PIG PROGRESS A research team has concluded that the viral disease - often considered the most deadly of all hog infections - spreads west at a speed of around 200 km per year. More here. The ear of an infected hog. ASF causes a condition called petechia - red or purple splotches due to bleeding into the skin. Photo credit - USDA RELATED: "In Hogs We Trust" - Part 3 - The consequences of animal diseases, worldwide.