NAVLE Respiratory High-Yield Guide: Lung Disease Across All Species

Respiratory disease is one of the most heavily tested areas on the NAVLE. Expect 20–30 questions distributed across every species block — from the coughing Labrador in your small animal rotation to the heaving horse at the barn. The NAVLE respiratory formula is consistent: signalment + clinical signs + radiograph or auscultation finding ? diagnosis ? treatment. Master this framework across all species and you will capture a significant portion of points on exam day.

This guide covers the highest-yield NAVLE respiratory topics, organized by species. It includes three reference tables, a step-by-step diagnostic approach, a FAQ with schema markup, and internal links to companion guides.

Respiratory Emergency Recognition

Before diving into species-specific disease, you must recognize a respiratory emergency. The NAVLE will test your ability to triage.

• Open-mouth breathing in a cat is always an emergency — cats are obligate nasal breathers.
• Orthopnea (inability to lie down without dyspnea) signals severe pleural space disease or congestive heart failure.
• Paradoxical breathing (abdomen moves opposite to chest) indicates respiratory muscle fatigue or flail chest.
• Cyanosis is a late and ominous sign of severe hypoxemia (SpO2 <80%).
• Inspiratory stridor localizes obstruction to the upper airway (larynx, trachea); expiratory wheeze localizes to the lower airways.

Initial stabilization always precedes diagnostics in a dyspneic patient: flow-by or cage oxygen, minimal restraint, and sedation if needed. Thoracocentesis is both diagnostic and therapeutic for pleural effusion or pneumothorax.

Canine Respiratory Disease

Canine Infectious Respiratory Disease Complex (CIRD / Kennel Cough)

CIRD is caused by multiple co-infecting pathogens. The most common bacterial agent is Bordetella bronchiseptica. Viral contributors include Canine Parainfluenza Virus (CPIV), Canine Distemper Virus (CDV), Canine Adenovirus type 2 (CAV-2), and Canine Respiratory Coronavirus (CRCoV). Mycoplasma cynos also plays a role in complicated cases.

Classic presentation: dry, hacking cough with tracheal sensitivity on palpation, in a dog recently exposed to a shelter, boarding facility, or dog park. Most cases are self-limiting in 1–2 weeks. Doxycycline or azithromycin are first-line antibiotics when treatment is warranted. Prevention: intranasal Bordetella vaccine (fastest onset of immunity) and core vaccines covering CDV and CAV-2.

Bronchopneumonia

Bacterial bronchopneumonia in dogs most commonly follows aspiration (megaesophagus, sedation, laryngeal dysfunction) or secondary infection post-viral illness. Radiographs show a ventral alveolar pattern (cranioventral distribution) — air bronchograms are the hallmark of alveolar disease. Treatment: broad-spectrum antibiotics (amoxicillin-clavulanate, fluoroquinolones), nebulization, coupage, and addressing the underlying cause.

Brachycephalic Obstructive Airway Syndrome (BOAS)

BOAS affects English Bulldogs, French Bulldogs, Pugs, and Boston Terriers. The four anatomical components are: stenotic nares, elongated soft palate, hypoplastic trachea, and everted laryngeal saccules. Affected dogs present with inspiratory stertor (snoring), exercise intolerance, regurgitation, and in severe cases, cyanosis. Grading (I–III) is based on clinical severity. Surgical correction — widening the nares, shortening the soft palate, and removing everted saccules — is the definitive treatment and should be performed early.

Laryngeal Paralysis

Geriatric Labrador Retrievers are the classic patient. Inspiratory stridor, voice change, exercise intolerance, and heat stress are hallmark signs. Laryngeal paralysis is often part of a generalized polyneuropathy (geriatric onset laryngeal paralysis and polyneuropathy — GOLPP). Diagnosis is confirmed by laryngoscopy under light sedation — the arytenoids fail to abduct on inspiration. Definitive treatment is unilateral arytenoid lateralization (tie-back surgery). Aspiration pneumonia is the most significant post-operative risk.

Tracheal Collapse

Tracheal collapse occurs in toy breeds — Yorkshire Terriers, Pomeranians, and Chihuahuas are classic. Tracheal cartilage weakens, causing a honking or goose-honk cough exacerbated by excitement, eating, or tracheal pressure (collar). Graded I–IV by the percentage of lumen reduction. Medical management: bronchodilators (theophylline, terbutaline), antitussives (butorphanol, hydrocodone), weight loss, and harness instead of collar. Severe or refractory cases may require intraluminal tracheal stenting.

Pulmonary Edema

In dogs, cardiogenic pulmonary edema (left-sided CHF from mitral valve disease in small breeds, dilated cardiomyopathy in large breeds) is the most common cause. Radiograph shows a perihilar alveolar pattern. Non-cardiogenic edema follows neurogenic events, near-drowning, or upper airway obstruction. Treatment: furosemide (loop diuretic), oxygen, and vasodilators for cardiogenic edema.

Canine and Feline Respiratory Disease Differentials

Feline Respiratory Disease

Upper Respiratory Infection Complex (URI)

Feline URI is caused primarily by Feline Herpesvirus-1 (FHV-1) and Feline Calicivirus (FCV). FHV-1 causes more severe ocular signs (conjunctivitis, corneal ulcers); FCV causes oral ulceration (stomatitis, tongue ulcers) and limping syndrome. Both are transmitted by direct contact and fomites. Treatment is supportive: nasal decongestants, nutritional support, and doxycycline for secondary bacterial infection. Lysine supplementation has been used for FHV-1 to reduce viral replication. Core feline vaccines (FVRCP) protect against both.

Feline Asthma

Siamese cats are predisposed. Feline asthma is characterized by episodic lower airway bronchoconstriction triggered by environmental allergens (dust, smoke, aerosols, litter dust). Classic radiographic finding: hyperinflated lungs (flattened diaphragm) with a bronchial pattern (donut/ring shadows, parallel lines). Acute management: albuterol metered-dose inhaler (MDI) via AeroKat spacer. Long-term maintenance: prednisolone (systemic) or inhaled fluticasone (Flovent). Environmental trigger elimination is essential.

Pyothorax

Pyothorax in cats most commonly results from bite wounds that penetrate the chest wall or from migrating foreign bodies. Common pathogens: Pasteurella multocida, Bacteroides, and Fusobacterium (anaerobes). Thoracocentesis yields thick, turbid, foul-smelling fluid. Management requires bilateral chest tube placement with repeated saline lavage plus prolonged systemic antibiotics for 4–6 weeks. Do not rely on penicillin alone — it does not cover all anaerobes and Gram-negatives. Amoxicillin-clavulanate, metronidazole + amoxicillin, or clindamycin combinations are appropriate.

Chylothorax and FIP Effusion

Chylothorax is accumulation of chyle (lymphatic fluid) in the pleural space. Fluid analysis shows a milky appearance with elevated triglycerides and chylomicrons. Treatment includes therapeutic thoracocentesis, a low-fat diet, rutin, and surgical thoracic duct ligation. FIP effusion (wet form) produces a straw-colored, viscous, protein-rich exudate — Rivalta test positive. FIP is caused by a virulent mutation of feline enteric coronavirus; GS-441524 (antiviral) has shown significant success in treatment.

Equine Respiratory Disease

Recurrent Airway Obstruction (RAO / Heaves)

RAO (formerly called heaves or COPD in horses) is an inflammatory lower airway disease triggered by environmental allergens — hay dust, fungal spores (especially Aspergillus and Faenia rectivirgula), and stable ammonia. Affected horses show chronic expiratory dyspnea, a characteristic "heave line" (hypertrophy of the external abdominal oblique), and mucus accumulation. Bronchoalveolar lavage (BAL) reveals airway neutrophilia. Treatment requires barn management (soaked hay or pelleted feed, outdoor turnover) combined with bronchodilators (clenbuterol) and corticosteroids (dexamethasone). Summer pasture obstructive disease (SPOD) is a related condition triggered by pasture allergens in summer.

Exercise-Induced Pulmonary Hemorrhage (EIPH)

EIPH is bilateral pulmonary hemorrhage from the caudodorsal lung fields occurring during strenuous exercise, most commonly in racehorses. Epistaxis (blood at the nostrils post-race) occurs in fewer than 5% of affected horses; the majority are subclinical. Endoscopy within 30–90 minutes post-exercise is the gold standard for diagnosis, revealing blood in the trachea. Furosemide administered IV before racing reduces severity and is FDA-approved for this indication in the United States. Nasal strips reduce upper airway resistance and are used prophylactically. Rest is indicated for horses with Grade 4–5 EIPH.

Strangles (Streptococcus equi equi)

Strangles is caused by Streptococcus equi subspecies equi, a highly contagious bacterial infection. Classic presentation: fever (often first sign), submandibular and retropharyngeal lymphadenopathy with progression to abscessation and purulent nasal discharge. Abscesses rupture and drain spontaneously. Treatment is primarily supportive; penicillin is used in early febrile stages or in severe cases, but is controversial once abscesses have formed because it may delay rupture. Guttural pouch carriers — horses that harbor the organism in the guttural pouches without clinical signs — are identified by ELISA serology and guttural pouch endoscopy with culture or PCR. Bastard strangles (internal dissemination to mesenteric lymph nodes, lungs, brain) carries a much worse prognosis and requires prolonged systemic penicillin or trimethoprim-sulfa.

Guttural Pouch Disease

The guttural pouches are diverticula of the Eustachian tubes unique to horses. Guttural pouch mycosis (fungal plaque, usually Aspergillus) erodes the internal carotid artery and can cause fatal epistaxis. Guttural pouch empyema (accumulation of pus or inspissated material) can serve as a reservoir for Streptococcus equi. Radiography and endoscopy are essential diagnostic tools.

Ruminant Respiratory Disease

Bovine Respiratory Disease Complex (BRD)

BRD is the single most economically important disease in the cattle industry. It is a multifactorial disease involving stress + viral immunosuppression + secondary bacterial infection. Key viral predisposing agents: BVDV (Bovine Viral Diarrhea Virus) — the most important immunosuppressant — IBR (BHV-1), BRSV, and BPIV-3. The primary bacterial pathogen causing severe disease is Mannheimia haemolytica, which produces leukotoxin and causes deep fibrinous pleuropneumonia with a cranioventral consolidation on radiograph or necropsy. Other significant bacteria: Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Treatment antibiotics: florfenicol, enrofloxacin, or tulathromycin. BVDV vaccination is the cornerstone of prevention.

Enzootic Pneumonia (Calves)

Enzootic pneumonia in pre-weaned dairy calves is caused by Mycoplasma bovis, Pasteurella multocida, and Mannheimia haemolytica. Calves show fever, nasal discharge, and coughing. Management focuses on ventilation, adequate colostrum, and early antibiotic intervention. Mycoplasma bovis is notably resistant to beta-lactams and many aminoglycosides.

Ovine Progressive Pneumonia (OPP) / Maedi-Visna

OPP (called Maedi-Visna in Europe) is caused by a lentivirus (OPP virus / Maedi-Visna virus). It causes a slowly progressive, chronic interstitial pneumonia in adult sheep. Affected sheep present with progressive weight loss and dyspnea without fever. There is no treatment or vaccine — eradication relies on serologic testing (AGID or ELISA) and removal of positive animals. Key NAVLE fact: this is a lentivirus, not a herpesvirus.

Mycoplasma in Ruminants

Mycoplasma mycoides subsp. mycoides causes contagious bovine pleuropneumonia (CBPP) — a notifiable (reportable) disease in many countries. In small ruminants, Mycoplasma capricolum subsp. capripneumoniae causes contagious caprine pleuropneumonia (CCPP). Both are OIE-listed diseases. The presence of either requires regulatory notification.

Porcine Respiratory Disease

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)

PRRSV is one of the most economically significant swine diseases globally. It causes reproductive failure (late-term abortions, mummified fetuses, stillbirths) and respiratory disease (dyspnea, fever, anorexia) especially in nursery pigs. PRRSV is an arterivirus. There is no treatment; modified live vaccines are available but may not cross-protect fully between PRRSV-1 and PRRSV-2 strains.

Mycoplasma hyopneumoniae (Enzootic Pneumonia)

Mycoplasma hyopneumoniae causes enzootic pneumonia, the most prevalent respiratory disease of swine worldwide. It presents as a chronic, non-fatal, dry cough in grower-finisher pigs with reduced growth performance. It is the primary predisposing pathogen for secondary bacterial infections (PRS complex). Diagnosis by PCR or serology. Control: vaccination + medication with tiamulin, lincomycin, or tulathromycin.

Actinobacillus pleuropneumoniae (APP)

APP causes porcine pleuropneumonia — a hemorrhagic, fibrinous pleuropneumonia with high mortality in acute cases. Affected pigs show sudden death, bloody frothy nasal discharge, and rapid spread within a group. Necropsy: dark red, consolidated, fibrinous lung lesions. Treatment with ceftiofur, amoxicillin, or florfenicol; often too rapid for individual treatment. Vaccination is available. Key NAVLE point: serotyping (16 serovars) may be asked.

Swine Influenza Virus (SIV)

SIV (H1N1, H3N2 subtypes in North America) causes acute respiratory disease in pigs with high morbidity and low mortality. Classic herd presentation: sudden onset of coughing and fever affecting nearly the entire group simultaneously (herd-level event). Treatment is supportive. SIV is a zoonotic concern and a NAVLE public health testing point.

Ruminant, Equine, and Swine Respiratory Disease Reference Table

Brachycephalic Breeds and Key Respiratory Abnormalities

Radiographic Interpretation: Patterns You Must Know

The NAVLE will ask you to interpret a radiographic pattern and link it to a disease. Four patterns are essential:

• Alveolar pattern: Air spaces filled with fluid/exudate. Key feature: air bronchograms (air-filled bronchi visible within consolidated tissue). Causes: pneumonia, pulmonary edema, hemorrhage, atelectasis.
• Interstitial pattern: Increased soft tissue opacity in the interstitium. Nodular (metastatic cancer) or diffuse (viral pneumonia, fibrosis, edema). No air bronchograms.
• Bronchial pattern: Thickened bronchial walls seen as rings ("donuts") or parallel lines ("tram tracks"). Classic for feline asthma, chronic bronchitis.
• Pleural effusion: Obliteration of lung detail in the ventral thorax; fluid meniscus; heart border effacement. Dorsoventral (DV) view better than lateral for early effusion.
• Pneumothorax: Absence of lung markings at the periphery; lung lobes retract toward the hilum. Treat with thoracocentesis or chest tube for tension pneumothorax.

For detailed radiographic and laboratory diagnostic approaches, see the NAVLE Diagnostics High-Yield Guide.

Oxygen Therapy and Respiratory Support

The NAVLE will test your knowledge of oxygen delivery methods and respiratory support options:

• Flow-by oxygen: Non-stressful, FiO2 ~25–40%; ideal for initial stabilization.
• Oxygen cage / incubator: FiO2 up to 40–60%; excellent for cats and small dogs who are stressed by handling.
• Nasal cannula / nasal prongs: FiO2 up to 40–50%; requires a cooperative patient.
• Intubation and mechanical ventilation: Required for respiratory failure (PaO2 <60 mmHg on room air or PaCO2 >60 mmHg); used post-operatively for severe BOAS or laryngeal paralysis patients.
• Furosemide: First-line for cardiogenic pulmonary edema; reduces preload and pulmonary capillary pressure.
• Bronchodilators: Albuterol (beta-2 agonist, short-acting) for acute bronchoconstriction in cats; terbutaline and theophylline for dogs with tracheal collapse or bronchospasm.

Step-by-Step NAVLE Respiratory Diagnostic Approach

Continue Your NAVLE Preparation

The NAVLE respiratory module connects closely to other high-yield areas. Use these guides to build a comprehensive study plan:

• NAVLE Exam Complete Guide — full exam overview, question distribution, and study strategy
• NAVLE Canine High-Yield Guide — complete canine disease review including cardiorespiratory, dermatology, and neurology
• NAVLE Bovine High-Yield Guide — BRD in depth plus reproductive, GI, and metabolic bovine diseases
• NAVLE Diagnostics High-Yield Guide — radiograph interpretation, BAL cytology, thoracocentesis fluid analysis, and CBC/chemistry patterns

Frequently Asked Questions: NAVLE Respiratory Questions