Page 862 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 837

VetBooks.ir 4.161 Table 4.10 Toxin production by different Clostridium

perfringens types

TOXINS
TYPE ALPHA BETA EPSILON IOTA BETA-2 ENTEROTOXIN
A √ ± ±
B √ √ √ ± ±
C √ √ ± ±
D √ √ ± ±
E √ √ ± ±

for monocytes. Most cases occur during summer
and early autumn. There tends to be close prox-
imity to freshwater. A variety of aquatic inverte-
Fig. 4.161 Marked hyperaemia of the serosal surface brates may be involved in the natural transmission
of the small intestine of a foal with fatal salmonellosis. of the disease. The mechanism by which N. risticii
causes diarrhoea and other clinical signs is unclear.
Interference with intestinal sodium and chloride
and produce toxins. It is unclear whether C. difficile absorption may be involved. The cause of lamini-
infection (CDI) develops following ingestion of toxi- tis, which frequently develops concurrently, is not
genic strains of C. difficile or overgrowth of C. difficile known.
residing in low levels in the GI tract; it is likely that
both situations occur. Although antimicrobial ther- Idiopathic colitis
apy is a risk factor for the development of CDI, the Idiopathic colitis is a syndrome likely to involve a
absence of a history of antimicrobial administration variety of different bacterial organisms and mech-
does not rule out CDI. anisms of disease. Presumably, disruption of the
normal microflora allows for the proliferation of
Clostridium perfringens-associated diarrhoea pathogenic organisms. Antimicrobial therapy, con-
C. perfringens is a gram-positive spore-forming current disease, transportation, diet changes and a
anaerobic bacterium that can produce a wide vari- high-grain diet are potential risk factors.
ety of toxins (Table 4.10). The clinical relevance of
some strains is unclear. C. perfringens enterotoxin Antimicrobial-associated diarrhoea
and beta-2 toxin have been associated with diar- Antimicrobial-associated diarrhoea is not a specific
rhoea in adult horses and foals. Type C strains have disease. Rather, it refers to cases of acute diarrhoea
been implicated in severe enterocolitis in foals. that are temporarily associated with antimicrobial
C. perfringens is a normal inhabitant of the GI tract administration. Administration of any antimicro-
in a large percentage of normal horses and foals. bial via any route can predispose horses to diar-
In some situations, C. perfringens can overgrow and rhoea; however, certain antimicrobials, including
produce a variety of toxins. Antimicrobial therapy, marcolides, are considered higher risk. Regional
dietary changes, stress, concurrent disease and differences also appear to be present. A variety of
transportation may be predisposing factors. infectious agents such as C. difficile, C. perfringens and
Salmonella spp. can be involved. It is presumed that
Potomac horse fever antimicrobials disrupt the normal protective bac-
N. risticii (formerly Ehrlichia risticii) is an obli- terial microflora in the intestinal tract, permitting
gate intracellular bacterium that has an affinity overgrowth of pathogenic bacteria.