Etiological diagnosis of bovine bronchopneumonia

In cattle, especially young ones, infectious bronchopneumonia is a major problem. While herd management and raising conditions are

In cattle, especially young ones, infectious bronchopneumonia is a major problem. While herd management and raising conditions are important risk factors, infectious agents ultimately are responsible for these pathologies.
Thus, several viruses such as BRSV, BVDV, BoHV1, BCoV, BPIV-3 and IVD, as well as mycoplasmas (especially Mycoplasma bovis), have the ability to damage the respiratory tract more or less severely and affect its natural defenses.

In addition, the lesions caused to the respiratory tract are likely to be superinfected by opportunistic pathogenic bacteria such as Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Bibersteinia trehalosi or Trueperella pyogenes.

Facing bronchopneumonia problems, the identification of the infectious agents involved (viruses and / or bacteria) allows better understanding of their dynamics within farms and guide the choice of specific preventive and curative measures (vaccinations or treatments).

In recent years, diagnostic methods have undergone remarkable developments. Thus, we now have real-time PCR tests that make it possible to detect most of the important infectious agents sensitively, specifically and quantitatively.

In addition, unlike traditional methods (viral isolation, bacterial culture), these PCRs are able to detect organisms that have not survived during transport to the laboratory and the results are available in a few hours instead of several days.

However, if the antimicrobial susceptibility of certain bacteria is to be assessed, bacterial culture is still required. As the samples are often polymicrobial, the laboratory will ideally use several culture media to maximize the chances of isolation (a “bacterial respiratory profile”).

The most representative samples of bronchopulmonary microbism, tracheal and bronchoalveolar aspirations, are difficult to obtain under regular cattle raising conditions. However, deep nasopharyngeal swabs are an excellent alternative both due to their easy execution and their representativeness of this microbism.
To take these samples, it is important to use long 30-inch double-guarded swabs (usually used for uterine swabs in mares) that allow the deep nasopharynx to be sampled while avoiding contamination of the samples by nasal flora.

If the samples are intended only for PCR examinations, it is unnecessary to place them in a specific transport medium: a saline solution (0.9% NaCl) is perfectly suitable. On the other hand, agar gel transport media that interfere with the extraction of nucleic acids must be prohibited.

Conversely, samples for bacteriological examinations require more precautions. Indeed, most respiratory bacteria die fairly quickly if they are not placed in suitable conditions. It is recommended to use an Amies liquid or agar gel medium, kept refrigerated (but not frozen!) and delivered quickly to the laboratory (<48 hours).

Regarding viruses and mycoplasmas, it is not useful to carry out individual examinations. On the contrary, it is even recommended to examine composite samples (pools of 3 to 5 samples). This reduces costs without significantly affecting analytical sensitivity while increasing diagnostic sensitivity.

The choice of animals to sample is obviously important. They must be at the beginning of clinical signs. Indeed, some viruses (especially BRSV) disappear quickly from the respiratory tract. In addition, animals that have recently been vaccinated with attenuated viruses must be avoided, as some of these viruses can persist for several days in the respiratory tract.

Unlike viruses, bacteriological examinations must be individual because the bacterial flora can vary considerably from one animal to another. If you want to obtain antibiograms, you must first use these examinations. Of course, samples must be taken from animals who have not previously received antimicrobials.

Biovet provides you with tubes containing Amies liquid transport medium that is suitable for both viruses and bacteria. The same sample (swab) can then be used for both PCR and bacteriology. For the samples to be examined in pool, we recommend submitting the samples individually, the laboratory will take care of constituting the pools.

In conclusion, when faced with bronchopneumonia problems, laboratory examinations, PCR and/or bacterial cultures, applied to carefully produced and preserved samples, can provide interesting help in determining the infectious agents involved and deploying appropriate preventive or curative measures.

PCR testing Bacteriological examinations
  • Applies to viruses and bacteria
  • Detects living and dead organisms
  • Very sensitive and specific method
  • Individual or composite samples
  • Refrigerated samples, eventually frozen
  • Simple (0.9% NaCl) or complex (Amies, liquid only) transport medium
  • Results available in a few hours
  • Applies to bacteria (except M. bovis)
  • Detects only living organisms
  • Very specific but less sensitive method
  • Individual samples only
  • Refrigerated but especially not frozen samples
  • Complex transport medium (Amies liquid or solid)
  • Results available after several days
  • Possibility to test antimicrobial susceptibility

For more information, feel free to contact us.

André Broes, D.V.M., Ph.D., Technical services Manager


References

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