Genital campylobacteriosis in cattle

Genital campylobacteriosis in cattle

P C IRONS, A P SCHUTTE, M L VAN DER WALT AND G C BISHOP*

Introduction

Bovine genital campylobacteriosis (vibriosis) is a venereal disease of cattle caused by Campylobacter fetus subsp. venerealis and is regarded as one of the most important infectious causes of poor calving crops in southern Africa. It causes embryonic mortality, aberrant oestrus cycles, delayed conception, reduced fertility and, on rare occasions, abortions. Bulls are transiently or permanently infected; younger bulls lose the infection, but those older than three years may remain permanently infected and carry the infection from one breeding season to the next. Heifers and cows of all ages are susceptible and they develop an incomplete and transient immunity after exposure.

Campylobacter fetus subsp. fetus is generally associated with sporadic abortions in cattle in mid- to late gestation following ingestion of infected material. This organism may also cause abortion in sheep and a variety of other syndromes including abortion in humans.

Campylobacter sputorum subsp. bubulus, a saprophytic inhabitant of the alimentary tract, is encountered in cultures of preputial samples and must be differentiated from the pathogenic subspecies of C. fetus.

Campylobacter fetus was first described as a cause of abortion by McFadyan and Stockman in 1913,96 but the bacterium received little attention until it was incriminated as an important cause of abortion and ‘temporary sterility’ in cattle in the USA.112, 115 Terpstra and Eisma presented evidence that the same organism was responsible for ‘enzootische steriliteit’ in cattle in the Netherlands.141 The suggestion by Snyman137 in 1931 and Canham31 in 1948 that C. fetus could be responsible for bovine infertility in southern Africa was confirmed by Van Rensburg in 1954146 and expanded by others.9, 120, 123, 126

Campylobacteriosis is probably widespread in nearly all countries where cattle are raised.38, 41, 54, 58, 86, 106, 138, 148, 149, 159 In southern Africa, it has been reported in beef and dairy breeds.110, 123, 129, 159

Aetiology

In 1956 Akkermans and his colleagues first reported a catalase- positive and weak H2S-positive isolate which differed from the other campylobacters in that it was associated with abortion.6 Two subspecies, formerly classified as varieties, namely Vibrio fetus var. venerealis (C. fetus subsp. venerealis) and Vibrio fetus var. intestinalis (C. fetus subsp. fetus) were subsequently established.55 Until the early 1960s, all the micro-aerophilic vibrios isolated from cattle and sheep were classified under the genus Vibrio. However, based on genotypic and phenotypic differences, these organisms were reclassified as C. fetus.150

Currently, Campylobacter is a well-defined genus, although taxonomic problems still exist at the species level.136 The organisms are slender, curved, Gram-negative rods, 0,01 to 0,08 μm in width and 0,5 to 0,8 μm in length. They may have one or more spirals, or appear to be S- or gull-wing-shaped. In culture, two or more organisms joined at their ends form a spiral chain. In older cultures, coccoid forms may be present. Campylobacter organisms are motile and are propelled by a single polar flagellum at one or both ends of the cells. They have a characteristic darting, corkscrew motion. They are best examined under phase-contrast illumination, where they are recognized by their typical morphology and motion.

Colonies on blood agar attain a diameter of 1 to 2 mm, and are convex and raised. They are colourless to grey, and are non-haemolytic. On moist media, growth may spread along the line of inoculation.

Campylobacter fetus is micro-aerophilic and will only grow on solid media in an atmosphere with a reduced (10 per cent) oxygen and increased (4 to 8 per cent) CO2 tension.

In semi-solid media, growth occurs under aerobic conditions. A suitable micro-aerophilic atmosphere can be achieved by the use of specially designed gas incubators, by gas-generating kits used in anaerobic jars, or through the evacuation of air from anaerobic jars and its replacement with a mixture of inert gases. The optimal growth temperature is 37°C, but C. fetus can also grow at 25°C. Cultures should be examined for growth after two to three days.

The biochemical properties of C. fetus are well documented. Both C. fetus subsp. venerealis and C. fetus subsp. fetus are catalase- and oxidase-positive, reduce nitrates and do not ferment carbohydrates. The latter is tolerant to 1 per cent glycine and produces H2S.15, 18, 42, 53, 88, 91, 135, 136

Campylobacter fetus has two types of surface antigens. A heat-stable O-antigen (somatic) is incorporated in the lipopolysaccharide cell wall structure. The subspecies C. fetus subsp. fetus contains the heat-stable antigens B and A-2, while antigens A and A-1 are limited to biovars of C. fetus subsp. venerealis. Campylobacter jejuni carries the heat-stable C antigen. There is no cross-reaction between antigens A, B or C.136

Seven heat-labile antigens (of which up to five may be present in a single strain) have been identified.12 They are antiphagocytic95 and undergo structural changes in the animal which enable the organisms to overcome or escape the immune response.39, 124, 153 This antigenic variation is accompanied by genomic rearrangements.61

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