HERD HEALTH
PIH-56
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Swine Dysentery
(Bloody Scours, Vibrionic Dysentery, Black Scours)
Authors
D. L. Harris, iowa State University
Robert D. Glock, Iowa State University
Reviewer
Roliand Paul, Willow Springs, Missouri
Swine dysentery occurs most frequently in 8-14-week-old pigs, although all ages may be affected with the disease. Typically, the pigs pass loose stools containing blood and mucus. When swine dysentery occurs in young weaned pigs, 90-100% of these pigs are affected, and 20-30% may die if an effective treatment is not administered. The disease may also appear in suckling pigs or adult swine. In such cases, the disease is usually mild and may not be readily diagnosed.

Due to unapparent infections of the disease, the economic significance is difficult to assess. In typical outbreaks, losses result from poor rate of gain and feed efficiency, medication costs and death. The Livestock Conservation Institute estimates that swine dysentery causes an annual loss of $64 million to the U.S. swine industry.
Cause
An anaerobic (growing only in the absence of oxygen) bacterium, Treponema hyodysenteriae, has been found to cause swine dysentery. Pathogenic (disease-producing) types of T. hyodysenteriae act synergistically with other anaerobic bacteria, which are normally present in the intestinal tract of pigs, to produce the disease. The interaction of pathogenic T. hyodysenteriae and the other anaerobic bacteria such as Bacteroides vulgatus causes excretion of fluid, electrolytes and excess mucus from the large intestine. As the disease progresses, blood may be lost through the damaged intestinal wall. Death usually results because of dehydration and a loss of electrolytes.

Most herds of pigs harbor a nonpathogenic type of T. hyodysenteriae. Although this type is very similar to the pathogenic type, nonpathogenic T. hyodysenteriae does not cause disease in pigs. The two types of T. hyodysenteriae can be identified by laboratory tests and oral inoculation into experimental pigs. A definitive diagnosis of swine dysentery should only be based on the isolation and identification of pathogenic T. hyodysenteriae.
Transmission
Pathogenic T. hyodysenteriae is present in the feces of pigs which either are affected with or have recovered from swine dysentery. After susceptible pigs ingest the organism, symptoms of swine dysentery usually occur in 2-21 days; however, longer incubation times have been reported. The incubation period is usually shortened by the ingestion of higher numbers of pathogenic T. hyodysenteriae.

It has been shown that sows may harbor pathogenic T. hyodysenteriae without having clinical evidence of swine dysentery. The organism is shed in the feces of the sow and transmitted to the suckling pigs. Often, it appears that most pigs are not susceptible to the disease while nursing the sow but subsequently are affected after weaning.

Although T. hyodysenteriae is an anaerobe, it will survive in feces for over 1 month. Exact survival time is not predictable because of the influences of variable environment factors such as temperature and moisture. The organism has been found in lagoon water collected from an infected premise. Pigs that have recovered from swine dysentery may shed pathogenic T. hyodysenteriae in their feces for over 2 months.

Infectious organisms can be transmitted from farm to farm in feces carried on contaminated boots or vehicle tires. There is also some evidence that other animals such as dogs, birds and flies may carry T. hyodysenteriae for periods adequate to permit movement from one premise to another.

Diagnosis
Typical outbreaks of swine dysentery may be diagnosed by observation of several pigs with watery feces containing blood and mucus and by the presence of appropriate lesions at necropsy. If possible, samples should be submitted to a laboratory for isolation and identification of pathogenic T. hyodysenteriae to make a definitive diagnosis of swine dysentery.

Several other diseases commonly confused with swine dysentery are: salmonellosis, trichuriasis (whipworm
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. G.Diesslin, Director, West Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.