Blood vessels in Trichinella spiralis infections: a study using vascular casts.

Larvae of Trichinella spiralis initiate the transformation of myocytes into nurse cells that become surrounded by elaborate networks of blood vessels. To examine the structure of these networks (i.e., retes), transcardic perfusion was used to clear the vascular tree of Trichinella-infected mice and to inject a plastic that polymerized in situ. Vascular complexes were found only around infected myocytes and were characterized by large circumferential vessels that give rise to the smaller channels of the retes. The secondary vessels vary widely in caliber and are distributed in a random fashion. Three types of network were found: simple, complex, and hypercomplex, and they were distributed normally, with the complex retes the most common. Comparison of the structure of the baskets with that of vessels in surrounding uninfected muscle strongly suggests that the vascular retes are the result of de novo angiogenesis induced during the infection. The parasite may elicit angiogenesis directly through secretion of unique products or may elicit a change in the nurse cell that, in turn, results in growth of new blood vessels.