How is swine dysentery–associated Brachyspira transmitted among pigs?

• A. Direct airborne spread between pigs
• B. Infected feces spread by dogs, rodents, and fomites
• C. Biting insects
• D. Contaminated water only

Answer: (B)

The main concept here is fecal-oral transmission through contaminated environments and vectors. Swine dysentery is caused by Brachyspira hyodysenteriae, which is shed in the feces of infected pigs. Pigs become infected when they ingest material contaminated with those feces, so the disease spreads primarily via the fecal material in the pen environment. This makes indirect spread via anything that can carry feces effective—dogs, rodents, and fomites (like equipment, boots, and other in-contact items) can move contaminated material from one pen to another, driving transmission.

Why the other ideas don’t fit as the primary route: the organism is not typically spread by direct airborne transmission between pigs, and biting insects aren’t recognized major vectors for this pathogen. Contaminated water can play a role, but saying “contaminated water only” is too narrow because transmission also occurs via contaminated feces carried by animals or fomites, not just water.