Fusobacterium necrophorum, Dichelobacter (Bacteroides) nodosus and Bacteroides spp. infections

GENERAL INTRODUCTION: ANAEROBIC GRAM-NEGATIVE, IRREGULAR RODS

Infectious diseases of the feet of cattle

Introduction

The lack of a standardized terminology is a serious limitation when studying the various infectious and non-infectious diseases of the feet of cattle.¹⁸³ Different terms are often used to describe the same condition. In an effort to clarify the situation it has been decided that the name given to a particular disease should be based on the anatomical structures and the part of the feet involved (Figure 1) rather than on the aetiology, which is often of a multifactorial nature or in some conditions uncertain.¹⁸³

Lameness in cattle is most commonly caused by conditions affecting the interdigital skin, or horn and corium (the latter being modified dermis) of the claws, whereas that which results from conditions affecting parts of the leg proximal to the feet (non-digital conditions) is relatively rare.¹²⁹ The hind feet are affected by a greater variety of diseases and are also far more commonly involved than the front feet;^{7, 8}  85 per cent of lesions involve the abaxial (or lateral) digits of the hind feet. In contrast, the prevalence of disease conditions in the medial and lateral digits of the front feet is more or less the same.

Infectious conditions— interdigital necrobacillosis (foot rot), interdigital dermatitis, bovine digital dermatitis and heel erosion — of the feet, of which interdigital necrobacillosis is the most important economically, account for approximately 70 per cent of cases of lameness.^{7, 8, 42} Interdigital necrobacillosis, interdigital dermatitis and to a lesser extent bovine digital dermatitis are common diseases worldwide which occur especially in dairy and beef cattle that are kept under intensive conditions, but they may also have a similar prevalence in cattle farmed under extensive conditions in areas with high rainfall and where muddy underfoot conditions prevail for prolonged periods.^{33, 107} Although interdigital necrobacillosis usually occurs as sporadic cases, 20 per cent or more of the animals in a herd may be affected over a period of several months.³³ During wet conditions between 40 and 60 per cent of cattle are likely to be affected by interdigital dermatitis, but as it is typically a mild disease it is usually not diagnosed clinically and is therefore of little or no consequence.³³

Collectively, the different conditions that affect the feet of cattle may cause significant economic losses. Studies have been done to determine the prevalence rates of some of them in affected herds in a number of countries.^{7, 8, 106, 169}

In this chapter the infectious conditions of the feet of cattle (namely interdigital necrobacillosis,  interdigital dermatitis and heel erosion) which are caused, or thought to be caused, primarily by Fusobacterium necrophorum, Dichelobacter (Bacteroides) nodosus or Prevotella melaninogenica, (formerly Bacteroides melaninogenicus) are discussed, whereas the non-infectious conditions that affect the feet are only described briefly, and particularly with a view to distinguish them from some of the infectious conditions. Several groups of spirochaete bacteria of the genus Treponema are most likely involved in the aetiology of bovine digital dermatitis, as these organisms are consistently found in lesions of this infectious condition.⁹⁵

Aetiology

The aetiologies of infectious conditions of the feet of cattle are multifactorial because of the interrelationships which exist between the infectious agents on the one hand, and the host and environmental factors on the other (see Epidemiology and Pathogenesis).

Several infectious agents, including F. necrophorum, D. nodosus, P. melaninogenica, and Trueperella (formerly Arcanobacter) pyogenes, as well as other facultative, spirochaetal and diphtheroid bacteria, have been isolated from cases of interdigital necrobacillosis and other diseases of the feet of cattle.^{15, 33}

Figure 1 Diagram indicating the location of the different conditions affecting the feet of cattle

Of these bacteria, F. necrophorum is considered to be of primary importance in the aetiology of interdigital necrobacillosis, while the others, particularly P. melaninogenica, D. nodosus and T. pyogenes, may in some instances play a contributory role.¹⁵ Interdigital dermatitis is caused by benign strains of D. nodosus and is considered to predispose to interdigital necrobacillosis.^{33, 65, 93, 164, 168, 181, 183} The aetiology of digital dermatitis is not yet fully understood, but...