An overview of calf diarrhea - infectious etiology, diagnosis, and intervention

Cho, Yong-il; Yoon, Kyoung-Jin

Clostridium perfringens is a Gram-positive, sporeforming anaerobic bacterium that causes a wide range of diseases in mammals and birds [137] . These microorganisms can be subdivided into five toxin types (A, B, C, D, and E) based on the production of four major toxins: alpha (α), beta (β), epsilon (ε), and iota (ι) [111] . Type A strains produce α toxin alone, type B stains produce α, β, and ε toxins; type C type strains manufacture α and β toxins; type D strains secrete α and ε toxins; and type E strains produce α and ι toxins. Among these groups, type C has been frequently reported in conjunction with calf diarrhea [119] but not as common as some other enteric pathogens such as BRV, BCoV, E. coli, Salmonella spp., and C. parvum. The α toxin is the main lethal toxin and promotes cell lysis through the hydrolysis of membrane phospholipids [110, 128] . The β toxin is highly trypsin-sensitive and induces mucosal necrosis [111] . The ε toxin causes lethal enterotoxemia in domestic animals, and the ι toxin is responsible for dermonecrosis due to its high vascular permeability [111] . Enterotoxin causes diarrhea and intestinal cramping due to its effects on epithelial tight junction protein [86] . Beta-2 toxin, which is produced by all types of C. perfringens, has been recently postulated to synergistically function with enterotoxin [50] . Most domestic animals are susceptible to all types of C. perfringens due to the ubiquitous nature of the bacterium in the environment. Newborn calves which produce a low level of proteolytic enzymes (e.g., trypsin) in the gastrointestinal tract can be easily infected by C. perfringens type C since β toxin is recognized as the main virulence factor responsible for clinical signs seen in animals affected by this bacterium. Intestinal lesions in these infected animals are characterized by diffuse or multifocal hemorrhagic necrotizing enteritis and bloody fluid distension [6] .