USDA continues monitoring for African swine fever as it persists globally

African swine fever (ASF) has not entered the U.S. thanks to continuing efforts to prevent this deadly swine disease from reaching the country’s borders. However, ASF continues to affect swine herds globally, entering five new European countries in 2023, according to a report from the Association of Pig Farmers in Germany (ISN).

Countries have been forced to slaughter herds, ban imports on pig products, and implement greater biosecurity measures on farms. Researchers are also working on developing vaccines.

The World Organisation for Animal Health (WOAH, formerly OIE) reports that in the past three years, ASF has been identified in five different regions in 52 countries. It’s currently widespread and endemic in sub-Saharan and parts of western Africa, and has spread through Europe, the Caribbean, the Pacific, and some Asian countries, notably China.

The highly contagious and deadly viral disease shows no signs of stopping. A surge in cases happened at the beginning of 2023 in China after COVID-19 restrictions were lifted and people traveled for the Lunar New Year.

Total cases across the EU were well above the previous year's level. With a total of 12,121 outbreaks, the numbers were almost double compared to 2022. Poland remains the country most affected by ASF. Outbreaks occurred for the first time in Greece, Croatia, Kosovo, Bosnia-Herzegovina, and Sweden. In Greece and Kosovo, it was apparently a point entry, as the virus no longer spread there, according to the ISN report. Russia and Ukraine reported recurrences of ASF in late 2023.

USDA APHIS and state efforts

Since ASF was detected in the Dominican Republic and Haiti in 2021, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) has enhanced existing safeguards. This includes strengthening its partnership with Customs and Border Protection (CBP) staff at ports of entry, increased inspection of passengers and products arriving from affected countries, and advanced risk-based restrictions on imports of pork and pork products from affected countries.

“The U.S. swine herd is a 100% naive population and an introduction into any pigs in the U.S. would eliminate our export markets immediately,” said Dr. Harry Snelson, executive director of the American Association of Swine Veterinarians (AASV). “U.S. pork producers export approximately 27% of the pork we produce, so, the loss of our export capabilities would be financially devastating in addition to the impact it would have on the health and wellbeing of the pigs we produce.”

APHIS continues to conduct surveillance for both ASF and Classical swine fever (CSF). Since August 2021, APHIS has tested almost 6,000 samples from higher risk domestic herds, and more than 26,000 case-compatible samples from veterinary diagnostic laboratories and production facilities.

Since May 2022, APHIS has surveyed feral swine in very high-risk counties within nine states where operational feral swine removal activities are underway and tested more than 3,600 samples, with no ASF detections. APHIS has also started to expand feral swine surveillance and removal activities along the U.S.-Mexico border and the Florida Gulf Coast.

Efforts to prevent the deadly disease have also taken place at the state level. In Ohio, for example, stakeholders from the private sector, nongovernmental organizations, federal and state governments, and academia convened the Ohio African Swine Fever Response Plan Workshop to aid the Ohio Department of Agriculture and Ohio-based USDA APHIS Veterinary Services in the development of the state response plan. This was described in a paper published in the January 2024 issue of JAVMA.

“USDA has been working closely with swine producers, researchers and veterinarians to increase our level of preparedness,” Dr. Snelson of the AASV said. “We are better prepared than we ever have been to diagnose and respond to an ASF introduction, but there's always more to be done.”

Vaccine trials

This past July, Vietnam approved two attenuated live-virus ASF vaccines.

Scientists at the USDA Agricultural Research Service previously discovered the ASF live vaccine candidate, which was then developed in Vietnam by pharmaceutical company AVAC Vietnam JSC. The AVAC ASF Live vaccine was recently trialed in the Philippines with 300,000 doses.

As AVAC was about to export five million doses of its vaccine to the Philippines and other Asia Pacific countries, WOAH warned of risks “from use of sub-standard vaccines.” It also stressed the importance of using high-quality ASF vaccines with proven efficacy and safety, which have been subject to regulatory evaluation and approval following WOAH international standards.

“The use of non-compliant and poor-quality vaccines may not confer any protection against ASF and risks spreading vaccine viruses that could result in acute or chronic disease. Additionally, these vaccine viruses could also recombine with field strains to generate novel strains that could evade detection and result in acute, chronic and persistent ASF infections on farms,” according to the announcement.

Further, WOAH says AVAC Vietnam JSC has not shared sufficient data with international researchers and bodies. The USDA says it did not have access to Vietnam's testing data, according to an agency spokesperson. AVAC says that its vaccine is not dangerous and that widespread use will demonstrate just that.

NAVET-ASFVAC, the second approved ASF vaccine is produced by Vietnam's Navetco Central Veterinary Medicine Joint Stock Company from a USDA platform. Navecto has shared positive results of trial data and the vaccine is being tested in the Dominican Republic.

The epidemiology of ASF is complex and varies depending on the environment, types of pig production systems, tick vectors, human behavior, and wild pigs.

In 2020, WOAH launched the Initiative for the Global Control of ASF in partnership with the Food and Agriculture Organization (FAO). The goal is to bring together governments, industry, and experts to support members in their effort to control the devastating pig disease.

Gregorio Torres, head of the science department at WOAH, said the agency was discussing a new draft standard for the production of safe and effective vaccines against ASF, which was proposed in the September 2023 report of the WOAH Biological Standards Commission.

The standard would not be required, but it could lead to trade restrictions against pork-exporting countries that vaccinate pigs with substandard shots. WOAH urges vaccine manufacturers and members to consider these draft standards when developing and evaluating ASF vaccine candidates for regulatory approval.