NAVLE Feline Infectious 5

Question 1

A 3-year-old intact male domestic shorthair presents with progressive neurological signs including ataxia, vertical nystagmus, and behavioral changes over 6 weeks. CSF analysis reveals a protein of 420 mg/dL with a mixed pleocytosis (predominantly neutrophils and macrophages). Coronavirus antibody titer in CSF is 1:3200. Abdominal ultrasound shows no effusion. Which histopathological finding in the brain would be MOST pathognomonic for the underlying diagnosis?

Accepted Answer

Perivascular pyogranulomatous inflammation with fibrinous vasculitis affecting small and medium vessels

Answer

Feline Infectious Peritonitis (FIP) caused by virulent feline coronavirus (FCoV) mutation produces a characteristic perivascular pyogranulomatous inflammation with fibrinous vasculitis. This reflects immune-complex deposition and Type III hypersensitivity driving vasculitis of CNS vessels. The non-effusive (dry) form disproportionately affects the CNS and eyes. The mixed neutrophilic-macrophage CSF pleocytosis with markedly elevated protein and high FCoV antibody titer in CSF strongly support neurotropic FIP, but the perivascular pyogranulomatous vasculitis is the pathognomonic histopathological hallmark.

Question 2

A shelter veterinarian is investigating a cluster of deaths in kittens 6–10 weeks old. Affected kittens show sudden onset of vomiting, hemorrhagic diarrhea, marked leukopenia (WBC 800/µL), and high mortality within 24–48 hours despite supportive care. Serology and PCR confirm feline panleukopenia virus (FPV). A litter of 4-week-old kittens born in the shelter to an unvaccinated queen survived without illness. Which explanation BEST accounts for the age-dependent mortality pattern?

Accepted Answer

Neonates lack the mature rapidly dividing intestinal crypt cells that serve as the primary FPV replication target

Answer

FPV (a parvovirus) requires rapidly dividing cells for replication. In neonates under 4 weeks, intestinal crypt epithelium is not yet mature/rapidly dividing, so the GI tract is largely spared. Instead, FPV in neonates and fetuses targets the cerebellum (Purkinje cells during cerebellar development), causing cerebellar hypoplasia. Kittens 6–10 weeks have highly mitotically active intestinal crypts and rapidly dividing bone marrow progenitors — making them maximally susceptible. Maternal antibodies DO transfer effectively via colostrum (IgG passes via Fc receptors), but if the queen is unvaccinated, no protection is conferred.

Question 3

A 7-year-old spayed female cat is presented for progressive weight loss, hyperglobulinemia (total protein 10.8 g/dL, globulins 7.2 g/dL), and a serum albumin:globulin ratio of 0.4. Serum protein electrophoresis reveals a polyclonal gammopathy. Abdominal ultrasound shows mesenteric lymphadenopathy and a focal hyperechoic jejunal mass. Fine needle aspirate of the mass reveals macrophages with intracytoplasmic coronavirus antigen confirmed by immunofluorescence. Which statement regarding antigen testing in this context is MOST accurate?

Accepted Answer

Positive immunostaining for coronavirus antigen within macrophages in a granulomatous lesion is highly specific for FIP and distinguishes virulent from avirulent FCoV strains

Answer

Immunohistochemistry (IHC) or immunofluorescence detecting coronavirus antigen within macrophages in pyogranulomatous tissue is considered highly specific for FIP — it reflects the macrophage-tropic phenotype of the mutant virulent FCoV. This distinguishes FIP from enteric (avirulent) FCoV infection, in which the virus remains confined to intestinal epithelium and does not productively infect monocytes/macrophages. Polyclonal (not monoclonal) gammopathy is the classic finding in FIP. FeLV co-infection is not required for macrophage tropism. While no test is 100% sensitive/specific, antigen-positive macrophages in a granuloma represent the closest thing to a definitive antemortem FIP diagnosis.

Question 4

A cat rescue organization routinely tests all cats for FeLV and FIV using a point-of-care ELISA combo test. A 2-year-old cat tests FIV antibody-positive. The organization plans to euthanize the cat per their protocol. The attending veterinarian recommends Western blot confirmatory testing. Which scenario would produce the MOST clinically significant false-positive FIV ELISA result and thus most strongly justify confirmatory testing?

Accepted Answer

The cat received an FIV vaccination (Fel-O-Vax FIV) within the past 4 years

Answer

Vaccination with the killed whole-virus FIV vaccine (Fel-O-Vax FIV, no longer commercially available but cats vaccinated years ago may still be seropositive) induces antibodies that are indistinguishable from natural infection antibodies on standard ELISA and IFA tests — this is the most clinically important cause of false-positive FIV serology in adult cats. Western blot can help differentiate in some cases, but even WB may be positive post-vaccination. PCR is the most reliable confirmatory test in vaccinated cats. FeLV does not cause cross-reactive FIV antibodies. Blood transfusion-transferred antibodies would wane by 2 weeks and are not a major confounder. Maternal antibody interference is significant in kittens under 6 months but the question asks for the most significant false-positive in the described adult context.

Question 5

A 5-year-old outdoor cat presents with a chronic non-healing ulcer on the nasal planum, conjunctivitis with corneal ulceration, and recurrent mucopurulent nasal discharge. Herpesvirus (FHV-1) is confirmed by PCR from conjunctival swab. The owner asks about long-term management. Which antiviral strategy has the STRONGEST evidence base for reducing FHV-1-associated ocular disease severity in cats, with the LEAST systemic toxicity concern?

Accepted Answer

Topical 0.5% cidofovir ophthalmic solution applied twice daily to the affected eye(s)

Answer

Topical 0.5% cidofovir (a nucleotide analog) applied twice daily has been shown in clinical studies to significantly reduce FHV-1 conjunctival disease severity and viral shedding with minimal systemic absorption and low local toxicity — making it superior in the topical antiviral category for feline herpesvirus ocular disease. Famciclovir is the preferred oral antiviral (prodrug converted to penciclovir in cats), but the dose is 90 mg/kg PO q12h (NOT q8h) and it is reserved for severe systemic disease. Acyclovir is CONTRAINDICATED in cats due to severe nephrotoxicity and bone marrow suppression. Lysine supplementation has been shown in multiple systematic reviews to have NO benefit for FHV-1 management and is no longer recommended by the American Association of Feline Practitioners (AAFP).

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Feline Infectious 5