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Bovine asthma
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.
Presenting signs
- Typically affects a group of cattle, found with acute onset labored breathing.
Acute presentation
- Cattle may be found dead.
Geographic incidence
- Any area using 'fog' pastures for grazing cattle (lush green re-growth of grass after silage has been cut).
- Cold weather causes pastures to wilt which contains less L-tryptophan and have a lower risk of disease. Warmer areas have a higher prevalence of disease.
- Increased incidence in late summer/autumn.
Age predisposition
- Adult animals are more susceptible.
- It is postulated that the rumen bacteria of more mature animals convert L-tryptophan to 3 methlyindole more effectively and hence have more severe signs.
- Youngstock are often unaffected.
Breed/Species predisposition
- Beef cattle appear to be more commonly affected, but this is probably due to management practices.
Public health considerations
- None.
Cost considerations
- Disease has a 30% mortality and 50% morbidity within a group.
- Individual animal losses.
- Treatment costs.
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. Vet Human Toxicol 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. Vet Rec 107 (14), 322-325 PubMed.
- Breeze R G (1975) Fog fever in cattle: cytology of the hyperplastic alveolar epithelium. J Comp Pathol 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.