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Aerosol challenge of calves with Haemophilus somnus and Mycoplasma dispar
C Tegtmeier1, AngenO, S N Grell
1Danish Veterinary Laboratory, Bülowsvej 27, DK-1790, Copenhagen, Denmark. cot@svs.dk
Abstract:
The aim of the study was to examine the ability of Haemophilus somnus and Mycoplasma dispar to induce pneumonia in healthy calves under conditions closely resembling the supposed natural way of infection, viz. by inhalation of aerosol droplets containing the microorganisms. The infections were investigated by recording clinical data, cytokine expression of peripheral blood cells and pathology. Twelve calves were included in the study: Three animals were exposed to H. somnus only, and two to M. dispar only, whereas five were challenged to M. dispar followed by exposure to H. somnus 11-14 days later. Also, one calf was exposed to M. dispar followed by exposure to a sterile saline solution 11 days later, and one calf was only exposed to a sterile saline solution. Just one animal, only challenged with H. somnus, developed a focal necrotizing pneumonia, from which H. somnus was isolated. Thus, the ability of H. somnus and M. dispar to act as primary pathogens under these conditions were minimal and inconsistent.However, a transient rise in body temperature, a marked granulocytosis and increased levels of interleukin-8 in peripheral blood after inoculation with H. somnus indicated a clear systemic response, probably as a consequence of the natural non-specific local and systemic defence mechanisms acting in healthy calves.
Insights
Haemophilus somnus and Mycoplasma dispar showed minimal ability to cause pneumonia in calves. However, Haemophilus somnus induced a systemic response, indicating calf immune defenses were activated.
Area of Science:
- Veterinary Medicine
- Bovine Respiratory Disease
- Microbiology
Background:
- Bovine pneumonia is a significant concern in calf health.
- Haemophilus somnus and Mycoplasma dispar are suspected contributors to calf pneumonia.
- Understanding infection pathways is crucial for prevention.
Purpose of the Study:
- To assess the pathogenicity of Haemophilus somnus and Mycoplasma dispar in calves.
- To simulate natural infection routes via aerosol inhalation.
- To evaluate clinical, immunological, and pathological responses.
Main Methods:
- Infection of calves with Haemophilus somnus and/or Mycoplasma dispar via aerosol.
- Monitoring of clinical signs, body temperature, and blood cell counts.
- Measurement of cytokine expression (interleukin-8) in peripheral blood.
- Post-mortem pathological examination and microbial isolation.
Main Results:
- Only one calf challenged with Haemophilus somnus developed focal necrotizing pneumonia.
- Haemophilus somnus and Mycoplasma dispar demonstrated minimal and inconsistent pathogenicity as primary pathogens.
- Haemophilus somnus inoculation triggered a transient fever, granulocytosis, and elevated interleukin-8 levels.
Conclusions:
- Haemophilus somnus and Mycoplasma dispar have limited capacity to initiate pneumonia in healthy calves under experimental conditions.
- Calf's natural defense mechanisms effectively responded to Haemophilus somnus challenge.
- Further research may be needed to understand synergistic effects or specific host factors.
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