Survival of Serpulina hyodysenteriae in an effluent lagoon

To determine the survival of Serpulina hyodysenteriae in an infected lagoon that received effluent from a confinement building housing swine dysentery-infected swine.

Prospective controlled trial.

48 shedder swine inoculated with S hyodysenteriae and housed in the building drained by the lagoon; 18 clinically normal detector swine confined in a separate building.

Shedder swine were inoculated with S hyodysenteriae by oral administration of 20 g of diced colon from swine infected with swine dysentery. The lagoon that received effluent from the building housing the shedder swine was assayed for S hyodysenteriae by providing lagoon effluent twice daily for 2 or 4 days to detector swine as their sole source of drinking water and by subsequently examining these swine for signs of swine dysentery. Smears from rectal swab specimens and sometimes fecal specimens were stained for detection of large spirochetes. Fecal and rectal swab specimens and colonic scraping specimens were examined for S hyodysenteriae by anaerobic microbial culture on blood agar containing 400 micrograms of spectinomycin/ml. All shedder swine were necropsied after removal from the confinement building, as were detector swine after developing diarrhea or after 42 days of monitoring.

For the first 5 to 6 days after removal of swine dysentery-infected shedder swine from the confinement building, lagoon effluent from the building remained infective. Detector swine, given lagoon effluent as their drinking water for a 2-day period, developed clinical swine dysentery, and S hyodysenteriae was cultured from specimens from these swine. Swine dysentery did not develop in each group of 2 detector pigs given lagoon effluent as their sole source of drinking water on days 7 and 8, 9 and 10, 11 through 14, or 15 through 18 after removal of the infected shedder swine. Large spirochetes were not observed on microscopy of stained colonic scraping specimens, and S hyodysenteriae and Salmonella spp were not cultured from specimens from these detector swine after being monitored for 42 days. Serpulina hyodysenteriae or Salmonella spp were not cultured from samples of the lagoon effluent.

Although many factors could influence the survivability of S hyodysenteriae in a lagoon, results suggested that a facility with an open gutter-flush system that housed swine dysentery-infected swine should remain idle for more than 5 to 6 days before repopulating with unexposed swine.