Knox: An update on African swine fever

By Robert V. Knox

The outbreaks of African swine fever have had a devastating impact on large populations of pigs, pork and export markets from China and its neighboring countries. The disease is not infectious to other species or humans, but it is highly contagious and lethal among pigs.

ASF is caused by a large DNA virus with multiple protein variants and a tough outer envelope. These attributes allow it to be resistant to harsh conditions such as freezing temperatures and chemical disinfectants and limits the effectiveness of most vaccines.

The virus can survive for months in frozen meat or carcasses and weeks in the blood and feces from infected pigs. Because of this, the virus can spread easily when materials from infected pigs are carelessly leaked during transport or when consumed by other pigs.

However, humans, pigs, scavengers and parasites have all played an important role in its spread. Much of the rapid spread in and around China during the past 18 months occurred due to a combination of failures in reporting, containment, the high number and density of pig farms, lack of information to the public and improper disposal of sick and dead animals.

In countries free of the disease, such as the United States, attention has been focused on tracking global outbreaks, industry education, border biosecurity, risk assessment and disaster preparedness.

ASF is not a new disease and is endemic to parts of Africa where the virus resides in African wild pigs — warthog and bush pig — that show no symptoms. Years ago, the ASF virus moved into Europe following the importation of infected domestic pigs and pork from Africa.

In parts of Europe, the virus spread quickly into the wild boar population where it killed many and created carriers. The ASF disease became endemic to several areas in Europe and continues to pose serious threats to both large and small pig farms.

Many farms with close proximity to wild pigs are at the highest risk, as they lack the resources to implement necessary biosecurity. Further, the spread of ASF from the wild pigs is facilitated by hunting, scavengers, including the wild boars themselves.

As might be suspected, the only way to eliminate the disease in the wild and domestic pig populations is through complete depopulation and proper carcass disposal. The 2018 outbreak in China is thought to have originated from the migration of infected wild pigs from Russia.

From a U.S. perspective, if virus introduction occurred, commercial and feral pigs would be susceptible and high mortality expected. From the time of introduction of the virus, there would be a seven-day incubation period, with symptoms of high fever, loss of appetite, incoordination, skin lesions and death occurring in the following seven to 10 days.

Government and industry organizations recognize the greatest risk for entry of ASF into the U.S. swine industry, would come from foreign pigs and contaminated products. As such, the focus is on major transportation sites such as airports, borders and shipping ports.

Numerous seizures of illegal pork products have been discovered by U.S. customs in the past year and include mailed packages, airline luggage and large shipping containers.

During this time, cooperative development of disease surveillance and preparedness programs have been underway. The program includes enhancing prevention, but also addresses surveillance, rapid detection and reporting systems.

In the case of a potential or confirmed outbreak on a farm, plans for tracing, containment, depopulation, disposal and disease clearance are included.

The program also recognizes the importance of involving numerous other national, state and local entities with experience in emergency preparedness.

Training exercises for outbreak scenarios have been run and are helping to develop resources and identify areas of strengths and weaknesses. The proactive approach that has been supported by a unified industry is an important and necessary step for protecting and preserving the future of our swine industry and pork supply.

Robert V. Knox is a University of Illinois Extension swine specialist.