Will a faster diagnosis make a significant difference in the fight against African swine fever?

These days we have grown accustomed to hearing talk of rapid diagnostic tests, and not exactly because of developments happening in the pig world, but because of the COVID-19 pandemic in which we are immersed. Rapid pathogen detection tests have never been widely accepted in our industry, perhaps only for diagnosing cases of diarrhea. In digestive cases, despite its reliability, the veterinarian may consider an accurate diagnosis less urgent than implementing corrective measures that, in many cases, would not be so different even with differing diagnoses. In this case, however, the rapid test would be intended for diagnosing a notifiable disease, namely African swine fever (ASF). From the information found in the article, it would appear that this rapid test would be able to detect even small amounts of virus (200 viral particles), which would make it very sensitive and specific, as for the trials performed, this test would not react to other viruses (neither viruses affecting pigs nor humans); and it could also have a low cost. But does it offer any advantage over the tests currently available?

The reality is that the only advantage would be speed and the possibility of performing it directly in the field. As the test is intended to diagnose a notifiable disease (included in OIE disease List ), its use would be limited to those official agencies responsible for animal health in the different countries. In such a case, speed would not represent a remarkable advantage, since upon suspecting an infection, the first step would be confining the farm (banning any movement of animals) and immediately afterwards, the collection of samples to confirm or rule out the suspicion. In this type of situation, reliability is more important than speed. We are talking about speeding up the diagnostic process by hours or one day at most, which would not substantially change the situation. A positive diagnosis involves the mandatory slaughter of all the animals on the farm, and I find it difficult to imagine that such a measure would be applied based on a diagnosis made directly on the farm, without laboratory confirmation by PCR (a technique recognized by the OIE).

ASF is not a zoonosis and therefore does not pose a threat to human health. If we imagine a situation (as some are already predicting) where the disease would become endemic and its notification wouldn’t lead to the mandatory slaughter of pigs, diagnostic tests could then be done freely. In an endemic situation we would have to expect a reduction in the virulence of the virus and, it would be more difficult to perform a diagnosis based on clinical signs , We could even imagine that an ASF vaccine existed and was available on the market. In this case, the speed, convenience, and reduced cost of diagnosis would be an advantage to consider. A rapid field diagnostic test would make it possible to quickly apply all biosecurity measures aimed at reducing its spread and, why not, assess the possibility of vaccinating neighboring farms in order to prevent worse consequences.

But let’s get back to reality. In the current conditions, I fear that speed and convenience of diagnostics will not make the difference in the fight against African swine fever but rather applying other measures that in some countries are now being considered iprioritary actions, such as the control of non-commercial production (wrongly called self consumption) and of alternative markets that still allow the slaughter and marketing of positive animals.

Summary

African swine fever virus (ASFV) is a dsDNA virus responsible for a severe, highly contagious, and lethal disease affecting both domestic and wild pigs. ASFV has brought enormous economic loss to a number of countries, and effective vaccine and therapy are still lacking. Therefore, a rapid, sensitive, and field-deployable detection of ASFV is important for disease surveillance and control. Herein, we developed a Cas12a-mediated portable paper assay to rapidly and precisely detect ASFV. We identified a robust set of crRNAs that recognized the highly conserved region of essential ASFV genes. The Cas12a-mediated detection assay showed low tolerance for mismatch mutations, and no cross-reactivity against other common swine pathogens. We further developed a paper-based assay to allow instrument-free detection of ASFV. Specifically, we applied gold nanoparticle–antibody conjugate to engineer homemade strips and combined it with Cas12a-mediated ASFV detection. This portable paper, instrument-free diagnostics, faithfully detected ASFV in swine samples, showing comparable sensitivity to the traditionally instrument-dependent qPCR method. Taking together, we developed a highly sensitive, instant, and economic Cas12a-mediated paper diagnostics of ASFV, with a great application potential for monitoring ASFV in the field.

Pig333 | Enric Marco | September 14