You may be frustrated by lab results where E. coli always seems to be the bacteria isolated. E. coli are common inhabitants in normal pig intestinal tracts, and many of the strains do not cause disease.
However, some strains cause significant disease, as shown in these two cases in nursery-age pigs. The strains that cause postweaning problems are almost always Beta-hemolytic, meaning they break down red blood cells.
E. coli grow rapidly and produce this hemolytic reaction after overnight incubation on culture plates. One recent case is typical of edema disease, while pigs in the second case had diarrhea and significant effects from bacterial toxins.
Case Study No. 1
During a recent visit to a 470-sow, farrow-to-finish farm, the manager reported nursery pigs weaned at about four weeks showed signs of acute Streptococcus. Five pigs in a room of 340 had died overnight and at least five more were down. A few pigs were showing nervous signs but minimal diarrhea. Eyelid swelling was evident.
Postmortems on three pigs indicated fluid accumulation (edema) in the stomach wall and intestinal lining. The small intestine was reddened, and one pig had developed a yellow membrane on the surface of the intestine. Other pigs had reddened intestinal tracts with a slight increase in fluid in the intestine. Lungs were normal and feed was present in the stomach.
Samples from the small intestine and brain yielded high numbers of hemolytic E. coli. Microscopic samples showed the edema, and the intestinal reaction was consistent with E. coli. The clinical signs, coupled with the hemolytic E. coli, were typical of edema disease. The isolate was saved for further testing in the event the problem returned.
Affected pigs were treated with injectable antibiotic and corticosteroid. Sulfamethoxazole-trimethoprim was added to the water. All pigs that were down died, but few additional pigs died. Subsequent groups haven't shown problems.
Edema disease usually occurs very suddenly; the affected pigs are difficult to treat, probably due to the shiga-like toxins associated with E. coli that caused the disease. The problem may occur at the time of feed change or stress. Treat repeated problems of edema disease with dietary changes or preventive antibiotics. It's important to correctly diagnose the disease, since infections that have similar signs, like strep, are treated differently.
Case Study No. 2
A nursery site receiving 1,000 pigs/week had a few pigs with diarrhea in March 2005. Cultures revealed a Beta-hemolytic E. coli typed as K88. A similar isolation was made in January 2006. In July 2009, three good pigs died. K88 and F18 E. coli strains were identified. Polymerase chain reaction tests were also positive for two different toxin genes (STa, STb).
Some changes were made in feed-grade antibiotics. Mortality averaged 1-2%, but by mid-August it was 4.5%. A direct-fed microbial product was tried in the water, and improved sanitation when moving between rooms (wash hands, foot baths) was recommended.
But clinical problems continued, and because both K88 and F18 were detected, diagnostics were repeated. This time only a K88 was detected, along with toxin genes LT, STa and STb. Mortality in two groups approached 10%. Pigs were gaunt, exhibiting sunken eyes and reddened skin. Watery diarrhea was occasionally present.
Antibiotic treatment became less effective, and the K88 water-based vaccination was tried on the Oct. 15, 2009 group. Pigs were vaccinated within 2-3 days of arrival with the vaccine given over a 4-6 hour interval. Sanitation procedures between groups are still in place.
Every group since October has received the vaccine, and mortality is now back to less than 2%. A few pigs are still treated by injection for clinical signs, and some are given neomycin in the water. Even though this vaccine is given a relatively short time before clinical signs appear postweaning, it has been effective. Possibly the avirulent vaccine is blocking the receptors where the E coli would like to attach, reducing the clinical problem.
Interestingly, another site in the area began receiving a small number of pigs from the same sow herd in the summer of 2009. This site has never had major problems with K88, and mortality is consistently 0.5-1%. This suggests the problem isn't coming with every group of pigs from the sow herd. If the problem site continues to stress sanitation, we hope to leave some groups unvaccinated.
These cases demonstrate that E. coli still can be a significant factor in weaned pigs; the clinical signs are usually different than those in neonatal pigs, and sample collection is important for an accurate diagnosis.