Edema Disease (ED) is an acute and often devastating bacterial infection that primarily targets pigs shortly after they are weaned. This enterotoxemia is caused by a toxin released by bacteria colonizing the gut. The disease typically strikes the healthiest, fastest-growing pigs in a group, often resulting in sudden and unexpected death. Once clinical signs appear, the fatality rate can approach 90%. This rapid progression and high mortality cause significant economic losses for swine producers globally.
The Etiology of Edema Disease
Edema Disease is caused by specific strains of Escherichia coli (STEC) that produce a powerful poison called Shiga toxin 2e (Stx2e). For the bacteria to establish an infection, they must first attach to the lining of the pig’s small intestine using specific adherence factors, most commonly the F18 fimbriae.
The disease is caused by the Stx2e toxin produced in the gut, not by the bacteria invading the body. Once released, the toxin is absorbed into the bloodstream and travels throughout the pig’s body. Stx2e specifically targets and damages the endothelial cells that line the small arteries and arterioles in various organs.
This damage increases vascular permeability, causing fluid to leak out of the circulation and accumulate in surrounding tissues, resulting in edema. The primary target organs for this vascular damage include the brain, the submucosa of the stomach, and the mesentery of the large intestine.
Identifying the Clinical Symptoms
The onset of Edema Disease is often sudden, sometimes resulting in the death of a healthy-looking pig with no previous signs of illness. These peracute deaths are often the first indication of an outbreak, typically occurring one to two weeks after weaning. Affected pigs may be found dead in good body condition, which can confound initial diagnosis.
In pigs that show symptoms before death, the characteristic sign is swelling, most noticeable around the face and eyelids. Swelling of the larynx can also occur, sometimes causing affected pigs to emit an altered squeal. Unlike other E. coli infections, Edema Disease often presents without diarrhea.
The most concerning symptoms are neurological, occurring when the toxin damages blood vessels in the brain. Pigs may display staggering, incoordination, and tremors as they walk. As the condition progresses, they may become recumbent, lying on their side and performing paddling movements. These signs indicate severe, often irreversible damage.
Immediate Treatment Protocols
Treatment for pigs showing clinical signs is often unrewarding due to the rapid progression of the disease and the toxin’s immediate impact. By the time neurological symptoms appear, the damage is often irreversible, and the prognosis is poor. Efforts focus on limiting the spread of the causative E. coli within the group and providing supportive care to surviving animals.
Antibiotics may be administered to clinically unaffected pigs, usually through the drinking water, to reduce the bacterial load and prevent further toxin production. The choice of antibiotic should be guided by sensitivity testing of the isolated E. coli strain. Moving affected pigs to a dark, quiet, and low-stress environment can help manage neurological symptoms.
Supportive measures include ensuring easy access to water and electrolytes to counteract dehydration. Sick pigs should be rapidly removed from the pen to a hospital area to prevent environmental contamination. In some outbreaks, abruptly limiting the feed for the entire group for a short period can help starve the E. coli population in the gut.
Long-Term Prevention and Herd Management
Controlling Edema Disease relies on a multi-faceted approach focused on reducing risk factors associated with weaning stress and nutritional changes.
Nutritional Management
Nutritional management is a primary control point, as E. coli thrive on undigested protein reaching the lower intestine. Producers should reduce the crude protein level in the post-weaning diet by two to four percentage points, using highly digestible protein sources.
Other dietary adjustments include:
- Incorporating higher levels of dietary fiber (e.g., oats or barley) to promote gut health.
- Limiting the amount of feed given to pigs in the first few days post-weaning to reduce undigested feed reaching the hindgut.
Vaccination and Pharmacological Tools
Vaccination is a direct and effective preventive strategy. Modern options include injectable vaccines that contain a genetically modified recombinant version of the Stx2e toxin. This toxoid neutralizes the toxin’s effect, providing active immunity to the pig.
Another management tool is the use of pharmacological levels of zinc oxide in the starter feed (typically 2,500 to 3,000 parts per million post-weaning, where permitted). Zinc oxide helps control E. coli proliferation in the gut.
Environmental and Genetic Controls
Environmental controls focus on minimizing stress factors like temperature fluctuations, drafts, and wet conditions. Maintaining excellent hygiene through scrupulous sanitation and using all-in/all-out management systems helps reduce the environmental load of the pathogenic E. coli. Some breeding programs utilize genetic selection to identify and remove pigs that lack the intestinal receptors for the F18 fimbriae, offering genetic resistance to the disease.