Clinical Signs Pigs of all ages are susceptible to swine dysentery, but the disease is most frequently seen in feeder pigs 8 to 14 weeks old. The incubation period for swine dysentery is highly variable and can range between 10 to 30 days. The acute form of the disease is characterized by severe and often fatal bloody diarrhea. Affected pigs may be wobbly in the hindquarters and show evidence of abdominal pain, such as stretching and kicking at the belly. The feces may be red, resembling tomato ketchup, or may have a black, tarry appearance.
Death usually results from dehydration caused by severe diarrhea.
In herds where the disease has become well-established, the only signs affected pigs may exhibit are lower weight gain and reduced feed efficiency. These carrier-shedder pigs are the major source of the disease on infected farms, and also transmit it to noninfected farms. Shedding of S. hyodysenteriae in the feces of birds, dogs and mice makes these species potential vectors of swine dysentery among herds. Several factors determine the extent and severity of swine dysentery in a swine herd. The dose of S. hyodysenteriae to which pigs are exposed depends on the degree of environmental contamination, which in turn is directly related to swine population density, level of hygiene, segregation of sick and poor-doing animals, and effectiveness of the medication strategy.