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The following sample collection would be a good starting point for sampling any enteric disease (diarrhea and/or vomiting) of unknown origin in both dogs and cats. While causes of diarrhea can be remote from the gastrointestinal system (heat shock, for example), MOST contagious or toxin‐associated GI disease results from a direct attack on the gastrointestinal system. Moreover, the distribution of lesions (grossly) is very helpful in determining the cause of disease. See Table 5.4

1 Feces:If abundant, feces collection can be made from the distal colon. Even if scant, feces can be scraped from the colonic mucosa or obtained by a swab. Postmortem feces are useful samples for multiple tests, including fecal antigen test (parvoviruses, see below). Pooling feces from the small intestine and colon has been noted to increase the sensitivity of the parvo antigen tests, which is sensible for a viral infection with a segmental distribution and episodic shedding. Also, the feces can be used for direct smear/fecal flotation/parasite analysis, or viral analyses. If collecting formalin‐fixed tissue for histologic correlate analysis, tissue should be collected from an undisturbed (unsampled) region of the colon (mucosa is fragile and will slough easily with handling).

2 Formalin‐fixed tissues:Histological samples should be taken in ALL CASES, no matter what supplementary diagnostic tests are chosen. Histology can provide a definitive diagnosis, it can direct to possible causes, or it will confirm or refute the results of other diagnostic tests. A general list for sampling an animal with enteric disease is found below. In nearly all cases, these samples would be sufficient to diagnose or exclude common shelter enteric pathogens. In cases where the agent or cause is unexpected, these samples would establish whether an enteric disease is inflammatory, infectious, toxic, or neoplastic.

Table 5.4 Necropsy and sampling for GI disease.

Feces

Formalin‐fixed tissues

Microbiology

Molecular diagnostics

Toxicology

Serology