Apparent Clostridium haemolyticum/Clostridium novyi infection and exotoxemia in two horses.

Abstract

Two clinical syndromes of ruminants are caused by exotoxemic infections with the Clostridium novyi group of bacteria: black disease (BD) from C. novyi type 8 and bacillary hemoglobinuria (BH) from C. haemolyticum (also known as C. novyi type D). 1,6 The pathogenesis of both BD and BH is generally believed to begin with ingestion of environmental organisms followed by seeding of liver Kupffer cells with spores. These spores lie dormant until some insult to the liver (e.g., trauma, parasite migration, infarction) results in the formation of a localized anaerobic environment that allows germination of the spores. The vegetative forms of these bacteria produce alpha and beta toxin (C. novyi type B) or beta toxin only (C. haemolyticum); the toxin(s), when absorbed systemically, cause the lesions and clinical signs of BD and BH, respectively. The salient lesion in both diseases is acute hepatic necrosis, with foci of exotoxigenic bacteria; other lesions are related to toxemia and generalized vascular damage. Ovine and bovine BD are characterized clinically by sudden death. There is usually evidence of liver fluke migration tracts in the liver; these are typically the inciting lesion. Bovine BH is characterized by peracute death and intravascular hemolysis with hemoglobinuria due to the action of the beta toxin. 6,8 Because of the overlap of clinical and pathologic findings between BD and BH, definitive diagnosis requires isolation and identification of the causative organism. However these organisms are extremely oxygen sensitive and have fastidious nutritional requirements making routine isolation difficult and unreliable as a diagnostic tool. Also, these organisms can be isolated from the livers of normal animals, which may result in false-positive diagnoses. Consequently, the diagnosis of BD or BH is usually made on the basis of clinical signs, gross and histologic lesions, and fluorescent antibody detection of C. novyi-group organisms in acetonefixed frozen sections or impression smears of affected liver. Clostridium novyi type B and C. haemolyticum are very closely related, and polyclonal antiserum made for either is typically cross-reactive and unable to differentiate between these 2 species. Although BD and BH are naturally occurring diseases of sheep, cattle, and other ruminants, BD has also been reported in pigs and there are 3 previous reports of BD in horses, all from Australia. BH has not been described in horses. Here, we describe a case of presumed BD in 1 horse (horse no. 1) and a case of presumed BH in another horse (horse no. 2). Both cases were submitted by veterinarians in private clinical practices to the Washington Animal Disease Diag-