Corynebacterium pseudotuberculosis infections

Corynebacterium pseudotuberculosis infections

M W PATON, M G COLLETT, M PÉPIN AND G F BATH

Introduction

Infection with Corynebacterium pseudotuberculosis (C. ovis) most commonly causes caseous lymphadenitis (CLA), a chronic disease of sheep and goats that is characterized by abscessation of one or more lymph nodes. Less commonly, it results in pneumonia, hepatitis, mastitis, arthritis, orchitis, subcutaneous abscesses, abortion, stillbirth and perinatal mortalities in these species. A syndrome associated with haemolysis and icterus in sheep and goats may follow natural infection or the inoculation of culture material. This infection is also the cause of ulcerative lymphangitis, pectoral abscesses, folliculitis and furunculosis (referred to as ‘contagious acne’), mastitis and abortion in horses, and ulcerative lymphangitis in cattle.

Corynebacterium pseudotuberculosis was first described in 1888 by the French veterinarian Nocard, who isolated it from a case of ulcerative lymphangitis in a bovine. Three years later the same organism was isolated from a renal abscess in a sheep by Von Preisz,26, 40 hence the term ‘Preisz- Nocard’ abscessation.

Caseous lymphadenitis is a highly prevalent and economically important disease of sheep and goats and is responsible for considerable financial losses in some countries as a result of the condemnation and downgrading of infected carcasses and skins at abattoirs (these are where the prevalence becomes most overtly obvious), and reduced wool production.6, 11, 12, 15, 54, 66, 120, 144, 151, 162 In other countries, the disease is becoming more important following the introduction of infected small stock. The disease occurs in all continents, but was absent from Britain until the late 1980s.67, 102

Sheep affected by CLA produce approximately 4 to 7 per cent less wool in the year of initial infection than unaffected sheep.126, 127 The total annual (1987/88) economic loss as a result of CLA in Australia was estimated at Aust. $25 million because of reduced wool production, condemnations and trimmings of carcasses, and the cost of meat inspection.119

It is the most common infection in the so-called thin-ewe syndrome in the USA.65, 143 In a study in the western USA, the average prevalence in adult ewes was 42,4 per cent,162 while the average prevalence in 412 western Australia sheep flocks was 45 per cent.120

In South Africa, CLA was first reported by Jowett in 1909.88 It appears to be more common in the drier areas of South Africa, such as the Karoo, and the Eastern Cape and Free State provinces;177 a prevalence of 2,4 per cent of CLA in Merino sheep less than one year old and 7,4 per cent in older sheep from the Karoo, has been reported.112 During the period 1986 to 1988, 18,7 to 20,3 per cent of condemned carcasses at Cato Ridge Abattoir in the KwaZulu-Natal Province contained lesions of CLA. These condemnations represented 0,24 to 0,3 per cent of all the sheep and goats slaughtered at that abattoir during the period, and amounted to an annual loss of more than R400 000 for carcass condemnations alone, to which should be added unmeasured but substantial trimmings from carcasses.177 Caseous lymphadenitis was the most important reason for carcass condemnation in sheep at South African abattoirs in 1990 and 1991.4

Aetiology

Corynebacterium pseudotuberculosis is a short (0,5–0,6 × 1,0–3,0 μm), irregular, ovoid, Gram-positive rod almost resembling a coccus, and is facultatively anaerobic. In smears made from lesions, the organisms show marked pleomorphism, with coccoid, bacillary and filamentous forms invariably being present. They are often clumped together and are more numerous in early lesions. The filamentous forms may exhibit a barred or beaded appearance when stained. Pleomorphism is not as marked in cultured organisms. After 48 hours’ incubation at 37°C on blood tryptose agar, slow-growing, light cream-coloured colonies are produced, surrounded by a narrow zone of β-haemolysis. The colonies are granular, opaque, and flat with a matt surface, do not attach to the medium and can be moved around on the surface of the agar.47

Although only a single species is recognized, isolates are classified into two genetically different biotypes:10, 19, 158, 166 a nitrate-negative biotype infecting sheep and goats and a nitrate-positive biotype infecting horses.48, 108, 132, 165 Isolates from sheep and goats have a higher minimum inhibitory concentration for amikacin than isolates from horses and cattle.48 Both nitrate-negative and nitrate-positive biotypes have been isolated from cattle.10, 185 There are no biochemical or antigenic differences between ovine and caprine isolates.12 Under natural conditions, no cross species infection occurs with the respective biotypes, although human infection with the nitrate-negative biotype has occurred following contact with infected sheep.77 At least two toxic factors are produced by the organism and these may vary between strains (see Pathogenesis).

The organism can survive on moist debris on pen floors at room temperature for at least 10 days83 and for several months, or even more than a year, on fomites (e.g. hay or bedding), particularly if environmental temperatures are low.7 It can also survive in organically rich soil for long periods, but it is not known whether it multiplies in soil. Despite this, dusty conditions are not...

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