Evaluation of a rabies ELISA as an alternative method to seroneutralisation tests in the context of international trade of domestic carnivores

Retrospective analysis of sero-prevalence and bait uptake estimations in foxes after oral rabies vaccination programmes at European level: Lessons learned and paths forward

Rabies caused by the Classical Rabies Virus (Lyssavirus rabies abbreviated RABV) in the European Union has been close to elimination mainly thanks to Oral Rabies Vaccination (ORV) campaigns targeting wildlife (primarily red foxes). ORV programmes co-financed by the European Commission include a monitoring-component to assess the effectiveness of the ORV campaigns at national level. This assessment is performed by a random collection of red foxes in the vaccinated areas with control of antibodies presence by serological analysis and control of bait uptake by detection of biomarkers (tetracycline incorporated into the baits) in the bones and teeth. ORV programmes aim to a vaccine coverage high enough to immunize (ideally) 70 % of the reservoir population to control the spread of the disease. European Union (EU) programmes that led to almost elimination of rabies on the territory have been traditionally found to have a bait uptake average of 70 % (EU countries; 2010-2020 period) while the seroconversion data showed an average level of 40 % (EU countries; 2010-2020 period). To better understand variations of these indicators, a study was been set up to evaluate the impact of several variables (linked to the vaccination programme itself and linked to environmental conditions) on the bait uptake and the seroconversion rate. Thus, pooling data from several countries provides more powerful statistics and the highest probability of detecting trends. Results of this study advocate the use of a single serological test across the EU since data variation due to the type of test used was higher than variations due to field factors, making the interpretation of monitoring results at EU level challenging. In addition, the results indicates a negative correlation between bait uptake and maximum temperatures reached during ORV campaigns questioning the potential impact of climatic change and associated increase of temperatures on the ORV programmes efficiency. Several hypotheses requesting additional investigation are drawn and discussed in this paper.

Evaluation of an iELISA for detection and quantification of rabies antibodies in domestic dog sera

Many rabies endemic-countries have recognized rabies as a public health problem that can be eliminated. As a result, some countries have started implementing small-scale vaccination programs with the aim of scaling them up. Post-vaccination serological monitoring is crucial to assess the efficacy of these programs. The recommended serological tests, the rapid fluorescent focus inhibition test, and the fluorescent antibody virus neutralization (FAVN) are accurate; however, the procedures require considerable expertise and must be carried out in high containment facilities, which are often not available in rabies endemic countries. Given these constraints, enzyme linked immunosorbent assays (ELISAs) have been considered as alternative methods to neutralization tests. This is the first study to evaluate, under field conditions, the performance of the commercial rabies indirect-ELISA (iELISA), the PlateliaTM Rabies II kit ad usum Veterinarium kit, using sera from domestic dogs. Serum samples were collected from two groups of community dogs in northern Tanzania: i) dogs with no history of vaccination against rabies (n = 100) and ii) dogs vaccinated with the Nobivac Canine Rabies® vaccine (n = 101) four weeks previously. When compared to the gold standard FAVN test, the iELISA was found to be 99% specific and 98% sensitive and there was a significant correlation between the two tests (p < 0.001, r = 0.92). Given these findings, we conclude that the PlateliaTM Rabies II kit ad usum Veterinarium can be considered a valuable tool for the rapid assessment of vaccination status of animals in vaccination programs.

Evaluation of In-House ELISA for Antirabies Antibodies Detection in Domestic Canine

Indonesia is known to be endemic for rabies in several areas, especially in Sumatra, Kalimantan, Sulawesi, and Flores Islands. Currently, vaccinating dogs has been shown to be the most cost-effective strategy for preventing rabies in humans. Postvaccination monitoring should be carried out to evaluate the success of vaccination by measuring antibody titers in serum of vaccinated dogs. Serological methods for monitoring rabies-specific antibody titers can be carried out using enzyme-linked immunosorbent assay (ELISA) methods as recommended by the World Organization for Animal Health (WOAH). Therefore, the development of the in-house ELISA (BukTi-Vet) that we have carried out in order to support postvaccination monitoring in dogs needs to be evaluated for its diagnostic performance compared to commercial ELISA kits. The diagnostic performance of each ELISA kit was evaluated using 111 known positive and 47 negative serums. Each known positive and negative serum will be tested using the three rabies ELISA kits used in this study. BukTi-Vet is an in-house ELISA for the detection of rabies-specific IgG antibodies that have been developed with sensitivity, specificity, and accuracy of 98.19%, 97.87%, and 98.1%, respectively. Based on the value of its positive and negative clinical utility index, BukTi-Vet is excellent for use in immunoassays directed for confirmatory (0.97) as well as screening (0.94) tests. BukTi-Vet shows a very good agreement with both Platelia II and RFFIT, so it is convincing to be further refined into a diagnostic kit. Tests of field sera from dogs vaccinated with various vaccines should be performed to provide more complete information on diagnostic performance. BukTi-Vet showed a very good agreement with RFFIT, while Pusvetma and Platelia II only showed good agreement. The average value of BukTi-Vet compatibility with RFFIT can reach 94%.

[Competitive ELISA test system for the detection of antibodies to the rabies virus in animals (Rhabdoviridae: <I>Lyssavirus</I>)]

INTRODUCTION

The main approach to the rabies prevention is the vaccination of domestic and wild carnivores. For the routine evaluation the anti-rabies vaccination effectiveness, World Organization for Animal Health (OIE) recommends various enzyme-linked immunosorbent assays (ELISA).The aim of the study was to design and validate a competitive ELISA (cELISA) test system for the detection of antibodies to the rabies virus (RABV).

MATERIALS AND METHODS

The development of the cELISA was carried out following the OIE recommendations.

RESULTS

The repeatability of the cELISA results within one laboratory was satisfactory (coefficient of variation 7.95-13.61%). The coefficient of determination (CD) between the results of the virus neutralization reaction (FAVN) and cELISA was 0.988, p &lt; 0.001. The lower threshold for antibody detection was less than 0.02 IU/ml. The cELISA did not demonstrate cross-reactivity against antibodies to canine distemper virus, parainfluenza virus, parvovirus, coronavirus, and canine adenovirus (types I and II). During the study of 137 dog blood sera, diagnostic specificity (DSp) and diagnostic sensitivity (DSe) for the cELISA were 83.1% and 94.9%, respectively, and CD between the cELISA and FAVN results was 0.968, p &lt; 0.001.

DISCUSSION

Indirect ELISA test systems for determining the level of antibodies to RABV are not sensitive enough compared to reference tests, unlike cELISA. The developed test system is not inferior for its DSp and DSe to the commercial cELISA BioPro ELISA Rabies Ab (DSp 66.7%, DSe 94.4%).

CONCLUSION

The developed cELISA test system can be used to detect antibodies to RABV in the blood serum of dogs for evaluating the effectiveness of mass vaccination programs.

Inhibitory effect of concomitantly administered rabies immunoglobulins on the immunogenicity of commercial and candidate human rabies vaccines in hamsters

The World Health Organization protocol for rabies post-exposure prophylaxis (PEP) recommends extensive wound washing, immediate vaccination, and administration of rabies immunoglobulin (RIG) in severe category III exposures. Some studies have shown that RIG can interfere with rabies vaccine immunogenicity to some extent. We investigated the interference of RIG on a next generation highly purified Vero cell rabies vaccine candidate (PVRV-NG) versus standard-of-care vaccines in a previously described hamster model. The interference of either human (h) or equine (e) RIG on the immune response elicited by PVRV-NG, Verorab^® (purified Vero cell rabies vaccine, PVRV), and Imovax^® Rabies (human diploid cell rabies vaccine; HDCV) was evaluated using the 4-dose Essen PEP regimen. The anti-rabies seroneutralizing titers and specific serum IgM titers were measured by fluorescent antibody virus neutralization test and enzyme-linked immunosorbent assay, respectively, for the vaccines administered with or without RIG. The RIG interference on PVRV-NG, observed transiently at Day 7, was similar to that on PVRV and tended to be lower than that on HDCV using both read-outs. In summary, the results generated in the hamster model showed that RIG induced similar or less interference on PVRV-NG than the standard-of-care vaccines.

Review of Detection and Quantification of Rabies Virus Antibodies

Rabies is an almost invariably fatal disease. According to the World Health Organization (WHO), rabies virus neutralizing antibody (RVNA) titers of ≥0.5 IU/mL are considered adequate for rabies protection. Therefore, detection and quantification of RABV antibodies are important. Many methods have been developed for detecting RABV antibodies. In the present study, we reviewed several methods of detecting RABV antibodies in human and animal samples and evaluated and compared their performance. Of 34 methods, 5 demonstrated unsatisfactory sensitivity or specificity. The others exhibited sensitivity and specificity of ≥75%. The correlation coefficient for five of eight methods was >0.8. The Bland-Altman mean bias of five of five methods was <±2.0. The kappa values of 25 of 28 methods were higher than 0.4, demonstrating at least moderate agreement. Analysis of the performance of these methods emphasized that any new technology should be considered carefully and objectively before being used as an appropriate and applicable alternative.

Detection and quantification of anti-rabies glycoprotein antibodies: current state and perspectives

Abstract

Rabies is an ancient fatal disease with no other available treatment than post-exposure vaccination, where the bite of infected animals, mainly dogs, is the leading cause of its transmission to human beings. In this context, global vaccination campaigns of companion animals, as well as wildlife reservoirs vaccination, are key factors to achieve the “Zero by 30” plan that pursues the eradication of dog-mediated human rabies by 2030. Rabies virus-neutralizing antibodies (VNAs) play an essential role in the disease protection, as it correlates with an adequate immune response and allows evaluating pre- or post-exposure prophylaxis efficacy. Hence, counting with reliable, accurate, and robust serological tests is of paramount importance. Currently, RFFIT and FAVN are the gold standard VNAs tests recommended by both the WHO and the OIE. Despite these methodologies are efficient and widely used, they present several drawbacks, as they are less easily to standardize and require the use of live rabies virus, containment facilities, and skilled professionals. Thus, in this review, we describe the state-of-the-art of alternative analytical methodologies currently available for rabies serology, with novel approaches based on pseudotyped recombinant viruses and emphasizing in the antigen binding methodologies that detect and quantify antibodies against the rabies glycoprotein. We discussed the wide range of assays that are interesting tools for a faster measurement of anti-rabies glycoprotein antibodies and, in some cases, less complex and more versatile than the gold standard methods. Finally, we discussed the key issues during the design and optimization steps of ELISA assays, highlighting the importance of validation and standardization procedures to improve rabies serology tests and, as a consequence, their results.

Key points

• An exhaustive revision of rabies serology testing was made.

• No rabies serology assay can be thought as better than others for all intents and purposes.

• The validation procedure guarantees reliable and consistent results among the globe.

Analysis of seroprevalence in target wildlife during the oral rabies vaccination programme in Lithuania

BACKGROUND

Rabies vaccination of wildlife carnivores is a powerful tool to prevent, control and eliminate rabies. The presence of neutralizing rabies antibodies in blood is considered a reliable indicator of adequate vaccination. The main purpose of the present study was to analyze the seroprevalence of specific antibodies in target populations of Lithuanian red fox (RF) and raccoon dog (RD) during the oral rabies vaccination (ORV) campaigns during the 2010-2019 period.

RESULTS

Over the ten-year period, 7,261 RF and 2,146 RD sera samples were collected post-mortem in field conditions and tested using a commercial standardized enzyme-linked immunosorbent assay (ELISA) kit in Lithuania. In the ORV spring and autumn vaccination periods, 31.8% (20.3-43.4 95% CI - 95% confidence interval) and 31.7% (21.2-42.1 95% CI) of RF, and 34.1% (22.5-45.7 95% CI) and 34.7% (22.7-46.7 95% CI) of RD sera samples, respectively, were identified as ELISA-positive (seroconversion ≥ 0.5 EU/mL-Equivalent Units per Millilitre). The seroprevalence analysis in adult/ juvenile animal subpopulations indicated that 34.9% (27.2-42.5 95% CI) and 29.2% (20.3-37.9 95% CI) of RF, and 35.6% (25.2-46.0 95% CI) and 30.6% (20.2-40.9 95% CI) of RD sera samples, respectively, were identified as ELISA-positive (seroconversion ≥ 0.5 EU/mL). Statistically strong determinate correlations (r) between the serological results (pos.%) in RF adult/juvenile animal subpopulations (r = 0.937) and between RF and RD positive seroconvert (pos.%) sera samples during the spring vaccinations (r = 0.864) were demonstrated. In different ORV periods, 14-29% of RF and 7-25% of RD sera samples were identified as ELISA-negative (seroconversion < 0.5 EU/mL), but with low (0.125 < 0.49 EU/mL) antibody (Abs) titres.

CONCLUSIONS

The 2010-2019 ORV programme has been an effective tool in both RF and RD populations in Lithuania. The rabies-free status of Lithuania was self-declared in 2015 with only three rabies cases identified in buffer zones since then. The percentage of ELISA-positive serum samples (seroconversion ≥ 0.5 EU/mL) during the different periods of vaccination was similar in RF and RD populations-32% and 34% respectively. The identified seroconversion average of 21.5% in RF and 16% in RD sera samples were officially identified as ELISA-negative (seronversion < 0.5 EU/mL), but with low 0.125 < 0.49 EU/mL Abs titres. That low, but positive seroconversion participated in the formation of populations overall immune status and can influence the interpretation of oral vaccination efficacy.

The Successful Elimination of Sylvatic Rabies Using Oral Vaccination of Foxes in Slovenia

Sylvatic rabies was present in Slovenia between 1973 and 2013, with the red fox as the main reservoir of the rabies virus. The first oral rabies vaccination (ORV) control program in foxes started in 1988, using the manual distribution of baits. Significant improvement of fox vaccination was achieved with the aerial distribution of baits, starting in 1995 and successfully finished with the final, fifty-ninth vaccination campaign in 2019. Between 1979 and 2019, a total of 86,471 samples were tested, and 10,975 (12.69%) rabies-positive animals were identified. Within the ORV, two different vaccines were used, containing modified live virus strain Street Alabama Dufferin (SAD) B19 and SAD Bern, while the last ORV campaigns were completed in 2019, with a vaccine containing a genetically modified strain of SPBN GASGAS. Molecular epidemiological studies of 95 rabies-positive samples, originating from red foxes, badgers, cattle, dogs, martens, cats, and horses, revealed a low genetic diversity of circulating strains and high similarity to strains from neighboring countries. During the elimination program, few vaccine-induced rabies cases were detected: three in red foxes and one case in a marten, with no epidemiological relevance. Slovenia has been officially declared a country free of rabies since 2016.

Active surveillance for antibodies confirms circulation of lyssaviruses in Palearctic bats

BACKGROUND

Palearctic bats host a diversity of lyssaviruses, though not the classical rabies virus (RABV). As surveillance for bat rabies over the Palearctic area covering Central and Eastern Europe and Siberian regions of Russia has been irregular, we lack data on geographic and seasonal patterns of the infection.

RESULTS

To address this, we undertook serological testing, using non-lethally sampled blood, on 1027 bats of 25 species in Bulgaria, the Czech Republic, Poland, Russia and Slovenia between 2014 and 2018. The indirect enzyme-linked immunosorbent assay (ELISA) detected rabies virus anti-glycoprotein antibodies in 33 bats, giving an overall seroprevalence of 3.2%. Bat species exceeding the seroconversion threshold included Myotis blythii, Myotis gracilis, Myotis petax, Myotis myotis, Murina hilgendorfi, Rhinolophus ferrumequinum and Vespertilio murinus. While Myotis species (84.8%) and adult females (48.5%) dominated in seropositive bats, juveniles of both sexes showed no difference in seroprevalence. Higher numbers tested positive when sampled during the active season (10.5%), as compared with the hibernation period (0.9%). Bat rabies seroprevalence was significantly higher in natural habitats (4.0%) compared with synanthropic roosts (1.2%). Importantly, in 2018, we recorded 73.1% seroprevalence in a cave containing a M. blythii maternity colony in the Altai Krai of Russia.

CONCLUSIONS

Identification of such "hotspots" of non-RABV lyssavirus circulation not only provides important information for public health protection, it can also guide research activities aimed at more in-depth bat rabies studies.

Dried blood spot cards: A reliable sampling method to detect human antibodies against rabies virus

Background

Although preventable by vaccination for more than a century, rabies virus still causes numerous fatalities every year. To determine antibody levels in humans, blood collected with a finger prick and applied on dried blood spot (DBS) cards is an alternative for venipuncture. The use of DBS is specifically valuable in remote areas, as it is easy to perform, store and transport. Therefore, the technique is frequently used for epidemiological studies of tropical diseases. Up to present, determination of rabies virus antibody levels on human DBS has not been validated.

Methodology/Principal findings

We evaluated the use of human DBS for rabies serology and analyzed 99 pre- or post-vaccination serum and DBS samples with a fluorescent antibody virus neutralization test (FAVNt), which is the gold standard to detect protective antibody levels, and a Bio-Rad Platelia Rabies II ELISA. Sensitivity and specificity of DBS eluates tested with the FAVNt were 97% and 92%, respectively and 87% and 96% when tested with the Platelia-II ELISA. Antibody levels measured in serum with the FAVNt, correlated best with antibody levels measured in DBS with the FAVNt (R = 0.88).

Conclusions/Significance

This is the first study that applies DBS for reliable detection of human antibodies against rabies virus. Both the FAVNt and Platelia-II ELISA demonstrate an acceptable performance on DBS, providing opportunities for rabies serology in remote areas. This technique could drastically ease studies evaluating (novel) rabies vaccination strategies and monitoring persisting immunity in humans at risk, living in rabies endemic regions.

Rabies is a nearly 100% fatal disease in humans. However, available vaccines are effective in preventing rabies infection. To investigate if a person is protected against rabies, rabies virus neutralizing antibody levels in the blood are determined. The World Health Organization defines protective immunity as a rabies virus antibody concentration of at least 0.5 IU/ml detected in serum using a virus neutralization test. Yet, in remote areas serum may be rather difficult to collect, process and transport. Whole blood collected with a finger prick and applied on filter paper cards, also known as dried blood spots (DBS), are an easier alternative. This collection method is frequently used for serology of several tropical infectious diseases, but never studied for rabies serology in humans. Therefore, we compared antibody levels measured in serum with those measured in DBS eluates, using the gold standard FAVNt and related it to another commonly used test for human rabies serology, the Platelia-II ELISA. We found that both assays had a good performance on DBS eluates. The reported high specificities provide confidence that unprotected individuals will rarely be missed. Therefore, the DBS is a promising sampling technique for evaluations of vaccination strategies and monitoring persisting immunity after vaccination in populations at risk for rabies.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

A Comparative Study of the RAPINA and the Virus-Neutralizing Test (RFFIT) for the Estimation of Antirabies-Neutralizing Antibody Levels in Dog Samples

The mass vaccination of dogs against rabies is a highly rational strategy for interrupting the natural transmission of urban rabies. According to the World Organization for Animal Health (OIE) and the World Health Organization (WHO), the immunization of at least 70% of the total dog population minimizes the risk of endemic rabies. Knowledge of the virus-neutralizing antibody (VNA) level against the rabies virus (RABV) is required to evaluate protective immunity and vaccine coverage of dogs in the field. The rapid focus fluorescent inhibition test (RFFIT) and the fluorescent antibody virus neutralization (FAVN) test are recommended by OIE and WHO to determine the VNA levels in serum. However, these tests are cell culture based and require the use of live viruses and specialized equipment. The rapid neutralizing antibody test (RAPINA) is a novel, immunochromatographic test that uses inactivated virus to estimate the VNA level qualitatively. It is a simple, rapid and inexpensive, although indirect, assay for the detection of VNA levels. The RAPINA has shown good positive and negative predictive values and a high concordance with the RFFIT results. In this study, we compared the performance of the two tests for evaluating the vaccination status of dogs in the Philippines, Thailand and Japan. A total of 1135 dog sera were analysed by the RAPINA and compared to the VNA levels determined by the RFFIT. The overall positive and negative predictive values of the RAPINA were 96.2-99.3% and 84.5-94.8%, respectively, with a concordance (kappa) of 0.946-0.97 among the three countries. The RAPINA results were highly homologous and reproducible among different laboratories. These results suggest that this test is appropriate to survey vaccination coverage in countries with limited resources.

First international collaborative study to evaluate rabies antibody detection method for use in monitoring the effectiveness of oral vaccination programmes in fox and raccoon dog in Europe

The most effective and sustainable method to control and eliminate rabies in wildlife is the oral rabies vaccination (ORV) of target species, namely foxes and raccoon dogs in Europe. According to WHO and OIE, the effectiveness of oral vaccination campaigns should be regularly assessed via disease surveillance and ORV antibody monitoring. Rabies antibodies are generally screened for in field animal cadavers, whose body fluids are often of poor quality. Therefore, the use of alternative methods such as the enzyme-linked immunosorbent assay (ELISA) has been proposed to improve reliability of serological results obtained on wildlife samples. We undertook an international collaborative study to determine if the commercial BioPro ELISA Rabies Ab kit is a reliable and reproducible tool for rabies serological testing. Our results reveal that the overall specificity evaluated on naive samples reached 96.7%, and the coefficients of concordance obtained for fox and raccoon dog samples were 97.2% and 97.5%, respectively. The overall agreement values obtained for the four marketed oral vaccines used in Europe were all equal to or greater than 95%. The coefficients of concordance obtained by laboratories ranged from 87.2% to 100%. The results of this collaborative study show good robustness and reproducibility of the BioPro ELISA Rabies Ab kit.

Rabies in the Baltic States: Decoding a Process of Control and Elimination

Rabies is a fatal zoonosis that still causes nearly 70, 000 human deaths every year. In Europe, the oral rabies vaccination (ORV) of red foxes (Vulpes vulpes) was developed in the late 1970s and has demonstrated its effectiveness in the eradication of the disease in Western and some Central European countries. Following the accession of the three Baltic countries--Estonia, Latvia and Lithuania--to the European Union in 2004, subsequent financial support has allowed the implementation of regular ORV campaigns since 2005-2006. This paper reviews ten years of surveillance efforts and ORV campaigns in these countries resulting in the near eradication of the disease. The various factors that may have influenced the results of vaccination monitoring were assessed using generalized linear models (GLMs) on bait uptake and on herd immunity. As shown in previous studies, juveniles had lower bait uptake level than adults. For the first time, raccoon dogs (Nyctereutes procyonoides) were shown to have significantly lower bait uptake proportion compared with red foxes. This result suggests potentially altered ORV effectiveness in this invasive species compared to the red foxes. An extensive phylogenetic analysis demonstrated that the North-East European (NEE) rabies phylogroup is endemic in all three Baltic countries. Although successive oral vaccination campaigns have substantially reduced the number of detected rabies cases, sporadic detection of the C lineage (European part of Russian phylogroup) underlines the risk of reintroduction via westward spread from bordering countries. Vaccine induced cases were also reported for the first time in non-target species (Martes martes and Meles meles).