New diagnostic technology to tackle the global threat of African swine fever

While the attention of public health authorities has been riveted on the current COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, many other viruses have sneaked around the world, causing serious illness and death in humans and other animals.

One of these pathogens is a virus that causes African swine fever (ASF). The highly contagious and often fatal disease has devastated pig populations around the world and is currently spreading rapidly in Africa, Europe, Asia and the Americas.

No treatment or vaccine exists for African swine fever. Pig herds should be continuously monitored for any signs of disease. If ASF is suspected, laboratory confirmation is performed. This is often a costly and time-consuming undertaking (usually a few days between sample collection and the release of test results), making it difficult to control African swine fever outbreaks. Positive test results are usually followed by the culling of all affected or exposed animals.

In a new study, a researcher from Arizona State University Chao Wang and his colleagues are proposing an innovative method to quickly diagnose the disease that could revolutionize the process and help protect millions of animals around the world. Wang is a researcher at Biodesign Molecular and Biomimetic Design Center and the School of Electrical, Computer and Energy Engineering.

The project is a collaboration between ASU and the Centro de Investigación en Sanidad Animal in Spain, which is also the European Union Reference Laboratory and the United Nations Food and Agriculture Organization Reference Center. agriculture for African swine fever.

Wang and his colleagues received approximately $750,000 in funding from the Agriculture and Food Research Initiative program of the National Institute of Food and Agriculture from the United States Department of Agriculture to pursue their diagnostic test, dubbed NaSRED, (for n / Ano particles-ssupported rquick, eelectronic Ddetection), a very precise means of detecting ASFV, the virus responsible for African swine fever.

NaSRED offers several advantages over existing methods. The test can be performed at a significantly reduced cost, delivering results in minutes rather than hours or days. It can easily be performed in the field, without the need for the sophisticated laboratory facilities required for processing similar diagnostic tests.

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

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

“I discovered the African swine fever virus and was immediately amazed by its complexity,” says Wang. “The virus particle itself is protected by multiple layers and decorated with more than 50 structural proteins, unlike the SARS-CoV-2 virus particle with a single lipid bilayer and few surface proteins. It is therefore extremely difficult to understand how the virus works to cause the damage. It is also one of the main reasons why there is no effective vaccine available. Therefore, virus diagnostics for African swine fever are of paramount importance.

Invisible threat

African swine fever is a highly contagious viral disease, which often spreads like wildfire through pig populations and inflicts mortality rates of 95-100%. The virus causes severe disease in domestic and feral pigs.

African swine fever was first detected in East Africa in the early 1900s, then spread to Europe in the late 1950s. More recently, ASF has wreaked havoc in many Asian countries . China has been particularly hard hit, losing around 50% of its pigs to the disease since it first emerged in 2018, resulting in direct economic losses of $141 billion in just one year.

The disease causes considerable socio-economic hardship in countries that export live pigs and pork products, as well as in countries where pigs are important food sources in the diet.

While the United States, including Puerto Rico and the US Virgin Islands, is currently free of African swine fever, it is thought to be at increased risk of importing the disease from other countries in the Americas where ASF is already present, particularly in the Dominican Republic and Haiti.

The effect of ASF reaching the states could be devastating as the United States is the third largest pork producer in the world, with more than 11.5 million tons of pork produced each year, and it is also the second largest exporter. pork in the world. The United States could face significant economic consequences if ASF is introduced.

Try the challenge

Existing diagnostic tests for African swine fever involve the detection of nucleic acid, antibodies or antigens specific to African swine fever virus. The most sensitive tests, including real-time polymerase chain reaction (PCR) and ELISA, require laboratory facilities and trained personnel to perform. They also often involve long delays in obtaining results, a significant disadvantage when monitoring a rapidly evolving and explosive contagious disease such as ASF.

Ideally, pig populations should be under continuous surveillance using portable diagnostics, stored near animal pens, allowing earlier and faster disease detection at lower cost. Such a method would also allow widespread and high-frequency testing, a crucial factor in disrupting the chain of virus transmission and containing an outbreak of African swine fever.

The project includes the design and validation of NaSRED, a portable diagnostic detection device, using metallic nanoparticles. The NaSRED test uses collections of metallic nanoparticles with different optical characteristics to flush out African swine fever biomarkers, signals indicative of the presence of the African swine fever virus.

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

The technology uses metal nanoparticles attached with specific molecular binders called ligands, which search for proteins and antibodies associated with the ASF virus. When nanoparticles encounter ASF proteins and antibodies in a blood sample, disease targets stick like glue to nanoparticle sensors.

When ASF proteins and antibodies adhere to 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 a positive identification of African swine fever virus, are observed when light passes through the solution.

Using simple and inexpensive electronic circuitry, the system can easily convert the optical signals produced by the metallic nanoparticles into a quantitative electronic readout of test results. The signals collected will be automatically recorded by circuits and transmitted to computers or a telephone, where the negative or positive results will be displayed, which will make the test even easier which could possibly be carried out by farmers.

The final detection system, ideal for pen-side testing, will be portable and the cost of materials is expected to be around $20, while individual tests can be performed for less than $1. Rapid tests, requiring less than a microlitre of blood, will provide results in minutes.

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


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