North American Veterinary Licensing Examination (NAVLE) Practice Test

Edema disease in recently weaned piglets is primarily caused by specific strains of Escherichia coli. This condition is characterized by swelling, particularly around the eyes and in the brain, leading to neurological signs. The pathogenic strains involved produce a toxin known as verotoxin (also referred to as Shiga-like toxin), which leads to vascular injury and subsequent edema, particularly in the central nervous system and the intestinal wall.

The disease typically occurs in pigs between 3 to 8 weeks of age, shortly after weaning, when there is a shift in stressors and diet. This makes them more susceptible to infections caused by pathogenic E. coli. While other organisms listed are associated with gastrointestinal or systemic diseases in pigs, they do not specifically cause edema disease as E. coli does. Brachyspira hyodysenteriae is associated with swine dysentery, Lawsonia intracellularis is responsible for proliferative enteropathy, and Streptococcus suis is linked to meningitis and other systemic infections but not edema disease specifically.

Thus, the relationship between the causal organism and the specific clinical manifestation in the context of weaned piglets identifies Escherichia coli as the responsible agent for edema disease.