An Overview Histophilus somni in Feedlot Cattle

Submitted by: buy generic cialis Megan Simard, UCVM Class of 2015


Histophilus somni is a common pathogen in feedlots and backgrounding operations common in Canada’s western provinces, with fall calves at the highest risk for infection (O’Toole et al. 2009).  It is one of the three major bacterial pathogens involved in the broader disease of bovine respiratory disease (BRD) which can affect up to 14.4% of all cattle entering a feedlot, along with Pasteurella multocida andMannheimia hemolytica (Portis et al. 2012).  H somni is a gram negative bacteria involved in many disease processes collectively called histophilosis.  It is a normal part of cattle microflora in the lower airways and is a commensal organism.  There are strains of pathogenic and non-pathogenic histophilus which have been isolated from cattle from both the nasal cavity and urogenital secretions in males and females (Janzen, Merck Manual).

 On culture it can be the only pathogen isolated from the nasal cavity, but more commonly it is seen in combination with other respiratory pathogens such as Mycoplasma bovis, Pasteurella multocida, and/or Mannheimia hemolytica (Headley et al. 2013).

Histophilus somni has specific bacterial characteristics which aid in its pathogenicity: 1) Its cell wall acts as an endotoxin, 2) Histophilus produces exotoxins which are damaging and potentially lethal to alveolar macrophages, neutrophils and vascular endothelium, 3) Histophilus cause the release of pro inflammatory cytokines and chemotactic factors.  These pro inflammatory cytokines also play a role in stimulating platelets and causing endothelial damage leading to thrombosis and vasculitis (Divers & Peak, 2008).

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