What is the mechanism through which ascites develops in cases of Feline Infectious Peritonitis (FIP)?

In cases of Feline Infectious Peritonitis (FIP), the development of ascites primarily occurs through the virus stimulating the production of Vascular Endothelial Growth Factor (VEGF). This protein plays a crucial role in increasing the permeability of blood vessels, allowing fluid to leak into the abdominal cavity. In FIP, the immune response to the infection leads to inflammation, which in turn triggers the release of VEGF. The resulting increased vascular permeability is a key factor in fluid accumulation, characteristic of the effusive form of FIP.

The other mechanisms presented in the options do not accurately describe the pathophysiology of ascites in FIP. For instance, while thrombin activation and clot formation, bacterial inflammation, and immune-mediated responses can contribute to other conditions and clinical presentations, they do not reflect the direct interaction of the virus with endothelial function that enables fluid leakage seen in FIP. This distinction emphasizes the specific viral pathogenesis that underlies the ascitic process in this disease.