After a 3-month absence, first cases of classical swine fever (CSF) have been confirmed on 2 farms in different regions of Japan.
At the end of December 2020, Japan recorded its first cases of classical swine fever (CSF) in domestic pigs for more than three months. Within days, a second outbreak was confirmed in another part of the country.
According to Nippon.com, the agriculture ministry reported that the CSF virus had been detected at a farm in Yamagata prefecture. This was the first outbreak among Japan’s domestic pig population since the end of September. Furthermore – affecting a farm in Tsuruoka — these were the first cases in the region of Tohuko.
Among the 1,327 pigs at the premises, a number were showing signs of fever, and 20 died, according to the official report to the World Organisation for Animal Health (OIE).
Three days later, CSF virus was found at a farm with 6,600 pigs in Mie prefecture. Here too, the agriculture ministry informed the OIE that 20 pigs had died. This outbreak — in the Iga city region — was the first in the prefecture since July 2019, according to Nippon.com.
The latest cases bring to 61 the number of Japanese farms where CSF outbreaks have occurred.
Developments in CSF control in Japan
When CSF is suspected at a farm, movement restrictions are imposed in the area within 10 kilometers of the outbreak. If no virus-positive results are found by surveillance in the 3-to-10-kilometer radius, these restrictions are lifted 17 days after stamping out and disinfection of the outbreak farm. For the area within 3 kilometers of the confirmed outbreak, restrictions are not lifted until 28 days of the same conditions.
After the latest outbreaks, tests on the genetic makeup of CSF viruses by the National Institute for Animal Health in Japan revealed the virus isolated from both farms was a wild type. This indicates that the animals were infected in some way from the environment.
According to the OIE report, Japan amended national livestock disease control guidelines in October 2019 to allow vaccination of domestic pigs against CSF in selected prefectures. Among these 27 regions were Mie and Yamagata. Akire prefecture has now been added to this list.
As well as domestic pigs, CSF has spread widely across the main island of Honshu among the wild boar population. Most recently, the Japanese agriculture ministry reported to the OIE 72 confirmed CSF cases in wild boar. Found in 16 different prefectures, the infected animals were found during the last week of November 2020.
In early 2019, a program to vaccinate wild boar against CSF was rolled out.
2018: CSF returned to Japan
First cases of CSF were identified in Japan in September 2018. Of the 610 pigs at a farm in the central prefecture of Gifu, 29 animals died. As the symptoms are similar, African swine fever was initially suspected. However, subsequent investigations identified the infection as CSF. Source of the original infection remains unknown. Japan had been free of this disease since 1992.
In September 2020, Japan lost its status as free of CSF from the OIE. This change followed a two-year suspension of status by the OIE, during which the disease was not brought under control. To regain its previous disease-free status, vaccination must cease, followed by a period of 12 months without any CSF cases.
Some of Japan’s previous export markets banned imports after CSF was first detected. This trade is unlikely to return until the country’s CSF-free status is restored.
CSF is a highly contagious disease, affecting only members of the pig family, according to the OIE. Depending on the viral strain, it causes varying levels of morbidity and mortality. The disease is endemic in much of Asia, Central and South America, and some Caribbean countries. While the symptoms are similar to African swine fever, CSF is caused by an unrelated virus. Neither infection affects people.