Avian Medicine

Clinical Reference Values by Species

Hematology: Nucleated RBCs and Heterophils

Nucleated red blood cells (nRBCs) are NORMAL in birds. Automated cell counters misinterpret them as WBCs, causing false leukocytosis. Manual differential is mandatory for avian samples.

Heterophils are the avian equivalent of mammalian neutrophils. They function similarly (phagocytic, acute-phase responders) but are morphologically distinct (bilobed, eosinophilic cytoplasm). Reference ranges:

• Heterophils: 40-70% of WBCs (normal).
• Lymphocytes: 20-50% (relatively high compared to mammals).
• Monocytes: 1-3%.
• Eosinophils: 1-3%.
• Basophils: 1-2%.

Stress leukogram: Acute stressors (handling, illness) cause heterophilia + lymphopenia (mild monocytosis) in birds, similar to mammalian response.

Renal Assessment: Uric Acid, Not BUN/Creatinine

Birds are uricotelic: They excrete nitrogenous waste as uric acid (not urea). Kidneys synthesize uric acid; circulating uric acid primarily reflects kidney function.

Normal uric acid: 3-10 mg/dL (species-variable; raptors sometimes higher).

• Elevated uric acid (>12 mg/dL): Indicates renal disease, dehydration, or gout (uric acid crystal deposition in joints).
• BUN/creatinine: Not reliable in birds; values may be present in some assays but have poor clinical correlation.
• Bile acids: NOT useful in avian medicine (different hepatic metabolism than mammals).

Gout: Uric acid crystal deposits in joints (visceral or articular gout). Causes lameness, swelling, pain. Associated with dehydration, high-protein diets, renal disease. Management: hydration, NSAIDs (cautiously), dietary adjustment, allopurinol (questionable efficacy).

Crop Anatomy and Emergency Considerations

Crop: A muscular sac cranial to the thoracic inlet (anterior to the thorax, dorsal to the esophagus). Functions in food storage and softening before passage to the proventriculus. In emergency settings, crop status determines feeding route and risk of aspiration.

Clinical significance:

• Full crop: Bird cannot take food or medication safely (aspiration risk). Must empty via gentle massage or tube feeding.
• Stagnant crop: Food remains in crop >2-4 hours. Indicates disease (crop stasis, systemic illness, obstruction). Causes fermentation, regurgitation, aspiration.
• Crop tube feeding: Only appropriate after crop is empty and bird is alert (prevents aspiration into air sacs).
• Crop impaction/foreign body: Requires endoscopy or crop marsupialization for removal.

Psittacosis (Avian Chlamydia) and Zoonotic Risk

Causative agent: Chlamydia psittaci (obligate intracellular bacterium). Transmitted via respiratory aerosols or ingestion of contaminated feces.

Clinical signs in birds: May be inapparent (carrier state), or present with respiratory disease (coughing, discharge), conjunctivitis, gastrointestinal signs (diarrhea), systemic illness (depression, anorexia, ruffled feathers).

Zoonotic transmission: Veterinarian, owner, handler risk. Humans develop influenza-like illness (fever, cough, malaise, headache); can progress to atypical pneumonia. Pregnant women and immunocompromised persons at higher risk of severe disease.

Diagnosis: Chlamydia antigen ELISA (rapid, most practical), PCR (sensitive, confirmatory), culture (requires specialized labs).

Management: Doxycycline (45-50 mg/kg daily, oral or injectable) for 45+ days. Requires client counseling on zoonotic risk, hygiene, and need for post-treatment testing. Quarantine of infected birds recommended.

PBFD (Psittacine Beak and Feather Disease)

Causative agent: Psittacine beak and feather disease virus (PBFDV), a circovirus. Highly contagious; transmission via respiratory, fecal, or contact routes.

Clinical signs: Progressive feather loss (symmetrical, especially remiges/rectrices), abnormal feather development (discolored, dystrophic), beak deformity/softening, immunosuppression (secondary infections). Acute form may present with sudden death in young birds.

Diagnosis: PCR (gold standard; differentiates infected from vaccinated), antigen ELISA, histopathology (intranuclear inclusions in feather epithelium).

Management: No cure. Supportive care, isolation (prevent spread), vaccination (preventive in negative birds; ineffective in infected). Prognosis poor; many infected birds die within 2 years.

Heavy Metal Toxicosis

Zinc toxicosis: Most common heavy metal toxicity in pet birds.

• Source: Galvanized cages, zinc-containing toys, pennies post-1982, brass fixtures.
• Pathophysiology: Zinc is absorbed in GI tract; hemolytic anemia (Zn damages RBC membranes), pancreatitis, neurologic signs (weakness, incoordination).
• Clinical signs: Lethargy, anorexia, diarrhea (green/yellow), pale mucous membranes, neurologic abnormalities.
• Diagnosis: Abdominal radiographs (metallic objects), blood zinc level (>15 μmol/L is concerning).
• Management: Remove source, chelation therapy (calcium EDTA), supportive care, transfusion if severe anemia.

Lead toxicosis: Less common but serious.

• Source: Lead paint, stained glass, lead-containing toys, shot, batteries.
• Signs: GI (vomiting, diarrhea), neurologic (tremors, ataxia, seizures), hemolytic anemia.
• Diagnosis: Radiographs, blood lead level (>10 μg/dL is abnormal).
• Management: Remove source, chelation (calcium EDTA), supportive care.

PTFE/Teflon (polytetrafluoroethylene) toxicity: Acutely fatal inhalation toxicosis. One of the most common causes of sudden death in household birds.

• Source: Overheated non-stick cookware (pans, baking sheets, drip pans), self-cleaning ovens, heat lamps with PTFE coatings, some space heaters and hair dryers.
• Mechanism: PTFE decomposes at temperatures above 280°C (536°F), releasing perfluorooctanoic acid (PFOA) and other toxic fumes. Birds' highly efficient respiratory system (cross-current gas exchange, air sacs) makes them exquisitely sensitive.
• Clinical signs: Acute dyspnea, ataxia, seizures, death — often within minutes to hours of exposure. Birds may be found dead with no premonitory signs.
• Treatment: Remove bird from environment immediately. Oxygen therapy, supportive care. Prognosis extremely poor once clinical signs develop.
• Prevention: No non-stick cookware in homes with birds. This is the single most important household safety recommendation for bird owners.

Prey Species Behavior and Illness Masking

Birds are prey animals; survival instinct suppresses visible signs of illness until disease is severe. This is the single most important factor in avian patient assessment:

• Subtle changes indicate serious disease: Mild feather fluffing, slight decrease in activity, minimal appetite reduction = potential emergency.
• Owners often miss early signs: Birds may seem "normal" until collapse (often sudden and life-threatening).
• Physical exam findings lag behind disease: A bird appearing alert may be profoundly hypoxic or have sepsis.
• Handling stress: Even gentle exam can precipitate collapse in fragile patients. Minimize restraint; have emergency equipment available.
• Night perching changes: Moving to lower perches, difficulty roosting, or sleeping on the cage floor is a red flag.

Species-Specific Differences: Parrots vs. Chickens vs. Raptors

Parrots (psittacines): Companion birds; frugivorous/granivorous. Long lifespan (20-80+ years). Social; behavioral problems common. Susceptible to dietary deficiencies (vitamin A, calcium). Feather damaging behaviors from stress/boredom.

Chickens (galliformes): Production/backyard birds; granivorous. Short lifespan (5-10 years). Prone to neoplasia (ovarian, liver), respiratory disease, parasitism. Anatomic differences (crop is more caudal; different organ sizing).

Raptors (accipiter, falco, strigiformes): Carnivorous; adapted for high-speed flight/hunting. High metabolic rate. Stress-sensitive; poor captive candidates. Specialized dietary needs (whole prey). Different cardiac anatomy. Higher normal temperature range.

Limitations

• Avian lab interpretation requires avian-literate laboratories; many general practices send samples to avian specialists.
• Heavy metal diagnosis relies on imaging + blood levels; GI foreign bodies may not be visible on radiographs (density-dependent).
• Psittacosis diagnosis is imperfect; negative tests do not rule out infection (chronic carriers may shed intermittently).
• PBFD prognosis is grave; infected birds are permanent sources of virus and pose transmission risk to other birds.
• This skill provides clinical frameworks, not flock-level management plans; avian specialists should guide biosecurity and preventive medicine strategies.
• Prey species behavior means birds require experienced avian veterinarians; emergency exotics expertise is essential for safe care.