Transmission of swine dysentery by carrier pigs.

Swine dysentery (SD) was transmitted to healthy pigs by contact with experimentally-induced carrier pigs. Carrier pigs were produced by exposure of specific pathogen-free (SPF) swine to swine acutely affected with SD. When carrier pigs became acutely affected with SD, they were allowed to recover naturally or were treated with dimetridazole or ronidazole. Recovery was based on disappearance of clinical signs of SD. At a given time after recovery, normal SPF swine were housed with the carriers in a disinfected isolation unit to determine the ability of carriers to transmit SD. In each of 3 experiments, carriers that had recovered and remained asymptomatic for 11 to 25 days transmitted SD to contacts in 14 to 51 days. In 2 experiments, pathogenic Treponema hyodysenteriae was isolated from carriers 12 days before clinical SD was observed in contacts. Carriers which had recovered and remained asymptomatic for 70 and 90 days transmitted SD to contacts in 1 of 3 experiments. Treponema hyodysenteriae was isolated only from contacts with clinical signs of SD. In 4 experiments, carriers that had been treated with nitroimidazole compounds and subsequently recovered for 19 to 44 days failed to transmit SD. Culture of fecal samples on trypticase soy agar with 5% bovine blood and 400 microgram of spectinomycin/ml was helpful in predicting the carrier state, but phase contact contact microscopy of wet fecal smears was not.