The National Institute of Animal Health, NARO (NIAH) performed experimental infection with classical swine fever virus (JPN/1/2018 strain) which was isolated from Gifu prefecture, Japan for the first time in 26 years. It was revealed that JPN/1/2018 strain causes high fever and leukopenia in pigs, this strain is less pathogenic than the highly pathogenic strain. Moreover, it was also found that it spreads to the cohabiting pigs. Virus was detected from blood, saliva, fecal and nasal discharge of infected pigs at least for 2 weeks. And the antibody was detected 2 weeks later after the co-rearing or virus inoculation.
NIAH isolated a causative virus of classical swine fever occurred in Gifu Prefecture in September 2018. For comparing the pathogenicity of isolated virus strain with typical type strain, the experimental infection of pigs was performed with 2 virus strains. The one is isolated strain in Gifu prefecture (JPN/1/2018 strain), the other one is already known highly pathogenic strain (ALD strain).
Due to the experimental infection with the intramuscular inoculation of ALD strain, infected pigs developed diarrhea, neurological symptoms, lie down on the floor and were dying in 5 days. On the other hand, pigs inoculated with JPN/1/2018 strain could survive for 15 days (the period of this study).
However, both the pigs which are inoculated intramuscularly by ALD strain and pigs inoculated by JPN/1/2018 strain developed high fever above 40°C and leukopenia (< 10 000 cells / μL). Likewise, high fever (above 40°C) and leukopenia (< 10,000 cells / μL) were observed in orally inoculated pigs with JPN/1/2018 strain, and the infected pigs could survive until 14 days (the period of this study) after the inoculation.The pigs which was co-reared with JPN/1/2018 strain inoculated pigs developed high fever above 40°C and leukopenia (< 10,000 cells / μL). In addition, JPN/1/2018 strain virus gene was detected for at least 2 weeks after infection from saliva, nasal discharge and feces from inoculated and cohabiting pigs. And the antibody was detected 2 weeks later after virus inoculation or cohabiting.
This study confirmed that the JPN/1/2018 strain causes clinical symptoms in infected pigs, but its pathogenicity is lower than that of the already known highly pathogenic virus strain.
The results of this study will be provided to the Ministry of Agriculture, Forestry and Fisheries(MAFF) and other organizations for epidemiological analysis. This result will be also used as a basic data for establishment of preventing protocols.
Experimentally infected pigs developed high fever and lie down on the floor.