What did the USDA-APHIS root-cause investigation identify as the most likely entry route for PED into the United States?

• A. A cross-species jump from prairie dogs
• B. Feral swine from Mexico
• C. The feeding of food waste containing undercooked pork (pig swill) from cruise ships to backyard pigs
• D. Flexible intermediate bulk containers containing pig feed

Answer: (D)

The main idea this question targets is how PED entered the United States in the observed outbreak pattern. The root-cause investigation concluded that contaminated pig feed delivered in bulk was the most likely entry route, specifically pig feed transported in flexible intermediate bulk containers. This makes sense because feed supply chains connect farms across wide areas, and FIBCs are widely used to move large quantities of dry feed, which can become contaminated and then disseminate the virus if not properly cleaned or segregated. PEDV can survive in dry feed ingredients for periods long enough to infect herds that later consume the product, so a single contaminated container or batch can affect multiple farms along the distribution network.

The other options don’t fit the evidence as well. A cross-species jump from prairie dogs isn’t supported by outbreak timing and patterns. Feral swine movements from Mexico would require strong, consistent wild-swine involvement that wasn’t demonstrated. Pig swill feeding from cruise ships to backyard pigs was possible in theory, but regulatory controls and patterns of spread pointed to feed ingredients and bulk packaging as the more plausible route in this investigation.