Despite vast improvements in pig care and management, some veterinary officials suggest that swine dysentery has returned.
Swine dysentery, a common bacterial malady known as bloody scours in the 1970s, was a reportable disease that could cause enteric problems up to slaughter weights. In 1982, an estimated 40% of herds in Iowa were infected with the disease, according to Robert Glock, DVM, Arizona Veterinary Diagnostic Laboratories.
Swine dysentery seemingly vanished by the mid-1990s, lost its reporting status and was all but forgotten by producers and veterinarians alike, who assumed it had been eradicated.
There were many reasons to believe the organism had virtually disappeared. Contributing factors included the move to slotted floors; the move away from pig commerce at sale barns; the development of three-site production systems; the exchange of continuous-flow production for all-in, all-out pig flow; consolidation with fewer producers; and the introduction of stringent biosecurity and hygiene programs, according to Kent Schwartz, DVM, senior diagnostician at the Iowa State University Veterinary Diagnostic Laboratory. “The adoption of all those strategies was kind of why we thought it had gone away,” he says.
The pseudorabies eradication campaign, which was going strong through the 1980s and 1990s (completed in 2004), also may have played a significant role in the reduction of swine dysentery cases, suggests Doug Weiss, DVM, technical services manager for Phibro Animal Health.
Interestingly, sporadic cases of swine dysentery began popping up in 2007. The presence of circovirus-associated disease (and perhaps Lawsonia and salmonella) may have masked signs of dysentery, Schwartz says. The successful control of these diseases has increased the likelihood of recognizing other disease agents, he adds.
As to its return to virulence, Schwartz points out that bacteria often diverge or change, and the alterations in immunity to bacteria could cause swine dysentery to resurface.
Schwartz and Weiss suggest that some information indicates that the latest, less severe form of swine dysentery surfacing in some Midwest hog operations has a historical basis and is being documented in Canada, England and across Europe.
North Carolina swine veterinarian Jarod Hanson reports that many parts of the world that do not use drugs to control swine dysentery are experiencing more severe signs or the classical form of the disease. He theorizes that “the aggressive antibiotic-based eradication strategies employed in the United States may have actually (inadvertently) selected for dysentery strains that produced less visible clinical signs. As a result, swine dysentery may have survived in production systems without causing clinical signs of the disease, but still causing real damage to the enteric health of the pig.”
Historically, swine dysentery was a deadly disease. Various antibiotics were commonly used to control outbreaks in the nursery through the end of finishing, Schwartz reports.
Current cases of swine dysentery can be deadly, Schwartz warns. “But the clinical presentation of what we are seeing today as Brachyspira hyodysenteriae (swine dysentery) is more transient (lasting only a short time), and is not as severe, with maybe less blood in many cases. But there is a spectrum (of severity), and that may have to do with dose levels,” he says.
When conducting a differential diagnosis, look at infectious and non-infectious causes, including feed, which can contribute to a non-specific colitis, Schwartz says. “We always need to be vigilant for the other confounders: ileitis (Lawsonia), endemic transmissible gastroenteritis (TGE), poorly digestible feedstuffs or mycotoxins in feed, salmonella, parasites and other risk factors.”
One thing appears to be nearly certain — bloody stools accompanied by mucus clearly point to this pathogen as a reemerging form of swine dysentery that is distinct from porcine proliferative enteropathy or ileitis, another common cause of grow-finish scours, Schwartz says.
The ISU diagnostician says the Brachyspira organism is responsible for both the original and new forms of swine dysentery, and a mild form of growing-finishing pig scours caused by Brachyspira pilisicoli, known as Porcine Colonic Spirochetosis. “All of these Brachyspira organisms love mucus, and seem to promote its production,” Schwartz says. Weiss says a producer describes mucus as “a broken egg-white material that provides a ring around the puddle of the stool on the slats.”
There are definite clinical complications beyond the diarrhea with swine dysentery. “This disease takes the vigor and vitality away from the pig. You will see poorer performance and feed conversion in affected groups,” Schwartz stresses.
This form of swine dysentery can crop up in the nursery, but is more common 3-4 weeks into the finisher and can be a threat through the finishing phase, he notes.
Hanson agrees the disease is mainly seen in the first half of the finishing phase when salmonellosis and/or ileitis also occurs, which can mask its signs. Careful analysis of fecal material is imperative for accurate diagnosis.
An infected population can be uneven at close-out, thus costly to marketing because lightweight market hogs are docked severely, Weiss adds.
If producers see blood and/or mucus in the stools of their pigs, proper diagnostics is vital, Weiss reinforces. Producers should contact their veterinarian for help in collecting the rectal swabs needed for a definitive diagnosis.
Phibro Animal Health is working with Schwartz and Iowa State to provide veterinarians in several states with the company’s diagnostic pack as part of a project to recover more bacterial samples of Brachyspira organisms for detection of this new form of swine dysentery.
The best candidate for sampling is a non-medicated pig with diarrhea containing mucus or blood. This pig will be necropsied, the colon scraped and swabbed. Collecting rectal swabs of live pigs is a second choice. Third would be samples of fresh feces containing mucus.
In Phibro’s program, the company will pay for the cultures of five samples submitted to isolate Brachyspira and salmonella and the polymerase chain reaction (PCR) testing for Brachyspira and Lawsonia. Typically, this would cost producers about $125 in lab fees, Weiss explains.
If Brachyspira hyodysenteriae or swine dysentery is confirmed on your farm, Weiss advises following these steps:
- Exercise an intensive rodent control program. “The mouse has been reported to carry this organism for six months, so it is very critical to manage this situation from one turn of the barn to the next,” he attests.
- Practice extensive removal of fecal material in the barn, followed by cleanup with soap and water. Allow the barn to dry. A fly can carry an infectious dose of this organism on its feet, Schwartz says, and fecal contamination can easily spread the organism from pig to pig.
- Increase biosecurity for people and vehicles returning to the farm. Ensure that all trailers transporting hogs to slaughter are thoroughly washed, disinfected and dried.
Carbadox (Mecadox from Phibro Animal Health) is a feed-grade product of choice to control swine dysentery scours in pigs, according to Weiss. Treat at 50 g./ton in the nursery diet, remove for several weeks to allow the development of natural immunity, then follow-up with 50 or 25 g./ton in the grower diet, depending on what kind of challenge the farm is experiencing.
Mecadox has a 42-day withdrawal period, so producers should switch to another antibiotic of choice to complete the treatment to slaughter weights, he says.
Water/feed-grade antibiotic choices include lincomycin (Pfizer Animal Health) and tiamulin (Novartis Animal Health).
In Hanson’s experience, carbadox has proven most effective of the three antibiotics for the treatment of swine dysentery.
A high mortality rate, combined with worse-than-average feed conversion for a given flow of pigs, should serve as a potential warning sign for swine dysentery.
“In general, if your system’s hygiene practices do not prevent the seasonal spread of TGE virus between sites or flows, they will likely not stop the transmission of swine dysentery either,” Hanson says.
“In the end, there are still a lot more questions than answers about this new form of swine dysentery. What we do know is that there are numerous cases that have been confirmed by culture of the organism and PCR tests,” Schwartz concludes.