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Current World Situation of Classical Swine Fever and Trends in the Control and Eradication

  • Akio Fukusho
  • OIE Reference Laboratory for Classical Swine Fever
  • Department of Exotic Diseases, National Institute of Animal Health
  • 6-20-1, Josui-honcho, Kodaira-shi, Tokyo 187-0022, Japan

Classical swine fever (CSF) is a highly infectious viral disease of swine. The disease often follows an acute course characterised by generalised haemorrhages, high morbidity and mortality, but it may be chronic, in which case clinical signs and lesions are often minimal or absent. The disease has a worldwide distribution, but the following countries are free of CSF at present: USA, Canada, Australia, New Zealand, Sweden, Finland, UK and some others. The United Kingdom had 16 outbreaks in 2000 after an interval of 12 years, but it has already eradicated the disease by stamping out. Sporadic or enzootic CSF still occurs in most countries in Europe, Asia and Middle/South America. Those countries are trying to eradicate the disease but are not successful so far for reasons including national economy, institutional frameworks, wild boar, and swill.

In 2002 the OIE revised the requirements for CSF-free status as follows:

  1. It is a notifiable disease;
  2. A reliable tracing back procedure such as indelible marking;
  3. The feeding of swill is forbidden, unless the swill has been treated to destroy any CSF virus;
  4. Animal health regulations to control the movement of commodities listed in Article 2.1.13.8 have been in place for at least two years.
  5. Where a stamping-out policy without vaccination has been practised, no outbreak has been observed for at least six months;
  6. Where a stamping-out policy with vaccination has been practised, i) vaccination should have been banned for at least one year, ii) if vaccination has occurred in the last five years, a serological monitoring system should have been in place for at least six months, and iii) no outbreak has been observed for at least 12 months;
  7. Where a vaccination strategy has been adopted without a stamping-out policy, i) vaccination should have been banned for at least one year, ii) if vaccination has occurred in the last five years, a serological monitoring system should have been in place for at least six months, iii) no outbreak has been observed for at least 12 months; and
  8. CSF infection is not known to occur in the wild pig (including wild boar) population.

In Japan, the first outbreak of CSF was reported in 1888. Since then many cases have been reported. Inactivated vaccines, such as phenol/glycerol, formalin or crystal violet, have been used in the field for many years, but before 1968 it was difficult to control the disease due to the lack of potency of these inactivated vaccines. In 1969, a CSF attenuated live vaccine (GP vaccine) was developed by our Institute in Japan.

Although there are no published trials comparing GP and C strains, field evidence would suggest that the safety and efficacy of both products is similar. The GPE-strain adapted in guinea-pig kidney cell cultures was used as the seed virus of GP vaccine.

It has the following unique characteristics:

  1. It dose not show the phenomenon of exaltation of Newcastle disease virus (END phenomenon), but shows unique, intrinsic interference with heterologous viruses, such as Newcastle disease virus, western equine encephalitis virus, and vesicular stomatitis virus (E marker);
  2. The strain grows readily in guinea-pig kidney cell cultures, unlike wild-type viruses which do not (G marker);
  3. The strain propagates better at 30oC than 40oC, while wild-type viruses propagate well both temperatures (T marker);
  4. Swine inoculated with GP vaccine show no anorexia, pyrexia, or other clinical signs of CSF, and leukopenia;
  5. GPE-strain rarely produces viremia in inoculated swine. When it dose occur, it is transient;
  6. As the strain is not shed in excreta, in-contact pigs do not become infected; and
  7. Protection occurs from three days after vaccination with GP vaccine.

Since GP vaccine was applied nation-wide in the field in 1969, outbreaks of CSF have decreased markedly. No outbreak of CSF was reported between 1975 and 1978. An unexpected local epidemic occurred in 1979 and was controlled by raising the vaccination rate (to more than 80 %). No CSF epidemic has been reported for nine years since the last outbreak in 1992.

An eradication programme was started in 1996, which consists of three phases: the first phase (two years) is to immunise the pig population by vaccination (as close to 100 % as possible); the second phase (two years) is to establish a CSF-free local area without vaccination, to confirm that the area is free of field CSF viruses; and the third phase (one year) is to suspend vaccination completely and confirm that the pig population is free of CSF. Before starting the eradication programme, two national committees (a general and a technical) had been organised, together with a regional committee in each of 47 prefectures, for the investigation and control of CSF. And also the principles for each of the three phases of the national eradication policy had been drawn up

For diagnosis, the following methods were developed in Japan:

  1. END method (based on exaltation of NDV) to assay most field viruses;
  2. END neutralization test;
  3. Interference method for GPE- strain;
  4. Establishment of cell lines (FS-L3 and CPK-NS cells, which grow in serum free medium) for virus assay and neutralization test of CSF based on cytopathic effect caused by GPE- strain;
  5. Monoclonal antibodies to distinguish field strains from GPE-strain of GP vaccine; and
  6. ELISA for antibodies screening.