Vascular permeability and coagulation during Rickettsia riekettsii infection in dogs

Abstract

SUMMARY The vascular permeability of the ocular fundus, alterations in the coagulation system, and plasma concentrations of thromboxane B 2 ( txb 2 ) and 6-keto-prostaglandin F 1α , (6-keto- pgf 1α ) were studied in dogs following intradermal inoculation with 5 × 10 5 tcid 50 of Rickettsia rickettsii . Twenty-four to 48 hours after the onset of fever and rickettsemia, multifocal areas of retinal vasculitis were evident, which corresponded to areas of altered vascular permeability demonstrated by fluorescein angiography. The number and intensity of retinal vessels with sodium fluorescein leakage peaked during the second week after inoculation, and retinal vascular permeability remained altered during the third week of infection, well past the phase of clinical and clinicopathologic recovery. Development of retinal vasculitic foci was associated with thrombocytopenia, increased concentrations of circulating fibrinogen, and slight prolongation of activated partial thromboplastin time. Increased concentrations of fibrin/fibrinogen degradation products were detected in 4 of 9 dogs. Despite the degree of vascular endothelial damage evident on fluorescein angiographic and histologic studies in these dogs, plasma txb 2 and 6-keto- pgf 1α concentrations were not increased.