Cardiopulmonary Lesions in Sheep Produced by Experimental Acute Clostridium Perfringens Type D Enterotoxemia

Intestinal pathology in goats challenged with Clostridium perfringens type D strain CN1020 wild-type and its genetically modified derivatives

Clostridium perfringens type D is the causative agent of enterotoxemia in sheep, goats, and cattle. Although in sheep and cattle, the disease is mainly characterized by neurological clinical signs and lesions, goats with type D enterotoxemia frequently have alterations of the alimentary system. Epsilon toxin (ETX) is the main virulence factor of C. perfringens type D, although the role of ETX in intestinal lesions in goats with type D enterotoxemia has not been fully characterized. We evaluated the contribution of ETX to C. perfringens type D enteric pathogenicity using an intraduodenal challenge model in young goats, with the virulent C. perfringens type D wild-type strain CN1020; its isogenic etx null mutant; an etx-complemented strain; and sterile, non-toxic culture medium. The intestinal tract of each animal was evaluated grossly, microscopically, and immunohistochemically for activated caspase-3. Both ETX-producing strains induced extensive enterocolitis characterized by severe mucosal necrosis, apoptosis, and diffuse suppurative infiltrates. No significant gross or microscopic lesions were observed in goats inoculated with the non-ETX-containing inocula. These results confirm that ETX is essential for the production of intestinal lesions in goats with type D disease. Also, our results suggest that the intestinal pathology of type D enterotoxemia in goats is, at least in part, associated with apoptosis.

Experimental acute Clostridium perfringens type D enterotoxemia in sheep is not characterized by specific renal lesions

Type D enterotoxemia, caused by Clostridium perfringens epsilon toxin (ETX), is one of the most economically important clostridial diseases of sheep. Acute type D enterotoxemia is characterized by well-documented lesions in the nervous, cardiocirculatory, and pulmonary systems. However, discrepancies and confusion exist as to whether renal lesions are part of the spectrum of lesions of this condition, which is controversial considering that for many decades it has been colloquially referred to as "pulpy kidney disease." Here, the authors assess renal changes in an experimental model of acute type D enterotoxemia in sheep and evaluate the possible role of ETX in their genesis. Four groups of 6 sheep each were intraduodenally inoculated with either a wild-type virulent C. perfringens type D strain, an etx knockout mutant unable to produce ETX, the etx mutant strain complemented with the wild-type etx gene that regains the ETX toxin production, or sterile culture medium (control group). All sheep were autopsied less than 24 hours after inoculation; none of them developed gross lesions in the kidneys. Ten predefined histologic renal changes were scored in each sheep. The proportion of sheep with microscopic changes and their severity scores did not differ significantly between groups. Mild intratubular medullary hemorrhage was observed in only 2 of the 12 sheep inoculated with the wild-type or etx-complemented bacterial strains, but not in the 12 sheep of the other 2 groups. The authors conclude that no specific gross or histologic renal lesions are observed in sheep with experimental acute type D enterotoxemia.

Pathology and Pathogenesis of Brain Lesions Produced by Clostridium perfringens Type D Epsilon Toxin

Clostridium perfringens type D epsilon toxin (ETX) produces severe, and frequently fatal, neurologic disease in ruminant livestock. The disorder is of worldwide distribution and, although vaccination has reduced its prevalence, ETX still causes substantial economic loss in livestock enterprises. The toxin is produced in the intestine as a relatively inactive prototoxin, which is subsequently fully enzymatically activated to ETX. When changed conditions in the intestinal milieu, particularly starch overload, favor rapid proliferation of this clostridial bacterium, large amounts of ETX can be elaborated. When sufficient toxin is absorbed from the intestine into the systemic circulation and reaches the brain, two neurologic syndromes can develop from this enterotoxemia. If the brain is exposed to large amounts of ETX, the lesions are fundamentally vasculocentric. The neurotoxin binds to microvascular endothelial receptors and other brain cells, the resulting damage causing increased vascular permeability and extravasation of plasma protein and abundant fluid into the brain parenchyma. While plasma protein, particularly albumin, pools largely perivascularly, the vasogenic edema becomes widely distributed in the brain, leading to a marked rise in intracranial pressure, coma, sometimes cerebellar herniation, and, eventually, often death. When smaller quantities of ETX are absorbed into the bloodstream, or livestock are partially immune, a more protracted clinical course ensues. The resulting brain injury is characterized by bilaterally symmetrical necrotic foci in certain selectively vulnerable neuroanatomic sites, termed focal symmetrical encephalomalacia. ETX has also been internationally listed as a potential bioterrorism agent. Although there are no confirmed human cases of ETX intoxication, the relatively wide species susceptibility to this toxin and its high toxicity mean it is likely that human populations would also be vulnerable to its neurotoxic actions. While the pathogenesis of ETX toxicity in the brain is incompletely understood, the putative mechanisms involved in neural lesion development are discussed.

Yellow Lamb Disease (Clostridium perfringens Type A Enterotoxemia of Sheep): A Review

Simple Summary

Yellow lamb disease is a poorly researched and understood condition that seems to affect young sheep. The disease is characterized by hemolysis and is thought to be caused by alpha toxin-producing Clostridium perfringens type A, although a definitive association with this microorganism has not been confirmed. This is due, in part, to the ubiquitous nature of C. perfringens type A, which is naturally present in the intestine of healthy sheep, a fact that complicates the diagnosis. In this review, we summarize the available information on the etiology, clinical signs, lesions, diagnosis, prevention and prophylaxis of yellow lamb disease.

Abstract

Yellow lamb disease is an infrequent disease in sheep for which there is scant literature, and that has been reported in the US, Australia, New Zealand, South Africa and Europe, although anecdotal evidence indicates that it may have also been diagnosed in South America. The disease is produced by some strains of Clostridium perfringens type A that produce unusually high levels of alpha- toxin. Because C. perfringens type A is ubiquitous and is found in the intestine of most clinically healthy sheep, diagnosis of yellow lamb disease is challenging and requires quantitating the amount of this microorganism present in feces and/or intestinal content. Clinically, yellow lamb disease is characterized by depression, anemia, icterus and hemoglobinuria. Occasionally, sudden death may occur. Gross findings include generalized icterus, red urine in the bladder, enlarged, pale, and friable spleen, enlarged liver with an acinar pattern, and dark, swollen kidneys. Microscopically, yellow lamb disease is characterized by centrilobular necrosis of the liver, hemoglobinuria-associated acute tubular injury, splenic congestion, pulmonary congestion and edema. Although there are no vaccines specifically designed to prevent yellow lamb disease, several vaccines against the different types of C. perfringens may afford at least some level of protection against yellow lamb disease.

Reevaluation of whether a Functional Agr-like Quorum-Sensing System Is Necessary for Production of Wild-Type Levels of Epsilon-Toxin by Clostridium perfringens Type D Strains

Clostridium perfringens type B and D strains produce epsilon-toxin (ETX). Our 2011 mBio study (mBio 2:e00275-11, 2011, https://doi.org/10.1128/mBio.00275-11) reported that the Agr quorum-sensing (QS) system regulates ETX production by type D strain CN3718. However, subsequent studies have brought that conclusion into question. For example, we reported in 2012 (Infect Immun 80:3008–3017, 2012, https://doi.org/10.1128/IAI.00438-12) that the Agr-like QS system is not required for wild-type ETX production levels by two type B strains. Consequently, we reexamined whether the Agr-like QS system regulates ETX production in type D strains by using Targetron insertional mutagenesis to construct new agrB null mutants of two type D strains, CN3718 and CN2068. Western blotting showed that both agrB mutants still produce wild-type ETX levels. However, the newly constructed agrB mutants of both type D strains produced reduced amounts of alpha-toxin, and this effect was reversible by complementation, which confirms loss of functional AgrB production by these mutants since alpha-toxin production is known to be regulated by AgrB. Coupled with the previously published results for type B strains, these new findings indicate the Agr-like QS system is not usually necessary for C. perfringens to produce wild-type ETX levels.