NetF-associated necrotizing enteritis of foals and canine hemorrhagic gastroenteritis

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NetF-associated necrotizing enteritis of foals and canine hemorrhagic gastroenteritis


Iman Mehdizadeh Gohari, Valeria R. Parreira, and John F. Prescott


Introduction


Clostridium perfringens type A-associated diarrhea and enteric disease in dogs and foals is not well characterized, since the association of disease is complicated by the common presence of type A organisms in the bowel and feces of healthy animals. The recent description of a novel pore-forming toxin, NetF, which is strongly associated with these diseases, has shed light on the role of type A isolates in enteric disease of animals.


Etiology


There is a highly significant association between the presence of the toxin NetF and isolates of C. perfringens recovered from severe canine hemorrhagic gastroenteritis as well as from necrotizing enterocolitis in foals aged 1–5 days. C. perfringens strains producing NetF are clonal (two clones), so that canine and equine strains cannot be distinguished.


The NetF toxin found in type A C. perfringens is a recently discovered toxin which is a member of the beta-pore-forming toxin leucocidin-hemolysin family, an important group of clostridial necrotizing toxins (Figure 9.1). The toxin was designated NetF for several reasons: it belongs to the same family of toxins as the relatively recently described NetB, associated with necrotic enteritis of chickens; it is associated with disease in foals (hence the “F”); and the strains could be considered to be “type F” if the current classification of C. perfringens as types A–E is to be expanded. C. perfringens strains producing NetF also produce another closely related toxin called NetE; both are encoded on the same large plasmid, whereas the enterotoxin (CPE) and often the beta2 toxin (CPB2) are encoded on a separate large plasmid, sometimes in conjunction with another, similar toxin called NetG. Analysis of the upstream region of these net genes has shown the presence of potential VirR boxes in the promoter region of netE and netG, but not of netF. VirR is a critical regulator of virulence in C. perfringens. An equine ovarian cell line has been found to be most susceptible to NetF, with canine cell lines the next most susceptible cells. Unlike NetF, NetE and NetG do not seem to have toxic activity, but they are expressed in vitro. Interestingly, since all NetF-producing strains also encode CPE, there may be a synergistic pathogenic effect in the intestine of NetF and CPE, as has been described for beta toxin (CPB) and CPE in rabbits.

Image described by caption.

Figure 9.1 Phylogenetic analysis of representative members of the leukocidin/hemolysin superfamily. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. Toxins that were used include: alpha-hemolysin of C. botulinum, hemolysin II of B. cereus, alpha-hemolysin of S. aureus, putative CctA of C. chauvoei, and beta toxin of C. perfringens.


Epidemiology and clinical findings


Acute canine hemorrhagic gastroenteritis may occur in any breed and at any age, but small-breed dogs are over-represented, as are dogs aged 2–4 years. There is no apparent seasonal or gender predisposition, and rarely are there reports of recent dietary changes. Clinical signs commonly include a sudden onset of vomiting blood-stained material, followed by bloody diarrhea, although a small proportion of dogs may produce bloody but non-diarrheic feces. The feces have a characteristic foul odor. About 50% of dogs appear depressed and approximately 20% of dogs have painful abdomens on palpation. Ileus may be diagnosed radiographically in about half the cases, but most dogs do not appear dehydrated. Increased packed cell volume, hemoglobin concentration, and red blood cell count may reflect rapid fluid loss into the intestine.

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Oct 28, 2017 | Posted by in GENERAL | Comments Off on NetF-associated necrotizing enteritis of foals and canine hemorrhagic gastroenteritis

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