Streptococcus suis leads SHIC’s Swine Bacterial Disease Matrix list


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Viruses tend to get first priority when it comes to monitoring swine diseases and herd health, but bacteria can wreak just as much havoc.

Layering bacterial issues onto a herd-health challenge not only complicates the diagnosis, it also affects the treatment success.

Between shifts in antibiotic usage and the bacteria’s endemic nature and their propensity to evolve, the time is right to prioritize bacterial pathogens when monitoring emerging-disease risks.

As the Swine Health Information Center (SHIC) states on its website, “The pork industry has spent millions to better understand viruses; however, it is often bacteria that kills the pig. In addition, current biosecurity practices are primarily devised to keep viruses out and potentially fail to address the endemic nature of bacteria in a herd.”

In response, the SHIC worked with expert bacteriologists and diagnosticians to score bacteria on a detailed set of criteria. From there, SHIC’s Monitoring and Analysis Working Group, which includes practicing swine veterinarians, reviewed and established final rankings for what is now the Swine Bacteria Disease Matrix.

Streptococcus suis ranks No. 1

Although more bacteria and the associated impact scores are listed within SHIC’s  Swine Bacterial Disease Matrix, here are the top 10.

  1. Streptococcus suis
  2. Salmonella enterica
  3. Mycoplasma hyopneumoniae
  4. Escherichia coli
  5. Haemophilus parasuis
  6. Mycoplasma hyorhinus
  7. Brachyspira hyodysenteriae
  8. Actinobacillus pleuropneumoniae
  9. Actinobacillus suis
  10. Brucella suis

A continuous concern

Streptococcus suis (Strep suis) is a ubiquitous bacterium that has presented a long-standing challenge in farrowing rooms and nurseries, with the diagnostic laboratory data in SHIC’s monthly monitoring report showing it as the leading cause of central nervous system syndrome, specifically meningitis.

On the farm, Strep suis is a nagging challenge that can be difficult to resolve. It often causes problems as a secondary pathogen, riding on the coattails of porcine reproductive and respiratory syndrome virus (PPRSv), swine influenza and other disease challenges.

According to April Estrada, PhD student in the comparative and molecular biosciences graduate program at the University of Minnesota, Strep suis continues to be a significant swine pathogen that can cause severe economic losses within a herd. It most commonly presents in a pig’s upper respiratory tract, causing pneumonia as a co-infection with Bordetella, Pasteurella and PRRS virus. Along with meningitis, Strep suis also can result in arthritis, endocarditis and septicemia.

As Estrada noted, there is limited information on Strep suis serotype and sequence type distributions in the US. Her research is investigating subtyping methods and whole-genome comparisons of Strep suis isolates to better understand its epidemiology and virulence, respectively.

Not surprising, Strep suis incidence tends to increase in the fall and winter months as fluctuating building environments deal with decreased ventilation rates and increased humidity levels. Other stressors such as overcrowded rooms add to the challenge.

Strep suis represents a unique threat to our industry for several reasons,” Clayton Johnson, DVM, Carthage Veterinary Service and member of SHIC’s expert working group, told Pig Health Today. “Strep suis is an endemic pathogen of swine; pigs all over the world are infected, and therefore transmission risk across herds is high. It is a zoonotic pathogen that can cause serious human-health consequences.”

Currently, there are no cross-protective vaccines. Consequently, control often involves antimicrobial use, “a practice we want to constantly challenge as we strive for judicious medication usage,” he added.

Matrix represents the most impactful bacteria

From a practicing swine veterinarian’s perspective, “the Swine Bacterial Disease Matrix is a critical stack ranking of bacterial pathogen risks that could emerge into disease emergencies for our industry,” Johnson said. “And it does so in an evidence-based manner.”

“The Swine Bacterial Disease Matrix complements the center’s Swine Viral Disease Matrix, which prioritized a list of endemic and foreign swine viruses,” said Paul Sundberg, DVM, SHIC executive director. “This new matrix is a comprehensive list of bacteria that we know can impact pig production and health.”

He emphasizes that through these matrixes, SHIC is monitoring for emerging diseases that can come from a number of different factors, whether they involve viruses, bacteria, antimicrobial resistance or increased virulence of an emerging disease.

The criteria that SHIC participants used to identify the top 10 bacteria for the US swine industry started with a literature review to identify bacteria known to infect pigs and considered a health risk. From there, the priority considerations included:

  • Potential public-health impact, with high emphasis placed on zoonotic potential. Other considerations included the food-safety risks, overall transmissibility and likelihood, bioterrorism prospects and antimicrobial resistance.
  • The need for more efficacious intervention tools, such as biosecurity and management, vaccines and antimicrobials.
  • The need for better diagnostic tools, especially related to isolation capability for confirmation and study, appropriate polymerase chain reaction tools, antibody detection, virulence factors and genetic markers.
  • Impact on pig health, welfare and production sustainability and efficiencies. Particular emphasis was placed on animal welfare, morbidity and mortality.
  • Market impact, both domestic and foreign.

The matrix is a living document and the list could change. “It is meant to guide emerging-disease efforts for SHIC’s domestic monitoring program, direct research funding  and identify knowledge gaps,” Sundberg noted. “Just like the viral matrix, which was modified in 2018, we’ll have the same opportunity to modify this matrix as we watch for emerging bacterial issues.”


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