ASF research projects shed light on situation in Vietnam

Field projects examined pen-side tests for African swine fever detection, pathways for introduction into boar studs, and rodents as possible vectors.

November 9, 2023

4 Min Read

In 2019, the Swine Health Information Center, with support from the National Pork Producers Council, received a grant from USDA’s Foreign Agricultural Service division to fund a multi-phase project including African swine fever field projects in Vietnam. Results of this now completed work help inform prevention and preparedness efforts for U.S. pork producers and practitioners while also helping inform response and recovery efforts for the ASF epidemic in Vietnam.

Among the grant-related efforts completed were sharing disease knowledge and strengthening veterinary services capacity for mitigating ASF impact on Vietnam and China, as well as on-the-farm field projects. Also, following a request from the Vietnamese Department of Animal Health, as a result of the introduction of the ASF vaccines, efforts were focused on supporting the DAH in the design and evaluation of the vaccination program.

In response to a SHIC open, competitive call for proposals in March 2020, 10 field projects were ultimately planned, funded and completed.

  • Potential of Rodents to be a Vector in the Transmission of ASF in Two Commercial Farms in Vietnam with Differing Biosecurity Levels: The two projects in this study did not provide evidence that rodents are significant factors in the transmission of ASFV between animals or farms.

  • Using Standard Laboratory PCR Testing, and Comparing Available POC Technology, to Assess the Validity of Current ASF Test and Remove Practices in Commercial Swine Farms within Vietnam: Results showed tooth extraction did not eliminate ASFV from sow farms and discovered ASFV DNA was detected in blood from sows showing no clinical signs, as well as indicated POC tests had poor diagnostic performance.

  • ASF Research Projects in Vietnam Examining the Use of Serum and Oral Fluid ELISAs: This unprecedented study showed there is no single best diagnostic approach for ASFV surveillance and demonstrates that the combined use of the Tetracore qPCR and indirect ELISA tests and serum/oral fluid sampling increase efficiency of ASF disease surveillance.

  • Determining the Pathways for ASF Introduction into Boar Studs and Risk of ASF Transmission via Semen Movements During an ASF Outbreak: The project used the experience with ASF in Vietnam to estimate the risk of ASF introduction into boar studs in the United States. The results varied from “negligible” due to water, as long as no surface water enters the facility, to “low” from people, fomites and other entries as long as current biosecurity practices are strictly implemented.

  • Time and Temperature Required for Complete Inactivation of ASFV: Heat treatment at 54oC and 63oC resulted in positive PCRs but negative viral isolation. However, after bioassay exposing pigs to ASFV-contaminated feces held at 54oC for 10 min, viral genomic DNA was detected in their blood at five days post-inoculation, indicating that ASFV infectivity remained.

  • Evaluate the Diagnostic Performance of Pen-side Tests for ASF Detection: The viral DNA PCR pen-side test had better performance than the viral antigen lateral flow test as it can detect infected pigs earlier and for a longer duration after infection.

  • Field Evaluation of Oral Fluids as a Convenient, Aggregate Sample for Early Detection of ASF: Based on the overall field data, ASFV DNA can be detected in oral fluids within 0-3 days of the initial detection of viremia in the pen. If the viral load in the pen is low, it may take up to three days to detect in oral fluids. This is consistent with the results from a previous study on experimentally inoculated animals under experimental conditions and further validates oral fluids as a reliable aggregate sample for screening swine herds for early detection of ASF.

  • Identifying Pathways of Entry of ASF Virus onto Farms to Enhance Information for Improving Biosecurity in Vietnam: The top 10 shared risks for the spread of ASF in Vietnam included entry of water, feed trucks, replacement breeding animals, semen, visitors, tools (both for breeding replacements and cull animals), livestock trailers (for both weaned pigs and replacement pigs) as well as pork and other food entering the premises.

  • Coordinated through the University of Minnesota’s ProgRESSVet program, building ASF response capacity in Vietnam included a series of ASF-related courses delivered in eBook format, including:

    • ASF Epidemiology and Risk Assessment

    • Biosecurity and ASFV Risk Management in Pig Farms

    • Organization of Control Plans at the Central Level

    • Introduction to Spatial Analysis

    • Introduction to Epidemiological Modeling

    • ASF vaccine evaluation & post-vaccination monitoring

Four on-line and in-person workshops with animal health officials of the Vietnam Department of Animal Health were conducted as well.

SHIC, NPPC, the National Pork Board and the American Association of Swine Veterinarians are working closely with USDA to help prevent ASF from entering the United States but also to be prepared to respond should an outbreak occur. The industry continues to actively identify and prioritize critical research needs and work in collaboration with state and federal animal health officials.

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