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Diagnostician zeroes in on emerging diseases

Veterinarian checking pigs in pen in a barn Getty Images/iStockphoto
Detection does not equal diagnosis.

While African swine fever, classical swine fever and foot-and-mouth disease are grabbing the headlines, there are other emerging diseases that U.S. pig farmers should have on their radar. Fortunately, diagnosticians such as Phil Gauger have their eyes on the radar for the industry.

Gauger, associate professor and veterinary diagnostician at the Iowa State University Veterinary Diagnostic Laboratory, offers a quick history lesson that porcine epidemic diarrhea virus and Senecavirus presented as far as emerging diseases go in the U. S. swine industry.

“Everybody remembers PEDV in 2013, and the idea that we could have a transboundary disease emerge in the U.S. swine population as easy as it did,” he says. “We can only speculate on ways perhaps it could have gotten into the country, but it was never totally figured out at least to this time, and thatʼs a little bit unnerving.”

Recent emerging diseases
Senecavirus reemerged in the United States in 2016, “which is maybe more of the prototype emerging infectious disease because we know that it was present in the U.S. before,” he says, “and then for some reason, kind of out of nowhere, it started to rear its head again and seemed to emerge as something more pathogenic than what it was before.” However, these strains of Senecavirus were genetically similar to what was circulating in other countries suggesting a new strain of Seneca had emerged in the U.S. He adds that with the PED and Seneca experience combined brings a heightened awareness of potential emerging infectious diseases, “and just that feeling that our swine populations are vulnerable to these emerging diseases, especially from other geographic regions.”

So, what does to the U.S. swine industry need to be concerned about right now and in the near future?

“Actually, viruses that currently affect the U.S. swine industry and continue to genetically evolve could also be considered emerging infectious diseases. These include virulent strains of PRRSV, new genotypes of porcine circovirus and new strains of influenza that often spillover from humans into the swine population,” he says. In addition, there strains of highly pathogenic PRRSV and highly pathogenic Pseudorabies virus in other geographic locations outside of the U.S. that could present a threat to the U.S. swine industry as well.

According to Gauger, porcine circovirus type 3 is an example of a virus that has been gaining headlines as of late in the U.S. swine industry. “While we now know that PCV3 has been circulating in the U.S. and in swine across the world for many years,” he says, “as time has gone on, we have learned more and more about this virus and its role in causing clinical disease in pigs.”

Check out this video interview with Phil Gauger, as he further explains emerging diseases.

Neurological diseases that have gained interest in the U.S. swine industry include porcine Sapelovirus, porcine Astrovirus type 3 and Atypical Porcine Pestivirus “which was determined the cause of the clinical signs responsible for ʻshaker pig disease,ʼ.” However, Sapelovirus and astrovirus Type 3 have been more recently recognized as causing some neurologic disease including paralysis in pigs “that previously were not fully characterized in swine,” he says.

Another virus showing up, but as of yet needing further confirmation it may be a potential pathogen in pigs, include porcine sapovirus that has been “implicated as a cause of enteric disease or diarrhea in young pigs,” and the emergence of virulent strains of Streptococcus equi subspecies zooepidemicus. “Thatʼs an example of a bacteria that has been recently implicated in causing high mortality in pigs as well.”

With current molecular diagnostic processes, such as whole-genome sequencing “weʼre able to detect new or emerging viruses or bacteria that might be involved in a clinical scenario, but of course need further confirmation before they are considered a new or emerging pathogen we would be concerned about in the swine industry.”

Diagnostic technology on horizon
As diagnostic technology improves, Gauger says it may be possible to detect disease-causing bacteria and viruses that have been present but, “were previously unknown or just not recognized in the disease process,” he says. “With this new technology, thereʼs a level of discovery of potential emerging or new strains of viruses or bacteria that were previously undetected but not necessarily known to be implicated in clinical disease, and those are ones that would be under further investigation or requiring additional diagnostic evidence that itʼs involved in a disease process.”

Gauger throws caution into the equation if one looks to technology such as next-generation sequencing to answer all swine disease questions. “Detection alone doesnʼt mean an element of causation or that itʼs definitely involved in clinical disease,” he says. “Thereʼs much more that has to happen after detection of an emerging pathogen to implicate it in a disease process. This includes an investigation often at the farm level with additional samples from affected pigs, additional diagnostic testing, and experimental evidence that an emerging agent is definitely a cause of clinical disease.”

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