Vascular perfusion of Onchocerca volvulus nodules.

Perfusion of the vascular bed was achieved in 24 freshly excised nodules of Onchocerca volvulus varying from 0.5 to 2 cm in diameter. India Ink, Microfil polymer, or acrylate perfusates were passed through the vascular supply via cannulation of superficial capsular vessels. After clearing in glycerol or methyl salicylate, or KOH corrosion in the case of the acrylate, nodules were examined microscopically. Small nodules had an extensive blood supply, diffusely distributed throughout the nodule matrix, and in close association with the coils of the worms. In bigger nodules the central area appeared more dense, and intense vascularization appeared to be more peripheral; in the largest nodules the central core was not well vascularized, but a band of heavy vascularization was seen at the margin of the core, fed by superficial vessels and in close contact with worm coils. Very fine branches of the vascular tree were perfused by all three contrast media, but histologically there was evidence of incomplete filling of the smallest vessels. However, there was no extravasation of per-fusates around parasites, even where the approximation between between vessels and parasite surfaces was close. The possibility is considered that O. volvulus may control blood vessel proliferation by release of angiogenesis factors, analogous to rapidly growing solid tumors.