This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
- Infected pigs can be asymptomatic carriers of African swine fever virus (ASFv)
- Timely detection with diagnostic testing, strict biosecurity measures and rapid removal of the source of infection are key to limit the transmission of the virus within and between sites.
In December 2014, ASFv was detected in a finishing site of a multiplier herd from a large commercial pig company located in the Russian Federation. The region had multiple reports of ASFv in backyard pigs before the outbreak. The affected company consisted of 80,000 sows in 15 farms organized as a three-site production system with each sow farm having a dedicated nursery and two finishers. The multiplier herd supplied gilts from the finisher to the gilt development unit (GDUs) for each farm. Each sow farm had a quarantine within the farm to receive the gilts from the GDU .
A 3% mortality increase was reported in one room of the finishing site. A few pens in one of the rooms had pigs affected with fever, purple ear and mild scouring. The site was being monitored for ASFv on a weekly basis before gilt shipment, following local regulations and results always came back negative.
Samples collected from the affected pigs were negative for ASFv, Classical Swine Fever, PRRSv, and Salmonella so the decision was made to resume shipment of gilts from a room with no clinical signs to the GDU.
As the days progressed, the clinical signs in the affected room worsened and affected more pens. The GDU that had just received gilts reported similar clinical signs and diagnostics on samples collected then from the multiplier finisher and the GDU confirmed the presence of ASFv at both sites.
At that time, all pig movements were stopped and a 5km quarantine area was imposed around the two affected sites. Gilts that had been sent from the GDU to five commercial sow farms, and were in quarantine tested negative to ASFv. Nevertheless as a precaution, the decision was taken to sacrifice all the gilts in the quarantines.
Protocols mandated by the government were implemented in the ASFv positive multiplier finisher and GDU which consisted of euthanasia of all pigs within a 5km radius, destruction with burial and burning of all carcasses, strict movement restrictions for vehicles and people and exhaustive disinfection protocols inside the farm and its territory.
Transportation of infected non-symptomatic animals from the multiplier finisher was the most likely route of infection to the GDU. The source of infection to the multiplier finisher is unknown, although people are thought to have played a role given the presence of ASFv in backyard farms in the area. Events such as introduction of infected pork meat, lack of proper disinfection of 3rd party trucks or non-compliance with the shower-in policy of the farm could not be ruled out. The outbreak occurred in December when temperatures were below zero Celsius and wild pig-tick-domestic pig interaction was unlikely.
It is important to point out that 12 of the 16 rooms in the multiplier finisher remained negative to ASFv until the moment of euthanasia. The sow farm and nursery multiplier were monitored for ASFv during the quarantine period and until the moment of euthanasia 6 months later. During this time, they remained negative to ASFv, even though they were within close proximity to the affected farm. Our experience indicates that a timely detection of ASFv with testing, strict biosecurity measures and removal of the source of infection as soon as possible can limit the transmission of the virus between sites.