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

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

J J VERMUNT AND D M WEST

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.164 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 168.1) rather than on the aetiology, which is often of a multifactorial nature or uncertain.164

Lameness in cattle is most commonly caused by conditions affecting the interdigital skin or horn and corium (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.48, 112, 122 The hind feet are affected by a greater variety of diseases and are also far more commonly involved than the front feet;5, 6, 122 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 the lateral digits of the front feet is more or less the same.

Infectious conditions— foot rot (interdigital necrobacillosis), interdigital dermatitis, digital dermatitis and heel erosion — of the feet, of which foot rot is the most important economically, account for approximately 70 per cent of cases of lameness.5, 6, 34, 122 Foot rot and interdigital dermatitis are common diseases worldwide which occur particularly in dairy and beef cattle 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 conditions prevail for prolonged periods.27, 94 Although foot rot 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.27 During wet conditions between 40 and 60 per cent of cattle are likely to be affected by interdigital dermatitis, but because it is a mild disease it is usually not diagnosed clinically and is of little or no consequence.27

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.5, 6, 91, 152 There is, however, very little information available on the prevalence of the various conditions in southern Africa.

In this chapter the infectious conditions of the feet of cattle (namely foot rot, interdigital dermatitis, digital dermatitis and heel erosion) which are caused, or thought to be caused, primarily by Fusobacterium necrophorum, Dichelobacter (Bacteroides) nodosus or Prevotella melaninogenica (Bacteroides melaninogenicus), are discussed, while the other non-infectious conditions that affect the feet are only described briefly, and particularly with a view to distinguishing them from some of the infectious conditions.

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 (Actinomyces) pyogenes, as well as other facultative, spirochaetal and diphtheroid bacteria, have been isolated from cases of foot rot and other diseases of the feet of cattle.15, 27

Figure 168.1  A sketch indicating the location of the different diseases of the feet of cattle

Figure 168.2  Chronic foot rot. (By courtesy of Prof. S.S. van den Berg, Department of Surgery, Faculty of Veterinary Science, Onderstepoort)

Of these bacteria, F. necrophorum is considered to be of primary importance in the aetiology of foot rot, 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 foot rot.27, 39, 55, 82, 147, 151, 162, 164 The aetiology of digital dermatitis is not yet fully understood, but spirochaetes (probably Treponema or Borrelia spp.) have been consistently isolated from lesions. It is suggested that these invasive spirochaetes, with a predilection for keratinized cells, produce a toxin which is keratolytic.23, 114 Although the aetiology of heel erosion is not well defined, subclinical laminitis has been implicated in its aetiology.58, 59 It has also been suggested that there is a linkage between interdigital dermatitis and heel erosion.151

Fusobacterium necrophorum is a frequent inhabitant of the gastrointestinal tract of healthy herbivores and pigs and is therefore commonly found in faecally contaminated environments. The pathogenic isolates of F. necrophorum that cause foot rot belong to either biovars A or AB and produce a soluble leukocidin and a haemolysin, while isolates that belong to biovar B produce little, if any, leukocidin or haemolysin, and are less pathogenic.45

Most sheep, goats, cattle and farmed deer are carriers of...

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