Focus issue on clostridial disease

Several clostridial diseases of humans and animals have been known for centuries. Botulism, for instance, was first recorded in 1735, after the consumption of German sausages, although the etiology was not discovered until 1895; its first neurotoxin was identified in 1944.¹ Many more clostridial diseases and their etiologies have been discovered since then and, more importantly, several vaccines and other preventive methods have been developed and are today commercially available worldwide.⁸ Notable progress has been made over the past 2 decades or so in fulfilling conventional and molecular Koch postulates for several clostridial diseases of humans and animals. This has contributed significantly to the understanding of the role of several clostridial species in human and animal disease.⁷

Clostridial diseases are, however, still alive and well today, and are among the main causes of disease, mortality, and loss of production in many animal species worldwide. The main reasons for the persistence of these diseases today are: 1) most clostridia are ubiquitous in the environment, and eradication of these microorganisms is virtually impossible; 2) vaccines and treatment are not yet readily available for some clostridial diseases; and 3) the diagnosis of several of these diseases remains challenging. Diagnosis is particularly complicated by the fact that several clostridia are found in tissues and body fluids of clinically healthy animals, which makes determination of their role in disease difficult. Because of this, diagnosticians must rely on diagnostic criteria other than the simple detection of a given microorganism to establish a diagnosis of most clostridial diseases. This highlights the difference between detection and diagnosis; one detects a microorganism or a toxin but diagnoses a disease or condition.³

Several clostridia may be detected frequently in specimens from sick animals, but this does not mean that they were responsible for disease. Diagnosing a clostridial disease requires meeting a set of diagnostic criteria that, for several of these conditions, have not been clearly defined. A classic example of this situation is the finding of Clostridium perfringens type D in the intestine of sheep. Because a variable percentage of healthy sheep can carry this microorganism in their intestines, its isolation from this environment does not equal a diagnosis of type D enterotoxemia. However, isolation of this microorganism from the intestine of a sheep with nervous signs, coupled with detection of epsilon toxin in the intestinal content, and observation of intramural vascular edema in the brain, is considered diagnostic for type D enterotoxemia.⁶ This and other sets of diagnostic criteria for several clostridial diseases are continuously evolving, and it is critical that diagnosticians are aware of them when dealing with these infections.

An important topic of which we know little, and that does not seem to be frequently considered regarding clostridial diseases, is the zoonotic or anthropozoonotic potential of these diseases. Although some evidence has been brought to light over the past few years that strongly suggests that several clostridial diseases may be transmitted from animals or animal products to people,^2,5 much remains to be done in this field.

Why a focus issue on clostridial diseases now? First, it is useful to bring together for the international literature some of the most important recent discoveries on a topic, in this case clostridial diseases. Among these discoveries are: new toxins (e.g., NetF); new detection methods and diagnostic criteria; and the ever-evolving field of taxonomy. Examples of taxonomic changes in the name of microorganisms include: Clostridium difficile is now Clostridioides difficile, and Clostridium sordellii is now Paeniclostridium sordellii; and there is a new toxinotyping system for Clostridium perfringens.⁴ Second, but no less importantly, there is still a great deal of confusion regarding some of the most prevalent clostridial diseases, their etiology, pathogenesis, diagnosis, and prevention. We hope that the articles presented in this focus issue will help dispel some of that confusion.