Haemophilus and Histophilus spp. infections

The members of the genus Haemophilus and Histophilus are classified in the family Pasteurellaceae. The bacteria in this genus are pleomorphic and vary in morphology from minute to medium sized coccobacilli or rods (usually less than 1 µm wide and of variable length) to filaments. Haemophilus spp. may have capsules, and, as is the case of other Gram-negative bacteria, they have cell walls with endotoxic activity — attributes that may be important in the pathogenesis of the diseases that they cause.⁷

Haemophilus spp. are Gram-negative, aerobic or facultatively anaerobic, and require preformed growth factors such as factor X (protoporphyrin IX) and/or factor V (nicotinamide adenine dinucleotide [NAD] or NAD phosphate [NADP]) in culture media. Both these factors are present in blood, and this dependence on blood for their growth gave rise to the name of the genus. Factor V is also present in yeast extract and is elaborated by staphylococci, the latter giving rise to the phenomenon known as satellitism which occurs when a mixed culture of Haemophilus organisms and staphylococci are grown on a solid medium. Haemophilus spp. grow more luxuriantly when adjacent to colonies of staphylococci because of the diffusion of factor V from them into the surrounding medium.⁴

Nicotinamide adenine dinucleotide dependence is a relatively stable genetic property, but genes conferring independence can be transferred to Haemophilus spp. that usually require NAD (V factor). Such strains can also arise independently,³ and virulence is not affected.^{2, 3}

Haemophilus spp. are part of the resident bacterial flora of the mucous membranes of the upper respiratory tract and oral cavity of a variety of animal species and humans, but they may also be isolated from the vagina and the intestinal tract. With the exception of H. parainfluenza, the individual species of Haemophilus are host-specific.⁷

Of the Haemophilus parasuis and Histophilus somni are of veterinary importance, but the taxonomic position of the latter two species is unclear. It has been suggested that H. somni, H. agni, and Histophilus ovis may belong to a single taxon.⁷ However, ribotyping and DNA analysis⁶ as well as polymerase chain reaction (PCR) methods and plasmid profile analysis¹ show that H. somni and Histophilus ovis are distinct.

Other studies showed that they are one species, but that there are phenotypic and putative virulence factor differences between strains.

Haemophilus parasuis is the cause of Glässer’s disease, a peracute to acute disease of young pigs characterized by a serofibrinous polyserositis, polyarthritis and meningitis. Histophilus somni infections are responsible for a variety of syndromes in cattle, including septicaemia, thrombotic meningoencephalitis, pneumonia, myocarditis, arthritis, mastitis and infections of the reproductive tract of cows and bulls. H. agni very rarely causes septicaemia in sheep. The disease in lambs is fulminating and is associated with sudden death, whereas in adult sheep it is less severe. At necropsy, the disease is a typical haemorrhagic septicaemia, which is also characterized by the presence of scattered haemorrhages throughout the carcass, and multifocal small areas of hepatic necrosis.⁵

Both H. parasuis and H. somni are ubiquitous, but H. agni is rarely encountered.⁵

References

1. APPUHAMY, S., LOW, J.C., COOTE, J.G. & PARTON, R., 1998. PCR Methods and plasmid profile analysis for characterization of Histophilus ovis strains. Journal of Medical Microbiology, 47, 987–992.
2. BRAGG, R.R., 2002. Virulence of South African isolates of Haemophilus paragallinarum. Part 2: Naturally occurring NAD-independent field isolates. Onderstepoort Journal of Veterinary Research, 69, 171–175.
3. GROMKOVA, R. & KOORNHOF, H., 1990. Naturally occurring NAD-independent Haemophilus parainfluenza. Journal of General Microbiology, 136, 1031–1035.
4. BUXTON, A. & FRASER, G., 1977. Animal Microbiology. Vol. I. Oxford: Blackwell Scientific Publications.
5. KENNEDY, P.C., FRAZIER, L.M., THEILER, G.H. & BIBERSTEIN, E.L., 1958. A septicaemic disease of lambs caused by Haemophilus agni (new species). American Journal of Veterinary Research, 19, 645–654
6. KIRKHAM, C., BIBERSTEIN, E.L. & LEFEBVRE, R.B., 1989. Evidence of host-specific subgroups among ‘Histophilus ovis’ isolates. International Journal of Systematic Bacteriology, 39, 236–239.
7. MANNHEIM, W., 1984. Pasteurellaceae. In: KRIEG, N.R. & HOLT, J.G., (eds). Bergey’s Manual of Systematic Bacteriology. Vol. I. Baltimore, London: Williams and Wilkins.
8. ANGEN, O, 2016. Taxonomy of Histophilus somni. Current Topics in Medical Immunology, 396, 1-14.