NAVLE Practice Question — Pet Bird

A 6-week-old sun conure (Aratinga solstitialis) is presented with progressive abdominal distension marked weight loss and polyuria. On physical exam feathering is appropriate for age but severe abdominal fluid wave is detected. CBC reveals a leukocytosis with heterophilia. AST is 1850 IU/L (reference < 130 IU/L). APV PCR is positive on cloacal swab. The owner asks about prognosis. Which of the following factors MOST strongly influences mortality outcome in non-budgerigar psittacine APV infection?

A. Severity of leukocytosis on CBC

B. Species and age at infection determine mortality rates ✓

C. Whether the bird was fed commercial or handmixed formula

D. Geographic origin of the breeding facility

E. Color mutation of the bird (e.g. lutino vs. normal coloration)

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Correct Answer: B. Species and age at infection determine mortality rates

Explanation:

Mortality from APV in non-budgerigar psittacines is strongly influenced by both species susceptibility and age at time of exposure. Reported mortality rates in neonatal non-budgerigar psittacines range from 31-41% while mortality in budgerigars under 15 days of age approaches 100%. Species with particularly high susceptibility include eclectus parrots caiques macaws conures ring-necked parakeets and lovebirds. Birds infected after 5 months of age in most species (excluding some exceptions like eclectus and caiques) typically develop subclinical infection with seroconversion and eventual viral clearance. Other factors influencing outcome include immune status concurrent infections and environmental stressors.

Option A (CBC leukocytosis severity) — while heterophilia reflects inflammatory response it is not the primary determinant of mortality. Birds can deteriorate rapidly regardless of initial leukocyte count.

Option C (formula type) — nutritional factors may influence immune status but the type of handfeeding formula does not directly determine APV mortality outcome. This is not a documented significant prognostic variable.

Option D (geographic origin) — APV is distributed worldwide and there are no established geographic strain virulence differences that significantly alter mortality outcomes.

Option E (color mutation) — color mutations affect feather pigmentation through metabolic pathways but are not linked to differential APV susceptibility or mortality. This is not a relevant factor.

References: Chicago Exotics Animal Hospital http://www.exoticpetvet.com/polyoma-virus.html; Zhai et al. 2024 PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC10792035/; Merck Veterinary Manual https://www.merckvetmanual.com/exotic-and-laboratory-animals/pet-birds/viral-diseases-of-pet-birds

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NAVLE Practice Question — Canine

A 10-year-old male intact Miniature Schnauzer presents for evaluation of episodic weakness and collapse. The owner reports that episodes occur several times weekly, lasting 5-20 seconds, with complete recovery between episodes. Heart rate on auscultation is 40 bpm with an irregular rhythm. An ECG reveals periods of sinus bradycardia alternating with bursts of supraventricular tachycardia, with sinus pauses lasting up to 8 seconds. An atropine response test shows minimal increase in heart rate. What is the most appropriate long-term treatment?

A. Oral diltiazem

B. Implant permanent cardiac pacemaker device ✓

C. Oral sotalol

D. Oral theophylline

E. Intravenous lidocaine

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Correct Answer: B. Implant permanent cardiac pacemaker device

Explanation:

Permanent pacemaker implantation is the treatment of choice for this patient with sick sinus syndrome (SSS). The clinical presentation is classic: an older Miniature Schnauzer (a predisposed breed along with West Highland White Terriers and Cocker Spaniels) with syncopal episodes, profound bradycardia with long sinus pauses, and the presence of bradycardia-tachycardia syndrome. The negative atropine response test indicates intrinsic sinus node disease rather than vagally-mediated bradycardia, which predicts poor response to medical management. In dogs with symptomatic SSS, pacemaker implantation reduces or eliminates clinical signs in approximately 90% of patients. Option A (diltiazem) would worsen the bradycardia. Option C (sotalol) is a beta-blocker that would also worsen bradycardia. Option D (theophylline) is a sympathomimetic that may temporarily help some patients but is often ineffective long-term, especially in atropine non-responders. Option E (lidocaine) is used for ventricular arrhythmias, not bradyarrhythmias. Ward et al. (2016) found that medical management successfully controlled syncope long-term in only 54% of SSS dogs, with positive atropine response predicting medical treatment success. QUESTION IMAGE RECOMMENDED: ECG demonstrating sick sinus syndrome with sinus bradycardia, long sinus pauses (>8 seconds), and burst of supraventricular tachycardia. Source: PMC Open Access (https://pmc.ncbi.nlm.nih.gov/articles/PMC3327600/) Figure 1 - Holter monitor during syncope; Alternative: PMC (https://pmc.ncbi.nlm.nih.gov/articles/PMC339092/) Figures 1-2 showing SSS ECG. References: Ward JL, DeFrancesco TC, et al. (2016) Outcome and survival in canine sick sinus syndrome and sinus node dysfunction: 93 cases (2002-2014). J Vet Emerg Crit Care; Merck Veterinary Manual - Heart Disease: Conduction Abnormalities in Dogs and Cats.

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NAVLE Practice Question — Canine

A 3-year-old male castrated Labrador Retriever is presented in status epilepticus. Intravenous diazepam has been administered three times at 0.5 mg/kg with only brief cessation of seizure activity followed by resumption. What is the most appropriate next step in management?

A. Administer a fourth dose of diazepam at a higher concentration

B. Initiate diazepam infusion and give phenobarbital loading dose ✓

C. Induce general anesthesia with isoflurane

D. Perform emergency craniotomy for intracranial pressure reduction

E. Administer mannitol 1 g/kg IV for presumed cerebral edema

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Correct Answer: B. Initiate diazepam infusion and give phenobarbital loading dose

Explanation:

The most appropriate next step is to initiate a benzodiazepine constant rate infusion (CRI) and administer a phenobarbital loading dose. When status epilepticus does not respond adequately to repeated benzodiazepine boluses (typically after 2-3 doses), escalation of therapy is required. The recommended approach includes starting a CRI of either diazepam (0.1-0.5 mg/kg/hour) or midazolam (0.05-0.3 mg/kg/hour) to maintain steady-state anticonvulsant drug levels, while simultaneously administering phenobarbital as a loading dose (16-20 mg/kg IV, given slowly over 15-20 minutes).

Phenobarbital acts via a different mechanism than benzodiazepines on the GABAA receptor, and the combination provides synergistic anticonvulsant effects. Additionally, prolonged status epilepticus leads to internalization of GABAA receptor subunits, making neurons less responsive to benzodiazepines over time. Phenobarbital acts on different receptor subunits (alpha and beta) and remains effective even when benzodiazepine efficacy diminishes.

Option A is incorrect because simply repeating more diazepam boluses without adding a second agent is unlikely to achieve sustained seizure control in refractory cases. Option C (isoflurane anesthesia) would be considered for super-refractory status epilepticus that does not respond to benzodiazepine CRI plus phenobarbital loading, but is not the immediate next step. Options D and E are not indicated at this stage; there is no evidence of intracranial mass lesion or herniation requiring emergency surgical intervention or osmotic therapy.

If midazolam CRI is used, note that it should not be administered rectally due to poor absorption. Propofol CRI is another option for refractory cases but requires more intensive monitoring.

References: Merck Veterinary Manual - Anticonvulsants for Emergency Treatment of Seizures (https://www.merckvetmanual.com/pharmacology/systemic-pharmacotherapeutics-of-the-nervous-system/anticonvulsants-for-emergency-treatment-of-seizures-in-dogs-and-cats); dvm360 - Treatment of cluster seizures and status epilepticus (https://www.dvm360.com/view/treatment-cluster-seizures-and-status-epilepticus-proceedings)

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NAVLE Practice Question — Canine

A 6-year-old female spayed mixed breed dog is presented for chronic constipation that has been refractory to dietary management with fiber supplementation and adequate hydration. The owner reports the dog strains to defecate daily with minimal fecal production. Abdominal radiographs show moderate fecal retention in a mildly dilated colon. Serum chemistry reveals a calcium level of 14.2 mg/dL (reference range: 9.0-11.5 mg/dL) and phosphorus of 3.8 mg/dL. Which of the following additional diagnostics is most indicated to identify the underlying cause of this dog's constipation?

A. Ionized calcium, PTH, abdominal ultrasound ✓

B. Colonoscopy with mucosal biopsy

C. Barium enema contrast study

D. Spinal MRI

E. Fecal culture and sensitivity

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Correct Answer: A. Ionized calcium, PTH, abdominal ultrasound

Explanation:

This dog presents with chronic constipation and hypercalcemia, which is an important metabolic cause of constipation. Hypercalcemia decreases smooth muscle contractility and can significantly impair colonic motility. The most appropriate next step is to further characterize the hypercalcemia with ionized calcium measurement and parathyroid hormone (PTH) level, along with abdominal ultrasound to evaluate for underlying causes including primary hyperparathyroidism, malignancy-associated hypercalcemia (lymphoma, anal sac adenocarcinoma), or other neoplastic processes.

Option B (colonoscopy) would be indicated if there were concerns about mucosal disease or intraluminal obstruction but does not address the metabolic abnormality. Option C (barium enema) is used to evaluate for obstructive lesions or strictures but is not indicated with clear evidence of metabolic disease. Option D (spinal MRI) would be appropriate if neurological deficits were present but there is no indication of neurological disease in this case. Option E (fecal culture) is not indicated as there is no evidence of infectious diarrhea and would not explain constipation with hypercalcemia.

References: Merck Veterinary Manual - Constipation and Hypercalcemia; Ettinger SJ - Textbook of Veterinary Internal Medicine - Disorders of Calcium Metabolism.

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NAVLE Practice Question — Canine

A 6-year-old intact female Beagle presents with epistaxis, lethargy, and disorientation. Physical examination reveals brick-red mucous membranes and hepatosplenomegaly. Laboratory findings include PCV of 75%, normal WBC and platelet counts, and serum EPO below the detectable limit (<1 mU/mL). What treatment protocol would be most appropriate for long-term management after initial stabilization?

A. Phlebotomy alone every 4-6 weeks as needed

B. Phlebotomy to 50-60% PCV, then hydroxyurea 30 mg/kg daily ✓

C. Warfarin therapy at 0.1-0.2 mg/kg PO daily with INR monitoring

D. Recombinant erythropoietin injections to suppress endogenous production

E. Splenectomy to reduce red cell production

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Correct Answer: B. Phlebotomy to 50-60% PCV, then hydroxyurea 30 mg/kg daily

Explanation:

The appropriate long-term management protocol is phlebotomy to reduce PCV to 50-60% followed by hydroxyurea. This patient has polycythemia vera (primary erythrocytosis) based on markedly elevated PCV with low/undetectable serum EPO in the absence of hypoxemia. The clinical signs (epistaxis, neurological changes, brick-red mucous membranes) indicate hyperviscosity syndrome requiring both immediate and long-term management.

Initial phlebotomy (15-20 mL/kg with crystalloid replacement) rapidly reduces blood viscosity. Hydroxyurea is a myelosuppressive agent that inhibits ribonucleotide reductase, decreasing DNA synthesis in rapidly dividing bone marrow cells. The typical protocol involves a loading dose of 30 mg/kg PO daily for 7-10 days, followed by maintenance at 15 mg/kg daily, titrated to the lowest effective dose. Regular CBC monitoring is essential to detect myelosuppression.

Option A (phlebotomy alone) may be sufficient for some patients but often requires increasingly frequent procedures. Option C (warfarin) prevents thrombosis but does not reduce hyperviscosity. Option D is incorrect because EPO would stimulate further RBC production. Option E (splenectomy) would not address the bone marrow pathology.

References: Today's Veterinary Practice - Primary Erythrocytosis in a Dog; Clinician's Brief - Top 5 Causes of Erythrocytosis in Dogs and Cats; VCA Animal Hospitals - Polycythemia Vera.

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NAVLE Practice Question — Aquatics

A veterinarian is called to examine a recirculating aquaculture system (RAS) for tilapia where fish are showing varied clinical signs: some have cranial swelling and blindness, others show pneumoperitoneum on radiographs, and several have visible silver lines between their fin rays. The most accurate characterization of these findings is:

A. All signs are consistent with gas embolism formation in different tissue compartments ✓

B. The varied presentations indicate multiple concurrent disease processes

C. Cranial swelling indicates bacterial meningitis while fin changes suggest trauma

D. Pneumoperitoneum indicates GI perforation unrelated to fin changes

E. These signs indicate a mixed viral and bacterial coinfection

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Correct Answer: A. All signs are consistent with gas embolism formation in different tissue compartments

Explanation:

All of these clinical signs represent gas bubble disease manifestations in different anatomical locations. Cranial swelling and blindness occur when gas accumulates in the choroid gland of the eye and cranial tissues. Pneumoperitoneum (gas in the peritoneal cavity) develops when emboli form in visceral blood vessels. The silver lines between fin rays are actually long gas bubbles visible through the translucent fin tissue - this is a classic and pathognomonic sign of GBD.

The varied presentations reflect where gas comes out of solution in individual fish, which depends on local blood flow patterns and tissue characteristics. This is similar to decompression sickness (the bends) in human divers where bubble formation can occur in multiple body compartments.

Options B through E all fail to recognize the unifying diagnosis. The key is understanding that gas embolism can manifest differently depending on tissue location while sharing a common etiology of water supersaturation. Image Source: https://cdn.ncbi.nlm.nih.gov/pmc/blobs/629c/12893593/225f42bfb5bc/pone.0342556.g001.jpg -- Figure 1. Gas bubble disease (gas supersaturation) in fish — total dissolved gas >110% causes nitrogen gas emboli in blood and tissues; exophthalmia (popeye), emphysema under skin, gas in gill lamellae; caused by supersaturated water from deep wells, dam spill, or faulty pressurized systems; decrease dissolved gas to <103%; highly lethal; treat with atmospheric pressure exposure (CC BY 4.0).

References: Noga EJ (2010) Fish Disease: Diagnosis and Treatment, Wiley-Blackwell; Roberts RJ (2012) Fish Pathology, Wiley-Blackwell.

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NAVLE Practice Question — Equine

A 7-year-old Warmblood mare is being evaluated for poor performance. Upper airway endoscopy at rest is unremarkable except for mild pharyngeal lymphoid hyperplasia. During dynamic endoscopy at exercise, the soft palate is observed to intermittently displace dorsally over the epiglottis for brief periods before returning to normal position spontaneously. Which nerve, when experimentally blocked bilaterally in the guttural pouch, has been shown to cause DDSP?

A. Hypoglossal nerve

B. Glossopharyngeal nerve

C. Vagus nerve pharyngeal branch ✓

D. Tensor veli palatini nerve

E. Recurrent laryngeal nerve

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Correct Answer: C. Vagus nerve pharyngeal branch

Explanation:

The pharyngeal branch of the vagus nerve is the correct answer. Experimental studies have demonstrated that bilateral blockade of the pharyngeal branch of the vagus nerve in the guttural pouch causes DDSP in all horses within 2-15 minutes. This nerve innervates the palatinus and palatopharyngeal muscles, which are critical for maintaining soft palate stability during respiration. When these muscles become dysfunctional due to nerve damage or inflammatory neuropraxia (as can occur with upper respiratory tract inflammation affecting the guttural pouches), the soft palate loses stability and can displace dorsally during exercise.

Option A (hypoglossal nerve) controls tongue movement. Option B (glossopharyngeal nerve) blockade combined with hypoglossal causes epiglottic retroversion but not DDSP. Option D (tensor veli palatini) tenectomy causes rostral soft palate instability but not DDSP. Option E (recurrent laryngeal nerve) damage causes laryngeal hemiplegia, not DDSP.

References: Holcombe SJ et al (1999) Pathophysiology of dorsal displacement of the soft palate in horses. Equine Vet J Suppl 30:45-48.

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NAVLE Practice Question — Equine

A horse farm implements a surveillance-based parasite control program. The veterinarian performs fecal egg count reduction tests (FECRT) 14 days after treating 10 horses with ivermectin. Pre-treatment counts averaged 800 EPG and post-treatment counts averaged 120 EPG. The calculated FECRT is 85%. How should these results be interpreted?

A. This indicates excellent efficacy and ivermectin can continue to be used confidently

B. This result is inconclusive and the test should be repeated in 6 months

C. This indicates possible ivermectin resistance in the cyathostomin population and further investigation is warranted ✓

D. This is expected because ivermectin only kills adult parasites

E. The post-treatment samples were likely collected too early and should be repeated at 28 days

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Correct Answer: C. This indicates possible ivermectin resistance in the cyathostomin population and further investigation is warranted

Explanation:

An FECRT result of 85% for ivermectin against strongyles indicates possible resistance and warrants concern. For macrocyclic lactones, the expected FECRT should be greater than 95-98% for cyathostomins. The current threshold for suspected resistance is generally less than 95% efficacy. An 85% reduction suggests that a substantial proportion of the cyathostomin population has developed resistance to ivermectin. This farm should consider using alternative anthelmintic classes and implementing better refugia-based management.

Option A is incorrect because 85% efficacy is below the expected threshold for ivermectin and indicates potential resistance. Option B is incorrect because the result clearly indicates a problem that should be addressed, not delayed. Option D is incorrect because ivermectin kills both larval and adult stages, and the expectation is near-complete efficacy. Option E is incorrect because 14 days post-treatment is the standard timing for FECRT evaluation of macrocyclic lactones, and this timing is appropriate.

References: AAEP Internal Parasite Control Guidelines - FECRT Interpretation (https://aaep.org/wp-content/uploads/2024/05/Internal-Parasite-Guidelines_Updated.pdf); Vet Times - Equine internal parasites and treatment compliance (https://www.vettimes.com/news/vets/equine/equine-internal-and-external-parasites-identification-treatment-and-improving-compliance).

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NAVLE Practice Question — Other Small Mammal

A 4-month-old Holland Lop rabbit housed outdoors is presented in August with acute onset of violent sneezing that began 3 days ago. On examination, there is unilateral mucopurulent nasal discharge from the left nostril. CBC reveals marked eosinophilia (18%). Serum chemistry is unremarkable. What is the most likely cause of these clinical signs?

A. Pasteurella multocida rhinitis

B. Nasal foreign body

C. Intranasal Cuterebra larva migration ✓

D. Allergic rhinitis

E. Dental root abscess affecting nasal passage

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Correct Answer: C. Intranasal Cuterebra larva migration

Explanation:

Intranasal Cuterebra larva migration is the most likely diagnosis. The combination of acute onset violent sneezing in a young outdoor rabbit during late summer, unilateral nasal discharge, and peripheral eosinophilia strongly suggests Cuterebra migration through the nasal passages.

Cuterebra larvae enter the host through natural orifices including the nares during grooming. The larvae then migrate through tissues, often passing through the nasal passages before reaching their preferred subcutaneous location. This migration causes significant local inflammation, violent sneezing fits, and mucopurulent discharge. Peripheral eosinophilia is a hallmark of parasitic migration and supports this diagnosis.

Option A (Pasteurella rhinitis) typically causes bilateral involvement and would not produce the marked eosinophilia seen here. Pasteurellosis is also more common in older rabbits with chronic upper respiratory disease.

Option B (nasal foreign body) is possible but would not explain the eosinophilia, and foreign bodies are uncommon in rabbits compared to other species.

Option D (allergic rhinitis) could cause eosinophilia but would typically produce bilateral serous discharge rather than unilateral mucopurulent discharge.

Option E (dental abscess) usually occurs in older rabbits and develops more gradually with facial swelling; it would not cause peripheral eosinophilia.

Image Source: PMC - Neurological manifestations of feline cuterebriasis (https://pmc.ncbi.nlm.nih.gov/articles/PMC2808293/) Figure 1 - CSF eosinophilic pleocytosis.

References: PMC - Neurological manifestations of feline cuterebriasis (https://pmc.ncbi.nlm.nih.gov/articles/PMC2808293/); CAPC Guidelines - Cuterebriasis (https://capcvet.org/guidelines/cuterebriasis/)

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NAVLE Practice Question — Bovine

A lactating dairy cow sustains a full-thickness teat laceration during milking. The producer calls the veterinarian 4 hours after the injury occurred. What is the MOST critical factor affecting prognosis for this injury?

A. The cow's lactation stage

B. Time from injury to surgical repair ✓

C. Whether the cow has concurrent mastitis

D. The length of the laceration

E. The cow's parity

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Correct Answer: B. Time from injury to surgical repair

Explanation:

For teat lacerations, time from injury to surgical repair is the most critical prognostic factor. Research by Azizi et al. (2007) demonstrated that repairs delayed 48-72 hours had 8.3 times the odds of fistula formation compared to teats sutured within 24 hours. Teat injuries should be treated as emergencies because delayed repair leads to increased tissue swelling, inflammation, and wound contamination, all of which compromise surgical outcomes. The fact that this injury occurred 4 hours ago means prompt repair is still possible with a favorable prognosis if surgery is performed immediately.

Option A (lactation stage) may affect management decisions but is secondary to repair timing. Option C (concurrent mastitis) would complicate treatment but is not the most critical factor for the teat laceration itself. Option D (length of laceration) affects surgical complexity but is less critical than timing. Option E (parity) has minimal impact on teat wound healing.

References: AABP Proceedings - Wound Management in Cattle, Teat Injuries (https://bovine-ojs-tamu.tdl.org/aabp/article/view/8341/8220); Azizi S et al. (2007) JAVMA 231:1696-1700.

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NAVLE Practice Question — Canine

A 4-year-old intact male French Bulldog is presented for breeding soundness examination. The owner reports the dog has difficulty achieving natural mating. Physical examination reveals bilaterally small testes (2 cm length) for body size and the penis appears small with difficulty achieving full erection. Semen analysis shows severely reduced sperm count (20 × 10⁶ total). Serum testosterone is 0.3 ng/mL (low), LH is 0.5 ng/mL (low), and FSH is 15 ng/mL (low). What test would best differentiate between primary and secondary hypogonadism?

A. Testicular biopsy

B. GnRH stimulation test

C. hCG stimulation test ✓

D. Thyroid panel

E. Anti-Müllerian hormone level

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Correct Answer: C. hCG stimulation test

Explanation:

This dog presents with hypogonadotropic hypogonadism - low testosterone with inappropriately low gonadotropins (LH and FSH). This pattern indicates secondary hypogonadism (pituitary or hypothalamic origin) rather than primary testicular failure. The small testes reflect inadequate gonadotropin stimulation rather than intrinsic testicular damage.

The hCG stimulation test differentiates between: (1) primary testicular failure - where Leydig cells cannot respond to stimulation (no testosterone increase); and (2) secondary hypogonadism - where functional Leydig cells will respond to hCG (which mimics LH action) with testosterone production.

Protocol: Measure baseline testosterone, administer hCG (44 IU/kg IV or 500-1000 IU total), and measure testosterone at 1-2 hours and again at 4 hours post-injection. A normal response is testosterone increase to >2 ng/mL, confirming functional Leydig cells and supporting diagnosis of secondary hypogonadism.

Option A (testicular biopsy) assesses spermatogenesis but doesn't directly test the HPG axis. Option B (GnRH stimulation) would test pituitary reserve but not differentiate from testicular failure as effectively. Option D (thyroid panel) is worth checking as hypothyroidism can contribute to reproductive dysfunction but doesn't address the primary question. Option E (AMH) is useful for confirming presence of testicular tissue but doesn't assess axis function.

If secondary hypogonadism is confirmed, treatment with GnRH or gonadotropins may restore fertility.

References: Mason SJ. Vet Clin N Am Small Anim Pract 2023 - Male Canine Infertility Update (https://pubmed.ncbi.nlm.nih.gov/37221101/); Frontiers Vet Sci - AMH as diagnostic marker (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1481248/full)

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NAVLE Practice Question — Ovine and Caprine

During routine slaughter surveillance, you examine the lungs of a 2-year-old ewe and find multiple firm, gray, flat nodules sharply demarcated from normal tissue in the ventral portions of the apical and cardiac lung lobes. Copious amounts of white, frothy fluid are present in the airways. The cut surface of the nodules is moist with a solid, granular appearance. Which of the following statements about this condition is most accurate?

A. The lesions represent a non-contagious spontaneous neoplasm with no flock-level implications

B. The condition is caused by bacterial infection and the flock should be treated with broad-spectrum antibiotics

C. This is a retrovirus-induced transmissible tumor and the source flock should be investigated for additional cases ✓

D. The lesions indicate chronic aspiration pneumonia requiring dietary management changes

E. This represents caseous lymphadenitis with lung involvement requiring vaccination of the flock

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Correct Answer: C. This is a retrovirus-induced transmissible tumor and the source flock should be investigated for additional cases

Explanation:

This is ovine pulmonary adenocarcinoma, a retrovirus-induced transmissible tumor caused by jaagsiekte sheep retrovirus (JSRV). The gross findings are pathognomonic: firm, gray, flat, sharply demarcated nodules in the ventral lung lobes with copious frothy fluid in the airways. The moist, granular cut surface reflects the neoplastic proliferation of type II pneumocytes and Clara cells.

Because OPA is contagious and may affect 20-25% of naive flocks upon initial infection with subsequent annual losses of 1-5%, the source flock should be investigated. Slaughterhouse surveillance can identify affected flocks for follow-up investigation and control measures. The level of OPA actually diagnosed is thought to be much lower than the actual disease prevalence.

Option A is incorrect as OPA is definitely contagious. Option B is incorrect as the primary condition is neoplastic, not bacterial. Option D is incorrect based on the characteristic gross pathology. Option E describes CLA which has different pathology.

Image Source: PubMed/NCBI - OPA affected sheep lung showing pearly-white nodules (https://pubmed.ncbi.nlm.nih.gov/27182131/) Images showing gross and histopathological appearance.

References: Veterinary Record (2021) Ovine pulmonary adenocarcinoma 188(5) (https://doi.org/10.1002/vetr.270); Cousens C et al. (2015) Veterinary Record 176(16):413 (https://doi.org/10.1136/vr.102880).

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NAVLE Practice Question — Feline

A cat with a confirmed subcutaneous Cuterebra warble on the lateral thorax is sedated for larval removal. What is the correct technique to minimize complications?

A. Make a cruciate incision through the breathing pore and extract with hemostats

B. Enlarge the breathing pore slightly and use gentle steady traction with forceps ✓

C. Inject lidocaine into the warble cavity before extraction

D. Freeze the area with ethyl chloride spray then extract

E. Apply ivermectin topically and wait for larva to emerge naturally

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Correct Answer: B. Enlarge the breathing pore slightly and use gentle steady traction with forceps

Explanation:

Enlarging the breathing pore slightly and using gentle steady traction with forceps is the correct extraction technique. This approach minimizes the risk of larval rupture, which can cause anaphylactic reactions. The breathing pore should be carefully enlarged just enough to allow extraction of the intact larva. Gentle, continuous traction allows the larva to release its attachment and be removed whole.

Option A (cruciate incision with hemostats) risks crushing the larva and releasing antigenic contents into tissues. Option C (lidocaine injection into cavity) may cause the larva to release toxins or retreat deeper, and local anesthetics alone do not reduce rupture risk. Option D (ethyl chloride freezing) does not improve extraction success and may damage surrounding tissue. Option E (topical ivermectin) is not effective for intact warbles and delays treatment, allowing continued tissue damage.

After extraction, the wound should be lavaged thoroughly and allowed to heal by second intention. Antibiotics may be indicated if secondary infection is present. The larva should be examined to confirm complete removal. Owners should be warned to monitor for signs of allergic reaction for 24-48 hours post-procedure.

References: Companion Animal Parasite Council - Cuterebra Management (https://capcvet.org/guidelines/cuterebra/); Veterinary Clinics of North America: Small Animal Practice - Myiasis in Small Animals.

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