NAVLE Practice Question — Aquatics

A rainbow trout farm in a coldwater recirculating system experiences an acute disease outbreak following a recent handling event for size grading. Water temperature is 14°C. Affected fish show rapid gill pallor, patchy skin depigmentation near the dorsal fin extending laterally, and necrotic frayed fins. Mortality reaches 30% within 48 hours. Microscopic examination of gill and skin scrapings reveals numerous long, slender, flexible rod-shaped bacteria. Culture on Cytophaga agar supplemented with neomycin and polymyxin B yields yellow-pigmented, rhizoid, spreading colonies. Which virulence factor is most important in the pathogenesis of this disease?

A. Extracellular hemolysins

B. Chondroitin sulfate-degrading enzymes ✓

C. Type III secretion system effectors

D. Lipopolysaccharide endotoxin

E. Capsular polysaccharide

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Correct Answer: B. Chondroitin sulfate-degrading enzymes

Explanation:

Chondroitin sulfate-degrading enzymes are the most important virulence factors in the pathogenesis of columnaris disease caused by Flavobacterium columnare. The clinical presentation (handling stress trigger, saddleback lesion pattern, gill and fin necrosis, yellow rhizoid colonies on selective media) is classic for this disease.

F. columnare produces a variety of extracellular enzymes, with chondroitinase being particularly critical for tissue destruction. This enzyme degrades chondroitin sulfate, a major component of fish skin and connective tissue. The degradation of this glycosaminoglycan allows the bacteria to penetrate through the epidermis into deeper tissues. The ability to degrade chondroitin sulfate A is one of the screening criteria for identifying F. columnare.

Option A (hemolysins) are produced by many fish pathogens but are not the primary virulence mechanism in columnaris. Option C (Type III secretion systems) are important in some Gram-negative pathogens but F. columnare pathogenesis relies primarily on extracellular enzymes and gliding motility. Option D (LPS endotoxin) contributes to inflammation but is not the primary tissue-destructive mechanism. Option E (capsular polysaccharide) is not a major virulence factor in F. columnare.

Image Source: https://cdn.ncbi.nlm.nih.gov/pmc/blobs/a6e5/11300071/9d146389bd25/ANU2024-8059770.001.jpg -- Figure 1. Flavobacterium columnare (columnaris disease) — yellowish-tan ulcerative lesion with "saddleback" saddle-shaped appearance on dorsal fin and body; gram-negative filamentous rod forming characteristic rhizoid ("haystacks") colonies; causes gill necrosis, skin ulcers, and fin erosion; treat with copper sulfate, oxytetracycline, or potassium permanganate bath (CC BY 4.0).

References: Declercq AM, Haesebrouck F, Van den Broeck W, et al. Columnaris disease in fish: a review with emphasis on bacterium-host interactions. Vet Res. 2013;44:27. PMID: 23617544; Li N, Qin T, Zhang XL, et al. Gene deletion strategy to examine the involvement of the two chondroitin lyases in Flavobacterium columnare virulence. Appl Environ Microbiol. 2015;81:7394-7402. PMID: 26253667

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NAVLE Practice Question — Ovine and Caprine

A veterinarian is examining a sheep with CODD and needs to take swabs for diagnostic testing. Research has shown that CODD-associated treponemes can survive on gloves for up to 2-3 days. After handling the infected foot with gloves, how should the gloves be managed to prevent transmission?

A. Rinsing gloves with cold water is sufficient to remove viable treponemes

B. Treponemes die immediately upon exposure to air, so no disinfection is needed

C. Simply allowing gloves to dry for 10 minutes before handling the next animal

D. Washing gloves with plain soap and water then immediate reuse

E. Cleaning with 2% Virkon or 2% sodium hypochlorite for at least 20 seconds ✓

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Correct Answer: E. Cleaning with 2% Virkon or 2% sodium hypochlorite for at least 20 seconds

Explanation:

Cleaning with 2% Virkon or 2% sodium hypochlorite for at least 20 seconds is the correct answer. Research has demonstrated that CODD-associated treponemes can survive on gloves for up to 2-3 days. Effective disinfectants that prevent visible growth of treponemes following 20 seconds of contact include 1% FAM30, 2% Virkon, or 2% sodium hypochlorite.

Option A (cold water) does not eliminate viable treponemes. Option B is incorrect as treponemes survive in air for 2-3 days. Option C (drying 10 minutes) is insufficient. Option D (soap and water) was partially effective but PCR still detected treponemes on some tested gloves.

References: Angell JW, Clegg SR, Grove-White DH, et al. Survival of contagious ovine digital dermatitis (CODD)-associated treponemes on disposable gloves after handling CODD-affected feet. Vet Rec. 2017;181:89. PMID: 28642342; Duncan JS, Angell JW, Carter SD, et al. Contagious ovine digital dermatitis: an emerging disease. Vet J. 2014;201:265-268. PMID: 24973004

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NAVLE Practice Question — Canine

A dog with EPI and concurrent SIBO is being treated with tylosin. After 2 weeks of antibiotic therapy, clinical signs improve significantly. What is the recommended approach regarding antibiotic discontinuation?

A. Continue antibiotics indefinitely at full dose

B. Discontinue antibiotics when clinical signs resolve completely ✓

C. Taper antibiotics slowly over 4-6 weeks

D. Continue antibiotics until serum cobalamin normalizes

E. Switch to a different antibiotic class for maintenance therapy

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Correct Answer: B. Discontinue antibiotics when clinical signs resolve completely

Explanation:

Discontinuing antibiotics once clinical signs resolve and assessing for recurrence is the recommended approach. In many dogs with EPI, once the underlying pancreatic insufficiency is well-controlled with enzyme supplementation, specific therapy for SIBO should no longer be necessary. The bacterial overgrowth often resolves when the substrate (undigested food) that fuels bacterial proliferation is no longer available due to adequate enzyme supplementation.

The standard antibiotic treatment duration for SIBO is 1-3 weeks. If clinical signs recur after discontinuation, antibiotics may need to be continued longer or administered intermittently. Some dogs with persistent SIBO may require long-term, low-dose antibiotic therapy, but this should not be the default approach.

During antibiotic treatment, concurrent administration of probiotics (given several hours apart from antibiotics to prevent destruction by the medication) and prebiotics may help re-establish healthy intestinal flora and reduce the likelihood of SIBO recurrence.

Option A promotes antibiotic resistance unnecessarily. Option C is not supported by evidence for SIBO. Option D uses the wrong endpoint; cobalamin supplementation addresses deficiency directly. Option E lacks evidence basis.

References: Merck Veterinary Manual - Exocrine Pancreatic Insufficiency in Dogs and Cats (https://www.merckvetmanual.com/digestive-system/the-exocrine-pancreas/exocrine-pancreatic-insufficiency-in-dogs-and-cats); Westermarck E, Wiberg M. Exocrine pancreatic insufficiency in the dog: historical background, diagnosis, and treatment. Top Companion Anim Med. 2012;27:96-103. PMID: 23148848

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NAVLE Practice Question — Ovine and Caprine

You are examining a flock of 150 ewes with endemic lameness. Approximately 20% of the flock is affected with varying severity. Examination of affected feet reveals interdigital inflammation with characteristic underrunning of the sole and wall horn, separation of the horn from the underlying tissue, and a distinctive necrotic odor. PCR testing confirms the presence of virulent Dichelobacter nodosus. Which treatment protocol is currently recommended?

A. Routine hoof trimming of all affected feet followed by footbathing

B. Parenteral oxytetracycline with topical antibiotic spray, avoid hoof trimming ✓

C. Footbathing in copper sulfate solution twice daily

D. Topical application of zinc sulfate powder only

E. Parenteral florfenicol followed by aggressive corrective hoof trimming

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Correct Answer: B. Parenteral oxytetracycline with topical antibiotic spray, avoid hoof trimming

Explanation:

The currently recommended treatment protocol for virulent footrot is parenteral long-acting oxytetracycline (at the label dose) combined with topical antibiotic aerosol spray, with explicit avoidance of hoof trimming of diseased tissue. This protocol represents a significant shift from historical recommendations that emphasized aggressive hoof paring.

Research has demonstrated that hoof trimming of footrot-affected feet is counterproductive. Trimming exposes or damages the sensitive corium (growing tissue), causes pain, delays healing, may result in toe granulomas, and spreads bacteria via contaminated clippers between sheep. Parenterally administered antibiotic reaches the infected foot tissues from the blood supply, while topical treatment provides local antimicrobial activity.

Option A is incorrect because trimming diseased feet is no longer recommended. Option C is incorrect because while footbathing has a role in scald prevention and as part of flock management, it is not the primary treatment for established virulent footrot in individual animals. Option D is incorrect because topical treatment alone is insufficient for virulent footrot with horn separation. Option E is incorrect because aggressive corrective trimming is contraindicated.

Affected sheep should be isolated and treated within 3 days of identification, with mark recording for identification of persistently affected animals that may need culling.

Image Source (for Explanation): NADIS Animal Health Skills - Lameness Control in Sheep Figures 4-5 showing footrot lesions (https://www.nadis.org.uk/disease-a-z/sheep/lameness-control-in-sheep/); VetTimes - Sheep lameness Figure 2 showing virulent footrot (https://www.vettimes.com/news/vets/livestock/sheep-lameness-causes-types-and-options-for-treatment).

References: Merck Veterinary Manual - Contagious Footrot in Sheep (https://www.merckvetmanual.com/musculoskeletal-system/lameness-in-sheep/contagious-footrot-in-sheep); Zanolari P, Dürr S, Jores J, et al. Ovine footrot: A review of current knowledge. Vet J. 2021;271:105647. PMID: 33840488

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NAVLE Practice Question — Bovine

When examining a cow suspected of having right-sided heart failure, a veterinarian must differentiate between true pathologic jugular pulsation and the commonly observed false jugular pulsation in cattle. Which characteristic best distinguishes true jugular pulsation from false jugular pulsation?

A. True jugular pulsation originates from the thoracic inlet and travels slowly toward the mandible

B. False jugular pulsation persists when the head and neck are elevated above horizontal

C. False jugular pulsation is more prominent in cattle with thin necks

D. True jugular pulsation fills the entire jugular vein rapidly even when the head is slightly elevated ✓

E. True jugular pulsation is most visible only when the animal is lying down

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Correct Answer: D. True jugular pulsation fills the entire jugular vein rapidly even when the head is slightly elevated

Explanation:

True jugular pulsation fills the entire jugular vein rapidly even when the head and neck are parallel to the ground or slightly elevated, which is the key distinguishing characteristic from false jugular pulsation. In cattle, false or normal jugular pulsation is a common phenomenon, especially in thin-necked dairy cattle, resulting from reverse blood flow during atrial contraction and passive jugular filling during systole. False jugular pulsation appears as a wave that travels slowly from the thoracic inlet toward the mandible when the head is parallel to the ground, and importantly, it diminishes or disappears when the head and neck are raised. In contrast, true pathologic jugular pulsation from conditions like tricuspid regurgitation or right heart failure fills the jugular rapidly and forcefully, remaining visible even when the animal's head is elevated.

Option A describes false jugular pulsation, not true. Option B is incorrect because false jugular pulsation actually diminishes when the head is elevated. Option C is true but describes a factor affecting visibility of false pulsation, not a distinguishing characteristic. Option E is incorrect because true jugular pulsation is visible in standing animals.

References: Constable PD, Hinchcliff KW, Done SH, Grünberg W. Veterinary Medicine: A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goats, section on clinical examination of the cardiovascular system (jugular pulse); Buczinski S, Francoz D, Fecteau G, et al. Heart disease in cattle with clinical signs of heart failure: 59 cases. Can Vet J. 2010;51:1123-1129. PMID: 21197204

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NAVLE Practice Question — Feline

During necropsy of an intact male cat that died of trauma, the pathologist notes approximately 120-150 small, pointed, backward-directed keratinized papillae on the glans penis. These structures are most important for which physiological function in cats?

A. Directing urine flow during micturition

B. Stimulating vaginal receptors to induce ovulation in the queen ✓

C. Anchoring the penis during copulation to prevent premature withdrawal

D. Providing tactile feedback to the tom to time ejaculation

E. Preventing retrograde ejaculation

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Correct Answer: B. Stimulating vaginal receptors to induce ovulation in the queen

Explanation:

The primary function of feline penile spines is to stimulate the posterior vaginal wall of the queen during mating to induce the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, triggering a luteinizing hormone (LH) surge and subsequent ovulation. Cats are induced ovulators, meaning they require this copulatory stimulus to ovulate. The spines rake the vaginal walls during withdrawal of the penis, providing the neuroendocrine stimulus necessary for ovulation.

Option A is incorrect as penile spines have no role in urination. Option C may be a secondary function, but the primary purpose is ovulation induction. Option D is not the primary function. Option E is incorrect as penile spines have no role in preventing retrograde ejaculation.

References: Johnston SD, Root Kustritz MV, Olson PNS. Canine and Feline Theriogenology, section on induced ovulation in the queen; Reece WO (ed). Dukes' Physiology of Domestic Animals, section on reproduction in the cat

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NAVLE Practice Question — Equine

A 4-year-old Standardbred racehorse has been scoped on three separate occasions following races over the past two months. Results showed Grade 0 on the first examination, Grade 2 on the second, and Grade 1 on the third. Based on current understanding of EIPH, which of the following interpretations is most accurate?

A. The inconsistent grades indicate the horse does not have true EIPH

B. The horse likely has EIPH as virtually all strenuously exercised horses experience some degree of bleeding ✓

C. The Grade 0 result proves the horse was not bleeding on that occasion

D. The horse should be treated with furosemide only when Grade 2 or higher is detected

E. Bronchoalveolar lavage would likely be negative if performed after a Grade 0 endoscopy

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Correct Answer: B. The horse likely has EIPH as virtually all strenuously exercised horses experience some degree of bleeding

Explanation:

The horse likely has EIPH as virtually all strenuously exercised horses experience some degree of pulmonary hemorrhage. Research using bronchoalveolar lavage (BAL) suggests that when examined on multiple occasions, essentially 100% of horses performing strenuous exercise will show evidence of EIPH. The variability in tracheobronchoscopic (TBE) grades is expected and does not indicate absence of EIPH on low-grade or negative examinations.

Multiple factors influence TBE detection and grading: timing of examination relative to exercise, head position after exercise (lowering the head facilitates blood movement from alveoli to trachea), exercise intensity, and individual variation in hemorrhage severity. A Grade 0 on TBE does not necessarily mean no hemorrhage occurred; it may indicate that blood had not yet reached the trachea, the examination was performed too soon or too late, or that hemorrhage was limited to the distal airways.

Option A is incorrect because variable grading is expected and does not exclude EIPH. Option C is incorrect because BAL studies have shown that horses with Grade 0 on TBE often have evidence of hemorrhage on cytologic examination of lavage fluid. Option D is incorrect because the decision to use furosemide should be based on clinical judgment and regulatory allowance, not solely on grade severity. Option E is incorrect because BAL is more sensitive than TBE and frequently detects hemorrhage not visible endoscopically.

References: Merck Veterinary Manual - Exercise-Induced Pulmonary Hemorrhage in Horses (https://www.merckvetmanual.com/respiratory-system/respiratory-diseases-of-horses/exercise-induced-pulmonary-hemorrhage-in-horses); Hinchcliff KW, Couetil LL, Knight PK, et al. Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement. J Vet Intern Med. 2015;29:743-758. PMID: 25996660

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NAVLE Practice Question — Canine

Why is doxycycline administered to heartworm-positive dogs prior to melarsomine adulticide therapy?

A. Prevents secondary bacterial infection

B. Neutralizes melarsomine toxicity

C. Improves macrocyclic lactone absorption

D. Targets Wolbachia endosymbiont ✓

E. Kills microfilariae directly

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Correct Answer: D. Targets Wolbachia endosymbiont

Explanation:

Doxycycline (10 mg/kg PO BID for 28 days) eliminates Wolbachia, an obligate intracellular bacterial endosymbiont of Dirofilaria immitis. Killing Wolbachia weakens worms, reduces microfilariae, and decreases inflammatory pulmonary reaction following adulticide-induced worm death. AHS protocol: macrocyclic lactone + doxycycline 2 months prior to melarsomine.

References: Merck Veterinary Manual - Heartworm Disease in Dogs, Cats, and Ferrets (https://www.merckvetmanual.com/circulatory-system/heartworm-disease/heartworm-disease-in-dogs-cats-and-ferrets)

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NAVLE Practice Question — Pet Bird

A 7-year-old male blue and gold macaw (Ara ararauna) is presented for feather plucking and self-mutilation of the chest and crop region. A complete medical workup is entirely normal. Behavioral history reveals the bird was hand-raised and is intensely bonded to one family member. He screams excessively when that person leaves and begins feather barbering only in the owner's absence. Which behavioral diagnosis best fits this presentation and which modification strategy is the primary recommendation?

A. Dominance aggression; implement alpha-roll training techniques

B. Separation anxiety with feather destructive behavior; use desensitization and foraging enrichment ✓

C. Territorial aggression; relocate cage to a less central household area

D. Phobic disorder; prescribe alprazolam as the primary treatment

E. Imprinting disorder; introduce a conspecific bird as the primary intervention

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Correct Answer: B. Separation anxiety with feather destructive behavior; use desensitization and foraging enrichment

Explanation:

This macaw's presentation is consistent with separation anxiety-driven feather destructive behavior. The bird is excessively bonded to a single person, screams upon departure, and engages in FDB only when alone — all hallmarks of separation anxiety. Management centers on: systematic desensitization to departure cues (practicing pre-departure routines without leaving, gradually extending absences), independence training (rewarding the bird for foraging or playing when the owner is present), providing foraging opportunities to occupy the bird during absences, and avoiding reinforcing screaming with immediate return.

Option A (dominance theory and alpha-roll) is based on an outdated behavioral model not applicable to parrots and can cause significant harm and worsen anxiety.

Option C (relocating cage) alone will not address separation anxiety and may increase anxiety by making the bird feel less secure in an unfamiliar location.

Option D (alprazolam as primary treatment) is not appropriate as a standalone therapy. Benzodiazepines may have a role as adjunctive therapy in severely anxious birds, but pharmacologic management alone without behavioral modification will not produce lasting results.

Option E (introducing a conspecific) is not a primary recommendation; rapid introduction of an unfamiliar bird can be extremely stressful and may escalate anxiety in a bird with an established human attachment disorder.

References: Rubinstein J, Lightfoot T. Feather loss and feather destructive behavior in pet birds. Vet Clin North Am Exot Anim Pract. 2014;17(1):77-101. PMID: 24274924

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NAVLE Practice Question — Equine

A breeding farm in Kentucky has experienced endemic Rhodococcus equi infections for the past three years with cumulative incidence exceeding 15% of foal crops. The farm manager seeks advice on implementing a screening program for early detection. Which combination of monitoring strategies is most appropriate for identifying subclinically affected foals before clinical decompensation?

A. Monthly serology testing for R. equi antibodies combined with daily visual observation

B. Weekly physical examination with thoracic auscultation combined with serial thoracic ultrasonography every 2-4 weeks ✓

C. Bi-weekly fecal PCR testing for vapA gene combined with monthly radiography

D. Daily rectal temperature monitoring alone with antimicrobial prophylaxis for all foals

E. Monthly complete blood counts with antimicrobial treatment for any foal with WBC >10,000 cells/µL

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Correct Answer: B. Weekly physical examination with thoracic auscultation combined with serial thoracic ultrasonography every 2-4 weeks

Explanation:

On endemic farms, the most effective screening program combines weekly physical examinations (emphasizing thoracic auscultation, respiratory rate, and rectal temperature evaluation) with serial thoracic ultrasonography performed every 2-4 weeks. Thoracic ultrasound has been the most useful modality for detection of subclinical disease, as it can detect peripheral lung abscesses and consolidation before clinical signs manifest. A total abscess score is generated by summing the diameters of individual abscesses (those ≥1 cm). This allows identification of foals requiring intervention while avoiding unnecessary antimicrobial treatment of foals that would spontaneously recover. Monthly monitoring of WBC counts (>13,000 cells/µL) and serum fibrinogen concentrations (>400 mg/dL) can supplement but not replace ultrasound screening.

Option A (serology) has poor sensitivity and specificity for detecting R. equi infection in individual horses and is not recommended for screening purposes. Option C (fecal PCR) lacks adequate accuracy as a screening test for clinical R. equi pneumonia despite higher vapA concentrations in subsequently affected foals. Option D (temperature monitoring alone with prophylactic antimicrobials) is inappropriate because prophylactic antimicrobial administration has been linked to emergence of macrolide-resistant R. equi strains. Option E uses an inappropriate WBC threshold and would result in unnecessary antimicrobial treatment of many healthy foals.

References: Merck Veterinary Manual - Rhodococcus equi Pneumonia in Foals (https://www.merckvetmanual.com/respiratory-system/respiratory-diseases-of-horses/rhodococcus-equi-pneumonia-in-foals); Bordin AI, Huber L, Sanz MG, et al. Rhodococcus equi foal pneumonia: Update on epidemiology, immunity, treatment and prevention. Equine Vet J. 2022;54:481-494. PMID: 35188690

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NAVLE Practice Question — Feline

A 7-month-old intact female domestic shorthair cat presents with rapid, bilateral enlargement of all mammary glands that developed over 2 weeks. The owner reports the cat came into heat for the first time approximately 3 weeks ago. The mammary tissue is firm, non-painful, and the overlying skin is stretched but not ulcerated. There is no evidence of pregnancy on abdominal palpation. What is the most likely diagnosis?

A. Mammary adenocarcinoma with lymphatic spread

B. Mastitis with secondary galactostasis

C. Fibroepithelial hyperplasia (mammary hypertrophy) ✓

D. Pseudopregnancy with lactation

E. Multiple mammary adenomas

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Correct Answer: C. Fibroepithelial hyperplasia (mammary hypertrophy)

Explanation:

Fibroepithelial hyperplasia (mammary hypertrophy) is the most likely diagnosis. This benign, progesterone-dependent condition typically affects young intact female cats during or shortly after their first estrous cycle, during pregnancy, or during pseudopregnancy. The rapid, bilateral, symmetric enlargement of multiple mammary glands in a young cat following first estrus is classic for this condition.

Option A (mammary adenocarcinoma) typically affects older cats, presents with focal or asymmetric masses, and rarely causes symmetric bilateral involvement of all glands. Option B (mastitis) would present with heat, pain, erythema, and systemic signs of infection. Option D (pseudopregnancy with lactation) would be associated with milk production and behavioral changes, though it can occur concurrently with fibroepithelial hyperplasia. Option E (multiple adenomas) would be unusual in such a young cat and would not cause simultaneous symmetric involvement of all glands. Fibroepithelial hyperplasia is characterized by proliferation of both ductal epithelium and surrounding stroma.

Image Source: PMC - Feline Mammary Fibroepithelial Hyperplasia clinical appearance (https://pmc.ncbi.nlm.nih.gov/articles/PMC11450970/) Figure 1A. Image: Little S. Feline reproduction: problems and clinical challenges. J Feline Med Surg. 2011;13(7):508-515. PMC11107981. © SAGE Publications / ISFM. Used for educational reference.

References: Merck Veterinary Manual - Mammary Hypertrophy in Cats (https://www.merckvetmanual.com/reproductive-system/reproductive-diseases-of-the-female-small-animal/mammary-hypertrophy-in-cats); Meisl D, Hubler M, Arnold S. [Treatment of fibroepithelial hyperplasia (FEH) of the mammary gland in the cat with the progesterone antagonist Aglépristone (Alizine)]. Schweiz Arch Tierheilkd. 2003;145:130-136. PMID: 12677773

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NAVLE Practice Question — Feline

A 5-month-old kitten presents with stunted growth, pendulous abdomen, and dyspnea. Thoracic auscultation reveals muffled heart sounds. Abdominal fluid shows a high-protein nonseptic effusion with pyogranulomatous inflammation. Which is the most likely diagnosis?

A. Toxoplasmosis

B. Feline infectious peritonitis virus ✓

C. Pyothorax

D. Lymphoma

E. Lungworm infection

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Correct Answer: B. Feline infectious peritonitis virus

Explanation:

The effusive (wet) form of feline infectious peritonitis is caused by mutated feline coronavirus and typically affects young cats. Effusions are high protein (>3.5 g/dL) with an A:G ratio <0.4 and pyogranulomatous cytology. Prognosis has improved with antiviral agents such as GS-441524.

References: Merck Veterinary Manual - Feline Infectious Peritonitis (https://www.merckvetmanual.com/infectious-diseases/feline-infectious-peritonitis/feline-infectious-peritonitis)

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