The owner of a small Tidewater farm raises a few pigs as a sideline. He sells dressed oven-ready piglets in the local Farmer's Market, but wants to expand into gourmet grocery stores in the DC and Richmond metropolitan areas. He wants to enlarge his production capability so he adds five more sows from a stock auction to his herd. Most of his older sows had already been bred with an eye to catching the peak holiday market for suckling pig orders and three of them were set to farrow between November 1st and 12th. Then disaster struck.
Six days days after the first litter was born the piglets began vomiting, developed a profuse watery diarrhea, and showed signs of excessive thirst. The entire litter of six piglets died three days later, and on that same day a second sow's litter aborted.
His veterinarian performed necropsies of three of first litter. Gross examination showed intestines bloated with gas and containing curdled milk (arrows, left). Intestinal segments from the dead piglets were collected for histological analysis as were fecal samples.
Three days after the death of the first litter, all his older (weaner) pigs also become sick, showing the same symptoms of diarrhea, vomiting, and severe dehydration. None of these died, but he lost the entire third litter within five days of its birth.
Based on the acute onset, 100% mortality among piglets between 5 and 7 days of age, the symptoms, and the necropsy findings, the veterinarian provisionally diagnosed an outbreak of transmissible gastroenteritis (TGE). TGE is a disease caused by a coronavirus that is easily passed from one pig to another.
Laboratory tests and immunostaining of the intestine of affected animals (right) confirm the diagnosis.
Ten months after the events, the weaner pigs that had become sick were apparently recovered, but all of them turned out to be "poor doers," failing to gain weight as rapidly as they should, despite quality feed.
Points to ponder:
1. What cells and tissues are affected by this virus? What, specifically, is happening in the piglets that's causing the diarrhea? What structural changes would you expect to see in the gut?
2. Why is the mortality so high in 4-7-day old piglets but not in weaned ones?
3. Why are the surviving 14-month-old pigs not doing well? What would be revealed by histological examination in these animals?
4. What triggered the outbreak?