Improving laboratory diagnostic capacities of emerging diseases using knowledge mapping

Over the last decade, European countries faced several emerging and re-emerging animal diseases as well as zoonotic diseases. During these episodes, the laboratory diagnostic capabilities were a key factor to rapidly control and/or eradicate them. Because of the associated socio-economic and health consequences, it is crucial to react rapidly and efficiently, not only during crisis but also in peacetime (i.e. preparedness). However, to date, there is no published method to identify diseases with diagnostic gaps and to prioritize assays to be implemented. This study was conducted based on the outcome of a prioritization exercise in which 29 epizootic and exotic diseases with high risk of emergence or re-emergence in Belgium (Bianchini et al., [2020] Transboundary and Emerging Diseases, 67(1), 344-376) were listed. Knowledge mapping was used to visualize and identify gaps in the diagnostic procedures for different epidemiological scenarios at national level. To fill these gaps, an overview of diagnostic capabilities at national and international level (laboratories and kits providers or manufacturers) as well as the published assays in the scientific literature and the prescribed assays by international institutions and kits providers was carried out. The outcome of this study revealed the usefulness of knowledge mapping as a tool to identify gaps and ultimately gain insight on alternatives for better preparedness and responsiveness. While this exercise was limited to Belgium, we believe this exercise can benefit other countries and thereby enhancing knowledge sharing and collaboration to increase diagnostic capabilities for a common list of (re-) emerging diseases in crisis situation.

Prioritization of livestock transboundary diseases in Belgium using a multicriteria decision analysis tool based on drivers of emergence

During the past decade, livestock diseases have (re-)emerged in areas where they had been previously eradicated or never been recorded before. Drivers (i.e. factors of (re-)emergence) have been identified. Livestock diseases spread irrespective of borders, and therefore, reliable methods are required to help decision-makers to identify potential threats and try stopping their (re-)emergence. Ranking methods and multicriteria approaches are cost-effective tools for such purpose and were applied to prioritize a list of selected diseases (N = 29 including 6 zoonoses) based on the opinion of 62 experts in accordance with 50 drivers-related criteria. Diseases appearing in the upper ranking were porcine epidemic diarrhoea, foot-and-mouth disease, low pathogenic avian influenza, African horse sickness and highly pathogenic avian influenza. The tool proposed uses a multicriteria decision analysis approach to prioritize pathogens according to drivers and can be applied to other countries or diseases.

Classification of adult cattle infectious diseases: A first step towards prioritization of biosecurity measures

An emphasis on biosecurity in the cattle industry was made over the years to improve animal and public health. Nevertheless, the level of implementation of biosecurity measures (BSM) remains largely insufficient due to certain constraints. It is therefore necessary to prioritize the different BSM to be applied in accordance with the individual context and the main infectious diseases affecting cattle. Previous prioritization exercises of infectious diseases were neither specific to Belgium nor based on an exhaustive list of diseases. This study aimed at classifying the most important infectious diseases affecting cattle in Belgium. A list of 74 cattle infectious diseases reported in Europe was compiled based on a literature review. Through an online survey, Belgian rural veterinary practitioners (RVP) were asked to assign a score to each disease according to their frequency (question 1), their trends estimated between 2013-15 (question 2), and finally to list the five most important diseases for adult cattle (question 3). Respectively, 107 and 93 RVP answered the first two questions and the last one. Results of the survey were used to classify the diseases based on their frequency, trends, and importance through an additional weighting system and a subsequent regression tree analysis. Belgian laboratory databases and previous disease prioritization exercises were also analysed and taken into account as additional data sources. For the most important diseases identified (those ranked as important by the three data sources), a literature review was performed in PubMed to identify their related risk factors and BSM. A total of 48 infectious diseases were classified as important in Belgium with six of them considered as important from the three data sources: bovine respiratory diseases (BRD), bovine respiratory syncytial virus (BRSV), bovine viral diarrhoea (BVD), infectious bovine rhinotracheitis (IBR), Q fever, and salmonellosis. Their related BSM should be prioritized in terms of BSM implementation.

Rapid and simple detection of foot-and-mouth disease virus: Evaluation of a cartridge-based molecular detection system for use in basic laboratories

Highly contagious transboundary animal diseases such as foot-and-mouth disease (FMD) are major threats to the productivity of farm animals. To limit the impact of outbreaks and to take efficient steps towards a timely control and eradication of the disease, rapid and reliable diagnostic systems are of utmost importance. Confirmatory diagnostic assays are typically performed by experienced operators in specialized laboratories, and access to this capability is often limited in the developing countries with the highest disease burden. Advances in molecular technologies allow implementation of modern and reliable techniques for quick and simple pathogen detection either in basic laboratories or even at the pen-side. Here, we report on a study to evaluate a fully automated cartridge-based real-time RT-PCR diagnostic system (Enigma MiniLab^® ) for the detection of FMD virus (FMDV). The modular system integrates both nucleic acid extraction and downstream real-time RT-PCR (rRT-PCR). The analytical sensitivity of this assay was determined using serially diluted culture grown FMDV, and the performance of the assay was evaluated using a selected range of FMDV positive and negative clinical samples of bovine, porcine and ovine origin. The robustness of the assay was evaluated in an international inter-laboratory proficiency test and by deployment into an African laboratory. It was demonstrated that the system is easy to use and can detect FMDV with high sensitivity and specificity, roughly on par with standard laboratory methods. This cartridge-based automated real-time RT-PCR system for the detection of FMDV represents a reliable and easy to use diagnostic tool for the early and rapid disease detection of acutely infected animals even in remote areas. This type of system could be easily deployed for routine surveillance within endemic regions such as Africa or could alternatively be used in the developed world.

Inter-laboratory evaluation of the performance parameters of a Lateral Flow Test device for the detection of Bluetongue virus-specific antibodies

Bluetongue (BT) is a viral vector-borne disease affecting domestic and wild ruminants worldwide. In this study, a commercial rapid immuno-chromatographic method or Lateral Flow Test (LFT) device, for the detection of BT virus-specific antibodies in animal serum, was evaluated in an international inter-laboratory proficiency test. The evaluation was done with sera samples of variable background (ruminant species, serotype, field samples, experimental infections, vaccinated animals). The diagnostic sensitivity was 100% (95% C.I. [90.5-100]) and the diagnostic specificity was 95.2% (95% C.I. [76.2-99.9]). The repeatability (accordance) and reproducibility (concordance) were 100% for seropositive samples but were lower for two of the seronegative samples (45% and 89% respectively). The analytical sensitivity, evaluated by testing positive sera at increasing dilutions was better for the BT LFT compared to some commercial ELISAs. Seroconversion of an infected sheep was detected at 4 days post infection. Analytical specificity was impaired by cross-reactions observed with some of the samples seropositive for Epizootic Haemorrhagic Disease Virus (EHDV). The agreement (Cohen's kappa) between the LFT and a commercial BT competitive ELISA was 0.79 (95% CI [0.62-0.95]). Based on these results, it can be concluded that the BT LFT device is a rapid and sensitive first-line serological test that can be used in the field, especially in areas endemic for the disease where there is a lack of diagnostic facilities.

Controlling of CSFV in European wild boar using oral vaccination: a review

Classical swine fever (CSF) is among the most detrimental diseases for the swine industry worldwide. Infected wild boar populations can play a crucial role in CSF epidemiology and controlling wild reservoirs is of utmost importance for preventing domestic outbreaks. Oral mass vaccination (OMV) has been implemented to control CSF in wild boars and limit the spill over to domestic pigs. This retrospective overview of vaccination experiences illustrates the potential for that option. The C-strain live vaccine was confirmed to be highly efficacious and palatable baits were developed for oral delivery in free ranging wild boars. The first field trials were performed in Germany in the 1990’s and allowed deploying oral baits at a large scale. The delivery process was further improved during the 2000’s among different European countries. Optimal deployment has to be early regarding disease emergence and correctly designed regarding the landscape structure and the natural food sources that can compete with oral baits. OMV deployment is also highly dependent on a local veterinary support working closely with hunters, wildlife and forestry agencies. Vaccination has been the most efficient strategy for CSF control in free ranging wild boar when vaccination is wide spread and lasting for a sufficient period of time. Alternative disease control strategies such as intensified hunting or creating physical boundaries such as fences have been, in contrast, seldom satisfactory and reliable. However, monitoring outbreaks has been challenging during and after vaccination deployment since OMV results in a low probability to detect virus-positive animals and the live-vaccine currently available does not allow serological differentiation of infected from vaccinated animals. The development of a new marker vaccine and companion test is thus a promising option for better monitoring outbreaks during OMV deployment as well as help to better determine when to stop vaccination efforts. After rabies in red fox, the use of OMV against CSF in European wild boar can be considered as a second example of successful disease control in wildlife. The 30 years of disease control experience included in this review may provide options for improving future disease management within wild populations.

The Assessment of African Swine Fever Virus Risk to Belgium Early 2014, using the Quick and Semiquantitative Pandora Screening Protocol

A risk assessment was organized during the early EU ASF outbreaks of early 2014 (February-April) and performed in cooperation with 15 Belgian and European experts on ASFV and its epidemiology in pigs/wild boar. African swine fever (ASF) is considered as one of the most dangerous infectious pig diseases, causing many outbreaks. Since the end of 2013 - early 2014, several outbreaks within the European Union (Lithuania, Poland, Estonia and Latvia) were reported to OIE, which prompted several risk assessments by (inter)national bodies and scientists. In this study, the open source, semiquantitative Pandora risk assessment tool was used for a quick overall screening of the risk posed by ASF to Belgium early 2014. A set of integrated risk scores was calculated within the Pandora framework. Experts scored the questions and uncertainty levels in the Pandora modules individually, after which the calculations were performed and averaged scores were used within pre-defined risk scales to define and visualize the ASF risk to Belgium. Emergence risk was considered low (Pandora score 0.29), while disease consequences were deemed high (0.93); the resulting multiplicative overall risk of ASFV for Belgium was low (0.27). The Belgian experts tended to give lower risk scores than the European experts, especially for entry risk and trade/public opinion consequences. These risk scores are further interpreted with a due consideration of the qualitative data in the expert remarks and of other ASF risk assessments. The results are similar to more extensive and elaborate risk assessment models/procedures which may require more time and resources. The Pandora tool allows sequential updates to monitor (rates of) increasing risk and provides information for risk managers to organize targeted control.

Substituted 2,6-bis(benzimidazol-2-yl)pyridines: a novel chemical class of pestivirus inhibitors that targets a hot spot for inhibition of pestivirus replication in the RNA-dependent RNA polymerase

2,6-Bis(benzimidazol-2-yl)pyridine (BBP/CSFA-0) was identified in a CPE-based screening as a selective inhibitor of the in vitro bovine viral diarrhea virus (BVDV) replication. The EC50-values for the inhibition of BVDV-induced cytopathic (CPE) effect, viral RNA synthesis and the production of infectious virus were 0.3±0.1μM, 0.05±0.01μM and 0.3±0.04μM, respectively. Furthermore, BBP/CSFA-0 inhibits the in vitro replication of the classical swine fever virus (CSFV) with an EC50 of 0.33±0.25μM. BBP/CSFA-0 proved in vitro inactive against the hepatitis C virus, that belongs like BVDV and CSFV to the family of Flaviviridae. Modification of the substituents on the two 1H-benzimidazole groups of BBP resulted in analogues equipotent in anti-BVDV activity (EC50=0.7±0.1μM), devoid of cytotoxicity (S.I.=142). BBP resistant BVDV was selected for and was found to carry the I261M mutation in the viral RNA-dependent RNA polymerase (RdRp). Likewise, BBP-resistant CSFV was selected for; this variant carries either an I261N or a P262A mutation in NS5B. Molecular modeling revealed that I261 and P262 are located in a small cavity near the fingertip domain of the pestivirus polymerase. BBP-resistant BVDV and CSFV proved to be cross-resistant to earlier reported pestivirus inhibitors (BPIP, AG110 and LZ37) that are known to target the same region of the RdRp. BBP did not inhibit the in vitro activity of recombinant BVDV RdRp but inhibited the activity of BVDV replication complexes (RCs). BBP interacts likely with the fingertip of the pestivirus RdRp at the same position as BPIP, AG110 and LZ37. This indicates that this region is a "hot spot" for inhibition of pestivirus replication.

Efficacy of marker vaccine candidate CP7_E2alf against challenge with classical swine fever virus isolates of different genotypes

Classical swine fever (CSF) is among the most important viral disease of domestic and feral pigs and has a serious impact on animal health and pig industry. In most countries with industrialized pig production, prophylactic vaccination against CSF is banned, and all efforts are directed towards eradication of the disease, e.g. by culling of infected herds and animal movement restrictions. Nevertheless, emergency vaccination remains an option to minimize the socio-economic impact of outbreaks. For this application, potent vaccines are needed that allow differentiation of infected from vaccinated animals. Among the promising candidates for next generation marker vaccines is the chimeric pestivirus CP7_E2alf. Efficacy studies are usually carried out using highly virulent CSFV strains of genotype 1 that do not mirror the current field situation where strains of genotype 2 predominate. To prove that CP7_E2alf also protects against these strains, efficacy was assessed after single oral vaccination of wild boar and single intramuscular vaccination of domestic pigs using challenge models with recent CSFV strains and the highly virulent strain "Koslov" (genotype 1.1). It could be demonstrated that CP7_E2alf pilot vaccine batches for intramuscular and oral use were able to protect pigs from challenge infection with a highly virulent CSFV. Moreover, solid protection was also achieved in case of challenge infection with recent field strains of genotypes 2.1 and 2.3. Thus, broad applicability under field conditions can be assumed.

Intra-host variation structure of classical swine fever virus NS5B in relation to antiviral therapy

Classical swine fever (CSF) is one of most important diseases of the Suidea with severe social economic consequences in case of outbreaks. Antivirals have been demonstrated, in recent publications, to be an interesting alternative method of fighting the disease. However, classical swine fever virus is an RNA virus which presents a challenge as intra-host variation and the error prone RNA dependent RNA polymerase (RdRp) could lead to the emergence/selection of resistant variants hampering further treatment. Therefore, it was the purpose of this study to investigate the intra-host variation of the RdRp gene, targeted by antivirals, in respect to antiviral treatment. Using the non-unique nucleotide changes, a limited intra-host variation was found in the wild type virus with 2 silent and 2 non-synonymous sites. This number shifted significantly when an antiviral resistant variant was analyzed. In total 22nt changes were found resulting in 14 amino acid changes whereby each genome copy contained at least 2 amino-acid changes in the RdRp. Interestingly, the frequency of the mutations situated in close proximity to a region involved in antiviral resistance in CSFV and bovine viral diarrhea virus (BVDV) was elevated compared to the other mutations. None of the identified mutations in the resistant variant and which could potentially result in antiviral resistance was present in the wild type virus as a non-unique mutation. In view of the spectrum of mutations identified in the resistance associated region and that none of the resistance associated mutations reported for another strain of classical swine fever for the same antiviral were observed in the study, it can be suggested that multiple mutations confer resistance to some degree. Although the followed classical approach allowed the analysis the RdRp as a whole, the contribution of unique mutations to the intra-host variation could not be completely resolved. There was a significant difference in de number of unique mutations found between: 1/wild type virus and the antiviral resistant variant and 2/between both and the number to be expected from the error rate of the RT-PCR process. This indicates that the some of the unique mutations contributed to the intra-host variation and that the antiviral pressure also shifted this pattern. This is important as one of the non-synonymous mutations found in the resistant variant and which was located in the antiviral resistance associated region, was present in the wild type virus as a unique mutation. The findings presented in this study not only show the importance of intra-host variation analysis but also warrants further research certainly in view of the potential inclusion of antivirals in a control/eradication strategy.

Association of environmental traits with the geographic ranges of ticks (Acari: Ixodidae) of medical and veterinary importance in the western Palearctic. A digital data set

We compiled information on the distribution of ticks in the western Palearctic (11°W, 45°E; 29°N, 71°N), published during 1970-2010. The literature search was filtered by the tick's species name and an unambiguous reference to the point of capture. Records from some curated collections were included. We focused on tick species of importance to human and animal health, in particular: Ixodes ricinus, Dermacentor marginatus, D. reticulatus, Haemaphysalis punctata, H. sulcata, Hyalomma marginatum, Hy. lusitanicum, Rhipicephalus annulatus, R. bursa, and the R. sanguineus group. A few records of other species (I. canisuga, I. hexagonus, Hy. impeltatum, Hy. anatolicum, Hy. excavatum, Hy. scupense) were also included. A total of 10,280 records was included in the data set. Almost 42 % of published references are not adequately referenced (and not included in the data set), host is reported for only 61 % of records and a reference to time of collection is missed for 84 % of published records. Ixodes ricinus accounted for 44.3 % of total records, with H. marginatum and D. marginatus accounting for 7.1 and 8.1 % of records, respectively. The lack of homogeneity of the references and potential pitfalls in the compilation were addressed to create a digital data set of the records of the ticks. We attached to every record a coherent set of quantitative descriptors for the site of reporting, namely gridded interpolated monthly climate and remotely sensed data on vegetation (NDVI). We also attached categorical descriptors of the habitat: a standard classification of land biomes and an ad hoc classification of the target territory from remotely sensed temperature and NDVI data. A descriptive analysis of the data revealed that a principal components reduction of the environmental (temperature and NDVI) variables described the distribution of the species in the target territory. However, categorical descriptors of the habitat were less effective. We stressed the importance of building reliable collections of ticks with specific references as to collection point, host and date of capture. The data set is freely downloadable.

CP7_E2alf oral vaccination confers partial protection against early classical swine fever virus challenge and interferes with pathogeny-related cytokine responses

The conventional C-strain vaccine induces early protection against classical swine fever (CSF), but infected animals cannot be distinguished from vaccinated animals. The CP7_E2alf marker vaccine, a pestivirus chimera, could be a suitable substitute for C-strain vaccine to control CSF outbreaks. In this study, single oral applications of CP7_E2alf and C-strain vaccines were compared for their efficacy to induce protection against a CSF virus (CSFV) challenge with the moderately virulent Bas-Rhin isolate, in pigs as early as two days post-immunization. This work emphasizes the powerful potential of CP7_E2alf vaccine administered orally by a rapid onset of partial protection similar to that induced by the C-strain vaccine. Furthermore, our results revealed that both vaccinations attenuated the effects induced by CSFV on production of the pig major acute phase protein (PigMAP), IFN-α, IL-12, IL-10, and TGF-β1 cytokines. By this interference, several cytokines that may play a role in the pathogeny induced by moderately virulent CSFV strains were revealed. New hypotheses concerning the role of each of these cytokines in CSFV pathogeny are discussed. Our results also show that oral vaccination with either vaccine (CP7_E2alf or C-strain) enhanced CSFV-specific IgG2 production, compared to infection alone. Interestingly, despite the similar antibody profiles displayed by both vaccines post-challenge, the production of CSFV-specific IgG1 and neutralizing antibodies without challenge was lower with CP7_E2alf vaccination than with C-strain vaccination, suggesting a slight difference in the balance of adaptive immune responses between these vaccines.

Efficacy of chimeric Pestivirus vaccine candidates against classical swine fever: protection and DIVA characteristics

Currently no live DIVA (Differentiating Infected from Vaccinated Animals) vaccines against classical swine fever (CSF) are available. The aim of this study was to investigate whether chimeric pestivirus vaccine candidates (CP7_E2alf, Flc11 and Flc9) are able to protect pigs against clinical signs, and to reduce virus shedding and virus transmission, after a challenge with CSF virus (CSFV), 7 or 14 days after a single intramuscular vaccination. In these vaccine candidates, either the E2 or the E(rns) encoding genome region of a bovine viral diarrhoea virus strain were combined with a cDNA copy of CSFV or vice versa. Furthermore, currently available serological DIVA tests were evaluated. The vaccine candidates were compared to the C-strain. All vaccine candidates protected against clinical signs. No transmission to contact pigs was detected in the groups vaccinated with C-strain, CP7_E2alf and Flc11. Limited transmission occurred in the groups vaccinated with Flc9. All vaccine candidates would be suitable to stop on-going transmission of CSFV. For Flc11, no reliable differentiation was possible with the current E(rns)-based DIVA test. For CP7_E2alf, the distribution of the inhibition percentages was such that up to 5% false positive results may be obtained in a large vaccinated population. For Flc9 vaccinated pigs, the E2 ELISA performed very well, with an expected 0.04% false positive results in a large vaccinated population. Both CP7_E2alf and Flc9 are promising candidates to be used as live attenuated marker vaccines against CSF, with protection the best feature of CP7_E2alf, and the DIVA principle the best feature of Flc9.

Towards licensing of CP7_E2alf as marker vaccine against classical swine fever-Duration of immunity

Classical swine fever (CSF) marker vaccine candidate CP7_E2alf was tested in a "duration of immunity" trial according to the World Organisation for Animal Heath (OIE) guidelines. To this means, 15 weaner pigs were either orally or intramuscularly vaccinated with a single dose of CP7_E2alf vaccine produced under Good Laboratory Practice (GLP) conditions. Ten additional pigs were included as controls. Six months later, all animals were oronasally challenged with highly virulent CSF virus (CSFV) strain "Koslov". Upon vaccination, all but one orally and all intramuscularly vaccinated pigs developed rising and later on stable CSFV glycoprotein E2-specific antibodies. In contrast, no CSFV E(rns)-specific "marker" antibodies were detectable prior to challenge infection. None of the co-housed control animals seroconverted. Upon challenge infection, all seropositive animals were protected from lethal challenge, whereas all control animals and the non-responder developed severe signs of CSF. One control animal recovered, the others had to be euthanised due to animal welfare reasons between days 4 and 7 post challenge infection. All protected animals showed quickly rising neutralizing antibodies reaching high titres by the end of the trial. At the end of the trial, the marker ELISA was positive for most challenged animals that survived the CSFV infection (27 out of 30). Using reverse transcription polymerase chain reaction, low level genome detection was seen in all vaccinated animals between days 4 and 10 post challenge infection, but no virus could be isolated from any samples of these animals. The OIE guidelines require seroconversion in at least 8 out of 10 vaccinated animals. This requirement was fulfilled. Moreover, only control animals should die. With this requirement, only the intramuscular vaccination fully complied as one orally vaccinated pig did not respond. Concluding, CP7_E2alf induced stable antibodies that led to protection from lethal challenge with highly virulent CSFV strain "Koslov" six months after vaccination, with the exception of one non-responder after oral vaccination.

Comparative evaluation of live marker vaccine candidates "CP7_E2alf" and "flc11" along with C-strain "Riems" after oral vaccination

Due to the tremendous socio-economic impact of classical swine fever (CSF) outbreaks, emergency vaccination scenarios are continuously under discussion. Unfortunately, all currently available vaccines show restrictions either in terms of marker capacities or immunogenicity. Recent research efforts were therefore directed at the design of new modified live marker vaccines. Among the most promising candidates the chimeric pestiviruses "CP7_E2alf" and "flc11" were identified. Within an international research project, these candidates were comparatively tested in challenge experiments after a single oral vaccination. Challenge infection was carried out with highly virulent CSF virus strain "Koslov", 14 or 21 days post vaccination (dpv), respectively. Safety, efficacy, and marker potential were addressed. All assessments were done in comparison with the conventional "gold standard" C-strain "Riems" vaccine. In addition to the challenge trials, multiple vaccinations with both candidates were performed to further assess their marker vaccine potential. All vaccines were safe and yielded full protection upon challenge 21 days post vaccination. Neither serological nor virological investigations showed major differences among the three vaccines. Whereas CP7_E2alf also provided clinical protection upon challenge at 14 days post vaccination, only 50% of animals vaccinated with flc11, and 83% vaccinated with C-strain "Riems" survived challenge at this time point. No marked differences were seen in protected animals. Despite the fact that all multiple-vaccinated animals stayed sero-negative in the accompanying marker test, the discriminatory assay remains a weak point due to delayed or inexistent detection of some of the vaccinated and subsequently infected animals. Nevertheless, the potential as live marker vaccines could be confirmed for both vaccine candidates. Future efforts will therefore be directed at the licensing of "Cp7_E2alf" as the first live marker vaccine for CSF.

Development and inter-laboratory validation study of an improved new real-time PCR assay with internal control for detection and laboratory diagnosis of African swine fever virus

A real-time polymerase chain reaction (PCR) assay for the rapid detection of African swine fever virus (ASFV), multiplexed for simultaneous detection of swine beta-actin as an endogenous control, has been developed and validated by four National Reference Laboratories of the European Union for African swine fever (ASF) including the European Union Reference Laboratory. Primers and a TaqMan(®) probe specific for ASFV were selected from conserved regions of the p72 gene. The limit of detection of the new real-time PCR assay is 5.7-57 copies of the ASFV genome. High accuracy, reproducibility and robustness of the PCR assay (CV ranging from 0.7 to 5.4%) were demonstrated both within and between laboratories using different real-time PCR equipments. The specificity of virus detection was validated using a panel of 44 isolates collected over many years in various geographical locations in Europe, Africa and America, including recent isolates from the Caucasus region, Sardinia, East and West Africa. Compared to the OIE-prescribed conventional and real-time PCR assays, the sensitivity of the new assay with internal control was improved, as demonstrated by testing 281 field samples collected in recent outbreaks and surveillance areas in Europe and Africa (170 samples) together with samples obtained through experimental infections (111 samples). This is particularly evident in the early days following experimental infection and during the course of the disease in pigs sub-clinically infected with strains of low virulence (from 35 up to 70dpi). The specificity of the assay was also confirmed on 150 samples from uninfected pigs and wild boar from ASF-free areas. Measured on the total of 431 tested samples, the positive deviation of the new assay reaches 21% or 26% compared to PCR and real-time PCR methods recommended by OIE. This improved and rigorously validated real-time PCR assay with internal control will provide a rapid, sensitive and reliable molecular tool for ASFV detection in pigs in newly infected areas, control in endemic areas and surveillance in ASF-free areas.

Classical swine fever virus detection

The current study reports on a real-time reverse transcription polymerase chain reaction (real-time RT-PCR) ring trial for the detection of Classical swine fever virus (CSFV) genomic RNA undertaken by 10 European laboratories. All laboratories were asked to use their routine in-house real-time RT-PCR protocols and a standardized protocol commonly used by the Friedrich-Loeffler-Institute (FLI) on a panel of well-characterized samples. In general, all participants produced results within the acceptable range. The FLI assay, several in-house assays, and the commercial kits had high analytical sensitivity and specificity values. Nevertheless, some in-house systems had unspecific reactions or suboptimal sensitivity with only a single CSFV genotype. Follow-up actions involved either improvement of suboptimal assays or replacement of specific laboratory assays with the FLI protocol, with or without modifications. In conclusion, the ring trial showed reliability of classical swine fever diagnosis on an international level and helped to optimize CSFV-specific RT-PCR diagnostics.

Methodology of the biological risk classification of animal pathogens in Belgium

Since many micro-organisms are a biological hazard, they have been categorised into risk groups by many countries and organisations and classification lists have been developed. Current classification systems rely on criteria defined by the World Health Organization, which cover the severity of the disease the micro-organism might cause, its ability to spread and the availability of prophylaxis or efficient treatment. Animal pathogens are classified according to the definitions of the World Organisation for Animal Health, which also consider economic aspects of disease. In Europe, classification is often directly linked to containment measures. The Belgian classification system, however, only considers the inherent characteristics of the micro-organism, not its use, making the risk classification independent of containment measures. A common classification list for human and animal pathogens has been developed in Belgium using as comprehensive an approach as possible. The evolution of scientific knowledge will demand regular updating of classification lists. This paper describes the Belgian risk classification system and the methodology that was used for its peer-reviewed revision (with a focus on animal pathogens).

The reduction of CSFV transmission to untreated pigs by the pestivirus inhibitor BPIP: a proof of concept

5-[(4-Bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a representative molecule of a novel class of highly active in vitro inhibitors of the replication of Classical swine fever virus (CSFV). We recently demonstrated in a proof of concept study that the molecule has a marked effect on viral replication in CSFV-infected pigs. Here, the effect of antiviral treatment on virus transmission to untreated sentinel pigs was studied. Therefore, BPIP-treated pigs (n=4), intra-muscularly infected with CSFV, were placed into contact with untreated sentinel pigs (n=4). Efficient transmission of CSFV from four untreated seeder pigs to four untreated sentinels was observed. In contrast, only two out of four sentinel animals in contact with BPIP-treated seeder animals developed a short transient infection, of which one was likely the result of sentinel to sentinel transmission. A significant lower viral genome load was measured in tonsils of sentinels in contact with BPIP-treated seeder animals compared to the positive control group (p=0.015). Although no significant difference (p=0.126) in the time of onset of viraemia could be detected between the groups of contact animals, a tendency towards the reduction of virus transmission was observed. Since sentinel animals were left untreated in this exploratory trial, the study can be regarded as a worst case scenario and gives therefore an underestimation of the potential efficacy of the activity of BPIP on virus transmission.

Proof of concept for the reduction of classical swine fever infection in pigs by a novel viral polymerase inhibitor

5-[(4-Bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a representative of a class of imidazopyridines with potentin vitroantiviral activity against pestiviruses including classical swine fever virus (CSFV). This study analysed whether the lead compound, BPIP, was able to reduce virus replication in infected piglets. The compound, administered in feed, was readily bioavailable and was well tolerated. Eight specific-pathogen-free pigs received a daily dose of 75 mg kg−1(mixed in feed) for a period of 15 consecutive days, starting 1 day before infection with the CSFV field isolate Wingene. BPIP-treated pigs developed a short, transient viraemia (one animal remained negative) and leukopenia (three animals did not develop leukopenia). Virus titres at peak viraemia (7 days post-infection) were markedly lower (∼1000-fold) than in untreated animals (P=0.00005) and the viral genome load in blood was also significantly lower (P≤0.001) in drug-treated animals than in untreated animals over the entire experiment. At the end of the experiment (day 33), no infectious virus was detectable in the tonsils of BPIP-treated animals, although low levels of viral RNA were detected. The inability to isolate infectious virus from the tonsils indicates that the risk of a persistent CSFV infection is negligible. Further optimization of the antiviral potency and bioavailability of this lead compound may result in molecules completely suppressing virus replication. A potent antiviral could potentially be used as a primary control measure against virus spread in case of an outbreak, in addition to present countermeasures. This study provides the first proof of concept for the prophylaxis/treatment of CSFV infection in pigs.

Type and frequency of contacts between Belgian pig herds

Knowledge of the frequency of direct and indirect contacts between pig herds is a requirement for understanding the potential between-herd transmission of pathogens. Our aim was to investigate the different contacts between Belgian pig herds. We obtained data by conducting a postal survey on 421 pig herds in August 2005 and by analysis of available information on livestock movements in the national identification-and-registration database (18-months period in 2004-2006). Direct contacts included transports of pigs by onto-farm, off-farm and between-farm movements. Indirect contacts included vehicles entering the herd and visitors entering the stables. The median number of direct contacts per herd made by onto-farm movements was 0.2/month (Q1: 0; Q3: 0.5). About 1.2% of herds had > or = 3 onto-farm movements/month. We used a zero-inflated negative-binomial regression model to describe differences in the number of onto-farm movements according to herd size and herd type. Piglet multipliers followed by finishing herds were predicted to have the most onto-farm movements. Farrow-to-finishing herds made less movements compared to breeding herds. A median of 3997 between-farm movements/month was made in Belgium; these mainly concerned piglets. The median number of origin herds during an 8-month period for between-farm movements was 4 (Q1: 2; Q3: 8). For a typical 1-month period, we constructed directed graphs of between-farm piglet and replacement stock movements, illustrating potential receivers and distributors of infection. Of these between-farm movements, many were made over a short distance (median straight-line distance 19 km (Q1: 8; Q3: 36)). The median number of vehicles entering a herd and visitors entering the stables was 8/month (Q1: 6; Q3: 13) and 3/month (Q1: 2; Q3: 6) respectively. The number of indirect contacts by vehicles and persons were associated with herd size (Spearman's r: 0.7 and 0.2), herd type and other factors. Skewness of both direct and indirect contacts, illustrated that there was a wide variety in contact structure between pig herds in Belgium. Infection control might benefit by accounting for this variation in contacts and by targeting 'high-risk' herds in case of animal-disease emergencies.

Comparative studies on the pathogenicity and tissue distribution of three virulence variants of classical swine fever virus, two field isolates and one vaccine strain, with special regard to immunohistochemical investigations

BACKGROUND

The aim of this study was to compare the tissue distribution and pathogenicity of three virulence variants of classical swine fever virus (CSFV) and to investigate the applicability of various conventional diagnostic procedures.

METHODS

64 pigs were divided into three groups and infected with the highly virulent isolate ISS/60, the moderately virulent isolate Wingene'93 and the live attenuated vaccine strain Riems, respectively. Clinical signs, gross and histopathological changes were compared in relation to time elapsed post infection. Virus spread in various organs was followed by virus isolation, by immunohistochemistry, applying monoclonal antibodies in a two-step method and by in situ hybridisation using a digoxigenin-labelled riboprobe.

RESULTS

The tissue distribution data are discussed in details, analyzing the results of the various diagnostic approaches. The comparative studies revealed remarkable differences in the onset of clinical signs as well as in the development of the macro- and microscopical changes, and in the tissue distribution of CSFV in the three experimental groups.

CONCLUSION

The present study demonstrates that in the case of highly and moderately virulent virus variants the virulence does not affect the pattern of the viral spread, however, it influences the outcome, the duration and the intensity of the disease. Immunohistochemistry has the advantage to allow the rapid detection and localisation of the virus, especially in cases of early infection, when clinical signs are still absent. Compared to virus isolation, the advantage of this method is that no cell culture facilities are required. Thus, immunohistochemistry provides simple and sensitive tools for the prompt detection of newly emerging variants of CSFV, including the viruses of very mild virulence.

Validation of two commercial real-time RT-PCR kits for rapid and specific diagnosis of classical swine fever virus

Two real-time RT-PCR kits, developed by LSI (TaqVet CSF) and ADIAGENE (Adiavet CSF), obtained an agreement to be commercialised in France, subject to conditions, defined by the French Classical Swine Fever (CSF) National Reference Laboratory. The producers were asked to introduce an internal control to check the RNA extraction efficacy. The different criteria assessed were sensitivity, "pestivirus specificity", reproducibility and ease of handling, using 189 different samples. These samples were either CSFV inactivated strains or blood/serum/organs collected from CSFV experimentally infected pigs or naturally infected wild boars. The reproducibility of the assays was confirmed by the analysis of a batch-to-batch panel control that was used for inter-laboratory tests involving nine laboratories. The two kits were also tested for the use in mass diagnostics and the results proved the kits to be suited using pools of blood, serum and tonsils. Moreover, a field evaluation, carried out on spleen samples collected from the CSF surveillance of wild boars in an area known to be infected and from domestic pigs at a slaughterhouse, confirmed the high sensitivity and specificity of the two kits. This step-by-step evaluation procedure confirmed that the two commercial CSF real-time RT-PCR kits have a higher predictive value than the current diagnostic standard, Virus Isolation.

Real-time laboratory exercises to test contingency plans for classical swine fever: experiences from two national laboratories

In order to adequately and efficiently handle outbreaks of contagious diseases such as classical swine fever (CSF), foot and mouth disease or highly pathogenic avian influenza, competent authorities and the laboratories involved have to be well prepared and must be in possession of functioning contingency plans. These plans should ensure that in the event of an outbreak access to facilities, equipment, resources, trained personnel, and all other facilities needed for the rapid and efficient eradication of the outbreak is guaranteed, and that the procedures to follow are well rehearsed. It is essential that these plans are established during 'peace-time' and are reviewed regularly. This paper provides suggestions on how to perform laboratory exercises to test preparedness and describes the experiences of two national reference laboratories for CSF. The major lesson learnt was the importance of a well-documented laboratory contingency plan. The major pitfalls encountered were shortage of space, difficulties in guaranteeing biosecurity and sufficient supplies of sterile equipment and consumables. The need for a standardised laboratory information management system, that is used by all those involved in order to reduce the administrative load, is also discussed.

Imidazo[4,5-c]pyridines inhibit the in vitro replication of the classical swine fever virus and target the viral polymerase

Selective inhibitors of the replication of the classical swine fever virus (CSFV) may have the potential to control the spread of the infection in an epidemic situation. We here report that 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a highly potent inhibitor of the in vitro replication of CSFV. The compound resulted in a dose-dependent antiviral effect in PK(15) cells with a 50% effective concentration (EC(50)) for the inhibition of CSFV Alfort(187) (subgroup 1.1) of 1.6+/-0.4 microM and for CSFV Wingene (subgroup 2.3) 0.8+/-0.2 microM. Drug-resistant virus was selected by serial passage of the virus in increasing drug-concentration. The BPIP-resistant virus (EC(50): 24+/-4.0 microM) proved cross-resistant with VP32947 [3-[((2-dipropylamino)ethyl)thio]-5H-1,2,4-triazino[5,6-b]indole], an unrelated earlier reported selective inhibitor of pestivirus replication. BPIP-resistant CSFV carried a T259S mutation in NS5B, encoding the RNA-dependent RNA-polymerase (RdRp). This mutation is located near F224, a residue known to play a crucial role in the antiviral activity of BPIP against bovine viral diarrhoea virus (BVDV). The T259S mutation was introduced in a computational model of the BVDV RdRp. Molecular docking of BPIP in the BVDV polymerase suggests that T259S may have a negative impact on the stacking interaction between the imidazo[4,5-c]pyridine ring system of BPIP and F224.

A survey on biosecurity and management practices in Belgian pig herds

We surveyed Belgian pig herds to describe their biosecurity status and management practices. Our written questionnaire was sent to a stratified random sample of 609 pig farms. We achieved a 71.6% response, and 421/609 farmers (69.1%) returned questionnaires suitable for analysis. We used multiple-correspondence analysis followed by a two-step clustering procedure. Herd size, herd type and occupation (commercial or hobby herd) were used to describe different groups. We differentiated four biosecurity groups, which we interpreted as indicating low- to high-biosecurity status. Although we felt that most farms had acceptable biosecurity, few used measures such as showering (2.1%) and quarantine periods for people entering the premises (7.1%). We also found three management-practices clusters, although their interpretation was not straightforward. Despite the industrialised character of pig production in Belgium, 9.4% of pig herds were small, hobby herds that reported different biosecurity and management characteristics (such as the equipping pigs on pasture and feeding kitchen waste).

Association of myocarditis with high viral load of porcine circovirus type 2 in several tissues in cases of fetal death and high mortality in piglets. A case study

During a period of 1.5 months, a newly established pig herd experienced a high number of mummifications and stillbirths, a high neonatal mortality rate, and many piglets with congenital tremors or hind leg ataxia. After clinical and histological investigations, the submitted animals were divided into 4 groups: mummified or stillborn (N = 6), live born with myocarditis (N = 5) (average age 22.8 days), live born without myocarditis (N = 14) (average age 20.0 days), and control animals from a different herd (N = 5) (newborn). Statistically significant differences were observed in the mean porcine circovirus 2 (PCV2) load among the 4 groups in the liver (P < 0.0001). The presence of PCV2 antigen within the myocardial lesions was confirmed by immunohistochemistry. A high load of PCV2 DNA was observed in myocardium, liver, and spleen from mummified or stillborn piglets (>1 x 10(7) copies per 500 ng DNA), lower in piglets with myocarditis (>1 x 10(5) copies per 500 ng DNA), and even further lower in pigs without myocarditis (<1 x 10(5) copies per 500 ng DNA), whereas no PCV2 DNA was detected in the control animals. Myocardium, liver, and spleen were well suited for routine testing of fetuses and young piglets by quantitative real-time polymerase chain reaction. Neither porcine parvovirus nor encepaholomyocarditis virus was detected. These results indicate that the PCV2 infection might have been of etiological importance for the fetal deaths and piglet mortality observed in this herd.

The imidazopyrrolopyridine analogue AG110 is a novel, highly selective inhibitor of pestiviruses that targets the viral RNA-dependent RNA polymerase at a hot spot for inhibition of viral replication

Ethyl 2-methylimidazo[1,2-a]pyrrolo[2,3-c]pyridin-8-carboxylate (AG110) was identified as a potent inhibitor of pestivirus replication. The 50% effective concentration values for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect, viral RNA synthesis, and production of infectious virus were 1.2 +/- 0.5 microM, 5 +/- 1 microM, and 2.3 +/- 0.3 microM, respectively. AG110 proved inactive against the hepatitis C virus and a flavivirus. AG110 inhibits BVDV replication at a time point that coincides with the onset of intracellular viral RNA synthesis. Drug-resistant mutants carry the E291G mutation in the viral RNA-dependent RNA polymerase (RdRp). AG110-resistant virus is cross-resistant to the cyclic urea compound 1453 which also selects for the E291G drug resistance mutation. Moreover, BVDV that carries the F224S mutation (because of resistance to the imidazopyridine 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine [BPIP]and VP32947) is also resistant to AG110. AG110 did not inhibit the in vitro activity of recombinant BVDV RdRp but inhibited the activity of BVDV replication complexes (RCs). Molecular modeling revealed that E291 is located in a small cavity near the tip of the finger domain of the RdRp about 7 A away from F224. Docking of AG110 in the crystal structure of the BVDV RdRp revealed several potential contacts including with Y257. The E291G mutation might enable the free rotation of Y257, which might in turn destabilize the backbone of the loop formed by residues 223 to 226, rendering more mobility to F224 and, hence, reducing the affinity for BPIP and VP32947. It is concluded that a single drug-binding pocket exists within the finger domain region of the BVDV RdRp that consists of two separate but potentially overlapping binding sites rather than two distinct drug-binding pockets.

Evidence of indirect transmission of classical swine fever virus through contacts with people

A strict system for visiting experimentally inoculated and susceptible weaner pigs was used to examine the potential indirect transmission of classical swine fever (CSF) virus by people wearing contaminated boots, gloves and coveralls. The inoculated and susceptible pigs were housed in separate compartments, between which the airborne transmission of the virus was impossible. A worst-case scenario with an intensive visiting protocol and no form of disinfection or hygiene was established. Fifteen days after the pigs were inoculated, infection was detected in one contact pig, and it was concluded that under the conditions of the experiment CSF virus could be transmitted by contact with people.

A novel, highly selective inhibitor of pestivirus replication that targets the viral RNA-dependent RNA polymerase

We report on the highly potent and selective antipestivirus activity of 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP). The 50% effective concentration (EC50) for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect formation was 0.04 +/- 0.01 microM. Comparable reduction of viral RNA synthesis (EC50 = 0.12 +/- 0.02 microM) and production of infectious virus (EC50= 0.074 +/- 0.003 microM) were observed. The selectivity index (ratio of 50% cytostatic concentration/EC50) of BPIP was approximately 2,000. BPIP was inactive against the hepatitis C virus subgenomic replicon and yellow fever virus but demonstrated weak activity against GB virus. Drug-resistant mutants were at least 300-fold less susceptible to BPIP than wild-type virus; showed cross-resistance to N-propyl-N-[2-(2H-1,2,4-triazino[5,6-b]indol-3-ylthio)ethyl]-1-propanamine (VP32947), and carried the F224S mutation in the viral RNA-dependent RNA polymerase (RdRp). When the F224S mutation was introduced into an infectious clone, the drug-resistant phenotype was obtained. BPIP did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of replication complexes (RCs). Computational docking revealed that F224 is located at the top of the finger domain of the polymerase. Docking of BPIP in the crystal structure of the BVDV RdRp revealed aromatic ring stacking, some hydrophobic contacts, and a hydrogen bond. Since two structurally unrelated compounds, i.e., BPIP and VP32947, target the same region of the BVDV RdRp, this position may be expected to be critical in the functioning of the polymerase or assembly of the RC. The potential of BPIP for the treatment of pestivirus and hepacivirus infections is discussed.

Factors related to the incidence of clinical encephalomyocarditis virus (EMCV) infection on Belgian pig farms

We set up a matched case-control study of potential risk factors for clinical encephalomyocarditis virus (EMCV) in 58 pig farms in West Flanders (Belgium). In total, 29 farms experienced a clinical outbreak of EMCV confirmed by EMC virus isolation. Mortality was seen only among suckling piglets (18 case farms), in piglets and other age-groups (4 case farms), or only among fattening pigs (7 case farms). Five farms had reproductive problems among the sows. Control farms were matched geographically on farm size and farm type and were selected on the absence of clinical signs. A questionnaire on potential risk factors for EMCV was developed to collect data at both case and control farms. The exploration of the data used clusters of factors associated with clinical EMCV infection: (a) rodents, (b) general farm set up and (c) general hygiene. The multivariable relationships between clinical appearance of EMCV and potential risk factors were tested with conditional logistic regression. The final model on all farms contained presence of mice (OR=8.3) as a risk factor for clinical EMCV infection while the flow of manure up through the slatted floor (OR=0.11) and movement of manure between manure pits in the pig stable (OR=0.14) were protective.

Transmission of encephalomyocarditis virus in pigs estimated from field data in Belgium by means of R0

Transmission of encephalomyocarditis-virus (EMCV) has been estimated in experiments, but never using field data. In this field study, a farm in Belgium was selected where the presence of EMCV was confirmed by necropsy and virus isolation. Serology was used to estimate the transmission parameter R0. In one compartment with 630 pigs, 6 pens were fully sampled, in the remaining 38 pens, 2 randomly selected pigs were bled. The 151 pigs were bled twice and their serum was tested in a virus neutralisation test. Seroprevalence at the first and second sampling was 41 and 43% respectively, with a cut off value of 1:40. R0 was estimated for 2 scenarios, in- and excluding mortality based on the final sizes from the serological results of the second sampling. The R0 for the fully sampled pens was estimated between 0.6 and 1.7, the combined estimated R0 of these 6 pens was 1.36 (95%-CI 0.93-2.23). The median of the estimated R0 of the partially sampled pens was 1.3 and 1.4. Sampling two pigs per pen provided insight into the spread of the virus in the compartment, while the fully sampled pens provided an accurate estimation of R0. The low R0 strongly suggests that EMCV is not very effectively transmitted between pigs. The number of seropositive pigs in a pen and the spread in the compartment suggests that other routes of infection are more important, in this case most likely rodents. Preventing viral spread should therefore be focussed on rodent control instead of reduction of contact between pigs.

Characterisation of the discrepancy between PCR and virus isolation in relation to classical swine fever virus detection

In order to confirm and characterise further the discrepancies observed between diagnostic RT-nPCR and virus isolation results for the detection of classical swine fever virus (CSFV), a test panel of three new RT-PCRs was designed, amplifying parts of the NS2, NS3 and NS5A regions. Screening of negative samples by virus isolation with the new panel not only confirmed the discrepancies previously observed but also indicated that these were not associated with a specific genomic region. However, none of the PCR-positive samples were positive on all the different PCRs and preferential amplification was not obtained even when a more sensitive real-time RT-PCR was used. Furthermore, the primer-dependent amplification, most likely caused by the presence of viral fragments, demonstrates the necessity of confirming a single positive PCR result, certainly in the presence of contradictory virus isolation results. The new PCR panel, in combination with sequencing, can be used as a tool to provide additional information on the nature of the viral RNA present in the sample.

Estimation of seroprevalence of encephalomyocarditis in Dutch sow herds using the virus neutralization test

Encephalomyocarditis virus (EMCV) has been found on pig farms worldwide and can cause myocarditis in young pigs and reproduction disorders in sows. So far, clinical signs of EMCV have not been reported in the Netherlands. The aim of this study was to estimate the seroprevalence of EMCV infection in Dutch sow herds. A total of 277 Dutch sow herds were randomly selected, from which 3237 serum samples were collected. These samples were tested for EMCV antibodies using the virus neutralization test (VN test). The apparent prevalence of EMCV antibodies was 9.3% in the total sow population, and the apparent herd prevalence was 58.8%. An exact determination of the prevalence of EMCV infections in the Dutch sow population was not possible because the characteristics of the VN test under field circumstances were not known. However, Dutch sow herds seem to be infected with EMCV because the distribution of positive blood samples in the tested sow population was significantly different from that expected if random false-positive reactions had occurred.

Genetic variability of encephalomyocarditis virus (EMCV) isolates

In order to evaluate the variability of encephalomyocarditis virus (EMCV), field isolates originating from different European regions and inducing different clinical pictures in pigs have been molecularly characterised. The regions targeted were the poly(C) tract, a part of the 5'-UTR (360 nucleotides), the Leader gene (201 nucleotides), the complete capsid coding region (2502 nucleotides), the 2A gene (403 nucleotides), the end of the 3D polymerase gene (305 nucleotides) and the 3'-UTR (123 nucleotides). Analyses have also been performed on a virulent field isolate, which had been subjected to serial passages in vivo and in vitro resulting, in the case of the in vitro passaged virus, in attenuation, as demonstrated by animal experiments. The present study shows that different clinical pictures, such as acute fatal myocarditis or reproductive failure, may not only be caused by EMCV isolates which are genetically diverse but also by the same isolate. Thus no correlation could be demonstrated between genotype and clinical disease. However, the European isolate which showed the highest genetic divergence also gave rise to a more complex clinical picture. Despite EMCV having been isolated from cases of acute fatal myocarditis in pigs in certain areas of the world for many years, clinical disease, including a variety of clinical pictures and pathogenicity, has only been recognised in Europe since 1986 and thus it can be considered an emerging disease in this region. These findings, associated with the reported phenotype changes of the virus under environmental changes (passages), along with its wide distribution among vertebrate species (including higher primates), shows the validity of considering EMCV as a potential pathogen for recipients in xenotransplantation.

Pathogenesis of encephalomyocarditis experimental infection in young piglets: a potential animal model to study viral myocarditis

The pathogenesis of encephalomyocarditis (EMC) due to the EMC virus (EMCV) was studied in 24 piglets oro-nasally infected with the field isolate B279/95. Two pigs were kept as negative controls and were euthanised at hour 0. The remaining 24 were euthanised every 6 h up to 78-h post infection (hpi). Virus isolation, histological examination and EMCV immunodetection were performed on the spleen, intestine, pancreas, liver, kidneys, heart, lungs, lymph nodes, tonsils and brain. EMCV was isolated at 6-hpi from the intestine and lymph nodes and at 12-hpi from the heart. From 6 to 12-hpi, scattered degenerate myocardiocytes were immunolabelled. Subsequently, myocarditis developed and progressively worsened. Immunopositive reaction in tonsil macrophages, observed in the early stage of infection (6-hpi), suggests that tonsils are the portal of entry, and by mean of wandering macrophages the EMC virus is then distributed through the body. Afterwards, EMCV-B279/95 replicates intensively in the cytoplasm of myocardiocytes and the acute myocarditis is strictly related to the tropism of these cells. Four pigs died spontaneously. In three animals no post mortem lesions or virus were isolated/detected, although all of them showed mild myocarditis. The experimental infection with EMCV B279/95 indicates: (i) the experimental protocol mimics the individual variability observed in natural disease, (ii) tonsils are the portal of entry of infection and the heart is the target organ, (iii) EMCV provides a valuable animal model for comparative studies on progressive viral myocarditis.

Evaluation of the epidemiological importance of classical swine fever infected, E2 sub-unit marker vaccinated animals with RT-nPCR positive blood samples

It has been demonstrated that pigs that have been double vaccinated with an E2 sub-unit marker vaccine and that are infected with classical swine fever virus (CSFV) through a natural contact infection may react positive in a CSFV detecting RT-nPCR test, whereas no virus could be isolated by using the conventional virus isolation (VI) technique. To evaluate whether these vaccinated and infected pigs may spread the virus, three experiments were set up. In the first, susceptible pigs were inoculated with serum originating from vaccinated RT-nPCR positive pigs. In the second, vaccinated RT-nPCR positive pigs were brought into contact with sentinel animals. In the third, vertical transmission was evaluated in RT-nPCR positive vaccinated pregnant gilts. In the first two experiments, no proof of virus transmission was found, whereas in the third vertical transmission was observed. The conclusion is that in vaccinated pigs that are positive in RT-nPCR but negative in VI, the level of circulating virus is probably not high enough for horizontal transmission, whereas vertical transmission of the virus is possible.

Estimating the probability of freedom of classical swine fever virus of the East-Belgium wild-boar population

A report of the Scientific Committee on Animal Health and Animal Welfare of the European Commission (CEC, 1999.) includes recommendations for setting up monitoring programmes for classical swine fever (CSF) infection in a wild-boar population, based on the assumption that one would detect at least 5% prevalence in a CSF-infected wild-boar population. This assumption, however, is not science based. We propose an alternative method to provide evidence for a wild-boar population being free of CSF and evaluate the efficiency of a surveillance programme that was implemented in Belgium in 1998. In our study, the probability of freedom of CSF-virus was estimated based on 789 samples; these were collected from wild-boars within the surveillance programme (within the three provinces which include 95% of the Belgian wild-boar population) and examined by three diagnostics methods (antibody detection, virus detection and virus RNA detection). A Bayesian framework was used for the estimation, accounting for the diagnostic test characteristics without the assumption of the presence of a gold standard. The median probability of freedom of CSF-virus was estimated at 0.970, with a 95% credibility interval of 0.149-1.000. Independent on the choice of the prior information, the posterior distributions for the probability of freedom of CSF-virus were always skewed close to the upper boundary of 1. This represents a big gain of knowledge since we did not use any prior information for the probability of freedom of CSF-virus and took the uncertainty about the accuracy of the diagnostic methods into account.

The occurrence of encephalomyocarditis virus (EMCV) in European pigs from 1990 to 2001

The occurrence of encephalomyocarditis virus (EMCV) among domestic pigs and wild boar in several European countries is described and discussed. From 1990 to 2001 clinical outbreaks were analysed and serum samples, partly from existing screening programmes, were tested for antibodies against EMCV. Most clinical EMCV outbreaks were reported in Belgium (320), followed by Italy (110), Greece (15) and Cyprus (6). The outbreaks appeared to be clustered in 'endemic areas' with an increase in outbreaks during the autumn and winter months. The within-herd seroprevalence measured in clinically affected pig farms varied considerably among farms (2-87%), with age (0-84%) and by country. Data from farms with no clinical disease showed that subclinical infection with EMCV was found both within (seroprevalence 6-62%) and outside (up to 17 %) the endemic areas of the clinically affected countries as well as in the non-clinically affected countries Austria and France (3-5.4%). Among wild boar, the seroprevalence varied between 0.6 and 10.8%, and a study in Belgium found a prevalence of virus infection of 3.3%.

Transmission of classical swine fever. A review

Classical swine fever (CSF) is one of the most important viral pig diseases. Basic measures to control epidemics of CSF comprise eradication of infected herds and preventive emptying of herds at risk. Identification of these herds at risk is based on knowledge of the different transmission routes of the virus. Direct transmission of CSF is undoubtedly the most efficient way of CSF virus transmission. Data on indirect transmission are variable and often equivocal. Various indirect transmission routes like swill feeding, wild boar and artificial insemination are well described, and the importance is beyond discussion. Mechanical transmission via vehicles and persons are categorized as very important based upon epidemiological research, whereas in experiments they can only be reproduced under worst case conditions. The role of arthropods, birds, rodents, and other animals in the spread of CSF virus remains doubtful. Active transmission by these has never been demonstrated and also very sparse indications for mechanical transmission are available. Also the role of airborne transmission remains debated. However epidemiological as well as experimental data indicate that airborne spread over short distances is probable.

An Experimental Infection (II) to Investigate the Importance of Indirect Classical Swine Fever Virus Transmission by Excretions and Secretions of Infected Weaner Pigs

An experiment was set up to investigate the role of excretions and secretions in the indirect transmission of classical swine fever virus (CSFV). In five small pens, 10 weaner pigs (two pigs per pen) were housed and inoculated with CSFV. Experimental infection was successful in all pigs. The infected pigs were kept in the pens for a period of 15 days after which the pens were depopulated and pigs were killed. At the moment of depopulation, all inoculated pigs were visibly clinically diseased and had high fever. Ten hours later the same pens were repopulated with five pairs of susceptible pigs. From inoculation onwards and especially between depopulation and restocking, the pens were neither cleaned nor disinfected. Four days post-repopulation, three of the susceptible pigs were detected positive on virus isolation. A fourth pig was detected positive 2 days later. Later on, the remaining pigs also became infected, most probably due to contact and between pen infections. It can be concluded that transmission of the virus via excretions and secretions succeeded in four of 10 pigs. This result indicates that transmission of CSFV via excretions and secretions can be of importance in a late, clinical stage of disease.

Efficacy of E2-sub-unit marker and C-strain vaccines in reducing horizontal transmission of classical swine fever virus in weaner pigs

At present, two types of vaccines against classical swine fever (CSF) virus are commercially available: E2 sub-unit marker vaccines and the conventional attenuated live C-strain vaccines. To evaluate the reduction of the horizontal virus transmission, three comparable experiments were carried out in which groups of weaner pigs (vaccinated with a marker vaccine or a C-strain vaccine) were challenged with CSF virus at 0, 7, and 14 days post-vaccination (dpv). Virus transmission was prevented totally when the challenge occurred at 14 dpv with an E2-marker vaccine (0/12 contact pigs positive in virus isolation (VI); R = 0 (0; 1.5)). At 7 dpv, transmission was reduced slightly (5/12 contact pigs positive in VI; R = 1.0 (0.3; 3.0)), whereas at 0dpv, vaccination had no effect on transmission (10/12 contact pigs positive in VI; R = 2.9 (1.5; 10.8)). In the C-strain-vaccinated pigs, no virus transmission was detected even when the challenge was performed at the same day as the vaccination (0/12 contact pigs positive in VI; R = 0 (0; 1.5)).

Transmission and pathogenicity of encephalomyocarditis virus (EMCV) among rats

Due to the probable role played by rodents as a reservoir for the transmission of the EMC virus to pigs, the experiment reported here was performed in order to assess the transmission rate of EMCV within a rat population. Twenty-five eight-week-old Wistar rats housed in individual plastic cages were experimentally infected either with a Greek myocardial EMCV strain (5 rats with a 0.2 x 10(6) TCID50 dose per rat and 10 rats with a 0.5 x 10(4.5) TCID50 dose per rat, oronasally) or a Belgian myocardial EMCV strain (10 rats with a 0.5 x 10(4.5) TCID50 dose per rat, oronasally). Two to five days later, each inoculated rat was moved to a new clean cage and coupled with a contact rat to compare the pathogenicity of the two strains and to estimate the basic reproduction ratio R0, indicating the level of EMCV transmission. During the experiments, faecal virus excretion was measured as well as the serological response against EMCV. After euthanasia, virus isolation was attempted from different rat tissues. Neither strains produced mortality, nor clinical signs and only low titres of neutralising antibodies were found. All contact rats, however, were infected and the virus was isolated from their faeces and from various tissues. Both 10-pair experiments revealed a point estimate for the R0 of infinity (95%-CI for both the Greek and Belgian EMCV strains = 4.48 - infinity), as did the 5-pair experiment with a higher dose of the Greek strain (95%-CI = 1.83 - infinity). Combining the results from the two 10-pair experiments resulted in an estimate for R0 of infinity (95%-CI: 9.87 - infinity). These results indicate that the EMC virus can spread very easily within a rat population by horizontal rat-to-rat transmission (R0 >> 1).

Analytical performance of several classical swine fever laboratory diagnostic techniques on live animals for detection of infection

The diagnostic properties of several assays on live animals were studied using data from different experiments. These experiments involved 128 classical swine fever virus (CSFV) infected pigs (weaner pigs, fatteners and sows). Since all pigs in the study were infected with CSFV, only the proportion of test positive results and the time until a test positive result is obtained were evaluated. The RT-nPCR detected the highest proportion of infected pigs (98.9%), whereas the Antigen ELISA gave the worst detection results (74.7%). Within the group of test positive animals, infection was detected earliest using the leukocyte count and latest using Antigen ELISA. Using the virus neutralisation test, antibodies against CSFV were detectable on average 7.6 days after the onset of viraemia in virus isolation in whole blood. Using survival analysis, the time until the first positive diagnosis and the proportion of detected animals were combined in one test. Results showed that RT-nPCR performed significantly better than either virus isolation in different blood fractions or antigen ELISA. It is concluded that the RT-nPCR technique is the best diagnostic tool available for early detection of a classical swine fever infection.

Effect of challenge dose and age in experimental infection of pigs with encephalomyocarditis virus

Two experiments were performed to compare the severity of encephalomyocarditis virus (EMCV) infection in pigs. The pigs were challenged with the Greek myocardial strain, at different ages and with different doses. In the first experiment, nineteen susceptible pigs, 40 days old, were divided into three groups and were experimentally infected with 10(6) TCID(50), 10(4) TCID(50) or 10(2) TCID(50) of the Greek EMCV strain. In the second experiment, 10 susceptible pigs, of either 20 or 105 days, were divided into two groups according to age and were experimentally infected with 10(6) TCID(50) of the Greek EMCV strain. In addition, five piglets, each one the same age as its experimental group, were used as uninfected controls. No clinical signs were observed after infection, except a transient temperature rise in some pigs. Another important observation was the difference in mortality between groups. The survival rate of the 40-day-old pigs was inversely related to the viral dose. In these pigs, a positive association between the viral dose and the severity of macroscopical and histopathological lesions of the heart was also evident. Viral isolations from various organs of the challenged 40-day-old pigs increased with the increasing dose level. When challenged with 10(6) TCID(50) of EMCV, there was no difference in the fatality rate of the 20- and 40-day-old pigs, but none of the 105-day-old pigs died. The severity of the macroscopical and the histopathological heart lesions was inversely related to the age of the pigs. Furthermore, viral isolations from the various organs were higher in 20- and 40-day-old pigs than in the older ones. In 40-day-old pigs, neutralizing antibodies linearly increased as the dose increased. These antibodies were consistently lower in 20-day-old pigs. Viraemia, and nasal and faecal excretions were detected in all groups and lasted 1-3 days, except for the 105-day-old pigs whose symptoms lasted for an additional day.