Table 3.
Overview of viruses and bacteria commonly isolated from samples of the respiratory tract in cattle
| Pathogen | Primary or Secondary Pathogen | Remarks | Reference |
|---|---|---|---|
| Bovine adenovirus | Primary, but controversial | Widespread, but generally mild disease, except immunocompromised calves (types 3, 4, and 7) Type 10 associated with lethal enteritis |
58, 59, 60, 61 |
| Bovine coronavirus | Primary, but controversial | As a sole agent, experimentally only able to induce mild disease. Outbreaks with single viral infection resulting in severe morbidity and mortality described in calves and adult cattle | 62,63 |
| BHV-1 | Primary | Limited to the nasal cavity, pharynx, and trachea. Immunosuppression by hampering function and number of white blood cells. Potentially lethal as a single agent | 62 |
| Bovine rhinitis virus A and B | Likely apathogenic | — | 39 |
| Bovine respiratory syncytial virus | Primary | As a single viral agent, able to cause lethal bronchopneumonia. In older animals frequently subclinical | 52,62 |
| Bovine viral diarrhea virus | Primary | Mainly immunosuppression by hampering function and number of white blood cells. Potentially lethal as a single agent | 62,64 |
| Parainfluenza virus type 3 | Primary | As a single agent, generally mild disease | 52,62 |
| Influenza D virus | Controversial, likely primary | As a sole agent, experimentally only able to induce mild disease. Epidemiologically linked with disease | 39,65 |
| Bibersteinia trehalosi | Secondary | Occasionally isolated from cattle. More pathogenic role attributed to this bacterium in sheep | 66 |
| Histophilus somni | Controversial, likely secondary | Part of the resident flora. Septicemia is a lethal complication resulting in myocarditis, polyserositis, and thrombotic meningoencephalitis. Risk factors of septicemia unclear | 52 |
| Mannheimia haemolytica | Controversial, likely secondary | Part of the resident flora, differences in strain virulence described possibly resulting in some primary pathogenic strains. Other studies show cattle to become ill from their own resident strain on exposure to other pathogens and/or risk factors | 11,49,52 |
| Chlamydia psittaci | Controversial, likely primary | Natural infections result in mild or subclinical disease | 75 |
| M bovis | Primary | Extended immunosuppressive effect on white blood cells combined with immune-evasive mechanisms resulting in chronicity. Clonal spread of a strain limited in time and space is the general rule | 46,47 |
| Mycoplasma bovirhinis | Apathogenic | — | 19 |
| Mycoplasma dispar | Controversial, likely apathogenic | Recently shown to be more part of the microbiome of feedlot cattle classified as healthy | 14,19,67 |
| Moraxella bovis/ovis | Secondary | Primary eye pathogen, occasionally isolated in pure culture from animals with bronchopneumonia | 68 |
| Pasteurella multocida | Secondary | Part of the resident flora. Strain virulence differences exist, and some disease presentations (eg, septicemia or peritonitis) have been linked to certain strains | 52,69 |
| Salmonella spp | Primary | Primary site of infection of most Salmonella spp is the gastrointestinal tract. Localization in the respiratory tract is possible, most likely after septicemic spread | 70 |
| Trueperella pyogenes | Secondary | Involved in purulent processes. Often regarded as characteristic for chronicity. However, naturally resistant to fluoroquinolones | 71 |
| Escherichia coli, Gallibacterium anatis, Enterobacter hormaechei, staphylococci, streptococci, fungi | Secondary | Single reports on cattle-specific strains isolated in pure culture in an outbreak of pneumonia in calves | 52,72, 73, 74 |
Multiple other bacterial species can be detected in the bovine respiratory tract. This table is limited to either known primary pathogens or frequently isolated pathogens, currently assumed to have a pathogenic significance.