ISSN 2398-2993      

Bovine asthma

obovis

Synonym(s): Fog fever, pulmonary emphysema, atypical interstitial pneumonia


Introduction

  • Cause: nutritional respiratory disease caused by the ingestion of the amino acid L-tryptophan from lush grass or mouldy sweet potatoes, and the consequent production of the pneumo-toxin 3-methylindole by rumen bacteria.
  • Signs: acute respiratory distress.
  • Diagnosis: based on a history of movement of cattle from dry, sparse pasture to lush pasture. Definitive diagnosis on pathology.
  • Treatment: no specific treatment, palliative therapy and minimizing stress.
  • Prognosis: guarded, up to 30% mortality.

Pathogenesis

Etiology

  • Lush pastures contain the amino acid L-tryptophan.
  • Rumen bacteria convert L-tryptophan to 3-methylindole. Rumen function and fermentation
  • 3-methylindole is absorbed into the blood stream.
  • 3-methylindole is pneumotoxic.
  • Clinical signs ensue: interstitial pneumonia, emphysema and edema.
  • Mouldy sweet potatoes contain 4-ipomeanol pneumotoxin.

Predisposing factors

General

  • Moving animals from a sparse, dry pasture to lush green grass.
  • Pasture type is insignificant.
  • Access to mouldy sweet potatoes.

Pathophysiology

  • The metabolite 3-methylindole produced, or the pneumontoxin from mouldy sweet potato, is pneumotoxic.
  • Metabolism of 3-methylindole produces reactive intermediates that cause cellular damage in ciliated (type 1 pneumocytes) and non ciliated respiratory Clara cells.
  • Cellular damage causes degeneration, necrosis and exfoliation of these cells.
  • Type 1 cells that are lost are replaced by type 2 pneumocytes (adenomatosis) and lose respiratory function.
  • Pulmonary edema and  alveolar epithelial hyperplasia results.
  • Emphysema occurs due to severe dyspnea.

Timecourse

  • Clinical signs appear within two weeks of the move to lush pasture, often within two days.
  • Some schools of thought maintain that if signs havent appeared within three to four days of the move then disease will not occur.
  • Disease is acute but transient.

Epidemiology

  • Disease is nutritional in origin.
  • In contact animals are not at risk from affected ones.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Kerr L A & Linnabary R D A (1989) Review of interstitial pneumonia in cattle. Veterinary and human toxicology. 31 (3), 247-254 VetMedResource.
  • Hammond A C, Carlson J R & Breeze R G (1980) Prevention of tryptophan-induced acute bovine pulmonary oedema and emphysema. The veterinary record 107 (14), 322-325 PubMed.
  • Breeze R G (1975) Fog fever in cattle: cytology of the hyperplastic alveolar epithelium. Journal of comparative pathology 85 (1), 147 - 156 PubMed.

Other sources of information

  • Smith B. Large Animal Internal Medicine. Published by The C V Mosby Company. pp 596 - 598.

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