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Haemophilus somnus

I. General Information

1. NCBI Taxonomy ID:

2. Introduction

Haemophilus somnus is a small, rod-shaped, gram-negative pleomorphic coccobacillus, (derived from the word cocci meaning “spherical shaped” and bacilli meaning “elongated”), with gram stain morphology similar to other species in this genus (as well as other genera of family Pasteurellaceae) . It is an encapsulated, non acid-fast, and non-motile organism with no observable flagella or pili for motility. First discovered in 1960, H. somnus was described as a “haemophillus-like organism” that caused infectious meningo-encephalitis (IME) of feedlot cattle in California and was also believed to be the infectious agent that caused the reported bovine central nervous system disease in Colorado of 1956. Although the organism does not produce a capsule, which is associated with the pathogenic properties of many bacteria, under certain conditions it does form an exopolysaccharide (slime layer). H. somnus can be either opportunistic pathogens or commensal of bovine mucosal surfaces. The bacteria commonly lives in the upper respiratory tract, prepuce and vagina of cattle and can also be found circulating in the bloodstream. H. somnus typically colonize in the respiratory tract, reproductive tract, and circulatory system of many herd animals such as cattle, sheep, and American bison. Cattle infections caused by this bacteria have been reported in many parts of the world including North and South America, Europe, Russia, Japan, Australia, New Zealand, South Africa, and Zimbabwe. Having the bacteria’s genome sequenced is useful because it can be compared to virulent strains to aid in the development of protective strategies and vaccines for cattle against diseases caused by H. somnus. H. somnus is a parasitic organism that typically lives as a commensal organism in its host. It is commonly found in upper respiratory tract, prepuce and vagina of cattle and can also be found circulating in the bloodstream. Like many haemophilus species, such as Haemophilus influenzae, H. somnus is a pathogen and is the cause of many fatal bovine diseases. They take over many of the host’s mechanisms in order to survive. Haemophilus somnus causes a wide variety of diseases ranging from pneumonia, abortion, arthritis, myocarditis, and septimia in cattle, sheep, and American bison. It is able to spread throughout cattle herds undetected until symptoms begin to occur. There are 3 primary forms that H. somnus is able to assume: reproductive tract, urinary tract, respiratory tract form (Microbe Wiki: H. somnus).

3. Host Ranges and Animal Models

Cattle, sheep, and American bison (Microbe Wiki: H. somnus).

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