The most common infectious agents with potential to cause post-weaning diarrhea includes:
Rotavirus: This virus affects pigs from 3 days to 12 weeks of age.
E. coli: This bacteria has many variants and affects pigs as diarrhea or edema disease from birth to 16 weeks of age.
Coccidia (Isospora): This parasite includes signs and lesions that are seen in pigs from 4 days to 4 weeks of age.
Coccidia (Eimeria): This parasite is a dose- and hygiene-related, sporadic disease that occurs in pigs from 3 weeks of age to maturity.
Salmonella: This bacteria affects pigs of any age and is usually associated with inadequate hygiene or concurrent disease.
Lawsonia: This bacteria affects pigs from 4 weeks of age to maturity.

Less common infectious agents include:
Brachyspira: There are various species of this bacteria that are associated with colitis of variable severity.
Whipworm (Trichuris): This parasite can occur in pigs over 3 weeks of age and is still a threat.
Transmissible gastroenteritis (TGE): This virus occurs in pigs at 3 days of age to maturity and is still a threat (discussion to follow).

Obviously, other contributors to outbreaks of diarrhea include variation in feed ingredients or feed quality as well as variations in environmental control.

Gastric ulcer is not thought to have a primary infectious component. Hemorrhagic bowel syndrome (HBS) rarely manifests with diarrhea.

Accurate Diagnosis
With the number of permutations of infectious and noninfectious contributors to diarrhea, an accurate diagnosis usually requires laboratory testing of specimens from acutely affected animals, as well as a thorough on-farm assessment. The number of appropriate samples for diagnostic laboratory submission will vary by agent. The benefit of the investment in diagnostic laboratory testing is the targeted intervention that can be made as the result of an accurate diagnosis. This investment is optimized when sample and test selections are supervised by a knowledgeable and conscientious swine veterinarian.

Biosecurity also has an impact on all of the infectious diseases listed. It is important to recognize the difference between internal biosecurity measures, which impact the first eight agents listed, and external biosecurity, which impacts TGE. Internal biosecurity concepts focus on hygiene. Prevention of new infections to the herd is what external biosecurity is all about. TGE provides an ideal example.

Transmissible Gastroenteritis (TGE)
An increase in numbers of cases and transmission of TGE virus during the winter has long been observed. Graph 1 (attached) demonstrates a relatively consistent number of cases presented for TGE testing and fairly consistent annual number of TGE cases confirmed positive by Iowa State University’s Veterinary Diagnostic Laboratory over the last seven years.

Graph 2 confirms the seasonal distribution of TGE-positive cases. It also suggests that the consistent occurrence of TGE virus in the winter months is not simply a function of the number of tests performed. The rate of diagnosis of TGE has not changed in the past seven years.

Historically, starlings, fomites and traffic from farm to farm were considered important sources of herd infections. TGE is naturally inactivated by heat, sunlight and dryness, which explains seasonal occurrence (all of which have been conspicuously absent recently). One may have predicted that the fairly extreme biosecurity measures for controlling porcine reproductive and respiratory syndrome (PRRS) virus may also prevent the occurrence of TGE.

However, diagnostic laboratory evidence suggests that this is not true. It is suspected that transport vehicles remain the most likely method for transmission of external pathogens, including relatively fragile TGE virus. We all know that cleaning and drying of transport vehicles (or other fomites) is challenging during the winter, but these are the months where it matters most. Until TGE is controlled by external biosecurity efforts, it is likely that PRRS virus and other more daunting agents will continue to move freely.

Click to view graphs.

Kent Schwartz, DVM
Iowa State University Veterinary Diagnostic Laboratory