A 2-year-old intact male DSH cat from a multi-cat household presents with progressive weight loss, anorexia, and a palpable abdominal mass. Abdominal effusion is present, and fluid analysis reveals a protein concentration of 5.8 g/dL, a Rivalta test that is positive, and a cell count of 4,200 cells/μL (predominantly non-degenerate neutrophils and macrophages). An immunofluorescence assay on the effusion detects coronavirus antigen within macrophages. Which statement BEST describes the pathogenesis underlying this cat's condition?
-
A
A biotype shift from enteric coronavirus to FIP virus occurs via two key mutations in the spike protein receptor-binding domain and the 3c accessory gene, enabling macrophage tropism and systemic spread.
-
B
The cat was infected with a highly virulent serotype II feline coronavirus strain acquired horizontally from a shedding cat, bypassing the need for any mutational events.
-
C
FIP develops exclusively in cats with concurrent FeLV or FIV co-infection, which suppresses regulatory T-cell responses and permits macrophage invasion.
-
D
Antibody-dependent enhancement allows serum anti-coronavirus IgG to facilitate viral entry into macrophages via Fc receptors, and this is the sole mechanism of monocyte/macrophage infection.