Classical swine fever.

Classical swine fever is a serious and economically important transboundary disease threatening pig production globally. The infection may occur in backyard pigs, feral pig populations and domestic pigs. Whereas there are proven control strategies for the latter pig population, control in backyard pigs with poor biosecurity settings or in wild boar populations of high density still poses a problem in some parts of the world. Laboratory diagnostic methods, efficacious vaccines and contingency plans are in place in most industrialised countries. So far modified live vaccines (MLV) are still the first choice for rapid and reliable immune protection. Since antibodies elicited by conventional MLV cannot be distinguished from antibodies after natural infection, considerable efforts are put into the development of a live marker vaccine accompanied by a serological test. Nevertheless, some remaining gaps with respect to the diagnosis of and vaccination against classical swine fever have been identified.

Virulence of classical swine fever virus isolates from Europe and other areas during 1996 until 2007.

Classical Swine Fever (CSF) has caused several outbreaks in EU Member States with grave economic consequences. Several times the diagnosis of CSF was made too late partially due to non-specific clinical signs which did not raise suspicion for CSF. Virulence of CSF virus isolates (CSFV) still remains a subject of discussion and speculation as sufficient knowledge is still not available. Six uncharacterised CSFV isolates from 1996 to 2007 were assessed in animal experiments for their clinical virulence in order to broaden the knowledge about circulating CSFV and thereby assist disease eradication. A clinical (CS) and pathological score was applied and further extended by additional parameters to a modified CS (mCS) including case fatality, antibody production and leukocyte count. The unknown CSFV isolates could be classified as moderately or highly virulent. The inclusion of additional parameters, especially case fatality, into the mCS gave a more reliable classification of virulence, proving that there are clinical signs and laboratory parameters of blood which can be recognised. Therefore a subclinical course of infection is unlikely, especially in weaner pigs.

Assessment of international inter-laboratory comparison tests for the diagnosis of classical swine fever from 1998 until 2007.

The inter-laboratory comparison tests for classical swine fever (CSF) laboratory diagnosis organised by the European Community Reference Laboratory for CSF are regularly performed within European Union Member States. The objective of this study was to evaluate the results of the inter-laboratory comparison tests carried out over the last decade, from 1998 until 2007, by using a statistical approach. A set of five or six lyophilised sera was sent to participants. These included sera containing CSF antibodies, sera containing antibodies against ruminant pestiviruses, sera containing CSF virus and negative sera. This study focused on the results of the diagnostic reference methods for CSF: the neutralisation test for the detection of CSF antibodies (including its interpretation) and virus isolation for the detection of CSF virus. For the detection of CSF antibodies, results were closest to what was expected by the Community Reference Laboratory when only neutralisation tests were performed. The percentage of correct results decreased as soon as the results of CSF antibody enzyme-linked immunosorbent assay were included or when sera with antibodies to ruminant pestiviruses were added to the panel. The results for the detection of CSF antibodies are still valid today, as no additional method has been introduced recently. Regarding CSF virus detection, CSF virus isolation is well established but on the way to being superseded as the reference test by reverse-transcription polymerase chain reaction.

Test strategies in bovine viral diarrhea virus control and eradication campaigns in Europe.

Several European countries have initiated national and regional control-and-eradication campaigns for bovine viral diarrhea virus (BVDV). Most of these campaigns do not involve the use of vaccines; in Germany, vaccination is used only in states in which it is considered necessary because of high BVDV prevalence. In European countries without organized BVDV control programs, vaccination is commonly used to control BVDV. Diagnostic test strategies are fundamental to all control-and-eradication campaigns; therefore, the purpose of this review is to describe how the available diagnostic tests are combined into test strategies in the various phases of control-and-eradication campaigns in Europe. Laboratory techniques are available for BVDV diagnosis at the individual animal level and at the herd level. These are strategically used to achieve 3 main objectives: 1) initial tests to classify herd status, 2) follow-up tests to identify individual BVDV-infected animals in infected herds, and 3) continued monitoring to confirm BVDV-free status. For each objective or phase, the validity of the diagnostic tests depends on the mode of BVDV introduction and duration of infection in test-positive herds, and on how long noninfected herds have been clear of BVDV. Therefore, the various herd-level diagnostic tools--such as antibody detection in bulk milk or in blood samples from young stock animals, or BVDV detection in bulk milk--need to be combined appropriately to obtain effective strategies at low cost. If the individual diagnostic tests are used with due consideration of the objectives of a specific phase of a BVDV control program, they are effective tools for controlling and eradicating BVDV in regions not using vaccination and where vaccination is a part of the control or eradication program.

[80 years of the Society of Friends of the University of Veterinary Medicine Hannover]. / 80 Jahre Gesellschaft der Freunde der Tierärztlichen, Hochschule Hannover e. V. (GdF).

The Society of Friends of the University of Veterinary Medicine Hannover was established in 1926, in times of severe economical distress. According to its statutes its main purpose from the beginning was to complement the governmental budget of the University. During its 80 years of existence the so called "Friendly Society" has contributed to overcome many financial shortages in research, clinics and institutes. In addition it supported veterinary students in need. Some aspects of the Society's history and activities will be communicated.

The control of bovine viral diarrhoea virus in Europe: today and in the future.

This paper summarises the views of a European group of scientists involved in the control of bovine viral diarrhoea virus (BVDV), as part of a European Union Thematic Network. The group concludes that the technical tools and the knowledge needed to eradicate BVDV are at hand, as proven by successful national control schemes in several European countries. A generic model for BVDV control is presented, which includes biosecurity, elimination of persistently infected animals and surveillance as central elements. These elements are termed 'systematic', in contrast to control efforts without clear goals and surveillance to evaluate progress. The network concludes that a systematic approach is needed to reach a sustainable reduction in the incidence and prevalence of BVDV in Europe. The role of vaccines in systematic control programmes is considered as an additional biosecurity measure, the effect of which should be evaluated against cost, safety and efficacy. It is also concluded that active participation by farmers' organisations is a strong facilitator in the process that leads up to the initiation of control, and that public funding to support the initiation of organised BVD control programmes can be justified on the basis of expected wider societal benefits, such as animal welfare and reduction in the use of antibiotics. If applied successfully, the focus on biosecurity in systematic BVD control programmes would also reduce the risk of the introduction and spread of other epizootic and zoonotic agents, thereby improving both cattle health and welfare in general, as well as increasing the competitiveness of the cattle industry.

Assessment of classical swine fever diagnostics and vaccine performance.

Rapid and accurate diagnosis is of the utmost importance in the control of epizootic diseases such as classical swine fever (CSF), and efficacious vaccination can be used as a supporting tool. While most of the recently developed CSF vaccines and diagnostic kits are mostly validated according to World Organisation for Animal Health (OIE) standards, not all of the well-established traditional vaccines and diagnostic tests were subject to these validation procedures and requirements. In this report, data were compiled on performance and validation of CSF diagnostic tests and vaccines. In addition, current strategies for differentiating infected from vaccinated animals are reviewed, as is information on the control of CSF in wildlife. Evaluation data on diagnostic tests were kindly provided by National Reference Laboratories for CSF in various European countries.

Implementation of two-step vaccination in the control of bovine viral diarrhoea (BVD).

Bovine viral diarrhoea (BVD) control/eradication programmes based on the test and removal of persistently infected cattle without use of vaccination were first introduced by the Scandinavian countries in the early 1990s. Within the last 10 years the programmes have proven to be very successful and have served as a blueprint for several other European regions. However, in areas with high cattle densities, intense animal trade and high BVD prevalence this control approach is risky, because there is a high probability that herds, which have been cleared of persistently infected (PI) animals and have become partly or fully susceptible to reintroduction of the virus, will come in contact with a BVD virus (BVDV) infected animal. A combination of the test and removal strategy with subsequent systematic vaccination of cattle could overcome this problem. The goals of vaccination in such a programme is protection against reintroduction of BVDV into herds free from PI cattle and foetal protection of pregnant animals accidentally exposed to the virus. Two-step vaccination is based on the use of inactivated BVDV-1 vaccine for priming followed by a live attenuated vaccine booster 4 weeks later. The immune response elicited by such a vaccination scheme has proven to be long lasting and foetal infection after challenge with BVDV-1 and BVDV-2 was prevented in pregnant animals 5 months after vaccination. These findings suggest that the implementation of a two-step vaccination in the initial phase of control programmes in addition to test and removal of PI animals in areas with high cattle densities and endemic BVD is practical and efficacious.

Eradication versus vaccination strategies to control infectious diseases--some lessons to be learned from terrestrial animals.

In the pre-vaccine era, highly contagious and dangerous animal virus diseases had enormous socio-economic impacts on societies, and the only way of control was a vigorous stamping-out strategy. Diseases that were difficult to diagnose on clinical grounds could not be contained and often became endemic. Considerable progress in the control of viral infections of farm animals was made when their viral aetiology became known and means for the propagation of the infectious agents, first in animals and later in cell culture, were developed. This led to the development of several generations of vaccines that were applied with increasing success in the control of infectious diseases. Inactivated as well as live attenuated vaccines were successfully used, as shown in the control of classical swine fever and foot-and-mouth disease. Recently both inactivated and live "marker" vaccines have been added or will be added to the repertoire of tools for the control and eradication of infectious diseases. Attempts to eradicate endemic Aujeszky's disease from pig populations are greatly facilitated by the systematic use of deletion marker vaccines. Currently the use of marker vaccines for emergency use to contain outbreaks of classical swine fever and foot-and-mouth disease is under discussion between stakeholders and legislators.

Quality management in reference tests for the diagnosis of classical swine fever.

Inter-laboratory comparison tests for the diagnosis of classical swine fever (CSF) have been established by the national swine fever laboratories of European Union (EU) Member States. They provide a method of measuring both the quality of the results of diagnostic tests performed by laboratories and the competence with which they were performed. The objective is that all laboratories obtain the same result when investigating the same sample. This study evaluates the results of serological and virological reference tests for CSF (neutralisation test and virus isolation) performed over a period of three years. The sensitivity of the serological diagnosis for the detection of CSF antibodies was very good and revealed a tolerance limit of the scored antibody titres of one dilution step. Results on the same sample in two consecutive years were similar. The variation of the scored antibody titres was larger when testing sera with a low CSF antibody titre. The interpretation of the antibody titres as 'CSF positive or negative' was only slightly altered by these variations. The backtitration of a neutralisation test (used as a control measure) is a more mathematical value which does not correlate directly with the biological system. Commercial CSF antibody enzyme-linked immunosorbent assays still display a lower sensitivity on individual samples compared to the reference neutralisation test. Classical swine fever virus isolation was well established in all participating laboratories and caused very few problems. Specificity of CSF diagnosis by investigating CSF antibody and CSF virus negative sera was not problematic either. In general, the reference tests for CSF diagnosis are well established in the EU. They are based on living systems, e.g. cells and virus, and consequently they have a different tolerance limit than pure mathematical values. What is important is that the interpretation of the test result is identical in all laboratories.

Virulence of recent and former classical swine fever virus isolates evaluated by their clinical and pathological signs.

The clinical diagnosis of classical swine fever (CSF) still caused problems to the veterinarians during the last decade. The primary CSF outbreak was often detected too late and, meanwhile, the virus had spread. Consequently, the recent classical swine fever virus isolates (CSFV) were suspected to be of low virulence. The purpose of the study was to quantify the virulence of four recent CSFV by evaluating the clinical and pathological signs caused by different CSFV. Pigs of the same breed and age group were inoculated intranasally with CSFV from recent epidemics in European Union (EU) member states. The CSFV used are registered in the data base of the EU Reference Laboratory for CSF and belong to different genotypes: 2.1, 2.2 and 2.3 respectively. Clinical signs of CSF were evaluated by using a score system suggested previously (Mittelholzer et al., 2000: Vet. Microbiol. 74, 293). For the evaluation of pathological lesions, a new pathological score was introduced. The four CSFV tested here were classified as moderately virulent in general, although one CSFV may cause different clinical courses, ranging from highly virulent to avirulent. This indicates the importance of additional factors in the host animal for virulence. Differences in the clinical and pathological signs between these four recent CSFV were rather minor, emphasizing that the genetic typing of CSFV is absolutely essential. Differences towards former CSFV (e.g. reference virus strain Alfort 187) were more pronounced, especially regarding the onset and duration of the disease, the occurrence of skin haemorrhages and pathological lesions of kidney, subcutis and serosae. It is concluded that clinical diagnosis of CSF is rather difficult in pigs up to 14 days post-CSFV infection using these four CSFV, emphasizing the need for careful differential diagnosis and the laboratory investigation for CSF at an early stage.

Clinical signs and epidemiology of classical swine fever: a review of new knowledge.

Although classical swine fever (CSF) has been well known for decades and epidemics still occur, clinical diagnosis continues to cause problems for veterinary practitioners. This is due to the extensive differential diagnosis, further complicated by the emergence of new diseases such as porcine reproductive and respiratory syndrome (PRRS) and porcine dermatitis and nephropathy syndrome (PDNS). In addition, acute, chronic and prenatal courses of CSF have to be distinguished. As a cause of considerable economical losses within the EU, control of CSF requires knowledge of the primary outbreaks and spread of the disease. Genetic typing of CSF virus isolates has proved to be a potent method of supporting epidemiological investigations. Phylogenetic analysis of CSF virus strains and isolates originating from different continents has allowed three genetic groups and several subgroups within these groups to be distinguished. Whereas isolates belonging to group 3 seem to occur solely in Asia, all CSF virus isolates of the 1990s isolated in the EU belonged to one of the subgroups within group 2 (2.1, 2.2, or 2.3) and were clearly distinct from former CSF reference viruses, which belong to group 1. Within the EU, different strategies are followed for the eradication of CSF in domestic pigs and in wild boar. While a strict non-vaccination policy is followed for domestic pigs, eradication of the disease in wild boar is more complex, and oral immunisation together with special hunting strategies have been applied. Recently, marker vaccines with a companion discriminatory test designed to allow differentiation between vaccinated animals and animals having recovered from field virus infection have been developed. Preliminary studies indicated that the discriminatory tests had a reduced sensitivity and specificity. Further improvements are therefore necessary before marker vaccines can be considered for emergency use in EU Member States. Prevention of CSF remains the main objective within the EU.

[Kinetics and persistence of neutralizing antibodies against bovine viral diarrhea virus-1 and -2 and border disease virus after two step vaccination of cattle]. / Kinetik und Persistenz neutralisierender Antikörper gegen das Bovine Virusdiarrhoe Virus-1 und 2 und das Border Disease Virus nach zweistufiger Impfung von Rindern.

The aim of the study was the assessment of rise and persistence of neutralizing antibodies (nAb) to bovine viral diarrhea virus (BVDV) and border disease virus (BDV) after a two step vaccination using an inactivated BVDV/BDV (Mucobovin) and a modified live BVDV vaccine (Vacoviron). In a first experiment eight heifers were kept in isolation and were serologically surveyed regularly over a three year period after vaccination. The same experiment was done with 80 vaccinated cattle kept under field conditions. Neutralizing antibody titres were monitored using homologous as well as heterologous BVDV and one BDV strain, respectively. Maximum titres were obtained two to three months after vaccination. During the three years of monitoring the antibody titres decreased but never fell below the detection limit. This slow antibody regression demonstrates that a single two step vaccination elicited high nAb titres which persist over at least three years. These results might serve as a decision tool when considering the necessity and time of revaccination of cattle, which have been vaccinated using the two step method.

Foetal protection against bovine virus diarrhoea virus after two-step vaccination.

In order to assess the efficacy of a two-step vaccination protocol with respect to foetal protection against transplacental infections with bovine virus diarrhoea virus (BVDV) with special attention to BVDV-2 seronegative heifers were vaccinated with an inactivated BVDV-1 vaccine and boostered with a modified live BVDV-1 vaccine after 4 weeks. A second group was left unvaccinated as control. Between days 30 and 120 of pregnancy the heifers of both groups were intranasally challenged with a mixture of BVDV-1 and -2. All heifers of the vaccinated group gave birth to nine clinically healthy, seronegative (precolostral) and BVDV-free calves. In contrast in the control group four BVDV viraemic underdeveloped calves were born. Additionally, one calf was stillborn and another viraemic calf was not viable and died 2 days after birth. All six calves of the control group were viraemic with BVDV-2. This study demonstrated for the first time that two-step vaccination of breeding cattle with a modified live BVDV vaccine 4 weeks after application of an inactivated BVDV vaccine was capable of providing a foetal protection against transplacental infection with BVDV-2.

Are low-density granulocytes the major target cells of classical swine fever virus in the peripheral blood?

The target cells of classical swine fever (CSF) virus in the peripheral blood of pigs infected with recent field isolates from Germany were studied. Eight weaned pigs were inoculated oronasally with the CSF virus field isolate Visbek/Han 95 and three weaners were inoculated with the isolate Losten/Freese 98. All pigs showed severe clinical signs typical of CSF and died or had to be euthanized between 9 and 24 days post-infection (dpi). The first cells in the peripheral blood which became infected with CSF virus were mixed granulocytes (a combination of low- and high-density granulocytes). These cells yielded the highest infectivity for PK 15 cell cultures. On day 7 post-infection, the peripheral blood mononuclear cell (PBMC) fraction was virus positive, while the peripheral blood leucocyte (PBL), peripheral blood T lymphocyte (PBT) and high-density granulocyte fractions were either negative or their infectivity was lower than the infectivity of the PBMC fraction. These results indicate that PBMC contain more virus-positive cells than other fractions of leucocytes. These findings may also have diagnostic implications for the detection of CSF virus in blood samples. Because PBMC showed the highest infectivity in the early stages of CSF, it should be the sample of choice for CSF virus isolation.

[Genetic typing of German isolates of classical swine fever virus]. / Genetische Typisierung von deutschen Isolaten des Virus der Klassischen Schweinepest.

During the last decade several outbreaks of classical swine fever (CSF) occurred in Germany in domestic pigs and in wild boar, respectively. Two major epidemics which also affected other EU Member States were recorded. To support epidemiological investigations genetic typing was applied and virus isolates originating from different outbreaks in Germany were assigned to groups and virus types. Two genomic regions were selected for the phylogenetic analysis, namely 150 nucleotides from the 5' non-translated region (5'-NTR) and 190 nucleotides from the E2 glycoprotein gene. All German CSF virus isolates of the nineties (Group 2) were distinct from former reference strains (Group 1). Within Group 2 both genomic regions allowed to distinguish three subgroups, namely 2.1, 2.2 and 2.3. Within subgroup 2.3 five virus types could be discriminated using the 5'-NTR sequences. These are 2.3*Uelzen and 2.3*Spreda, mainly with isolates from Lower Saxony, as well as 2.3*Rostock, 2.3*Güstrow and 2.3*Spante, mainly with isolates from Eastern Germany. Analysis of the E2 gene fragment allowed a better discrimination between single isolates, but only two virus types could be defined: 2.3*MV/BB, comprising the isolates from Eastern Germany, and 2.3*NI, with the isolates from Lower Saxony. Genetic typing allowed to discriminate between isolates involved in different CSF epidemics, and was useful for tracing the origin and spread of CSF viruses. Due to the close relationship between German CSF virus isolates, epidemiological data are a prerequisite for the interpretation of the results obtained by genetic typing. In addition, at least both genomic regions suggested here should be analysed to determine the identity of a new isolate.

[Differential diagnosis of classical swine fever and border disease: seroepidemiological investigation of a pestivirus infection on a mixed sheep and swine farm]. / Zur Differentialdiagnostik Klassische Schweinepest/Border Disease: Seroepidemiologische Untersuchung einer Pestivirusinfektion auf einem schaf- und schweinehaltenden Betrieb.

During recent years neutralizing antibodies against Border Disease Virus (BDV) were found repeatedly in German pig herds. Consequently there was a demand for a differential diagnostic system. A permanent sheep cell line and BDV reference strain Moredun were chosen and were applied in a could be used case study. A pestivirus could be isolated from piglets on a mixed farm and was characterised as 'non-Classical Swine Fever' (CSF) by using monoclonal antibodies. Due to a CSF suspicion the pig herd was destroyed immediately. Serum samples of sheep from the same farm were used for further characterisation of the new virus isolate. A neutralization test of the sheep sera was performed against different pestiviruses and the new isolate. Neutralizing antibody titres against the new virus pig isolate were significantly higher than against all other pestiviruses. BDV strain Moredun recognised the antibodies clearly, whereas CSF viral strain Alfort 187 and several isolates of bovine viral diarrhoea virus (BVDV) strains scored the lowest cross reaction.

Prevalence of genotypes 1 and 2 of bovine viral diarrhea virus in Lower Saxony, Germany.

The aim of this study was to find whether an antigenic drift had occurred in Lower Saxony in the past 40 years. For this, the genetic diversity of bovine viral diarrhea virus (BVDV) isolates mainly from Lower Saxony was estimated by RT-PCR and sequencing of a 420 bp fragment of the E2 glycoprotein gene. Sixty-one field virus isolates collected during routine diagnostics between 1960 and 2000 in Lower Saxony, Northern Germany, were analyzed. Phylogenetic analysis allowed discrimination of genotypes BVDV 1 and 2. Excepting two isolates, which were of BVDV type 2, most of the isolates were classified as BVDV type 1. This group could be further subdivided into four subgroups and one disparate isolate. Independent of the year of isolation and geographical localization, 54 isolates clustered in two subtypes (BVDV subtypes 1b and 1d). Only one isolate was classified as BVDV type 1a, thus being similar to the North American NADL strain, and to the vaccine strain Oregon C24V, which was extensively used for vaccination in Germany. The remaining isolates belonged to new clusters tentatively designated as BVDV subtypes 1g and 1f. To compare the cluster designation with that of other studies, phylogenetic analysis of representatives of each of the subgroups based on the 5' untranslated region (5'UTR) was performed. It grouped the viruses similarly. The results indicate that the BVDV population seems to be relatively stable over 40 years in Lower Saxony.

Epidemiology of classical swine fever in Germany in the 1990s.

In Germany, 424 outbreaks of CSF in domestic pigs and a great number of cases in wild boar were recorded between 1990 and 1998. Most of the federal states ('Bundesländer') were affected. Epidemiological data from field investigations combined with genetic typing allowed to distinguish seven unrelated epidemics and a number of sporadic outbreaks in domestic pigs. Detailed epidemiological data was available for 327 outbreaks. It was found that 28% of these were primary outbreaks. Most of them were due to indirect or direct contact to wild boar infected with CSF virus or swill feeding. Infected wild boar remain the main risk for domestic pigs. The most frequent sources of infection in secondary or follow up outbreaks were the trade with infected pigs, neighbourhood contacts to infected farms and other contacts via contaminated persons and vehicles, respectively. An increased risk of virus transmission from infected herds to neighbourhood farms was observed up to a radius of approximately 500m. More than two thirds of the infected herds were discovered due to clinical signs. About 20% were identified by epidemiological tracing on and back. These were scrutinised because contacts to infected herds were evident. In conclusion, tracing of contact herds and clinical examination combined with carefully targeted virological testing of suspicious animals is likely to be the most important measure to immediately uncover secondary outbreaks. Obligatory serological screening in the surveillance and the restriction zones do not seem to be efficient measures to detect follow-up outbreaks.