Fighting an Animal Health Endemic

Limiting the spread of African Swine Fever

African swine fever (ASF) is a highly contagious and usually fatal viral disease affecting domestic pigs and wild boar. Since the first recorded description of ASF in Kenya in 1921, the virus has spread throughout Africa, Europe, the Americas and Asia, with a huge impact on the swine industry. Despite several eradication programmes, the virus has continued spreading and remains endemic in some areas. Gold Standard Diagnostics Madrid, at the time Eurofins Ingenasa, has carried out important work to fight this animal disease for more than 40 years.

ASF is caused by the African swine fever virus (ASFV), which spreads among domestic pigs through contact with a sick animal, an asymptomatic carrier or a soft tick, or through the consumption of contaminated animal feed. Usually suffering a high fever and visible haemorrhages, infected pigs can also experience weight loss, pneumonia, skin ulcers, and tremors, before many fall into a comatose state and die within just a few days of infection. The impact on a pig farm is catastrophic: infection not only spreads rapidly but means that any surviving pigs in the herd must be culled to stop the spread of the virus.

In 1984, following an outbreak of ASF in Europe, Gold Standard Diagnostics Madrid, at the time Eurofins Ingenasa, developed the first commercial ELISA test capable of detecting antibodies against ASFV in serum samples of pigs and wild boar, which was evaluated according to the Office International des Epizootie (OIE) rules and validated by the EU Reference Laboratory. The company quickly leveraged its network of veterinary experts and deployed the ELISA test as part of successful national eradication programmes between 1985 and 1995. During this period, monitoring through antibody tests was conducted on all pig farms in Spain. The use of this assay, together with other diagnostic techniques and strict sanitary measures, contributed to the success of the eradication programme.

In recent decades, the virus has spread rampantly across continents again, posing a huge threat to the world’s pork production. Although ASFV does not cause disease in humans, virus outbreaks are having a significant socioeconomic impact on communities that rely on the swine industry, as they result in major economic losses through the extensive culling of affected farms. For example, within seven years of ASF reaching China in 2018, millions of pigs died from the disease or had to be culled. Stringent biosecurity management and animal quarantine measures have now become the norm in the industry, with strict limitations on animal movement and exportation during outbreaks, all taking a further toll on the economic viability of pig farming.

In response, Gold Standard Diagnostics Madrid has now developed a full catalogue of tests for specific ASFV antigen and antibody detection. The suite of tests has been used to carry out eradication or control programmes in for example Sardinia, the Dominican Republic, and many countries in Asia. To support improved on-site diagnosis of this disease, Gold Standard Diagnostics Madrid has enhanced its rapid tests (LFA) catalogue. The updated tests provide greater accuracy in antigen and antibody detection. Additionally, a unique in market combined test has been developed to detect both antigen and antibody simultaneously, extending the diagnostic window.

Since eradication programmes have struggled to eliminate the virus for good, control measures remain a costly necessity for pig farmers. Though no vaccine against ASFV is currently commercially available worldwide, important efforts are being carried out. Recently, Gold Standard Diagnostics Madrid participated in the European project ‘A Safe DIVA (Differentiating Infected from Vaccinated Animals) Vaccine for African Swine Fever Control and Eradication (VACDIVA)’, which focused on developing a safe and effective vaccine for domestic and wild swine populations, along with accompanying DIVA tests to accurately monitor their vaccination status and differentiate between infected and vaccinated animals.

The science behind

The African Swine Fever Virus is complex and variable, as a large enveloped double-stranded DNA virus, classified as the sole member of the Asfarviridae family of viruses. To test for infection with ASFV, Gold Standard Diagnostics Madrid uses different platform diagnostics, including ELISA, PCR and LFA tests.

ELISA (enzyme-linked immunosorbent assay) is a plate-based assay technique used to detect and quantify soluble substances such as antibodies. Antigens are immobilised on the plate and bind with antibodies linked to a specific enzyme. By measuring the activity of this enzyme, it can subsequently be determined whether (and how many) antibodies have bound.

Gold Standard Diagnostics offers two types of ELISA tests for ASF antibody detection: a competitive ELISA test, capable of detecting any immunoglobulin against a specific epitope of the virus, and an indirect ELISA test, specifically for IgG detection, based on two viral antigens.

Polymerase chain reaction (PCR) is a laboratory technique that detects minute traces of DNA, in this case viral DNA, in a sample. This is accomplished by multiplying the DNA present in the sample to create billions of copies, using specific enzymes and by changing temperatures.

Finally, based on the same immunoassay design as ELISA tests, Lateral Flow Assays (LFAs) enable rapid, on-site use, which is essential for point-of-care diagnosis. This is especially important for controlling contagious diseases like ASF, for which timely detection is critical.