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Actinomyces bovis infections

Actinomyces bovis infections

M M HENTON AND M G COLLETT

GENERAL INTRODUCTION: IRREGULAR, NON-SPORING, GRAM-POSITIVE RODS

Introduction

Actinomyces bovis is the cause of focal, pyogranulomatous osteomyelitis of the mandible (‘lumpy jaw’), and sometimes also of the maxilla in cattle. In horses, the organism has been implicated in ‘poll evil’ and ‘fistulous withers’, while in pigs, a closely related organism, A. hyovaginalis, causes a granulomatous mastitis.

Actinomyces bovis, isolated from cows with lumpy jaw, was first described by Harz in 1877.11, 21 The disease has been recorded in most countries,24 but it usually occurs sporadically in cattle in southern Africa.11 In the past ten years, A. bovis has been isolated only rarely at the Onderstepoort Veterinary Research Institute in South Africa, probably because clinical diagnosis is easy and specimens are seldom submitted for confirmation of the diagnosis.12

Aetiology and epidemiology

Actinomyces bovis is a facultative anaerobe. Colonies on brain–heart infusion agar are white to greyish-white. The organisms are straight or slightly curved Gram-positive rods (0,2 to 1,0 μm thick) or slender, branching filaments (1 μm thick and 10 to 50 μm long). Two serovars are recognized, one of which tends to be more filamentous.28 Some growth and biochemical characteristics are given in the introduction, Irregular, non-sporing Gram-positive rods: Table 1.

Actinomyces bovis is believed to be a commensal on the oropharyngeal mucosa of cattle;8, 20, 27, 28, 31 the oral mucosa of calves appears to be colonized during the immediate postpartum period when they are licked by their dams.14 The bacterium is not a normal soil inhabitant and has not been isolated from plants or soil.11 It may, however, be transiently presenton feed contaminated with saliva or exudate, but probably does not survive for long outside the body of the animal.11

In cattle, lesions commence when A. bovis gains a foothold in the submucosal tissues following mechanical trauma to the oral mucosa (e.g. by foreign bodies, coarse feed or silage), after the shedding and eruption of teeth,8, 14 or as a complication of periodontitis.20, 24, 31

Actinomycosis generally affects cattle between two and five years old.11 Of the laboratory animals, only the hamster is fairly susceptible to artificial infection with A. bovis.10

Pathogenesis, clinical signs and pathology

Little is known of the host–parasite interaction in A. bovis infections. 8 The presence of A. bovis in the oral cavity may explain why lesions occur more frequently here than at other sites of the body. The initial lesion, a necrogranulomatous inflammation, usually occurs in the mucosa and submucosa of the gums, from where it extends to, and invades, the adjacent mandibular or maxillary bone, causing a chronic, pyogranulomatous osteomyelitis.

In lumpy jaw, the first sign is usually a painless, localized, hard, immovable swelling of the mandible or maxilla at the level of the central molars. The lesion develops slowly over months. The swelling is often not detected clinically until a discrete, hard, osseous enlargement develops on the lateral surface of the mandible or maxilla, at which time the teeth in the affected area are often malaligned, buried in granulation tissue, and painful. The infection may extend to the adjacent soft tissues of the tongue, pharynx and subcutaneous tissues of the head and neck to cause further disfigurement and, in some animals, impairment of mastication or breathing.11, 20, 24, 31 Spread to the regional lymph nodes34 may occur, while involvement of the lungs, liver and vertebrae is rare.8 The animal may eventually become emaciated, in which case it will have to be culled.24

In the affected bone, necrosis and proliferation of bone and granulation tissue occur together and give rise to an enlarged, honeycomb appearance (Figure 192.1). Small abscesses, sinuses and sequestrated trabeculae of the affected bone (‘bone sand’) are also found in the lesions20 and there is extensive proliferation of granulation tissue in the soft tissues adjacent to the affected bone. Frequently, multiple sinuses open onto the skin of the head or mucous membrane of the oral cavity, discharging a thick, mucoid, tenacious, copious, greyish-yellow, non-odorous exudate which contains small granules of 1 to 3 mm in diameter. During the earlier stages of their development, these granules are soft and yellowish-white, but later they become opaque and hard as a result of mineralization, at which time, because of their consistency and colour, they are referred to as ‘sulphur’ granules.1, 3, 13, 20, 24

Figure 192.1 Actinomycotic lesion in an ox. Note the honeycomb appearance caused by extensive necrosis and concurrent proliferation of bone

Actinomycotic granulomas are characterized by the presence of ‘sulphur’ granules in an exudate composed of varying numbers of neutrophils and large epithelioid cells in the centre, and Langerhans’ giant cells, lymphocytes, plasma cells and dense connective tissue on the periphery of the lesions.13, 18, 19

Smears made from crushed granules reveal a conglomerate of filamentous bacteria surrounded by tissue reaction material and pus.24, 28 ‘Sulphur’ granules observed histologically in tissue sections are smaller than those in smears prepared from the exudate. In tissue sections, the granules are eosinophilic and consist of a matrix composed of a hyaline, polysaccharide- protein complex in which, particularly in the peripheral zone, is embedded a mycelial mass of tangled, delicate, Gram-positive, bacterial filaments and coccoid forms.18, 20, 22, 23 The surface of the granule usually contains radiating eosinophilic, Gram-negative ‘clubs’ (15 × 3,5 μm) composed of lysed bacteria encased in layers of a calcium phosphate-protein complex which is generated by phosphatase activity in the inflammatory exudate.3, 8, 22 About half the composition of granules is calcium phosphate.22 Immunohistochemical studies19 have shown that the clubs (also called Splendore-Hoeppli material) do not represent antigen- antibody complexes as has been previously suggested.8 Club formation indicates bacterial regression accompanied by progressive mineralization of the granules.3, 22

In addition to lumpy jaw, actinomycotic infections in cattle are rarely the cause of localized granulomas in the trachea2, 30 and lungs,4, 9 and of orchitis.16

In horses, A. bovis may cause ‘poll evil’ (supra-atlantal bursitis) and ‘fistulous withers’ (supraspinous bursitis).15, 20, 26, 27, 31 Chronic purulent discharging fistulas in the region of these bursas are typical.25 Abscessation of mandibular lymph nodes due to A. bovis infection has also been described.5 Actinomycosis in pigs is now considered to be caused by A. hyovaginalis (see Actinomyces hyovaginalis infections).

Diagnosis

A provisional clinical diagnosis of lumpy jaw can be made on the physical appearance of the lesions in the mandible or maxilla. The diagnosis can be confirmed by microscopic examination of ‘sulphur’ granules or of biopsy specimens of the lesions. Smears of pus taken at random for examination may be unrewarding. For better results, the tenacious pus should be collected in a test tube containing saline, broth or 10 per cent KOH, and shaken in order to loosen the granules from the adhering pus. The resulting mixture is then poured into a petri dish and the granules collected, crushed on a glass slide, stained with Gram’s method and examined microscopically.11, 22, 23, 31 A great diversity of Gram-positive bacterial forms are evident, including branching filaments, cocci and rods of varying sizes, creating the impression of a mixed infection.

Since A. bovis organisms fragment readily, they should be differentiated from Trueperella (Corynebacterium) pyogenes, which may also be cultured from specimens obtained from the lesions of lumpy jaw.17, 20

Confirmation of the diagnosis of lumpy jaw require laboratory culture and identification of the organism. Anaerobic culture of soft-tissue lesions may yield Fusobacterium necrophorum, Bacteroides spp., Peptostreptococcus spp. and Trueperella spp. in addition to A. bovis,2 as the latter organism is able to reduce the redox potential in the affected tissues (see the introduction, Anaerobic Gram-negative irregular rods).

Differential diagnosis

Lumpy jaw of cattle is sometimes confused with ‘wooden tongue’ caused by Actinobacillus lignieresii infection.8 Osteomyelitis of the mandible and maxilla may also be caused by a variety of other bacteria (such as T. pyogenes) following periodontitis. Abscesses in subcutaneous soft tissues of the head caused by T. pyogenes are generally moveable, in contrast to the firm swelling and involvement of bone in A. bovis infection. Grass awns may penetrate and cause abscesses in the oropharyngeal submucosa.24 Examination of the pus obtained by needle puncture is a helpful procedure that may assist in differentiating between these infections.

The presence of ‘sulphur’ granules is not specific for A. bovis infections since they also occur in the pus from lesions caused by Nocardia spp. (variably acid-fast), Streptomyces spp., Actinobacillus lignieresii (Gram-negative) and Staphylococcus aureus (botryomycosis) infections in cattle.34 Most of the ‘sulphur’ granules of A. bovis infections are 2 to 3 mm in diameter,20, 27, 31 while granules from non-A. bovis lesions are generally much smaller and softer and difficult to detect on macroscopic examination.3, 11, 31 Laboratory culture and identification of the organism is essential for a definitive diagnosis.

Apart from A. bovis, ‘poll evil’ and ‘fistulous withers’ in horses may also be caused by Brucella abortus and Brucella suis, Streptococcus zooepidemicus, Staphylococcus spp., Pasteurella spp., a number of enterobacteria, as well as the nematode, Onchocerca cervicalis.7, 20, 25

Control

Actinomycetes are sensitive to iodine14 and penicillin.28 Localized skin or mucosal lesions can be treated by the topical application of Lugol’s solution or tincture of iodine. 11 Treatment of lumpy jaw and other actinomycotic granulomas should involve the intravenous administration of sodium iodide at the dosage rate of 1 g NaI/15 kg body weight dissolved in a litre of sterile isotonic polyionic fluid, given every second day for three treatments, followed by the administration of NaI administered per os on a daily basis at the same dosage rate until signs of iodism appear, 32 and intramuscular penicillin G (10 000 000 IU per day for three weeks).2, 24, 31 Apart from iodism, abortion in pregnant cows is another potential complication of systemic iodine treatment.2, 6

Other antibacterial drugs which can be used include the tetracyclines, cephalosporin, chloramphenicol, lincomycin, rifampicin, erythromycin, and vancomycin.28, 29 Although good therapeutic results have been claimed for streptomycin17 and isoniazid33 in the treatment of lumpy jaw, Actinomyces spp. are generally resistant to the aminoglycosides, antifungal drugs and most tuberculostatics.29

Surgical drainage, curettage and iodine irrigation may be beneficial in circumscribed lesions.11 Because of the nature of the bony lesion, however, clinical cure in advanced cases is unlikely, although further enlargement of the lesion may be arrested and significant reduction in size may even occur. 17, 33 Recurrence of lesions is common in both medically and surgically managed cases.2

Very coarse feed should be milled in order to minimize possible oral trauma.

Fistulous withers are treated by parenteral administration of antibacterial drugs as well as surgically by radical excision of affected tissue and the spinous rocesses of affected vertebrae, but about 30 per cent of cases recur.7

References

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