Genital campylobacteriosis in cattle

GENERAL INTRODUCTION: AEROBIC/MICRO-AEROPHILIC, MOTILE, HELICAL/VIBROID GRAM-NEGATIVE BACTERIA

Introduction

Genital campylobacteriosis in cattle is caused by Campylobacter fetus venerealis, which is an obligate pathogen of the bovine genital tract.^{31, 53} A related species, Campylobacter fetus fetus, is an intestinal inhabitant that may also be found in the genital tract following ascending infection or venereal introduction. ³⁹ The primary mode of transmission of C. fetus venerealis is natural service,⁶⁷ but due to its ability to survive in cryopreserved semen, it can also be transmitted via artificial insemination.³⁹  Genital campylobacteriosis present with clinical signs in cows predominantly, while bulls are mostly asymptomatic. The clinical signs in cows  are associated with genital infection and abortion.⁷⁵

Campylobacteriosis is regarded as one of the most important causes of poor calving rates in cattle, and closely resembles the clinical appearance of infection caused by Tritrichomonas foetus.^{43, 73}  Campylobacter fetus venerealis and T. foetus often occur together.¹⁷

Aetiology

Campylobacter fetus was first described in the 1950’s by Akkermans and colleagues, and initially referred to as Vibrio fetus.^{4, 90} Within the Campylobacter genus two species are distinguished – C. fetus venerealis and C. fetus fetus.  The biotype intermedius is associated with C. fetus venerealis.¹⁰

Campylobacter bacteria are slender, curved, Gram-negative rods, 0.01 to 0.08 mm in width and 0.5 to 0.8 mm in length.  They appear spiral in shape, and in culture, two or more organisms can join at their ends to form a spiral chain.  Older cultures also sometimes display coccoid forms of the organisms.  The bacteria are motile due to propulsion from a single polar flagellum at one or both ends of the cells. Campylobacter fetus venerealis bacteria are characterized by their distinctive motion and morphology.

Campylobacter fetus is micro-aerophilic and requires an atmosphere with reduced O₂ (10 per cent) and increased (4 – 8 per cent) CO₂ to grow on solid media.  In semi-solid media, growth can occur under aerobic conditions.  While growth will occur at 25°C, the optimum temperature for growth is 37°C.  Cultures should be examined for growth after two to three days.  Colonies on blood agar attain a diameter of 1 -2 mm, are convex and raised. They are colourless to grey in appearance and non-haemolytic.  On moist media, growth may occur along the line of inoculation.

The biochemical properties of C. fetus includes reduction of nitrates and inability to ferment carbohydrates.  They are catalase- and oxidase-positive.  Campylobacter fetus venerealis is tolerant to 1 per cent glycine and produces H₂S.^{10, 32, 81}

Campylobacter fetus incorporates a heat-stable somatic antigen (O-antigen) into its lipopolysaccharide wall. While the subspecies C. fetus fetus contains the heat-stable antigens B and A-2, C. fetus venerealis contains antigens A and A-1 and Campylobacter jejuni carries the heat-stable C antigen.  There is no cross-reaction between these antigens.⁸¹

Several heat-labile antigens have been identified and many may be present in a single strain.⁷ They are antiphagocytic⁶³ and undergo structural changes in the animal which aids immune evasion. ^{29, 78} Antigenic variation is accompanied by genomic rearrangements.⁴⁵ The genus Campylobacter is characterized by a process of genome decay, made possible by the relatively small genome size (~1.5 Mb) and the loss of metabolic genes.⁴⁶

Epidemiology

Campylobacter fetus venerealis has a worldwide distribution. It has been reported in a number of countries including the USA,^{11, 74, 82} Canada,⁹¹ Australia,²⁶ South Africa,^{70, 77} Poland,⁸³ Great Britain,⁶⁵ and Nigeria.^{6, 61} While sporadic abortion storms have been reported mostly from developing countries in Africa and South America, it has also been reported in the developed world.⁴⁹

Genital campylobacteriosis in cattle occurs more common in production systems that make use of natural service.⁶⁷ Lack of regulatory control schemes and inadequate laboratory facilities are often cited as reasons for the poor control and widespread distribution of C. fetus venerealis, and the underestimation of its profound impact on profitability of beef farming through smaller calf crops, prolonged intercalving periods, replacement costs of infected bulls and reduced weaning weights.⁶⁶

Prevalence of C. fetus varies greatly across different regions in the world. Some surveys have failed to detect the organism in bulls.⁵⁹ A prevalence rate of 40 and 47 per cent have been recorded in seropositive cows during a rare outbreak in the USA.^{1, 3} In Australia, abortions due to C. fetus have been reported on 37 farms, and positive...