This zoonotic disease agent rarely affects people.
Although most producers and farm staff would quickly recognize Streptococcus suis as a significant health problem for pigs, they may think of it only as a pig disease.
In fact, Strep suis is a zoonotic disease — one that can be transmitted from animals to humans, albeit rarely reported.
But in 2005, a case from the Sichuan Province in China received considerable attention and concern from health officials and veterinarians. In this case, there was high mortality in pigs (640) and people (39). Overall, 198 people were affected with the disease; all had contact with the diseased pigs.
Strep suis causes a host of problems in pigs: meningitis, arthritis, heart valve infections, polyserositis, pneumonia, vaginitis and abortions.
The bacteria can reside in the tonsil and/or genital tract of pigs; 35 types of Strep suis have been identified.
The most common clinical signs are meningitis (nervous signs) and arthritis (joint swellings) in nursery pigs. Strep infections are a common problem in today's production units, even in some of the “high health” herds.
A production system producing 1,000 pigs/week from two sow herds and a comingled nursery experienced reoccurring strep problems over seven years.
Nursery pigs had done well and were moved to the finisher at 8 weeks of age. One week later, seven pigs died at 9 weeks of age, and nine pigs died at 11 weeks of age. Pigs showed few lesions; brain and spleen were positive for Strep suis Type 2, and microscopic lesions were consistent with septicemia.
Pigs were treated with sulfadimethoxine in the water. Few pigs died.
The second case, from this same farm, was a much more chronic strep problem in the more usual age range, 2-4 weeks postweaning. Pigs showed nervous signs (recumbency, paddling) typical of meningitis and swollen joints (arthritis). Porcine reproductive and respiratory syndrome was present but didn't cause this infection.
The owner also felt strep was triggered by the stress of mycoplasma vaccination. However, changes in the vaccine timing didn't alter the problem. Average nursery mortality was 2.38% for 2004.
In the spring of 2005, problems increased and mortality on closeouts increased to 3.3%. Traditional treatments for strep had been amoxicillin-dexamethasone injections and amoxicillin in the water.
A switch was made to a different amoxicillin product with higher availability. Because prophylactic water treatment had not seemed to stop strep in the past, treatment was initiated at the onset of clinical signs for three days. Individual injections of affected pigs were continued as usual. If signs or mortality reappeared, pigs were placed back on water medication for 24-48 hours.
The idea behind this medication scheme was to reduce clinical signs while providing exposure to stimulate natural immunity to strep. The changes reduced the mortality back to acceptable levels.
A farrow-to-finish farm in Indiana weans 750 pigs every two weeks to double-stock wean-to-finish barns. Mild strep problems have occurred occasionally in the nursery. Individual treatments are the primary response. Water medication has been used to reduce individual treatments.
On one occasion, a group of 15- to 16-week-old pigs had a higher prevalence of thin, fall-behind pigs. Two pigs were euthanized and posted. Both had lesions indicating severe damage to the heart valves. Culture of the heart valves revealed pure isolates of Strep suis Type 2. It is likely that this infection was initiated by early exposure to strep after weaning.
It was useful to have made the diagnosis, avoiding unnecessary treatment for conditions that might mimic this problem clinically, such as ileitis.
This case demonstrates that another manifestation of Strep suis can occur and reinforces the need to make an accurate diagnosis.
Although strep can survive in feces and dust for 104 and 54 days at 32°F, respectively, it cannot survive longer than 24 hours in dust at room temperature and are easily inactivated by soaps and disinfectants.
Thus, the risk of strep becoming a zoonotic concern can be minimized by good sanitary practices, such as washing hands and covering open skin wounds promptly. Use gloves when performing obstetrical procedures.
Florfenicol from Schering-Plough Animal Health is the only approved water-based antibiotic for strep. A feed-grade product should be on the market soon, providing another tool for strep control.