Comparison of two real-time RT-PCR assays for differentiation of C-strain vaccinated from classical swine fever infected pigs and wild boars

Classical swine fever is one of the most important infectious diseases for the pig industry worldwide due to its economic impact. Vaccination is an effective means to control disease, however within the EU its regular use is banned owing to the inability to differentiate infected and vaccinated animals, the so called DIVA principle. This inability complicates monitoring of disease and stops international trade thereby limiting use of the vaccine in many regions. The C-strain vaccine is safe to use and gives good protection. It is licensed for emergency vaccination in the EU in event of an outbreak. Two genetic assays that can distinguish between wild type virus and C-strain vaccines have recently been developed. Here the results from a comparison of these two real-time RT-PCR assays in an interlaboratory exercise are presented. Both assays showed similar performance.

Development of a real-time RT-PCR assay based on primer-probe energy transfer for the detection of all serotypes of bluetongue virus

A real-time RT-PCR assay based on the primer-probe energy transfer (PriProET) was developed to detect all 24 serotypes of bluetongue virus (BTV). BTV causes serious disease, primarily in sheep, but in other ruminants as well. A distinguishing characteristic of the assay is its tolerance toward mutations in the probe region. Furthermore, melting curve analysis following immediately PCR confirms specific probe hybridization and can reveal mutations in the probe region by showing a difference in the melting point. The assay sensitivity was in the range of 10-100 target copies and the specificity tests showed no positive results for heterologous pathogens. The assay was tested on clinical samples from BTV 8 outbreaks in Sweden and Denmark in 2008. The lowest detection limit for that serotype, determined with PCR standards, was 57 genome copies. The assay sensitivity for some other serotypes that circulate currently in Europe was also determined. BTV 2, 4, 9 and 16 were tested on available cell culture samples and the detection limits were 109, 12, 13 and 24 copies, respectively. This assay provides an important tool for early and rapid detection of a wide range of BTV strains, including emerging strains.

Improved diagnosis for nine viral diseases considered as notifiable by the world organization for animal health

Nine viral diseases included in the World Organization for Animal Health list of notifiable diseases (former list A) were chosen for their contagiousness and high capacity of spreading to improve their diagnosis using new and emerging technologies. All the selected diseases--foot-and-mouth disease, swine vesicular disease, vesicular stomatitis, classical swine fever, African swine fever, bluetongue, African horse sickness, Newcastle disease and highly pathogenic avian influenza--are considered as transboundary diseases, which detection causes the prohibition of livestock exportation, and, thus, it leads to high economical losses. The applied diagnostic techniques can fall into two categories: (i) nucleic-acid detection, including padlock probes, real-time PCR with TaqMan, minor groove binding probes and fluorescence energy transfer reaction probes, isothermal amplification like the Cleavase/Invader assay or the loop-mediated amplification technology and the development of rapid kits for 'mobile' PCR and (ii) antigen-antibody detection systems like simplified and more sensitive ELISA tests. Besides, internal controls have been improved for nucleic acid-detecting methods by using an RNA plant virus--Cowpea Mosaic Virus--to ensure the stability of the RNA used as a positive control in diagnostic real-time RT-PCR assays. The development of these diagnosis techniques has required the joint efforts of a European consortium in which nine diagnostic laboratories and an SME who have collaborated since 2004 within the European Union-funded Lab-on-site project. The results obtained are shown in this paper.

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.

Vertical transmission of bovine viral diarrhoea virus (BVDV) in mousedeer (Tragulus javanicus) and spread to domestic cattle

This study investigates the transmission of bovine viral diarrhoea virus (BVDV) 1f from a persistently infected (PI) lesser Malayan mousedeer to two bovine calves. Different contact routes to two calves were analysed: 1) aerosol contact between two adjacent pens without physical contact; 2) indirect contact by use of common utensils; 3) direct nose-to-nose contact for 30 seconds. One of the calves was infected either by aerosol or indirect contact. The virus sequence in 247 nucleotides in the 5'-UTR was 100% identical in mousedeer and calf. To elucidate the distribution of BVDV within the affected mousedeer family the captive population in a Zoo was analysed. The maternal line of PI animals was maintained, whereas a PI male was able to reproduce and have a non-PI calf. As a consequence of this, six female PI mousedeer were killed; subsequent autopsies did not reveal any lesions. Sequencing mousedeer BVD virus in the E2 region (420 nucleotides) through 4 generations showed only 7 mutations, which were maintained from mother to offspring.

Development of a real-time PCR assay based on primer-probe energy transfer for the detection of swine vesicular disease virus

A real-time PCR assay based on primer-probe energy transfer (PriProET) was developed to detect swine vesicular disease virus (SVDV). Specificity tests of SVDV and heterologous virus showed specific amplification of SVDV strains only. The amplification plot for the closely related Coxsackievirus B5 remained negative. The sensitivity of assay was five copies of viral genome equivalents. A key point of the assay is tolerance toward mutations in the probe region. Melting curve analysis directly after PCR, with determination of probe melting point, confirmed specific hybridisation of the SVDV strains. Eight of twenty SVDV strains tested, revealed shifted melting points that indicated mutations in the probe region. All predicted mutations were confirmed by nucleotide sequencing. With the PriProET system there is a chance to identify phylogenetically divergent strains of SVDV, which may appear negative in other probe-based real-time PCR assays. At the same time, any difference in melting points may provide an indication of divergence in the probe region. The high sensitivity, specificity, and tolerance toward mutations in the probe region of the SVDV PriProET assay may improve the early and rapid detection of a wide range of SVDV strains, allowing reduced turnaround time and the use of high-throughput, automated technology.

Genetic diversity of bovine viral diarrhoea viruses (BVDV) in Denmark during a 10-year eradication period

A 243 base-pair fragment of the 5'- untranslated region (5'-UTR) of bovine viral diarrhoea virus (BVDV) was RT-PCR amplified from tissue samples (after one passage) or from plasma collected from Danish cattle in 1962 (1), 1993 (7), or in 2002-03 (28) when BVD was almost extinct as a result of a 6-year eradication programme. The PCR products were sequenced and phylogenetically analysed. All 36 samples were BVDV species 1 (BVDV-1), 29 sequences belonged to the BVDV 1d subtype, 6 to the BVDV 1b subtype, and one sequence to the BVDV 1e subtype. While all samples from 1993 and 1962 were of 1d subtype, the samples collected in 2002-2003 belonged to 1d (22 samples), 1b (5 samples) and 1e (1 sample) subtypes. In five herds, materials from two animals were obtained for PCR analysis. In four of five herds the sequences of the two viruses were identical, but in one herd the obtained sequences belonged to two different subtypes. Routine analysis detected 11 PI calves older than 2 months of age. For early detection of infected calves it is recommended that antigen ELISA be replaced by PCR detection. Here we present the first sequence analysis of Danish BVDV strains.

Development of a novel quantitative real-time RT-PCR assay for the simultaneous detection of all serotypes of foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) spreads extremely fast and the need for rapid and robust diagnostic virus detection systems was obvious during the recent European epidemic. Using a novel real-time RT-PCR system based on primer-probe energy transfer (PriProET) we present here an assay targeting the 3D gene of FMDV. The assay was validated for the efficacy to detect all known FMDV serotypes. The test method was linear over a range of at least 7 orders of magnitude and the detection limit was below the equivalent of 10 genomic copies. Analysing recent African probang samples the method was able to detect FMDV in materials from both cattle and buffalo. When compared to traditional virus cultivation the virus detection sensitivity was similar but the RT-PCR method can provide a laboratory result much faster than virus cultivation. The real-time PCR method confirms the identity of the amplicon by melting point analysis for added specificity and at the same time allows the detection of mutations in the probe region. As such, the described new method is suitable for the robust real-time detection of index cases caused by any serotype of FMDV.

Characterisation of a pestivirus isolated from persistently infected mousedeer ( Tragulus javanicus)

Serum samples from the male Mousedeer A and the mother, father and sister of A were tested for bovine virus diarrhoea viruses (BVDV) by isolation, and for BVDV antibodies by blocking ELISA and homologous neutralisation test. Further, RNA was extracted and tested by RT-PCR protocol analysing the 5'-untranslated region and the E2 gene of pestivirus. The RT-PCR products were subsequently sequenced. Mousedeer A was positive in virus isolation on three occasions (days 1, 19 and 40) and by RT-PCR. The sister and mother of Mousedeer A were also found virus positive by isolation and RT-PCR. Mousedeer A, its sister and its mother, all had an antibody neutralisation titer below 10. The father of A was virus negative but was positive in the blocking antibody ELISA and had a high neutralisation antibody titer. The repeated detection of BVDV in Mousedeer A, the high amount of virus in serum, the lack of antibodies and the virus positive family members documented that the mousedeer were persistently infected with a pestivirus. The father of A probably had an acute infection resulting in antibodies to pestivirus and viral clearance. Sequence analysis and phylogenetic analysis revealed that the mousedeer pestivirus was closely related to BVDV Type 1f. The existences of persistently infected animals in non-domestic species have great implications for BVDV eradication campaigns in cattle.

An experimental infection model for reproduction of calf pneumonia with bovine respiratory syncytial virus (BRSV) based on one combined exposure of calves

Bovine respiratory syncytial virus (BRSV) has been recognised as an important pathogen in calf pneumonia for 30 years, but surprisingly few effective infection models for studies of the immune response and the pathogenesis in the natural host have been established. We present a reproducible experimental infection model for BRSV in 2-5-month-old, conventionally reared Jersey calves. Thirty-four colostrum-fed calves were inoculated once by aerosol and intratracheal injection with BRSV. Respiratory disease was recorded in 91% of the BRSV-inoculated calves, 72% had an accompanying rise in rectal temperature and 83% exhibited >5% consolidation of the lung tissue. The disease closely resembled natural outbreaks of BRSV-related pneumonia, and detection of BRSV in nasal secretions and lung tissues confirmed the primary role of BRSV. Nine mock-inoculated control calves failed to develop respiratory disease. This model is a valuable tool for the study of the pathogenesis of BRSV and for vaccine efficacy studies.

Classical swine fever (CSF) marker vaccine. Trial I. Challenge studies in weaner pigs

Two commercial marker vaccines against classical swine fever virus (CSFV) and companion diagnostic tests were examined in 160 conventional pigs. To test the vaccines in a "worst case scenario", group of 10 weaners were vaccinated using a single dose of an E2 (gp55) based vaccine at days -21, -14, -10 or -7, and subsequently challenged at day 0. The challenge virus was CSFV 277, originating from a recent outbreak of classical swine fever (CSF) in Germany. In all groups, only 5 out of 10 pigs were challenged; the remaining 5 pigs served as vaccinated contact controls. Also, three control groups, each consisting of 10 non-vaccinated pigs, were challenged in parallel to the vaccinated animals. CSFV could be isolated from all non-vaccinated pigs. Among these pigs 40% displayed a chronic course of the infection (virus positive for more than 10 days). Pigs vaccinated 21 or 14 days before challenge displayed no clinical signs of CSFV after challenge. However, they were still able to replicate CSFV when challenged, as measured by reisolation of CSFV from leukocytes of the directly challenged pigs. CSFV could be isolated from the leucocytes of 25% of the pigs vaccinated 21 days before challenge and 50% of the pigs vaccinated 14 days before challenge. Chronic infection was not observed, but transmission to one vaccinated contact pig occurred. From all pigs vaccinated 10 or 7 days before challenge, CSFV could be reisolated. We observed a chronic course of infection in 5% of pigs vaccinated 10 days before challenge and in 30% of pigs vaccinated 7 days before challenge. The mortality rate was 20% in the pigs vaccinated 10 days before challenge, and varied between 20 and 80% in pigs vaccinated 7 days prior to challenge. The contact animals had lower mortality (0-20%) than directly challenged pigs, probably mirroring the delayed time point of infection. There was thus some protection against clinical illness by both marker vaccines, but not a solid protection against infection and virus shedding. The efficacy of the vaccine was best if used 3 weeks before challenge and a clear correlation between time interval from vaccination to challenge and the level of virus shedding was observed. Each vaccine had its own accompanying discriminatory ELISA, but 18% of the virus positive pigs never seroconverted in these tests.

Antibody dynamics in BRSV-infected Danish dairy herds as determined by isotype-specific immunoglobulins

Using specific ELISAs, antibody levels of four different isotypes to bovine respiratory syncytial virus (BRSV) were determined in calves, following experimental BRSV infection. Most calves experienced an increase in the specific IgM and IgG1 titres about 6-10 days after infection with BRSV. The IgM titre was transient showing positive titres for only 5-10 days, while specific IgG1 was present for a longer time. IgA was detected concomitantly with IgM but at a lower level. Production of IgG2 anti-BRSV antibodies was detected from 3 weeks after infection. In two closed herds, repeated blood samplings were performed on young stock to analyse maternal immunity. The passively transferred antibodies were mainly of the IgG1 isotype and the half-life of IgG1 to BRSV was estimated to be 26.6 days. One of the herds had an outbreak of enzootic pneumonia, diagnosed to be caused by BRSV. Furthermore, another herd with acute BRSV was followed by weekly blood samples in six calves; in both herds IgM and IgG1 was detected shortly after the appearance of clinical signs. Serum samples from 50 Danish dairy herds (453 samples) were tested for immunoglobulins of the isotypes IgG1, IgG2 and IgM. The presence of antibodies to BRSV was widespread and more than 54% of the samples had BRSV antibodies of both the IgG1 and IgG2 isotypes indicating a high herd prevalence to BRSV. Test samples from two herds out of 50 were free from all isotypes to BRSV.

Pathological and microbiological studies on pneumonic lungs from Danish calves

During 1 year, the association between microbiological and pathological findings in 72 lungs from calves submitted to the Danish Veterinary Laboratory for diagnostic purposes was studied. All cases were evaluated pathologically and bacteriologically, whereas only 68 cases were examined for the presence of bovine respiratory syncytial virus (BRSV), parainfluenza-3 virus (PI-3 virus) and bovine coronavirus, 62 cases for bovine viral diarrhoea virus (BVD), 45 cases for bovine adenovirus and 51 cases for mycoplasmas. Based on histopathological examination, the cases were diagnosed as fibrinous and/or necrotizing bronchopneumonia, suppurative bronchopneumonia, embolic pneumonia and others. The diagnoses were based on the dominating and most severe lesions in each lung. Haemophilus somnus, Pasteurella multocida, Actinomyces pyogenes, P. haemolytica and BRSV were the most commonly found bacterial and viral lung pathogens, respectively. Pasteurella spp. and H. somnus were often associated with the more severe fibrinonecrotizing type of bronchopneumonia, whereas BRSV was primarily detected in cases of suppurative bronchopneumonia. Mycoplasma bovis was isolated from one case only, whereas M. dispar, M. bovirhinis and Ureaplasma diversum were present, often concomitantly, in the majority of cases. Aspergillus fumigatus was isolated from one case.

Diagnosis of enzootic pneumonia in Danish cattle: reverse transcription-polymerase chain reaction assay for detection of bovine respiratory syncytial virus in naturally and experimentally infected cattle

A reverse transcription-polymerase chain reaction (RT-PCR) assay was developed for detection of bovine respiratory syncytial virus (BRSV) in lung tissue of naturally and experimentally infected cattle. Primers were selected from the gene coding the F fusion protein, which is relatively conserved among BRSV isolates. The RT-PCR assay was highly specific, it yielded positive reactions only when performed on BRSV-infected cell cultures or tissues. The detection limit of the RT-PCR assay was assessed as 5 TCID50. BRSV was detected in tissues of the respiratory tract and in the tracheobroncheal lymph node of calves euthanized 2-8 days after experimental infection with BRSV, whereas samples of other tissues and samples from mock-infected animals were negative at all time points. Examination of lung samples from 8 different regions of the lungs revealed that although the virus was most often found in the cranioventral lobules, it was frequently present in all lung lobules. Microbiologic examinations of all acute fatal cases of pneumonia (135 animals) in cattle submitted for diagnostic purposes during 1 year revealed that Actinomyces pyogenes (11%), Haemophilus somnus (10%), Pasteurella sp. (7%), and Pasteurella haemolytica (7%) were the most common bacterial agents found in the lungs. BRSV was identified using a conventional antigen enzyme-linked immunosorbent assay (ELISA) in 23 (17%) animals. The established BRSV-specific RT-PCR assay yielded positive results for the same 23 animals. In addition, 10 animals that were negative with the ELISA were positive with the RT-PCR assay. These results indicates that the RT-PCR assay can be a sensitive, reliable alternative to conventional diagnostic procedures.

Mink enteritis parvovirus. Stability of virus kept under outdoor conditions

Feces from mink with acute mink enteritis were pooled and then allowed to dry out in open tubes kept under a roof in an open shed for one year starting in January. Samples of feces were harvested approximately once a month. These were reconstituted to their original volume and tested for antigen content and infectivity both in in vitro cell cultures and - on selected samples - in vivo. During the first 8 months, the antigen level in the feces samples decreased slowly. At this time point, a plateau was reached at 30-40% of the original viral antigen contents. The infectivity in vitro was unchanged for the first 5 months, but after mid-summer it decreased abruptly to below the detection level. Based on the in vitro infectivity, 10 samples were selected for inoculation into mink to measure the in vivo infectivity. The transmission of the infection to the experimental animals was successful for all samples showing infective virus by cultivation. In addition, it was possible to infect mink using material harvested one month after the cell culture test had turned negative. One mink inoculated with material collected in October excreted virus. We conclude that parvovirus can survive for at least 5-10 months (or during the winter period) under natural conditions, but complete drying out seems to lead to its inactivation. Mechanical cleaning of the premises is thus as critical as disinfection since virus can only survive the dry summer period if protected by protein or buried in moist soil on the premises.

Genetic and antigenic analysis of the G attachment protein of bovine respiratory syncytial virus strains

Antigenic and genetic studies of bovine respiratory syncytial virus (BRSV) were made on isolates obtained from three continents over 27 years. Antigenic variation between eight isolates was initially determined using protein G-specific monoclonal antibodies. Four distinct reaction patterns were observed, two of which corresponded to the previously established subgroups A and AB. A third pattern was produced by five Scandinavian strains and a fourth was observed from a single Dutch isolate. The genetic diversity of 27 strains of BRSV was investigated by comparative nucleotide sequence analysis of a 731 nucleotide fragment in the G protein gene. Nine of the BRSV strains were analysed by direct sequencing of RT-PCR amplicons whereas sequences of 18 BRSV and three human respiratory syncytial virus (HRSV) strains were obtained from GenBank. The analysis revealed similarities of 88-100% among BRSV strains and 38-41% between BRSV and HRSV. A phylogenetic tree created for BRSV revealed two main branches, one of which divided into five further lineages, each representing a geographic cluster. A correlation was evident between the positions of some strains in the phylogenetic tree and their antigenic pattern. For HRSV strains, a genetic similarity of only 62% allowed the distinction of two antigenic subgroups, A and B, a pattern which was not seen for BRSV. This study showed that genetic analysis was an accurate method for discriminating BRSV strains and that these viruses should be regarded as a single genetic and antigenic group, within which variants can be distinguished.

Serological and genetic characterisation of bovine respiratory syncytial virus (BRSV) indicates that Danish isolates belong to the intermediate subgroup: no evidence of a selective effect on the variability of G protein nucleotide sequence by prior cell culture adaption and passages in cell culture or calves

Danish isolates of bovine respiratory syncytial virus (BRSV) were characterised by nucleotide sequencing of the G glycoprotein and by their reactivity with a panel of monoclonal antibodies (MAbs). Among the six Danish isolates, the overall sequence divergence ranged between 0 and 3% at the nucleotide level and between 0 and 5% at the amino acid level. Sequence divergences of 7-8%, 8-9% and 2-3% (nucleotide) and 9-11%, 12-16% and 4-6% (amino acid) were obtained in the comparison made between the group of Danish isolates and the previously sequenced 391-2USA, 127UK and 220-69Bel isolates, respectively. Phylogenetic analysis showed that the Danish isolates formed three lineages within a separate branch of the phylogenetic tree. Nevertheless, the Danish isolates were closely related to the 220-69Bel isolate, the prototype of the intermediate antigenic subgroup. The sequencing of the extracellular part of the G gene of additional 11 field BRSV viruses, processed directly from lung samples without prior adaption to cell culture growth, revealed sequence variabilities in the range obtained with the propagated virus. In addition, several passages in cell culture and in calves had no major impact on the nucleotide sequence of the G protein. These findings indicated that the previously established variabilities of the G protein of RS virus isolates were not attributable to mutations induced during the propagation of the virus. The reactivity of the Danish isolates with G protein-specific MAbs were similar to that of the 220-69Bel isolate. Furthermore, the sequence of the immunodominant region was completely conserved among the Danish isolates on one side and the 220-69Bel isolate on the other. When combined, these data strongly suggested that the Danish isolates belong to the intermediate subgroup.

Plant-derived vaccine protects target animals against a viral disease

The successful expression of animal or human virus epitopes on the surface of plant viruses has recently been demonstrated. These chimeric virus particles (CVPs) could represent a cost-effective and safe alternative to conventional animal cell-based vaccines. We report the insertion of oligonucleotides coding for a short linear epitope from the VP2 capsid protein of mink enteritis virus (MEV) into an infectious cDNA clone of cowpea mosaic virus and the successful expression of the epitope on the surface of CVPs when propagated in the black-eyed bean, Vigna unguiculata. The efficacy of the CVPs was established by the demonstration that one subcutaneous injection of 1 mg of the CVPs in mink conferred protection against clinical disease and virtually abolished shedding of virus after challenge with virulent MEV, demonstrating the potential utility of plant CVPs as the basis for vaccine development. The epitope used occurs in three different virus species-MEV, canine parvovirus, and feline panleukopenia virus- and thus the same vaccine could be used in three economically important viral hosts-mink, dogs, and cats, respectively.

Viral aetiology of enzootic pneumonia in Danish dairy herds: diagnostic tools and epidemiology

Ten outbreaks of calf respiratory disease in Danish dairy herds were investigated by lung lavage, and in eight of the herds paired blood samples were tested serologically. In six of the 10 herds bovine respiratory syncytial virus (BRSV) antigen was detected in the lung lavage fluids. In only one calf was coronavirus and BRSV detected simultaneously. The paired blood samples confirmed that four of the herds were BRSV-infected, and in one herd the BRSV infection was diagnosed by the paired blood samples alone. Significant increases in antibody titres against coronavirus were observed in two herds, both in combination with other virological agents. No adenovirus antigen was detected in any of the lavage samples, but in two herds a significant increase in antibody titres against adenovirus was observed. Parainfluenza-3 (PI-3) virus was not detected in the lung lavage fluids, and in four of the herds, no antibodies to PI-3 were detected. In three herds no viral involvement could be found. The findings suggest that BRSV may be an important causative agent in calf respiratory disease in Denmark, even in very young calves.

Sites of replication of bovine respiratory syncytial virus in naturally infected calves as determined by in situ hybridization

Replication of bovine respiratory syncytial virus (BRSV) was studied in three naturally infected calves by in situ hybridization using strand-specific RNA probes. One of the calves was a 5-month-old Friesian, the other two calves were a 3-month-old and a 3-week-old Jersey. Two Jersey calves, 3 months and 3 weeks of age, served as controls. Replication of BRSV took place in the luminal lining of the respiratory tract. In one of the BRSV infected animals (calf No. 1), replication was especially seen in the bronchi, whereas in the two other animals (calf Nos. 2 and 3) replication of BRSV was demonstrated in the bronchiolar epithelial cells and in alveolar cells. Syncytia were often observed in the bronchiolar walls and in alveoli and such syncytia were always replicating BRSV. By immunohistochemistry it was possible to demonstrate BRSV antigen at the same location as replication of BRSV was detected. In tissue outside the respiratory tract neither BRSV antigen nor replication of BRSV could be demonstrated.

Full protection in mink against mink enteritis virus with new generation canine parvovirus vaccines based on synthetic peptide or recombinant protein

Two recently developed vaccine--one based on synthetic peptide and one based on recombinant capsid protein--fully protected dogs against heavy experimental canine parvovirus (CPV) infection. The high sequence homology ( > 98%) and antigenic similarity between CPV and mink enteritis virus (MEV), feline panleukopenia virus, and raccoon parvovirus, suggest that both vaccines could protect mink, cats and raccoons against these respective host range variants. This was tested in mink and turned out to be the case. The two vaccines were fully protective and as effective as a conventional commercial vaccine based on inactivated virus. Surprisingly, this protection was obtained after only a single injection. Furthermore, the vaccinal dose of 150 micrograms of conjugated peptide or 3 micrograms of recombinant VP2 particles per animal, are sufficiently low to be cost-effective and applicable on a large scale.

Seroprevalence of Toxoplasma gondii in Danish farmed mink (Mustela vison S.)

One hundred and ninety-five mink sera randomly selected from 17 Danish mink farms were evaluated for the presence of Toxoplasma gondii antibodies in the latex agglutination test. Six (3%) sera contained T. gondii antibodies in titres of 1:64 or more. The estimated 3% prevalence means that 300,000 mink out of a total mink population of ten million might be infected with Toxoplasma gondii. This large number of possible sero-positive mink in Denmark indicates that there exists a potential risk of acquiring toxoplasmosis by pelting mink.

Acute interstitial pneumonia in mink kits inoculated with defined isolates of Aleutian mink disease parvovirus

The present study addressed the causal role of Aleutian mink disease parvovirus (ADV) in acute interstitial pneumonia in mink kits. All the examined isolates of ADV caused interstitial pneumonia in newborn kits, although the severity of disease and the mortality varied. These findings indicate that ADV is the direct causal agent of this disease in mink kits and that cofactors, which could have been present in the original ADV-K isolate, do not play a role. Acute interstitial pneumonia characterized by hypertrophy and hyperplasia of alveolar type II cells, intranuclear viral inclusions, interstitial edema, and hyaline membrane formation was experimentally reproduced in mink kits infected as newborns with five different isolates of ADV. Four hundred forty-nine newborn mink kits were included in the study, of which 247 were necropsied. The lesions caused by the different isolates were indistinguishable by histopathologic examination, but the incidence (50-100%) and severity (mortality of 30-100%, n = 218) of disease among the mink kits varied. Also, the content of ADV antigens in the lungs of infected kits varied among the groups. According to these features, the examined isolates could be placed in groups of high and low virulence. ADV-K, ADV-Utah I, and ADV-DK were in a highly virulent group producing a mortality of 90-100% (n = 110) in mink inoculated as newborns. ADV-GL and ADV-Pullman belonged to a group of low virulence, with an incidence of clinical disease of 50-70% and a mortality of approximately 30-50% (n = 118) in kits inoculated as newborns. The mortality in the control group receiving a mock inoculum was around 12% (n = 34). The period from infection to development of fatal disease varied from approximately 12 days for the highly virulent isolates up to around 20 days for the isolates of low virulence. The 107 mink kits that survived inoculation with ADV as newborns developed lesions typical of classical Aleutian disease irrespective of the ADV isolate used. The lesions consisted of chronic immune complex-mediated glomerulonephritis and infiltrations with mononuclear cells, including plasma cells in lung, liver, spleen, kidney, mesenteric lymph node, and intestine. Surviving kits also had hypertrophy of the bronchus-associated lymphoid tissue and focal subpleural, intraalveolar accumulations of large cells with foamy cytoplasm, so-called lipid pneumonia.

Production of mink enteritis parvovirus empty capsids by expression in a baculovirus vector system: a recombinant vaccine for mink enteritis parvovirus in mink

The VP-2 gene of mink enteritis parvovirus (MEV) was amplified by the polymerase chain reaction using MEV DNA isolated from the faeces of a naturally infected mink. Subsequently the VP-2 gene was cloned into a baculovirus expression vector. Recombinant baculoviruses were isolated and the MEV VP-2 gene product was characterized after expression in Sf9 insect cells. The MEV VP-2 product had the same size as that reported for the wild-type MEV VP-2 protein and was recognized by convalescent sera from MEV-infected mink and a panel of monoclonal antibodies reactive to MEV. Furthermore, the VP-2 protein was able to form parvovirus-like particles, which had haemagglutinating properties comparable with the wild-type MEV. The cloned VP-2 gene was sequenced and only five nucleotide differences were found after alignment with the known sequences of the MEV type 1 and type 2 isolates. Surprisingly, the VP-2 gene encoded a valine and a tyrosine at amino acid positions 232 and 234, identical to the situation found in MEV type 1, but at position 300 there was a valine which is a determinant of MEV type 2. Immunization of mink with approximately 40,000 haemagglutinating units of recombinant MEV VP-2 induced a measurable antibody response as tested by haemagglutination inhibition. Furthermore, the immunized mink did not excrete virus and did not develop clinical disease upon challenge with a virulent isolate of MEV.

Coronavirus infection in mink (Mustela vison). Serological evidence of infection with a coronavirus related to transmissible gastroenteritis virus and porcine epidemic diarrhea virus

Antibodies to a transmissible gastroenteritis virus (TGEV)-related coronavirus have been demonstrated in mink sera by indirect immunofluorescence, peroxidase-linked antibody assays and immunoblotting. This is the first serological evidence of a specific coronavirus infection in mink. The putative mink coronavirus (MCV) seems to be widespread in the Danish mink population with a prevalence approaching 100%. Analysis by immunoblotting has shown that MCV is closely related to TGEV by the spike (S), matrix (M) and nucleoprotein (N) polypeptides. Furthermore, antibodies to MCV also cross-reacted with N and M polypeptides of porcine epidemic diarrhea virus (PEDV). Thus MCV may occupy an intermediate position between the TGEV group of coronavirus and PEDV. The possibility that MCV may be associated with syndromes of acute enteritis in preweaning mink is discussed.

Analysis of experimental mink enteritis virus infection in mink: in situ hybridization, serology, and histopathology

Strand-specific hybridization probes were used in in situ hybridization studies to localize cells containing mink enteritis virus (MEV) virion DNA or MEV replicative-form DNA and mRNA. Following the experimental MEV infection of 3-month-old unvaccinated mink, a significant increase in serum antibodies to MEV was detected at postinfection day (PID) 6, 2 days after the onset of fecal shedding of virus. Prior to the appearance of virus in feces, viral DNA could be detected in the mesenteric lymph node and intestine. The largest percentage of cells positive for virion DNA was 10% and was detected in the intestine on PID 6. However, replication of the virus apparently peaked at PID 4. The number of MEV replicative-form DNA and mRNA molecules was found to be approximately 250,000 copies per infected lymph node cell or crypt epithelial cell. The localization, levels, and time course of viral replication have important implications for the pathogenesis of MEV-induced disease. The data presented on MEV are correlated with earlier results on the other mink parvovirus, Aleutian mink disease parvovirus, and a possible explanation for the remarkable differences in pathogenesis of disease caused by these two parvoviruses is discussed.

Passive transfer of antiviral antibodies restricts replication of Aleutian mink disease parvovirus in vivo

When mink kits were infected neonatally with a highly virulent strain of Aleutian disease virus (ADV), 100% of both Aleutian and non-Aleutian genotype mink died of interstitial pneumonia characterized by permissive ADV infection of alveolar type II cells. Treatment of infected kits with either mink anti-ADV gamma globulin or mouse monoclonal antibodies against ADV structural proteins reduced mortality by 50 to 75% and drastically reduced the severity of clinical signs. Interestingly, mink kits that survived the acute pulmonary disease all developed the chronic form of immune complex-mediated Aleutian disease. Thus, the antibodies directed against ADV structural proteins were capable of modulating the in vivo pathogenicity from an acute fulminant disease to a chronic immune complex-mediated disorder. The mechanism of this modulation was examined by strand-specific in situ hybridization. We found that the number of ADV-infected type II cells was the same in both untreated and antibody-treated kits. However, in the treated kits, viral replication and transcription were restricted at the cellular level. These data suggested that antibodies prevented acute viral pneumonia by restricting the intracellular level of viral replication and that the relevant antigenic determinants were contained within the viral structural proteins. The restricted levels of viral replication and transcription seen in antibody-treated mink kits resembled the levels observed in infected adult mink and suggested a role of antiviral antibodies in development of persistent infection and chronic immune complex disease.

Apparent lack of effect of vaccination against mink enteritis virus (MEV). A challenge study

The mink enteritis virus part of a triple vaccine was tested in mink. No raise in antibody response was measured after vaccination. Subsequent challenge of groups of vaccinated or not-vaccinated animals revealed no differences in virus excretion or antibody response in the different animals.

Reactivity of eleven anti-human leucocyte monoclonal antibodies with lymphocytes from several domestic animals

Nine commercially available monoclonal antibodies and two monoclonal antibodies from The American Type Culture Collection, raised against various human leucocyte surface antigens, were tested on lymphocytes from cow, sheep, goat, swine, horse, cat, dog, mink, and rabbit as well as man. Four antibodies bound to lymphocytes from some of the animals. These were the antibodies against CD8 and CD4 antigen, the antibody to C3b-receptor, and the antibody to the HLA-DR antigen. The CD8 antigen-reactive antibody reacted with lymphocytes from mink, cat, dog, and sheep, while the CD4 antigen-reactive antibody reacted with lymphocytes from mink. The anti-C3b-R antibody reacted with lymphocytes from horse, swine, dog, and cat, and the anti-HLA-DR reacted with lymphocytes from cow, goat, sheep, horse, dog, cat, and mink.