Wednesday, July 16, 2003

The Interstitial Pneumonias

The term interstitial pneumonia or alveolar epithelial hyperplasia has been used to designate the lung diseases in which there are inflammatory lesions of the septa or dividing wall of the air sacs or alveolar of the lung.

The term and understanding of atypicalpneumonia has been difficult, particularly in regard to terminology and etiology. All of these terms have been used interchangeably:
     1.Acute Bovine Pulmonary Emphysema (ABPE) Fog Fever
     2.Atypical Interstitial Pneumonia (AIP) Usually seen in the feedyard environment.
     3.Pulmonary Adenomatosis Farmers Lung
     4.Acute Respiratory Distress Syndrome (ARDS) Plant toxins, etc

Acute Bovine Pulmonary Emphysema (ABPE),Fog Fever, is an acute respiratory distress syndrome that usually occurs in the fall in adult beef cattle moved from dry, sparse overgrazed pasture to lush, green pasture. Almost all
outbreaks of ABPE occur within two weeks of pasture change. ABPE is caused by ruminal production of 3- methylindale (3MI) from ingested
L-tryptophan (TRP) in the feedstuffs.
Adult breed cows are most commonly affected because this is the type of animal most likely to be subjected to abrupt pasture change.The type of pasture appears to be unimportant, as long it is lush.
In severe cases there is an acute onset of severe dyspnea (difficult breathing) with a loud expiratory grunt, frothing at the mouth and open mouth breathing with tachypnea (rapid breathing). It is important to note that coughing is not
In animals that die, ecchymotic to petechial hemorrhages occur in the larynx, trachea and bronchi with frothy fluid is present in the airways, and there will be congestion and edema of the lung giving it a smooth, glistening, and
glasslike appearance.

An Acute Respiratory Distress Syndrome (ARDS) is any respiratory condition characterized clinically by a sudden onset of severe dyspnea (difficult breathing) and pulmonary lesions of congestion, edema, thickening of the alveolar epithelium and interstitial emphysema. One example of ARDS would be Moldy Sweet Potato toxicity, which is caused by ingestion of a furanoterpenoid toxin.
There is an acute onset of tachypnea and hyperpnea (rapid excessive breathing), tachycardia, and dyspnea with loud expiratory grunting, frothing at the mouth, extension of the head and neck, flaring of the nostrils and frequent deep coughing. Signs usually occur within 1 day of exposure and death may occur 2-5 days.
At necropsy the lungs are wet, firm, enlarged and fail to collapse with yellow gelantinous edema fluid and emphysema throughout.

Pulmonary adenomatosis, Farmers Lung, is an allergic respiratory disease caused by inhalation of organic dusts. Farmers Lung is caused by exposure
to the dust from moldy hay, grain, or other vegetable matter containing spores and products of themophilic actinomycetes such as Micropolyspora
faeni and Thermoactinomyces vulgaris.
Pulmonary adenomatosis is a disease of confined adult cattle, primarily dairy cattle. Typically a succession of acute cases occurs during the winter housing period. The acute form is indicative of recent exposure and is characterized by a sudden onset of dullness, decreased appetite, hypogalactia, coughing, expiratory tachypnea, and dyspnea. There is a moderate transit fever. The chronic form is insidious in onset and may not be detected until there is considerable fibrosis. Some may not be detected until turned out in the spring
when increased exercise causes an acute crisis. There is a history of weight loss and coughing for several winters with remission in the grazing season.
If the condition can be arrested before significant fibrosis occurs, the prognosis is good.
Farmers Lung is a problem in areas with wet summers and severe winters, a situation that results in the combination of moldy hay and housing of cattle in the winter. Bailing and stacking of hay with a high moisture content results in overheating of the stacks. Thermophilic molds are released when the hay is distributed for feeding.
At necropsy, in acute cases, the lungs are superficially grossly normal; however, with closer examination small gray spots in many lobules
will be noticed.

The primary interstitial pneumonia of feedlot cattle is Atypical Interstitial Pneumonia (AIP) which is also accompanied with edema and emphysema of the lung.
Affected animals have an acute onset of severe breathing difficulty and majority die regardless of treatment. Lungs from animals that have died from AIP are enlarged, rubbery and have a mottled (checkerboard) interstitial emphysema appearance. In the Bovine Respiratory Disease Complex (BRDC) the pathology involvement of the lung is usually fibrinous and found in the lower ventral portion of the lung whereas in AIP the upper or dorsal part of the
lung is involved.
The exact cause is not known. Some studies suggest that it may be related to dietary factors, and dust since it is most often seen in the summer months and also may be associated with lung disease such as Bovine Respiratory Syncytial Virus (BRSV).

The diseases discussed are all characterized by diffuse pulmonary involvement and by marked alveolar epithelial hyperplasia. The disease called AIP includes those cases that are pathologically similar to ABPE and ARDS but epidemiologically different. Future research can be expected to reveal additional etiologic agents.

A survey is presently being conducted in cooperation with University of Georgia and Colorado State University and with feedlots and veterinary consultants regarding the management factors and other diseases that may lead to the
development of AIP. The aim of this survey is to gather information regarding size, geographic location, and management factors from feedlots where AIP is a problem and also from feedlots where the disease is not a problem. The information will help point researchers in the right direction in future research to determine the cause of Atypical Interstitial Pneumonia.

Breeze, Roger, Carlson, James R.; Current VeterinarymTherapy I – Food Animal Practice, pp 832-725
Hjerpe, C.A.; The Lungs and Mediastinum. Bovine Medicine and Surgery – Second Edition, pp 714-725
Smith, J.A., The Interstial Pneumonia,Large Animal Medicine, 1990 Bradford P.Smith, pp 596-608