Epidemiological aspects of the infectious biology of classical swine fever

In order to obtain reliable data on the influence of viral and host factors on the course of classical swine fever (CSF), comprehensive animal experiments were conducted with the CSF field isolates Diepholz 1/Han94 and Visbek/Han95. The viruses were isolated during the recent epidemic of CSF in Lower Saxony/Germany. All known and described clinical pictures of the postnatal CSF virus infection (acut-letal, acut-transient, chronic) could be induced with both viruses. The incubation period was about one week (5 to 9 days) in all pigs, irrespective of the clinical course. Four out of 40 weaner pigs developed the chronic form of CSF. The ''typical'' CSF symptoms noticed in pigs with the acute-lethal form of CSF were not present in the chronically infected pigs. However, CSF virus could be isolated regularely out of the blood of the chronically sick pigs, even during periods when they had no fever. The different courses of the disease were seen in intranasally inoculated pigs as well as in pigs which were infected by contact with diseased animals. The virus dose had no effect on the course of the disease. The clinical picture mainly depended on the age and the genetic characteristics of the pigs. It was concluded that the changing clinical picture of CSF observed during the recent epizootic in Germany was mainy related to host factors and less to the virulence of CSF virus.