The Role of Histophilus somni (Haemophilus somnus) in Bovine Reproduction

Abstract

Histophilus somni (previously known as Haemophilus somnus) is a pathogen of cattle worldwide and it is a small, Gram-negative, coccobacillary, facultative anaerobic, non-spore forming, non-motile, non-capsulated, fastidious bacterium. The genus ‘Histophilus’ containing the single species “Histophilus somni” was recommended within the family Pasteurellaceae and includes bacteria previously described as Haemophilus somnus. Infection of cattle with H. somni may cause septicemia, thrombotic meningoencephalitis (TME), polyarthritis, fibrous pleuritis, suppurative bronchopneumonia, myocarditis, otitis media, mastitis and reproductive tract diseases. In the study from Pápa, Hungary there were in total 90 animals tested for H. somni infestation. The tested animals were separated in two groups, one with vaginal discharge (75 animals, out of which 60 were cows and 15 were heifers) and the other one without vaginal discharge (15 animals, out of which 10 were cows and 5 were heifers). It was revealed, that out of the group with vaginal discharge 53% of the cows and 47% of the heifers were infected with H. somni (solitary infection with H. somni or mixed infection with pathogenic or possible pathogenic bacteria). In the control group 29% of the cows, and 60% of the heifers were infected. A common finding in this study was, that H. somni was found most frequently in the animals with vaginal discharge either alone or in combination with Enterococcus spp. or Trueperella pyogenes and other pathogenic or possible pathogenic bacteria. The understanding of the virulence potential of H. somni is until to this date only partly understood, using traditional genetic, biochemical, and immunologic methods. Also identification of H. somni is difficult, as other aerobic bacteria (e.g. Proteus spp., Corynebacterium spp., Escherichia coli and Streptococcus spp.) tend to overgrow it. The spreading of H. somni has to be controlled, with the today’s most efficient way of artificial insemination and strictly controlled hygienic measures.