Hemorrhages seen in the skin of animals infected with CSF, ASF, Salmonella, and Erysipelas are a result of:

• A. Virulence factors that act on the bone marrow to decrease platelet production
• B. Damage to the liver and decreased production of clotting factors
• C. Toxins produced which act on platelets
• D. Infection of and/or secretion of cytokines that damage endothelial cells

Answer: (D)

Hemorrhages in the skin from these infections come from injury to the small blood vessels, not mainly from lack of platelets or clotting factors. These pathogens commonly cause damage to the endothelial lining of vessels either by direct infection of endothelial cells or by inflammatory mediators they trigger. Viral infections like CSF and ASF can infect or inflame the endothelium and promote vascular leakage; Salmonella septicemia with endotoxemia and cytokine release also harms endothelium and can drive widespread coagulation abnormalities; Erysipelothrix infection produces vasculitis and endothelial injury in the skin. The shared mechanism is endothelial damage due to infection and cytokine-mediated effects, leading to hemorrhages in the skin.