Two cases of Streptococcus suis turn out to be much more serious.
Due to the unprofitability of the hog market recently, I find myself trying to take shortcuts in order to save my producers money.
Diagnostics is one area producers always like to skip because they would rather you just give them the answer based on your experience. I have learned that skipping the steps to a successful treatment plan eventually leads down the wrong diagnostic path.
Case Study No. 1
My producer receives weaned pigs from a shareholder-owned sow farm. He gets 650 pigs, which is a week's weaning, three consecutive weeks out of an eight-week cycle. The piglets are weaned at 18-25 days of age and about 650 head per week are delivered for three weeks. Our clinic provides the veterinary care for both the sow farm and my client's nursery/finishing site.
The producer called me on a Friday afternoon (Murphy's Law for swine veterinarians) to complain about sick pigs in the nursery. Three pigs were dead and two more were down on their sides “paddling” with jerky eye movements (nystagmus). Four or five other pigs were showing clinical signs of “fuzzy hair” and shivering. There were 1,967 pigs in the group, and the clinically affected pigs were from the youngest of the three groups. They had been weaned one week.
Due to the timing of the call and the nature of the clinical signs, we made an over-the-phone diagnosis of Streptococcus suis meningitis and elected to treat the sick animals with injectable penicillin intramuscularly. On Saturday morning, the treated pigs looked better, but there were four or five more cases of shivering pigs. At this point, we decided to use potassium penicillin in the water to treat the entire group of pigs in addition to injections of penicillin for those exhibiting clinical signs.
By Monday, six piglets had died (0.3%) and 10 head looked suboptimal (0.5%). Although no new cases of meningitis had occurred since implementing the water therapy, the number of poor-doing pigs climbed.
Two weeks later, the producer complained about continued poor nursery performance. I finally concluded we needed to do the diagnostic work to confirm the strep or find out what was really going on.
Reluctantly, the producer agreed. Postmortem exams were done on three poor-performing nursery pigs and serum was collected for analysis. Unfortunately for the producer, tissues and serum were positive for PRRS (porcine reproductive and respiratory syndrome). This was a surprise as the sow herd had been PRRS-negative for five years.
We may never know for certain how the pigs became PRRS infected. But we have concluded the truck used to haul hogs to market was the most likely culprit, as the finishers were PRRS-positive on the same site at subsequent testing. This would explain the poor response to therapeutics and the lingering issues leading to suboptimal performance. Strep. suis was certainly a player, but probably secondary to PRRS virus. To correct the problem, we needed to address the PRRS virus.
Once the full diagnostic picture was clear, we eliminated PRRS from the site and tightened up the biosecurity to prevent reinfection. By doing so, we have eliminated the Strep. suis problem as well. The herd remains PRRS-negative today.
Case Study No. 2
This producer weans about 2,000 pigs per week into off-site nurseries. Pig performance was great early on, but mortality climbed (4-6%) by late nursery. After collecting 4-5 postmortem tissue samples, our in-house bacterial culture showed pure Strep. suis.
Since the culture was pure and the antibiotic sensitivity test indicated tetracycline was a good choice, we skipped the rest of the diagnostics and proceeded to treatment. With tetracycline in the water, signs of Strep. Suis resolved, but performance did not improve as much as expected.
Realizing our mistake, we submitted tissues to the diagnostic lab for a full workup. It was then that we discovered signs of lymphoid depletion, and as it turned out, the pigs were positive for porcine circovirus. Strep. suis was there too, but just like the first case, it was merely an underlying viral issue.
This case is still pending, as these pigs were actually vaccinated for circovirus, but it wasn't as effective as our previous experiences have proven to be. Strep. Suis reared its ugly head, but circovirus appeared to be the instigator.
Hopefully, hogs will return to more profitable margins soon. We will always be tempted to take the easier road and do such things as give a diagnosis over the phone based on clinical signs. However, when profit margins are higher, there is less pressure to cut corners.