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Opportunistic bacterial challenges

Keep opportunistic bacterial challenges in pigs at bay

Bacterial challenges facing pigs can be traced back to other shortfalls that weaken their immune system.

Primary viral challenges such as porcine reproductive and respiratory syndrome (PRRS) and influenza-A virus (IAV) lead the list. But management factors, such as improper ventilation, poor sanitation, inadequate diet or an incorrect feed budget, also open the door to bacteria, said Cameron Schmitt, DVM, Pipestone Veterinary Services.1

“Ninety-nine percent of the time, the opportunistic bacteria that I see on farms fits into these areas—respiratory, enteric and septic,” he added.

Respiratory challenges

Although viral diseases such as PRRS and IAV often dominate producers’ and veterinarians’ focus, the defense void that these viruses create allows secondary bacteria to exploit the animal. Most commonly these include Haemophilus parasuis, Streptococcus suis, Actinobacillus suis and Mycoplasma hyopneumoniae.

This leads veterinarians to recommend antimicrobials to address a broad spectrum of bacterial pathogens while the animal recovers from the viral assault. But with a heightened focus on reducing antibiotic use on the farm, Schmitt questions the long-term access to such products.

“Constraints are here, and more are likely coming,” he added. “Focused application will continue to be important.”

In the nursery, he prefers injectable antibiotics because they’re applied to the individual pig and better assure a correct dose. Improving the growing pig’s environment, providing a clean, dry, draft-free space and improving air quality are management steps to minimize bacterial challenges.

Anti-inflammatory treatments can help reduce fevers, which can keep pigs eating and drinking. Of course, vaccinations against viral agents should be part of the on-farm plan, and biosecurity is important to address both bacterial and virial threats, he added.

“As for herd visits, veterinarians need to determine if the clinical signs are the same or different, and follow up with laboratory diagnosis, if needed, to be sure,” Schmitt said.

Enteric challenges

Enteric bacteria present the greatest challenge during the first 8 to 9 weeks after weaning. Schmitt cited hemolytic Eschericia coli K88 and Eschericia coli F18 as the culprits behind rapid mortalities adding up to 10% or more in a group of nursery pigs. Tools to prevent or reduce losses include sanitation, vaccination, dietary modification and antimicrobials.

“However, resistance is becoming more common among E. coli variants, driving the need for better preventative measures,” the veterinarian added.

Salmonella occurs less frequently than E. coli, but it takes advantage of immunocompromised pigs and when the environment or diet doesn’t match the pig. “Diet changes can disrupt the microflora in a nursery pig’s gut,” Schmitt said, “so it’s important to get the diet right.”

Of course, viruses such as rotovirus, porcine epidemic diarrhea virus, delta coronavirus and transmissible gastroenteritis also will take advantage of management missteps in the nursery.

Again, antimicrobials can help address Salmonella, but moving to an older weaning age and preparing the gut through creep feeding are starting points. Incorporating gruel feeding or feeding pigs on mats multiple times a day to prompt early feed acceptance in the nursery are sound options as well.

Septic challenges

Septic bacterial infections are most frequently seen in PRRSV-infected pigs, Schmitt noted. Again, taking advantage of the compromised immune system, S. suis, A. suis and H. parasuis gain access to the pig’s bloodstream and attack specific sites within the body. The areas most typically affected are meninges, pleura, pericardium, peritoneum and synovia. The eventual result is lameness, but early clinical signs are often minimal and hard to detect.

“This puts the veterinarian behind the curve before treatment can even begin,” Schmitt said. “Because there is little blood flow to these areas, it’s difficult to deliver therapeutic medications.”

Certain antimicrobials can be used to fight these infections, but preventing the primary challenge, such as PRRS, is the more prudent path.




1Schmitt C. Opportunistic Bacterial Pathogens: Battles Fought in Daily Practice. Proceedings of the 48th American Association of Swine Veterinarians’ Annual Meeting. 2017;325.

Posted on June 20, 2017

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  • Opportunistic pathogens prey on newly weaned pigs infected with a primary virus

    Around 50% of pigs weaned today likely are infected with a primary viral pathogen, like porcine reproductive and respiratory syndrome (PRRS) or swine influenza, reported Cameron Schmitt, DVM, Pipestone Veterinary Services, Pipestone, Minnesota.

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Challenges associated with controlling porcine reproductive and respiratory syndrome virus (PRRSV) have resulted in the increased use of molecular diagnostic tests and sequencing, according to Phillip Gauger, DVM, PhD, Iowa State University.

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