An Electron Microscopic Study of Penetration by Trypanosoma rangeli into Midgut Cells of Rhodnius prolixus Marco Antonio de Oliveira* and Wanderley de Souza* , † *Laborato ´rio de Biologia Celular e Tecidual, Centro de Biocie ˆncias e Biotecnologia, Universidade Estadual do Norte Fluminense, Av. Alberto Lamego, 2000, 28015-6210 Campos dos Goytacazes, RJ, Brazil; and †Laborato ´rio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofı´sica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21949-900 Rio de Janeiro, RJ, Brazil E-mail: wsouza@biof.ufrj.br Received September 22, 1999; accepted October 30, 2000; published online January 11, 2001 The process of interaction of the Choachi strain of Trypanosoma rangeli with intestinal epithelial cells of Rhodnius prolixus was analyzed in experiments car- ried out in vitro and in vivo. For the in vitro experi- ments small fragments of the anterior region of the posterior midgut were incubated in the presence of the parasites, fixed, and processed for observation with the scanning electron microscope. Parasites at- tached to the surface of some epithelial cells, espe- cially to the extracellular membrane layers (perimi- crovillar membranes), were observed. For the in vivo experiments insects were infected with cultures of T. rangeli, sacrificed at different time intervals, and then processed for scanning and transmission electron mi- croscopy. An intimate contact between the parasites and the membrane layers was observed. The parasites penetrated into cells that showed an electronlucent cytoplasm and a damaged surface, moved within the cytoplasm of the epithelial cell, reached the basal re- gion, crossed the basal lamina, and entered the hemocoel. © 2001 Academic Press Key Words: Trypanosoma rangeli; Rhodnius prolixus; midgut infection; life cycle; parasite vector relation- ship. INTRODUCTION Trypanosoma rangeli is a digenetic hemoflagellate widely distributed in Central and South America, in- fecting wild and domestic mammals as well as humans (Steindel et al., 1991). Its life cycle is completed in the invertebrate host, members of the family Reduviidae, especially in Rhodnius prolixus. This species is also a vector of Trypanosoma cruzi, the causative agent of Chagas’ disease (D’Alessandro-Bacigalupo and Sara- via, 1992). In nature, triatomines are frequently found infected by both flagellates and may cause mixed in- fections in vertebrate hosts (Sousa and Johnson, 1971). T. rangeli is harmless to mammals; however, the parasitemia can persist for months or years (Herbig- Sandreuter, 1957). The infection triggers an immune response that is able to produce antibodies against T. rangeli that can cross-react with T. cruzi (Gro ¨gl and Kuhn, 1984; Guhl et al., 1987; Hudson et al., 1988). The life cycle of T. rangeli in the vertebrate host is poorly known. Some evidence suggests that prolifera- tion occurs within monocytes (Osorio et al., 1995). In the invertebrate host, its life cycle is better character- ized. The cycle starts with the ingestion of trypomas- tigotes occurring in vertebrate blood. Within the intes- tine, the parasites differentiate into epimastigotes that are able to multiply and pass through the intestinal epithelium. Upon reaching the hemocoel the parasites further multiply in the hemolymph or in hemocytes. From the hemocoel, the parasites migrate to salivary glands where metacyclic trypomastigote forms are formed. These are able to infect the vertebrate host during bloodmeal (D’Alessandro, 1976; D’Alessandro- Bacigalupo and Saravia, 1992). A fundamental step in the life cycle of T. rangeli in the invertebrate host is the passage of the parasite from the lumen of the midgut to the hemocoel. Watkins (1971) reported that damage to the intestinal epithe- lium of R. prolixus occurred during infection with T. rangeli. However, Hecker et al. (1990) showed that T. rangeli pass through the intestinal cells by an intra- cellular route without damaging the cells. The aim of the present study was to further charac- terize the interaction of T. rangeli with intestinal epi- thelial cells of R. prolixus using both in vivo and in vitro systems. MATERIALS AND METHODS Parasites We used the Choachı ´ strain of T. rangeli, which was originally isolated from R. prolixus in Colombia (Schot- Journal of Invertebrate Pathology 77, 22–26 (2001) doi:10.1006/jipa.2000.4988, available online at http://www.idealibrary.com on 22 0022-2011/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.