjected to the three tests simultaneously. The results confirm 100% corroboration between DFA and dRIT, buttress the applicability of dRIT in the simple and rapid diagnosis of rabies in animals, and reaffirm the suitability of RT-PCR for samples unfit for testing either by DFA or dRIT.

Development and evaluation of an anti-rabies virus phosphoprotein-specific monoclonal antibody for detection of rabies neutralizing antibodies using RFFIT

BACKGROUND

Rabies is a major public health problem with a fatality rate close to 100%; however, complete prevention can be achieved through pre- or post-exposure prophylaxis. The rapid fluorescent focus inhibition test (RFFIT) is one of the recommended testing methods to determine the production of neutralizing antibodies after vaccination. Here, we report the development of a new monoclonal antibody (mAb) designed to react specifically with Rabies virus (RABV) phosphoprotein (P protein), and the evaluation of its applicability to the RFFIT and its effectiveness as a diagnostic reagent for human rabies.

METHODOLOGY/PRINCIPAL FINDINGS

The mAb KGH P 16B8 was produced to target the P protein of the Korean KGH RABV strain. An indirect immunofluorescence assay (IFA) was conducted to detect various strains of RABV in various cell lines. Alexa-conjugated KGH P 16B8 (16B8-Alexa) was developed for the RFFIT. The IFA test could detect RABV up to a 1:2,500 dilution, with a detection limit comparable to that of a commercial diagnostic reagent. The sensitivity, specificity, positive predictive value, and negative predictive value of the RFFIT using 16B8-Alexa in 414 clinical specimens were 98.67%, 99.47%, 99.55%, and 98.42%, respectively. The results of the RFFIT with 16B8-Alexa were strongly correlated with those obtained using an existing commercial diagnostic reagent (r = 0.995, p<0.001).

CONCLUSIONS/SIGNIFICANCE

The mAb developed in this study shows high sensitivity and specificity, confirming its clinical utility with the RFFIT to measure the rabies neutralizing antibody titer and establish a diagnosis in human. Thus, 16B8-Alexa is expected to serve as an alternative diagnostic reagent that is widely accessible, with potentially broad applications beyond those of the RFFIT in Korea. Further studies with 16B8-Alexa should provide insight into the immunological mechanism of the P protein of Korean RABV.

First detection of European bat lyssavirus type 2 (EBLV-2) in Norway

BACKGROUND

In Europe, bat rabies is primarily attributed to European bat lyssavirus type 1 (EBLV-1) and European bat lyssavirus type 2 (EBLV-2) which are both strongly host-specific. Approximately thirty cases of infection with EBLV-2 in Daubenton's bats (Myotis daubentonii) and pond bats (M. dasycneme) have been reported. Two human cases of rabies caused by EBLV-2 have also been confirmed during the last thirty years, while natural spill-over to other non-flying mammals has never been reported. Rabies has never been diagnosed in mainland Norway previously.

CASE PRESENTATION

In late September 2015, a subadult male Daubenton's bat was found in a poor condition 800 m above sea level in the southern part of Norway. The bat was brought to the national Bat Care Centre where it eventually displayed signs of neurological disease and died after two days. EBLV-2 was detected in brain tissues by polymerase chain reaction (PCR) followed by sequencing of a part of the nucleoprotein gene, and lyssavirus was isolated in neuroblastoma cells.

CONCLUSIONS

The detection of EBLV-2 in a bat in Norway broadens the knowledge on the occurrence of this zoonotic agent. Since Norway is considered free of rabies, adequate information to the general public regarding the possibility of human cases of bat-associated rabies should be given. No extensive surveillance of lyssavirus infections in bats has been conducted in the country, and a passive surveillance network to assess rabies prevalence and bat epidemiology is highly desired.

An inter- laboratory proficiency testing exercise for rabies diagnosis in Latin America and the Caribbean

The direct fluorescent antibody test (DFA), is performed in all rabies reference laboratories across Latin America and the Caribbean (LAC). Despite DFA being a critical capacity in the control of rabies, there is not a standardized protocol in the region. We describe the results of the first inter-laboratory proficiency exercise of national rabies laboratories in LAC countries as part of the regional efforts towards dog-maintained rabies elimination in the American region. Twenty three laboratories affiliated to the Ministries of Health and Ministries of Agriculture participated in this exercise. In addition, the laboratories completed an online questionnaire to assess laboratory practices. Answers to the online questionnaire indicated large variability in the laboratories throughput, equipment used, protocols availability, quality control standards and biosafety requirements. Our results will inform actions to improve and harmonize laboratory rabies capacities across LAC in support for the regional efforts towards elimination of dog-maintained rabies.

Vaccine-induced rabies case in a cow (Bos taurus): Molecular characterisation of vaccine strain in brain tissue

Rabies is a fatal neuropathogenic zoonosis caused by the rabies virus of the Lyssavirus genus, Rhabdoviridae family. The oral vaccination of foxes - the main reservoir of rabies in Europe - using a live attenuated rabies virus vaccine was successfully conducted in many Western European countries. In July 2015, a rabies vaccine strain was isolated from the brain tissues of a clinically suspect cow (Bos taurus) in Romania. The nucleotide analysis of both N and G gene sequences showed 100% identity between the rabid animal, the GenBank reference SAD B19 strain and five rabies vaccine batches used for the national oral vaccination campaign targeting foxes.