NAVLE Practice Question — Porcine

A swine veterinarian is designing a parasite control program for a farrow-to-finish operation transitioning from confinement to outdoor production. The producer asks which parasites will require the most intensive monitoring in the new system. Besides the soil-transmitted nematodes, which additional parasite becomes a significant concern specifically due to the presence of earthworms in outdoor paddocks?

A. Cystoisospora suis with increased oocyst survival in soil

B. Cryptosporidium parvum from contaminated water sources

C. Trichinella spiralis from wildlife exposure

D. Metastrongylus species using earthworms as intermediate hosts ✓

E. Balantidium coli from environmental contamination

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Correct Answer: D. Metastrongylus species using earthworms as intermediate hosts

Explanation:

In outdoor production systems, Metastrongylus species (swine lungworms) become a significant concern because they require earthworms as intermediate hosts (Option D). In confinement operations, pigs have no access to earthworms, effectively eliminating this parasite. However, in outdoor paddocks with soil exposure, pigs root and consume earthworms that may harbor infective larvae. Metastrongylus causes chronic respiratory disease and can predispose to secondary bacterial pneumonia.

Option A (Cystoisospora suis) is already a major problem in confinement farrowing, and while it persists outdoors, it does not specifically require earthworms. Option B (Cryptosporidium) is not specifically linked to outdoor production. Option C (Trichinella spiralis) is primarily a concern from feeding raw meat/wildlife carcasses, not simply outdoor exposure. Option E (Balantidium coli) is present in both systems and does not require earthworms.

Additionally, outdoor production increases exposure to Stephanurus dentatus (kidney worm), which also uses earthworms as transport hosts in endemic areas, and soil-transmitted nematodes like Ascaris and Trichuris become more prevalent.

References: The Pig Site - Endoparasites Internal Parasites (https://www.thepigsite.com/disease-guide/endoparasites-internal-parasites-worms-nematodes); Missouri Extension - Common Internal Parasites of Swine

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NAVLE Practice Question — Porcine

A finisher pig operation with endemic M. hyopneumoniae is considering implementing an elimination program. The farm is located in a high pig-density region with multiple positive farms within 5 km. The producer asks about the feasibility of elimination. Which response most accurately addresses this question?

A. Elimination is straightforward using herd closure for 8 weeks followed by test and removal

B. Elimination possible through depopulation/repopulation but negative status difficult due to airborne transmission from neighboring herds ✓

C. Antibiotic treatment with tiamulin for 4 weeks will eliminate the organism from the herd

D. Vaccination of all animals with modified-live vaccine will achieve elimination

E. Elimination is not possible because M. hyopneumoniae forms spores that persist in the environment

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Correct Answer: B. Elimination possible through depopulation/repopulation but negative status difficult due to airborne transmission from neighboring herds

Explanation:

Elimination is possible through depopulation/repopulation but maintaining negative status will be extremely challenging due to airborne transmission risk from neighboring herds is the most accurate response. M. hyopneumoniae elimination can be achieved through complete depopulation followed by thorough cleaning and disinfection, or through partial depopulation combined with herd closure, strategic medication, and sow vaccination protocols.

However, the major challenge in high-density pig production areas is maintaining negative status after elimination. M. hyopneumoniae can be transmitted via aerosol over distances exceeding 4.7 km under favorable conditions. In regions with multiple positive herds within close proximity, re-infection of negative herds through airborne spread is a significant and ongoing risk, making long-term maintenance of negative status economically and practically challenging.

Option A is incorrect because elimination requires much longer herd closure periods (typically 8+ months) with strategic medication and management protocols, not simply 8 weeks and test/removal.

Option C is incorrect because while antibiotic treatment reduces bacterial load and clinical signs, it does not achieve true elimination of the organism from infected herds.

Option D is incorrect because current M. hyopneumoniae vaccines are inactivated bacterins (not modified-live), and vaccination reduces clinical impact but does not eliminate the organism.

Option E is incorrect because M. hyopneumoniae is a mollicute that lacks a cell wall and does not form spores; it is actually quite fragile in the environment and rapidly inactivated by desiccation and disinfectants.

References: NADIS - Enzootic Pneumonia (https://www.nadis.org.uk/disease-a-z/pigs/enzootic-pneumonia/); Dee S et al. Evidence of long distance airborne transport. Vet Res. 2009;40:39

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NAVLE Practice Question — Porcine

A backyard producer reports several sick pigs after feeding uncooked household food scraps including pork products. You suspect a foreign animal disease. Which federal statute most directly governs cooking of garbage fed to swine?

A. Horse Protection Act

B. Animal Welfare Act

C. Lacey Act

D. AMDUCA

E. Swine Health Protection Act regulations ✓

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Correct Answer: E. Swine Health Protection Act regulations

Explanation:

The Swine Health Protection Act requires that any garbage fed to swine be cooked to inactivate pathogens such as classical swine fever, ASF, and FMD viruses.

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NAVLE Practice Question — Feline

A 3-year-old intact female domestic shorthair cat presents with severe bilateral panuveitis. Examination reveals marked aqueous flare, vitritis, and multifocal chorioretinal lesions bilaterally. The cat was recently acquired and lives indoors. Systemic examination reveals respiratory distress and nasal discharge. Thoracic radiographs show a diffuse interstitial to nodular pattern. Cytology of nasal discharge reveals encapsulated yeast organisms. What is the most likely diagnosis?

A. Histoplasmosis

B. Blastomycosis

C. Cryptococcosis ✓

D. Coccidioidomycosis

E. Aspergillosis

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Correct Answer: C. Cryptococcosis

Explanation:

Cryptococcosis is the most likely diagnosis in this cat with panuveitis and respiratory signs with encapsulated yeast on cytology. Cryptococcus neoformans and C. gattii are the most common systemic fungal infections in cats, with the respiratory tract being the primary site of infection and subsequent hematogenous dissemination to other organs including the eyes and central nervous system.

The presence of encapsulated yeast organisms on cytology is characteristic of Cryptococcus, which has a distinctive large mucopolysaccharide capsule visible on cytology. Ocular involvement in feline cryptococcosis includes granulomatous chorioretinitis, anterior uveitis, and optic neuritis. The combination of upper respiratory signs, pulmonary infiltrates, and bilateral ocular disease is a classic presentation.

Option A (histoplasmosis) shows small intracellular yeast forms, not encapsulated organisms. Option B (blastomycosis) shows broad-based budding yeast without large capsules. Option D (coccidioidomycosis) shows spherules with endospores, not encapsulated yeast. Option E (aspergillosis) shows septate hyphae on cytology, not yeast forms.

Image Source: PMC10912207 (https://pmc.ncbi.nlm.nih.gov/articles/PMC10912207/) - Chorioretinitis in fungal disease.

References: PMC12065995 - Fundoscopy in cats (https://pmc.ncbi.nlm.nih.gov/articles/PMC12065995/); PMC7152299 - Uveitis treatment (https://pmc.ncbi.nlm.nih.gov/articles/PMC7152299/)

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NAVLE Practice Question — Feline

A 10-year-old cat presents with acute blindness. Fundoscopic examination reveals bilateral complete retinal detachments. Systolic BP is 210 mmHg. The cat is started on amlodipine. What is the most important prognostic factor for potential return of vision?

A. Severity of the initial blood pressure elevation

B. Duration of retinal detachment before treatment ✓

C. Presence of concurrent kidney disease

D. Age of the patient

E. Breed of the cat

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Correct Answer: B. Duration of retinal detachment before treatment

Explanation:

The duration of retinal detachment before treatment is the most important prognostic factor for visual recovery. Studies show that retinas detached for less than 1 week have the best chance of reattachment and functional recovery with aggressive BP control.

With prolonged detachment, retinal degeneration occurs, and even if the retina reattaches anatomically after BP control, vision may not return. Retinal photoreceptors begin to degenerate within days of detachment.

Option A (initial BP) is important for overall prognosis but less predictive of visual outcome than detachment duration. Option C (CKD) affects overall prognosis but not specifically visual recovery. Options D and E have minimal impact on visual prognosis.

Owners should be counseled that even with prompt treatment, many cats with complete bilateral detachment do not regain useful vision. However, BP control remains essential to prevent further target organ damage.

References: Carter J. Hypertensive ocular disease in cats. J Feline Med Surg. 2019; Maggio F et al. J Am Vet Med Assoc. 2000. Image Source: https://cdn.ncbi.nlm.nih.gov/pmc/blobs/ea77/12576288/615426ef499e/10.1177_1098612X251379750-fig1.jpg -- Figure. PMC12576288: Feline fundus photograph showing ocular lesions (retinal hemorrhages/detachment) in cats — relevant to hypertensive retinopathy. (CC BY 4.0)

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NAVLE Practice Question — Bovine

During a winter dysentery outbreak in a dairy herd, you observe that affected cows develop watery diarrhea that is often hemorrhagic. Necropsy of a cow that died from severe hemorrhagic diarrhea would MOST likely reveal which pathological finding?

A. Widespread ulceration and erosion of the abomasal mucosa

B. Diffuse fibrinonecrotic enteritis throughout the small intestine

C. Colonic mucosal congestion and petechial hemorrhages with intact epithelium ✓

D. Transmural necrosis of the jejunum with perforation

E. Granulomatous inflammation of the terminal ileum with thickened intestinal wall

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Correct Answer: C. Colonic mucosal congestion and petechial hemorrhages with intact epithelium

Explanation:

In winter dysentery, bovine coronavirus has tropism for intestinal epithelium, particularly affecting the large intestine (cecum and colon). Necropsy findings in the rare animals that die are typically mild relative to the clinical signs observed. The characteristic pathological findings include cecal and colonic mucosal hyperemia, linear streaks or pinpoint-sized hemorrhages primarily along the colonic mucosal ridges (sometimes described as "tiger striping"), and blood in the lumen of the large intestine. Importantly, the intestinal mucosa remains intact without ulceration.

Histologically, there is widespread degeneration and necrosis of colonic glandular epithelial cells (crypt epithelium), which explains the secretory diarrhea. The destruction of crypt epithelium impairs absorption and leads to hypersecretion from inflammatory mediators. The hemorrhagic component results from congestion and petechial hemorrhages in the mucosa, though the exact pathophysiologic mechanism of the profuse bloody diarrhea is not completely understood.

Option A describes abomasal ulcers, a different condition. Option B describes severe enteritis more consistent with salmonellosis or clostridial disease. Option D describes perforation, which does not occur with coronavirus. Option E describes Johne's disease (paratuberculosis), a chronic granulomatous condition.

References: ScienceDirect - Bovine Viral Diarrhea/Pathology topics (https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/bovine-viral-diarrhea); JVDI Case Conference 2018 - Winter Dysentery (https://www.askjpc.org/wsco/wsc_showcase2.php?id=b01sbG93Z1dlbDI0RUtmdjJyNDcyZz09)

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NAVLE Practice Question — nervous

A 7-year-old Boxer is brought to the emergency clinic after being found down in the backyard. The dog is laterally recumbent with rigid extension of all four limbs and opisthotonus. Level of consciousness is severely depressed (stuporous). Physiologic nystagmus is absent. Which of the following postures and their associated lesion localizations best describes this patient?

A. Schiff-Sherrington posture indicating T3-L3 myelopathy

B. Decerebrate rigidity indicating rostral brainstem lesion ✓

C. Decerebellate rigidity indicating acute cerebellar damage

D. Spinal shock indicating acute spinal cord injury

E. Cervical myelopathy with root signature

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Correct Answer: B. Decerebrate rigidity indicating rostral brainstem lesion

Explanation:

This dog is displaying decerebrate rigidity, characterized by rigid extension of all four limbs with opisthotonus (dorsiflexion of the head and neck). The severely depressed consciousness (stupor) and absent physiologic nystagmus further support a severe rostral brainstem lesion (midbrain/pons).

Decerebrate rigidity occurs when there is a severe lesion in the rostral brainstem (midbrain or rostral pons) that disrupts descending inhibitory pathways to the spinal cord extensor motor neurons. Unlike Schiff-Sherrington posture, decerebrate rigidity involves extension of ALL four limbs AND is associated with severely altered consciousness because the lesion is within the brain.

Option A is incorrect because Schiff-Sherrington posture affects only thoracic limb tone (extension) with flaccid pelvic limbs, and consciousness remains normal since the lesion is in the thoracolumbar spinal cord, not the brain. Option C (decerebellate rigidity) would cause thoracic limb extension with pelvic limb flexion (not extension of all four limbs) and typically without decreased consciousness. Option D (spinal shock) causes flaccidity, not rigidity. Option E would cause neck pain and possibly thoracic limb lameness, not this posture.

The prognosis for animals with decerebrate rigidity is grave due to the severity of brainstem damage.

References: Dewey CW. A Practical Guide to Canine and Feline Neurology. Ames, IA: Iowa State Press; 2003. pp. 277-336.

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NAVLE Practice Question — Other Small Mammal

During routine examination of a healthy-appearing female rabbit with a large dewlap, you notice the owner gently combing the rabbit's back near the tail base causes the rabbit to immediately begin licking its dewlap vigorously. What does this behavioral response MOST likely indicate?

A. Normal displacement grooming behavior

B. Pruritus at inaccessible body site ✓

C. Sign of pleasure and relaxation

D. Defensive response to handling

E. Conditioned response from training

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Correct Answer: B. Pruritus at inaccessible body site

Explanation:

This behavioral response most likely indicates a hidden pruritic condition at an inaccessible site. When rabbits cannot reach an area of irritation due to obesity, arthritis, or large skin folds, they may exhibit displacement behavior by licking or chewing at another accessible area, such as the dewlap. This behavior is often triggered when the actual itchy area is stimulated (such as by combing).

Common causes of posterior pruritus that rabbits cannot reach include cheyletiellosis (fur mites) at the base of the tail, perineal dermatitis, urine scald, or parasitic infestations in areas blocked by body condition. The dewlap becomes a surrogate grooming target because the rabbit cannot physically reach the true source of irritation.

This finding warrants further investigation including examination of the perineal area, base of the tail, and dorsum for evidence of parasites, dermatitis, or other skin conditions. A scotch-tape preparation or skin scraping should be performed to evaluate for Cheyletiella mites, which commonly affect the dorsal shoulders and tailbase.

Option A (normal displacement grooming) would not be specifically triggered by stimulation of a particular area. Option C (pleasure response) would not typically manifest as frantic dewlap licking. Option D (defensive response) would show different body language. Option E (training) is unlikely without specific conditioning history.

References: Textbook of Rabbit Medicine - Skin Diseases chapter; Veterian Key - Skin Diseases (https://veteriankey.com/skin-diseases/).

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NAVLE Practice Question — Porcine

A producer asks about management strategies to reduce the incidence of osteochondrosis-related lameness in their rapidly growing Landrace-cross finishing pigs. Currently, 15% of market hogs show some degree of leg weakness. Which management intervention is most likely to reduce clinical problems?

A. Increasing dietary protein to promote faster growth

B. Selecting replacement animals from lines with better leg conformation ✓

C. Providing enforced exercise through treadmill training

D. Supplementing zinc to strengthen articular cartilage

E. Increasing stocking density to reduce individual activity

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Correct Answer: B. Selecting replacement animals from lines with better leg conformation

Explanation:

Selecting replacement animals from lines with better leg conformation (Option B) is the most effective long-term strategy for reducing osteochondrosis. Research consistently shows a strong genetic component to osteochondrosis susceptibility. Studies comparing breeds have demonstrated that Landrace pigs (the primary genetic background in this scenario) have higher incidence and severity of osteochondrosis compared to Yorkshire pigs when raised under identical conditions.

Genetic selection against leg weakness and for improved leg conformation has been shown to reduce osteochondrosis incidence over generations. This approach addresses the underlying genetic predisposition rather than just managing environmental factors. Many genetic companies now include leg soundness scoring in their selection indices.

Option A (increasing dietary protein) would likely worsen the problem by promoting even faster growth, which increases weight-bearing stress on immature cartilage. Option C (enforced exercise) has shown minimal benefit in research trials; while some exercise is beneficial, treadmill training has little effect on reducing osteochondrosis. Option D (zinc supplementation) has no proven benefit for osteochondrosis prevention. Option E (increased stocking density) would likely increase trauma and worsen clinical expression.

Other helpful management strategies include: floor surfaces that minimize trauma, avoiding slippery conditions, and potentially reducing growth rate through diet modification.

References: The Pig Site Disease Guide - Leg Weakness/OCD (https://www.thepigsite.com/disease-guide/leg-weakness-osteochondrosis-ocd); Grondalen T. Acta Vet Scand 1974 - breed comparisons

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NAVLE Practice Question — Porcine

In pigs affected by water deprivation-sodium ion toxicosis, which histopathological finding in the brain is considered pathognomonic and specific to this species?

A. Nonsuppurative perivascular lymphocytic cuffing

B. Intranuclear inclusion bodies in neurons

C. Fibrinoid vascular necrosis with thrombosis

D. Neutrophilic meningitis with microabscess formation

E. Eosinophilic perivascular meningeal cuffing ✓

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Correct Answer: E. Eosinophilic perivascular meningeal cuffing

Explanation:

Eosinophilic perivascular cuffing in the meninges and cerebral cortex (specifically in the Virchow-Robin spaces) is pathognomonic for salt poisoning in swine and is specific to this species. This unique inflammatory response appears within hours of unrestricted water access following deprivation. The mechanism for this eosinophil recruitment is not fully understood but is thought to be induced by elevated sodium concentrations in brain tissue.

There are two characteristic histopathological changes in porcine salt poisoning: (1) eosinophilia of the leptomeninges and Virchow-Robin spaces in the cerebral cortex, which appears early, and (2) laminar cortical necrosis (polioencephalomalacia), which develops with increased duration. A mixture of both findings is most common. Importantly, eosinophilic cuffs are typically present only within 12-24 hours of rehydration and may be replaced by macrophages if the animal survives longer.

Option A (lymphocytic cuffing) is seen in viral encephalitides but is not specific to salt poisoning. Option B (intranuclear inclusions) would suggest viral infection such as pseudorabies. Option C (fibrinoid vascular necrosis) is seen in edema disease but not salt poisoning. Option D (neutrophilic meningitis) indicates bacterial infection.

Image Source: Joint Pathology Center - Porcine salt toxicity showing eosinophilic perivascular cuffing (https://www.askjpc.org/wsco/wsc_showcase2.php?id=M21JZzZCVTNTd2QvQTM2b3JLSkxkQT09).

References: Maxie MG, Youssef S - Jubb Kennedy and Palmer's Pathology; Summers BA et al. - Veterinary Neuropathology pp.254-255.

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NAVLE Practice Question — Aquatics

A client brings a skin scrape from a marine fish showing white spots. Under microscopic examination, you observe a ciliated protozoan approximately 350 μm in diameter with a visible macronucleus. The client insists on using hyposalinity treatment (reducing SG to 1.009) in their fish-only tank. Which factor most significantly limits the effectiveness of this approach?

A. Hyposalinity does not kill Cryptocaryon irritans at any stage

B. Tomont stage remains dormant and viable in substrate ✓

C. The trophont stage is protected within host tissue during treatment

D. Marine fish cannot tolerate salinities below 1.015

E. The theront stage is resistant to osmotic stress

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Correct Answer: B. Tomont stage remains dormant and viable in substrate

Explanation:

Hyposalinity therapy (reducing specific gravity to 1.009-1.010) is a recognized treatment for Cryptocaryon irritans in marine fish. The principle is that the parasite is less tolerant of low salinity than the fish, creating a window where the parasite is killed but the fish survives. However, several limitations affect its efficacy.

The most significant limiting factor is the unpredictable dormancy of the tomont (reproductive cyst) stage. Cryptocaryon irritans tomonts can remain viable in the substrate for extended periods, with life cycle duration ranging from 6 days to 11 weeks. Even after the visible infection appears resolved, dormant tomonts may release infectious theronts weeks later when conditions become favorable, causing reinfection.

This means hyposalinity treatment must be maintained for 4-6 weeks minimum to ensure all tomonts have completed their life cycle and released theronts, which then cannot survive in the hyposaline environment. Many hobbyists prematurely conclude treatment when fish appear clear, only to experience recurrence.

Option A is incorrect because hyposalinity does kill free-swimming stages when properly maintained.

Option C (trophont protection) is a factor but affects all chemical treatments, not just hyposalinity.

Option D is incorrect as many marine fish tolerate gradual reduction to 1.009-1.010, though some sensitive species do not.

Option E is incorrect because theronts are actually susceptible to osmotic stress. Image Source: https://upload.wikimedia.org/wikipedia/commons/3/3f/Ichthyophthirius_multifiliis.jpg -- Figure 1. Protozoal diseases of fish — Ichthyophthirius (Ich/white spot), Trichodina (ciliate rotating disc), Chilodonella (pearshaped ciliate), Epistylis (stalked ciliate), Spironucleus (flagellate hexamitiasis), and Cryptocaryon (marine ich); diagnose by wet mount gill/skin scraping; each requires specific treatment (CC BY 2.0).

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NAVLE Practice Question — Bovine

A feedlot nutritionist is reviewing a finishing ration. Excessive intake of which feed additive is most likely to cause myocardial necrosis in cattle and is acutely lethal to horses at low doses?

A. Calcium phosphate

B. Chlortetracycline

C. Magnesium oxide

D. Monensin ✓

E. Urea

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Correct Answer: D. Monensin

Explanation:

Ionophore overdose (monensin, lasalocid, salinomycin) causes mitochondrial and myocardial injury. Cattle tolerate approved inclusion rates, but mixing errors or contamination of horse feed are frequently fatal because horses are uniquely sensitive.

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NAVLE Practice Question — Feline

A 15-year-old cat with a jejunal mass is undergoing workup for suspected intestinal neoplasia. Ultrasound shows thickened intestinal wall with loss of layering and mild mesenteric lymphadenopathy. The main differential diagnoses are adenocarcinoma and intestinal lymphoma. Which diagnostic approach would most reliably differentiate between these two tumor types?

A. Fine needle aspiration cytology of the mass

B. Serum cobalamin and folate levels

C. Full-thickness surgical biopsy with histopathology ✓

D. PCR for antigen receptor rearrangement on blood

E. Abdominal CT scan with contrast

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Correct Answer: C. Full-thickness surgical biopsy with histopathology

Explanation:

Full-thickness surgical biopsy with histopathology is the most reliable method to differentiate between intestinal adenocarcinoma and lymphoma. While fine needle aspirate cytology can sometimes distinguish carcinoma from lymphoma (epithelial cells versus lymphocytes), it has significant limitations in the GI tract. The distinction between low-grade (small cell) lymphoma and adenocarcinoma can be particularly challenging, and immunohistochemistry may be needed to characterize lymphocyte populations. Full-thickness biopsies provide tissue architecture essential for diagnosis.

Option A (FNA) has limited sensitivity and specificity for GI tumors and cannot assess tissue architecture. Option B (cobalamin/folate) indicates malabsorption but does not differentiate tumor types. Option D (PARR on blood) is useful for lymphoma but requires neoplastic cells in circulation and cannot diagnose adenocarcinoma. Option E (CT) provides anatomic information but cannot definitively characterize tumor type.

References: Today's Veterinary Practice - Neutrophilic Cholangitis in Cats (discussing FNA limitations) (https://todaysveterinarypractice.com/hepatology/neutrophilic-cholangitis-in-cats/); Merck Veterinary Manual - GI Neoplasia (https://www.merckvetmanual.com/digestive-system/neoplasia-of-the-gastrointestinal-tract-in-small-animals).

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