Aspiration or inhalation pneumonia
is a common and serious disease
of farm animals. Cases occur after careless drenching or passage of a stomach
tube during treatment for other illnesses, for example administration of mineral
oil to horses with colic. Even when care is taken these procedures are not
without risk. Other causes include the feeding of calves on fluid feeds in
inadequate troughing, inhalation occurring in the struggle for food. Dipping of
sheep and cattle when they are weak, or keeping their heads under for too long,
also results in inhalation of fluid. Vomiting in ruminants and horses may be
followed by aspiration, especially in cattle with parturient paresis or during
the passage of a stomach tube if the head is held high.
Rupture of a pharyngeal abscess
during palpation of the pharynx or passage of a nasal tube may cause sudden
aspiration of infective material. Animals suffering from paralysis or
obstruction of the larynx, pharynx, or esophagus may aspirate food or water
when attempting to swallow.
Aspiration pneumonia is the
consistent lesion of crude oil poisoning in cattle and probably results from
vomiting or regurgitation.
Lipid pneumonia
Lipid pneumonia usually results
from aspiration of mineral oil (liquid paraffin) administered for gastrointestinal
disease. Pneumonia is sometimes the result of inadvertent administration of the
oil into the trachea through a misplaced stomach tube, or inhalation following
oral administration of oil. However, aspiration of oil can occur even when it
is delivered into the stomach through a nasogastric tube, presumably because of
regurgitation of oil either around the tube or after the tube has been removed.
Administration of oil to sedated or severely depressed animals may increase the
risk of aspiration. Clinical signs include cough, tachypnea, tachycardia,
pyrexia, respiratory distress and abnormal lung sounds. Radiographs can reveal
an alveolar and interstitial pattern. Examination of tracheal aspirates reveals
a neutrophilic inflammation and the presence of lipid. Lipid can be readily identified
by Sudan or oil red 0 staining of smears of the aspirate in acute cases.
Necropsy examination reveals consolidated lungs. On cut section of these areas oil can be visible. Chronic cases have tissue necrosis and severe interstitial pneumonia. Lipid droplets can be identified in affected lung tissue after oil red 0 staining of sections. The presence and nature of the lipid can be demonstrated by thin-layer chromatography and gas chromatography. The prognosis for recovery is poor. Treatment is supportive and includes anti-inflammatory drugs, antimicrobials, and oxygen. There is no specific treatment. Prevention includes careful insertion of nasogastric tubes, verification of their placement in the stomach and not administering mineral oil to animals with a distended stomach or ones that are heavily sedated or severely depressed.
Oesophagal obstruction:
Esophageal obstruction is a common and important
cause of pneumonia in horses. Of 18 horses with esophageal obstruction that had
thoracic radiographs performed, eight had evidence of aspiration pneumonia.
Obstruction of the esophagus in horses, and in other species, leads to the
accumulation of saliva and feed material in the esophagus oral to the obstruction.
When the esophagus is full, this material accumulates in the pharynx with
subsequent aspiration into the trachea resulting in contamination of the trachea
and lower airways with feed material and oropharyngeal bacteria. Feed material
is irritant and also causes obstruction of the smaller airways. Pulmonary defense
mechanisms are weakened or overwhelmed by the contamination and infection and
pneumonia result. The duration of esophageal obstruction is a good indicator of
the risk of aspiration pneumonia, although the extent of contamination of the
trachea with feed material is not. Affected horses are pyrexic, tachycardic,
and toxemic. Lung sounds can include crackles and wheezes, but the only
auscultatory abnormality can be decreased breath sounds in the ventral thorax.
Radiography reveals a characteristic pattern of bronchopneumonia restricted, at
least initially, to the cranioventral and caudoventral lung lobes in adult
horses. Ultrasonography reveals comet tail lesions in the ventral lung fields and
variable consolidation. Pleuritis is a not uncommon sequel to aspiration pneumonia.
Examination of tracheal aspirates demonstrates neutrophilic inflammation with
presence of degenerate neutrophils, bacteria that are both intracellular and
extracellular, and plant material. Culture of tracheal aspirates yields one or
more of a wide variety of bacteria including zooepidemicus, Pasteurella sp.,
Actinobacillus sp, E. coli, and anaerobes. Treatment involves prompt relief of
the esophageal obstruction and administration of broad-spectrum antimicrobials such
as a combination of penicillin, aminoglycoside, and metronidazole. The
prognosis for recovery from aspiration pneumonia secondary to esophageal
obstruction is guarded to fair, partly because the animal has to recover from
two diseases - the pneumonia and the esophageal obstruction. Prevention of aspiration
pneumonia in horses with esophageal obstruction includes prompt relief of the
obstruction and administration of broad -spectrum antimicrobials. Meconium aspiration
syndrome Aspiration of meconium during parturition is associated with severe
lung disease in newborns. Passage of meconium in utero, and subsequent
aspiration by the fetus, is a sign of fetal distress. It is suggested that fetal
distress results in expulsion of meconium into the amniotic fluid. This is followed
by aspiration of contaminated amniotic fluid. The passage of meconium contaminated
amniotic fluid into the lungs may occur prior to birth when the fetus gasps for
air in an attempt to correct hypoxemia or when the calf takes its first breath
and aspirates meconium from the oropharynx. Normally, fetal aspiration of amniotic
fluid does not occur because the inspiratory forces are insufficient to allow amniotic
fluid to reach the lungs, and the lung liquid, a locally produced viscous material
present in the trachea and lungs, constantly flows up the major airways to the
oropharynx. The result is that the fetus is doubly challenged in that it must
deal with both the cause of the fetal distress and the pneumonia induced by
aspiration of meconium. Although meconium is sterile, it induces a severe
inflammatory response in the lungs.
The meconium aspiration syndrome is
best described in newborn calves, although there are numerous reports of its experimental
induction in piglets and lambs as a model of the human disease. In a series of
calves under 2 weeks of age submitted to a diagnostic laboratory, 42.5% had
evidence of meconium, squamous cells or keratin in the lung. Diffuse alveolitis
with exudation of neutrophils, macrophages, multinucleated cells and
obstruction of small airways with atelectasis were common. Treatment of
aspiration pneumonia in farm animals is not well described.
Administration of antimicrobials
is prudent. Anti - inflammatory drugs are indicated. Pentoxifylline is used in
human neonates with meconium aspiration, but there are no reports of its use
for this purpose in farm animals.
Dusty feed
Although farm animals fed on
dusty feeds inhale many dust particles and bacteria, which can be readily
isolated from the lung, this form of infection rarely results in the
development of pneumonia. Much of the dust is filtered out in the bronchial tree
and does not reach the alveoli. However, this may be of importance in the production
of the primary bronchiolitis that so often precedes alveolar emphysema in
horses. The inhalation of feed particles in pigs in a very poorly ventilated environment
has been demonstrated to cause foreign body pneumonia. Also, a dry, dusty
atmosphere can be created in a piggery by over frequent changing of wood
shavings used as bedding, and this can lead to the production of foreign body pneumonia.
Liquids and droplets penetrate to the depths of the alveoli and run freely into
the dependent portions, and aspiration pneumonia often results.
0 Comments