For years there have been K88, 987P, F41 and K99 in the group of E. colis that mainly affects pigs before weaning. Add to that list F18, the newest E. coli pilus that carries a twist: it strikes pigs 10 days postweaning.

And it can strike with a vengeance, according to Harley Moon, DVM, professor in charge, Veterinary Medical Research Institute, Iowa State University (ISU).

"This E. coli seems to colonize and be shed in tremendous numbers in association with disease in the second week postweaning," he says. F18 can appear in conjunction with K88, producing profuse and sometimes fatal watery diarrhea and sudden deaths.

Particularly in large farms, gut edema has also been seen in association with F18 and K88 E. coli, producing death losses in the 10-20% range. Just as high can be impaired weight gains and other performance problems.

Survivors do reportedly develop an immunity to the infection. However, the arrival of new pigs in the system all of the time, provides a succession of susceptible pigs for this enteric nursery disease.

There are reports of nurseries experiencing the problem for months on end. There been a few cases of F18 E. coli now and then, but not an overabundance of reported problems, according to the ISU diagnostic laboratory.

To some industry sources, it's not that this newer E. coli has so much emerged as a major pathogen as it is that farms are so much larger, magnifying problems.

Therapy Moon says antibiotic therapy has proven frustrating for producers trying to cope with lethargic pigs off feed. The antibiotics seem to work for a while then resistance develops. Neomycin and gentomycin are two possible antibiotics to try.

Producers are also trying to encourage these weaned pigs to eat better by providing them with many small feedings per day and improving hygiene to prevent fecal-oral spread of the E. coli strain, he comments.

Some suggest that this E. coli infection is being precipitated by ration changes and/or pigs not having adequate feed available at all times. And one idea is to try and add fiber to the diet in the form of ground, whole oats or alfalfa meal to reduce diarrhea problems.

"There are likely some things we could do to modify the diet to help alleviate this problem," says Jerry Shurson, swine nutritionist and director of the Swine Center, University of Minnesota. He suggests adding high levels of zinc oxide, 2,000-3,000 ppm to the postweaning diet for up to two weeks as drug therapy.

Diet acidifiers may also make a difference by boosting acid levels of young pigs, keeping gut pH levels low, and thus helping to fend off disease organisms, says Shurson.

As far as suggestions of increasing fiber content to relieve diarrhea, he cautions that the use of less palatable feed ingredients such as ground, whole oats or alfalfa meal may further reduce feed consumption.

"High-fiber ingredients reduce the energy concentration of the diet, which further reduces energy consumption of the pig," he says.

The ultimate answer for treating the F18 E. coli probably lies with development of a vaccine, observes Moon. The challenge is much greater than developing a vaccine to protect the pre-weaning pig which is infected with E. coli during the first few days of life. Killed virus vaccines can be injected into the sow and the passive antibody response is passed along quite nicely to the pig via her milk, he notes.

But in the case of the postweaned pig, the job is more complicated because antibodies aren't coming out of the blood and into the sow's milk.

Instead, the vaccine must provide protection right to the gut of the pig, which must develop its own active immunity at the site, explains Moon. The other challenge is to time vaccination to avoid being blocked by maternal antibody, yet providing active antibody soon enough to protect nursery pigs from this newer E. coli challenge, he stresses.

It's a job that researchers globally are working on, says Moon. Best chance is to develop a modified live virus vaccine from isolates positive for the F18 E. coli, but negative for gut edema disease. It is the latter which seems to accompany and exacerbate the E. coli infection in young nursery pigs.

That way the vaccine could stimulate immunity, but wouldn't give off the enterotoxin associated with E. coli infections.

There's no doubt that F18 E. coli strains produced by the interaction of the bacterial and gut edema infections are in a class by themselves, states Dick Wilson, director of the E. Coli Reference Center at Pennsylvania State University. He says when you take an E. coli toxin and combine it with a Shiga-like toxin, as is seen with gut edema disease, you produce a dangerous combination. Shiga toxins can affect all animals and humans. The F18 E. coli is only found in young nursery pigs.