Diagnosis Of Classical Swine Fever Research Articles

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.

Detection of classical swine fever virus in semen of infected boars.

During the Classical Swine Fever (CSF) epidemic in 1997 in the EU member states Germany, Italy, Spain and The Netherlands, boars in an artificial insemination (AI) centre were found to be infected with CSF virus. This raised a question of epidemiological importance which could not be answered immediately. Can CSF virus be shed by semen of infected boars and what conclusions concerning the risk of spreading CSF infection by semen can be drawn. Experimental studies were conducted to answer this question. Four young boars were infected with a CSF field virus isolate from Germany, which had been characterised in a previous animal experiment. Semen was collected at least every other day after infection. The semen was subjected to the standard diagnostic procedure for the detection of CSF virus and to semen quality assessment. The boars were euthanized at day 8, 12, 16 and 21 post infection, respectively. A post mortem examination was done and organ samples were taken from the CSF reference organs and genital organs for the detection of virus and antigen. The course of CSF infection of the boars was mild but detectable during the second week of infection. CSF virus could be isolated from semen of two animals during the pyrexic phase and from the epididymis but not from the testes. Since CSF virus shedding via semen could be proven, it was concluded that the disease may also be transmitted by artificial insemination. However analysis of semen in cell culture for the presence of CSF virus is not suitable as a routine method for CSF diagnosis.

The classical swine fever epidemic 1997–1998 in the Netherlands: descriptive epidemiology

The objective of this paper is to describe the severe epidemic of classical swine fever (CSF) in The Netherlands in 1997–1998 under a policy of non-vaccination, intensive surveillance, pre-emptive slaughter and stamping out in an area which has one of the highest pig and herd densities in Europe. The primary outbreak was detected on 4 February 1997 on a mixed sow and finishing pig herd. A total of 429 outbreaks was observed during the epidemic, and approximately 700 000 pigs from these herds were slaughtered. Among these outbreaks were two artificial insemination centres, which resulted in a CSF-suspect declaration of 1680 pig herds (mainly located in the southern part of The Netherlands). The time between introduction of CSF virus (CSFV) into the country and diagnosis of CSF in the primary outbreak was estimated to be approximately 6 weeks. It is presumed that CSFV was spread from The Netherlands to Italy and Spain via shipment of infected piglets in the beginning of February 1997, before the establishment of a total stand-still of transportation. In June 1997, CSFV is presumed to be introduced into Belgium from The Netherlands. Pre-emptive slaughter of herds that had been in contact with infected herds or were located in close vicinity of infected herds, was carried out around the first two outbreaks. However, this policy was not further exercised till mid-April 1997, when pre-emptive slaughter became a standard operational procedure for the rest of the epidemic. In total, 1286 pig herds were pre-emptively slaughtered. (approximately 1.1 million pigs). A total of 44 outbreaks (10%) was detected via pre-emptive slaughter. When there were clinical signs, the observed symptoms in infected herds were mainly atypical: fever, apathy, ataxia or a combination of these signs. In 322 out of 429 outbreaks (75%), detection was bases on clinical signs observed: 32% was detected by the farmer, 25% by the veterinary practitioner, 10% of the outbreaks by tracing teams and 8% by screening teams of the veterinary authorities. In 76% of the outbreaks detected by clinical signs, the farmer reported to have seen clinical symptoms for less than 1 week before diagnosis, in 22% for 1–4 weeks before diagnosis, and in 4 herds (1%) the farmer reported to have seen clinical symptoms for more than 4 weeks before diagnosis. Transportation lorries played a major role in the transmission of CSFV before the primary outbreak was diagnosed. It is estimated that approximately 39 herds were already infected before the first measures of the eradication campaign came into force. After the first measures to stop the spread of CSFV had been implemented, the distribution of the most likely routes of transmission markedly changed. In most outbreaks, a neighbourhood infection was indicated. Basically, there were two reasons for this catastrophe. Firstly, there was the extent of the period between introduction of the virus in the region and detection of the first outbreak. As a result, CSFV had opportunities to spread from one herd to another during this period. Secondly, the measures initially taken did not prove sufficient in the swine- and herd-dense region involved.

Classical swine fever: the European experience and a guide for infected areas.

Classical swine fever (CSF) (hog cholera) virus infection is still of world-wide concern, either because of the direct effects of the disease on swine breeding in areas where the virus is epizootic or enzootic, or as a threat in areas where the virus has been eradicated. The authors provide an overview of the characteristics of the disease. Special emphasis is placed on the chronic form of disease, particularly in the late stages of eradication programmes. In the early 1980s, the European Union (EU) was composed of countries which were officially free of the disease (absence of infection and no vaccination) and countries in which vaccination was either permitted or was compulsory. To ensure free trade between the Member States, an eradication plan was agreed upon and implemented. Initially, the plan consisted of a combination of vaccination with the Chinese strain of the virus and slaughter and removal of infected herds. Consequently, when the number of infected herds was low, vaccination was abandoned and the control of CSF was conducted exclusively by eradication (removal and slaughter). The United Kingdom, Austria, Denmark, Ireland, Luxembourg, Finland and Sweden ceased vaccination before 1980. In the other countries, vaccination was useful in controlling the last epidemics and was finally ceased as follows: France in 1983, the Netherlands in 1986, Belgium, Spain and Greece in 1988, Germany in 1989 and Italy in 1990. From 1990 onwards, no vaccination against CSF has been performed in the EU. New techniques for the diagnosis of CSF (for example, the enzyme-linked immunosorbent assay based on the detection of the p125 antigen of the virus) have been shown to be of value in the early detection of infected animals. In enzootic areas, the use of vaccines based on the Chinese strain has been successful. Vaccines with at least 100 PD50 of virus per dose are able to significantly limit the replication of virulent virus in the tonsils. Consequently, shedding of virus after infection can be reduced considerably. In heavily infected areas, vaccination plays a crucial role. The European experience shows that eradication may be achieved when vaccination with highly effective vaccines is combined with effective identification of swine, movement control, early diagnosis and the rapid elimination of infected herds.

Development and standardization of an indirect ELISA for the serological diagnosis of classical swine fever

An indirect enzyme linked immunoassay (ELISA-I) was developed and standardized for the serological diagnosis of classical swine fever (CSF). For the comparison, nine hundred and thirty-seven swine serum samples were tested by serum neutralization followed by immunoperoxidase staining (NPLA), considered as the standard. Of these, 223 were positive and 714 negative for neutralizing antibodies to classical swine fever virus (CSFV). In relation to the NPLA, the ELISA-I presented a 98.2% sensitivity; 92.86% specificity, 81.11% positive predictive value, 99.4% negative predictive value and a 94.1% precision. Statistical analysis showed a very strong correlation (r=0,94) between both tests. When compared to a commercially available ELISA kit, the performance of both, in relation to the NPLA, was similar. It was concluded that the ELISA-I is suitable for large scale screening of antibodies to classical swine fever virus, although it does not distinguish antibodies to classical swine fever virus from those induced by other pestiviruses.

Serological Diagnosis of Classical Swine Fever

Antibody levels in post-infection sera from a pig inoculated with a low virulent strain of classical swine fever virus (Hannover 62) and in sera from two pigs inoculated with another low virulent strain (Spielbach 66) and from an in-contact pig were assayed by complement fixation and immunofluorescence using classical swine fever virus (ALD strain) and bovine virus diarrhoea virus (UG 59 strain) as antigens. The complement fixation test used was modified by addition of a preparation of porcine Glq to the complement and by mercaptoethanol treatment of the immune serum before use. The mercaptoethanol treatment of the immune serum resulted in complete elimination of a haemolytic prozone often seen with porcine immune sera. In the sera from the inoculated animals complement-fixing antibodies appeared earlier than neutralizing antibodies. A few weeks after inoculation there was a correlation between the presence of complement-fixing and neutralizing antibodies. During the entire observation period of 13 weeks it was not possible to demonstrate complement-fixing or neutralizing antibodies in serum from a pig exposed to infection by contact with the two pigs inoculated with the Spièlbach 66 strain of classical swine fever virus.