Chlamydiae have been isolated from fecal samples of clinically normal cattle, goats, sheep, and pigs in many parts of the world. Animals with clinically inapparent intestinal infections may shed chlamydiae in the feces for months and possibly years. Accordingly, the GI tract serves as an important reservoir and source for the transmission of these organisms. Chlamydiae, which may cause abortions (see Abortion in Large Animals: Abortion in Cattle) and pneumonia (see Chlamydial Pneumonia), can readily be isolated from feces of normal sheep and cattle. They have also been recovered from intestinal samples of animals affected with polyarthritis (see Arthropathies in Large Animals: Chlamydial Polyarthritis-Serositis in Large Animals), encephalomyelitis (see Sporadic Bovine Encephalomyelitis), and conjunctivitis (see Chlamydial Conjunctivitis). Most fecal isolates from ruminants are Chlamydophila (Chlamydia) pecorum, but Chlamydophila abortus can also be isolated. Chlamydia suis and Chlamydophila psit-taci are the most frequent species found in swine and avian feces, respectively. Intestinal infection plays an important role as an initiating event in the pathogenesis of several chlamydia-induced diseases, including avian chlamydiosis (see Avian Chlamydiosis).

While most intestinal chlamydial infections are clinically quiescent, primary chlamydia-induced enteritis has been seen under field conditions in newborn calves. Such infections may also lead to a change in the number of Escherichia coli in the GI tract, with abnormally high numbers in the abomasum and upper small intestine. Signs are more severe in colostrum-deprived calves or in those with only a partial transfer of colostral immunity. Affected newborn calves may have a transient watery to mucoid diarrhea with slight fever and nasal discharge. Rare natural cases of diarrhea in suckling piglets infected with Chlamydia suis have also been reported and reproduced experimentally in germ-free pigs, but both experimental and field studies indicate that infection in weaned pigs is typically asymptomatic. Many veterinary diagnostic laboratories do not routinely check diarrheic feces for chlamydiae; therefore, such an examination must be requested specifically. Treatments of choice are high doses of tetracyclines, administered parenterally or orally, or both.

Last full review/revision March 2012 by Jerome C. Nietfield, DVM, PhD, DACVP