resp notes horse diseases

Question 1

Common respiratory viral infections in Ontario horses include:
- general diseases caused

Answer 1

• Equine herpesviruses-1 and 4 (Equine viral rhinotracheitis)
• Equine influenza (currently due to A/equi 2 = H3N8, formerly due to A/equi 1 = H7N7)
• Equine rhinitis viruses
• (Equine viral arteritis, but this is rare in Ontario)
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• These viruses are common causes of upper respiratory illness
• equine herpesvirus-1 or -4 and equine influenza can cause pneumonia (secondary bacterial pneumonia risk)
• EHV-1 can cause abortion, neonatal illness, encephalitis

Question 2

strangles
- pathogen
- transmission
- disease progression
- signs

Answer 2

• Streptococcus equi ssp. equi
• Infection is by inhalation or ingestion
• the bacterium colonizes the mucosa of the nasopharynx and guttural pouch, then spreads to local lymph nodes
• mucopurulent nasal discharge, swollen retropharyngeal and submandibular lymph nodes, and fever
• The lymph nodes eventually rupture and drain pus, which is highly infectious to other horses.

Question 3

strangles gross lesions? sequelae?

Answer 3

• Gross lesions: mucopurulent rhinitis and suppurative lymphadenitis with abscessation.
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  Sequelae are important in this disease:
• Bacterial bronchopneumonia due to aspiration of exudate from the nasopharynx
• Guttural pouch empyema
• “Bastard strangles” refers to hematogenous spread of infection to colonize lymph nodes and result in abscesses. Abscesses of the abdominal (mesenteric) lymph nodes are particularly consequential and may cause colic.
• Purpura hemorrhagica refers to systemic immune-complex-mediated vasculitis. This manifests as disseminated hemorrhages and edema in the skin of the distal limbs.

Question 4

guttural pouch mycosis
- agent?
- lesion
- consequences

Answer 4

• Aspergillus sp.
• unilateral plaque of fungal hyphae covering a fibrinonecrotic and ulcerative lesion
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• fungal plaque causes inflammation and necrosis of anatomically important structures in the guttural pouch:
• Internal carotid artery → epistaxis
• Vagus and glossopharyngeal nerves → dysphagia
• Sympathetic ganglion or nerve → Horner’s syndrome
• Laryngeal nerve → laryngeal paralysis

Question 5

heaves in horses
- what is this?
- clinical signs?
- origins?
- histologic lesions
- causes of airway obstruction
- tx

Answer 5

• severe equine asthma
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• episodes of inflammation that result in obstruction of the small airways
• clinical signs of respiratory distress and cough
• episodes of clinical signs separated by periods of normality
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• hypersensitivity reaction to inhaled substances in dusty or mouldy feed
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  The histologic lesions target the bronchioles and include:
• Neutrophils and mucus filling the lumen of the bronchioles
• Lymphocytes and neutrophils in the walls of bronchioles
• Hypertrophy of bronchiolar smooth muscle
• Goblet cells, which are normally present only in the larger airways, are present in the small bronchioles (mucous metaplasia)
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• Airway obstruction due to inflammatory response: bronchoconstriction, mucus hypersecretion, leukocyte infiltration, and mucosal edema
• inhaled corticosteroids
• also, bronchodilators, mucinolytics

Question 6

Rhodococcus equi
- where its found
- type of pathogen
- who is affected?
- duration of lesions, clinical signs
- forms
- lesions
- histology

Answer 6

• gram-positive bacterium present in soil
• facultative intracellular pathogen that survives within macrophages (many antibiotics not effective)
• 2-6-month- old foals
• infection and the lesions are always chronic, but clinical signs may be either acute or chronic
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• respiratory form (due to inhalation of bacteria) is most common:
• coughing, depression, fever, and weight loss
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• colonic form causing diarrhea (due to ingestion of bacteria from the environment, or expectoration of bacteria from the lungs)
  > abscesses in colonic lymph nodes and sometimes colonic ulcers
• polyarthritis causing lameness and swollen joints
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• lung lesions are often very extensive before clinical signs become apparent
• cranioventral pattern of consolidation, and these consolidated lesions contain multifocal pyogranulomas that develop into abscesses
• Bronchial lymph nodes also contain pyogranulomas or abscesses
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• infiltrates of neutrophils and macrophages in alveoli and bronchioles

Question 7

pleuropneumonia in horses
- who gets this?
- pathogenesis
- clinical signs
- lesions

Answer 7

• often young adults after transportation
• Most cases have an underlying bronchopneumonia, with pleuritis developing as bacteria migrate into the pleural space
• Many cases represent aspiration pneumonia that develops when horses are transported with their heads held up
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• fever, variable dyspnea, depression and anorexia, and muffled or absent heart and lung sounds
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• abundant, often foul-smelling, cloudy fluid with fibrin clots and/or fibrous adhesions
• underlying lung lesion: often localized area of bronchopneumonia that is firm, deep red, and may have areas of necrosis

Question 8

interstitial pneumonia of foals
- age
- cause?
- signs
- gross appearance
- histo lesions

Answer 8

• 2-8-month-old foals
• cause unknown:
  > ??? unidentified viral infection, hyperthermia caused by erythromycin therapy for Rhodococcus, or an aberrant inflammatory response to Rhodococcus infection ???
• sporadic disease
• acute onset of severe dyspnea, and poor response to therapy
• lungs are diffusely firm with rubbery texture
• bronchiolar necrosis, hyaline membranes, and/or proliferation of alveolar type II pneumocytes

Question 9

equine adenovirus
- causes what? in who?

Answer 9

• Fatal pneumonia in immunosuppressed foals

Question 10

hyaline membrane disease
AKA
Neonatal equine respiratory distress syndrome “NERDS”
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- pathogenesis
- clinical signs

Answer 10

• Premature foals have immature type II pneumocytes, and these cells have not matured enough to produce adequate surfactant
• increased surfacant tension within the lung, atelectasis because the alveoli can’t inflate
  > abnormal pressures on the alveolar surface > physical damage to type I pneumocytes leads to formation of hyaline membranes
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• dyspneic, hypoxemic, sometimes have secondary cerebral injury due to hypoxemia

Question 11

septicemia in neonatal foals
- pathogens
- causes?
- lesions?

Answer 11

• Actinobacillus equuli
• Klebsiella pneumoniae
• E. coli
• etc…
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• inadequate intake of colostrum, concurrent diseases including bronchopneumonia, chilling, or dirty environments
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• lungs are diffusely edematous and may be firm, and there may be pinpoint white foci in lungs, kidneys, and other tissues.
• Lesions are more florid in other cases, with fibrinous exudates in body cavities.

Question 12

meconium aspiration syndrome
- causes what in the lungs?

Answer 12

Aspiration of meconium by a distressed fetus causes interstitial pneumonia in neonatal foals, calves, and human infants. The diagnosis is based on histologic findings.

Question 13

viral cause of diffuse interstitial lung disease in neonatal foals

Answer 13

EHV-1

Question 14

exercise-induced pulmonary hemorrhage
- clinical manifestation

Answer 14

• bilateral epistaxis immediately after racing
• Infrequently, hemorrhage is so massive that it causes sudden death during a race, and this condition is known as exercise- associated fatal pulmonary hemorrhage (EAFPH)

Question 15

dictyocaulus arnfieldi
- host?
- disease in horses?
- where to look for worms?

Answer 15

• Donkeys are the natural host, and this nematode may cause disease in horses exposed to pastures contaminated by donkey feces
• the worms are grossly visible in the caudal bronchi