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ASU research examines new method for diagnosing African swine fever

Plum Island Animal Disease Center NHF-ASF-huddling.jpg
NaSRED's diagnostic sensitivity is estimated to exceed that of ELISA by more than 10 times and surpass ELISA's dynamic range by over 100 times.

Since no treatment or vaccine is currently available for African swine fever, swine herds must be continuously monitored for any signs of the disease. If ASF is suspected, laboratory confirmation is carried out. This is often a costly and time-consuming undertaking, (typically a few days from sample collection to test result output), which makes containing ASF outbreaks challenging. 

In a new study, Arizona State University researcher Chao Wang and his colleagues have advanced an innovative method for rapidly diagnosing the disease, which they say could revolutionize the process and help safeguard millions of animals worldwide. Wang is a researcher with the Biodesign Center for Molecular Design and Biomimetics and the School of Electrical, Computer and Energy Engineering.

The project is a collaboration between ASU and Centro de Investigación en Sanidad Animal in Spain, which is also the European Union reference laboratory and the Food and Agriculture Organization reference Centre for ASF.

Wang and his colleagues have received about $750,000 in funding from the Agriculture and Food Research Initiative program of the National Institute of Food and Agriculture of USDA to pursue their diagnostic test, dubbed NaSRED, (for nanoparticle-supported rapid, electronic detection), a highly accurate means of detecting ASFV.

NaSRED offers several advantages over existing methods. The test can be performed at drastically reduced cost, yielding results in minutes rather than hours or days. It can easily be carried out in the field, without recourse to the sophisticated laboratory facilities required for processing similar diagnostic tests.

Remarkably, NaSRED's diagnostic sensitivity is estimated to exceed that of enzyme-linked immunosorbent assays, the current gold standard for such tests, by more than 10 times and surpass ELISA's dynamic range by over 100 times. (The dynamic range is the range from the lowest to the highest quantities a diagnostic test can measure.)

The basic technique has already shown impressive results, where an earlier prototype was used to pinpoint the presence of two global human pathogens, SARS-CoV-2 and Ebola.

'“I came across the ASF virus and was immediately amazed by its complexity," Wang says. "The virus particle itself is protected with multiple layers and decorated with more than 50 structural proteins, in contrast to the SARS-CoV-2 virus particle with only one single lipid bilayer and a few surface proteins. This makes it extremely difficult to understand how the virus works to cause the damage. This is also one big reason there is no effective vaccine available. Therefore, virus diagnostics for ASF are of paramount importance."

Meeting the challenge
Existing diagnostic tests for ASF involve the detection of nucleic acid, antibodies or antigens specific to the ASF virus. The most sensitive tests, including real time polymerase chain reaction and ELISA require laboratory facilities and trained personnel to perform. They also often involve long turnaround times for results, a significant drawback when tracking a fast-moving, explosively contagious disease like ASF.

Ideally, swine populations should be under continual surveillance by means of a portable diagnostic, stockpiled near animal pens, enabling earlier and faster disease detection at reduced cost. Such a method would also permit widespread, high-frequency testing, a crucial factor in disrupting the transmission chain of the virus and containing an ASF outbreak.

The project involves the design and validation of NaSRED, a portable diagnostic sensing device, using metal nanoparticles. The NaSRED test uses collections of metal nanoparticles with different optical characteristics to ferret out ASF biomarkers—telltale signals of the presence of the ASF virus.

The project proposal describes detection of a specific ASF protein known as p72 and two ASF antibodies, anti-p54, anti-p30, making for a much more accurate and sensitive test, compared with diagnostics that only test for one of these disease signatures.

The technology uses metal nanoparticles affixed with specific molecular binders known as ligands, which seek out proteins and antibodies associated with the ASF virus. When the nanoparticles encounter ASF proteins and antibodies in a sample of blood, the disease targets stick like glue to the nanoparticle sensors.

As the ASF proteins and antibodies adhere to the nanoparticles, they aggregate to form clusters. The increased weight of these clusters causes them to sink to the bottom of the test tube, causing a detectable color change in the solution. The unique optical properties of these clusters, which signal positive identification of the ASF virus, are observed when light is passed through the solution.

Using simple and inexpensive electronic circuits, the system can easily convert the optical signals produced by the metal nanoparticles into a quantitative electronic readout of test results. The collected signals will be automatically recorded by circuitry and transmitted to computers or phone, where negative or positive results will be displayed, making the testing an even easier task that could eventually be performed by farmers.

The final sensing system, ideal for pen-side testing, will be hand-held and the cost of materials is expected to be around $20, while individual tests can be performed for under $1. Rapid testing, requiring less than a microliter of blood, will deliver results within minutes.

The technology is a particularly attractive option for testing swine in resource-limited settings and promises to dramatically enhance efforts to combat this global scourge.

Source: Arizona State University Biodesign Institute, which is solely responsible for the information provided, and wholly owns the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

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