As African Swine Fever (ASF) outbreaks sweep through China and other countries, swine producers and their leaders have become fixated on keeping it out of our national swine herd. Should the unthinkable happen and ASF breaks through our firewalls, however, rapid detection of the first infected pigs might mean the difference between a containable problem and the ruination of US pork production.
The responsibility for this rapid detection falls on veterinary diagnostic labs such as the Animal Disease Research and Diagnostic Lab (ADRDL) here at South Dakota State University. Interestingly, we don’t have to guess what ASF testing would look like because it’s already being done here.
Specifically detecting the virus that causes ASF is critical, simply because the signs it causes in pigs will not be obvious. Those signs (lethargy, fever, discolored skin, increased death loss) could easily be chalked up to a “normal” pig disease such as porcine circovirus or PRRS. Should ASF hit our domestic pig population, it’s going to sneak in rather than loudly announce its presence.
With this in mind, the USDA has already implemented active surveillance for ASF, and labs like the ADRDL are key players. Considering how ASF would first pop up, they’ve targeted pigs condemned at slaughter, feral swine, and – this is where the ADRDL comes in – sick pigs submitted from veterinarians for routine diagnostics.
If submissions from vets match a list of ASF attributes (acute whole-body infections, skin discoloration, swollen lymph nodes, enlarged spleen, or abortions), or are from groups experiencing increased death losses, they qualify for testing. Again, these signs are also typical of many regular domestic swine diseases.
Right now, only certain parts of the pig are appropriate to be tested for ASF. Organs that belong to the lymphoid portion of the pigs’ immune system, such as spleen, tonsils, or lymph nodes are on the list for the surveillance program. All these parts are there when whole pigs show up to the lab, but vets doing necropsy examinations out in the field might not always send these in.
Once all those conditions are met, then ASF testing can proceed. At the ADRDL, the tissues are taken from the necropsy floor to the molecular diagnostics lab upstairs. Every virus has its own particular fingerprint, and these staff members use specialized equipment to detect whether ASF Virus’ fingerprint is present in the sample they get. The process is called Polymerase Chain Reaction (PCR), and the fingerprint is found in the nucleic acid (RNA, for example) of the virus. They use a special process to squeeze all the nucleic acid from the sample, then an artificial mirror image of a chunk of the ASF fingerprint is added. Through many cycles, the specific fingerprint portion accumulates until a marker on the molecule alerts the machine of a “hit.”
It’s important to note that this process strictly takes place with non-infectious materials: no live ASF virus is involved!
Should a sample test positive for ASF at the ADRDL, it’s considered a presumptive positive, then forwarded overnight to the USDA’s Foreign Animal Disease Diagnostic Laboratory (FADDL) on Plum Island for confirmation.
A positive ASF confirmation at FADDL – needless to say – would set off a remarkable chain of events! If the sample is negative, it’s not subject to further testing or confirmation – although regular testing will continue in order to diagnose the problem. There is no charge to the veterinarian or producer for ASF testing.
Veterinarians and swine producers, therefore, assist our ASF preparedness when they make regular submissions (provided they include spleen, tonsil, or lymph nodes) to the ADRDL. From a wider standpoint, if more conventional disease surveillance samples – such as oral fluids – could be approved as ASF-appropriate samples, ASF surveillance in the US could be taken to a whole new level.
Every one of those submissions helps ADRDL personnel keep their skills honed – not only with the PCR testing protocols, but also with how they communicate results. A robust approach to dealing with a foreign animal disease attack means preparing the staff at our vet labs for ASF testing challenges, in addition to beefing up our national biosecurity and other surveillance.