PAGES: 141-143 DOI: Technical notes
The Occurrence of Rhodnius prolixus Stal, 1859, Naturally Infected by Trypanosoma cruzi in the State of Rio de Janeiro, Brazil (Hemiptera, Reduviidae, Triatominae)

Ana Paula Pinho, Teresa Cristina M GonçalvesI, Regina Helena MangiaII, Nédia S Nehme RussellII, Ana Maria Jansen +

Departmento de Protozoologia
IDepartmento de Entomologia
IIDepartmento de Bioquímica e Biologia Molecular, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brasil


Rhodnius prolixus, one of the most important vector of Chagas' disease in Venezuela, was basically considered in this country as related to the domiciliar transmission cycle (O Cova-Garcia et al. 1959 Publ Div Malariol 11: 209-253). In the sylvatic environment it was observed that this species was mainly adapted to palm tree crowns and nests of Mycteria americanaR. prolixus is a very eclectic species feeding on marsupials, rats, birds and reptilians. Moreover, it is agreed that the adaptation of R. prolixus to human dwellings was a consequence of human colonization of the natural foci of Trypanosoma cruzi (F Pifano1973 Arch Venezol Med Trop Parasitol Med 5: 3-29).

During a search for triatomids performed in an Atlantic rain forest area in TeresópolisState of Rio de Janeiro, we collected a total of 23 specimens (2 adults and 21 nymphs) of R. prolixus from which 13 were infected by T. cruzi. Eleven nymphs were found in the axils of Pteridophyta leaves; 2 adults and 4 nymphs in leafages, probably opossum nests and 6 nymphs were collected on the trunk of palm-tree. Several eggs could be found in the axils of 1 Pterydophyta (Fig. 1).

The studied area, Granja Florestal, Teresópolis, can be characterized as a secondary rain forest with poor human dwellings on the forests borders. The local population live basically on small agriculture and hunting. Weekly searches were performed between September and March (1994-95) and included palm-trees, bracts of pteridophyta, bird and mammal nests, leafages and bromeliaceae.

The collected insects were maintained in glass flasks, fed through a membrane (ES Garcia et al. 1975 Rev Brasil Biol 35: 207-210) and the nymphs were allowed to moult. Seven isolates of T. cruzi were obtained through inoculation of swiss mice with the feces of the infected bugs. Axenic medium derived metacyclic forms (105) from each isolate and were intraperitoneally inoculated in five swiss outbred mice weighing 18-20g. No mortality occurred and only rare flagellates during a 2-3 day period could be observed in the fresh blood preparations examined every other day, during two months. Furthermore, the experimental infection by the isolates was stable as confirmed by the positive hemocultures made three months after the inoculation.

Five of the isolates were amplified for schizodeme analysis and the digestion was performed by EcoRI according to C Morel et al. (1980 Proc Natl Acad Sci USA 77: 6810-6814). No differences the profiles of the fragments were observed, suggesting that the infected specimens were involved in the same transmission cycle of the parasite (Fig. 2).

Biometrical analysis - A total of 13 specimens, 7 males and 6 females were analyzed. The morphometry was based on the characteristics of the head and of the pronotum. The males external genitalia were treated in 10% KOH, phenol, creosote and mounted in Canada balsam. All examined material, as well as the external male genitalia, were consigned to the Herman Lent Collection, Instituto Oswaldo Cruz, under the following numbers: 2852, 2853, 2869 and 2879.

The total length of 4 females and 3 males was slightly smaller than the standard established for this species by H Lent and P Wydgodzinsky (1979 Bull Am Mus Nat Hist 163: 127-519).

The male external genitalia presented the dorsal phalloteca plate and the median process of the pygophore similar to that described by H Lent and J Juberg (1969 Rev Brasil Biol 29: 487-560) (Fig. 3). Moreover, all specimens displayed rounded, not very prominent anterolateral angles of the pronotum, the dark stripes of the lobe of pronotum fully separated and the urosternites dark brown. Those characteristics are typical of R. prolixus.

The homogeneity of 13 specimens (5 females and 8 males) was observed through the mor-phometrical analysis of the following parameters: length of the head, anteocular region, length of the eye, postocular region, synthlipsis and length and width of the pronotum (Table).

The occurrence of R. prolixus in Brazil is controversial and many misleading identifications have been made due to the difficulty to distinguish among this and related species like R. nasutus and R. neglectus in which the occurrence is much more frequent. It is actually accepted that R. prolixus occurs basically in the states of Amazonas and Pará but there are also reports on the occurrence of this species in the states of Piauí, Goiás, Amazonas, Minas Gerais, Maranhão, Rio de Janeiro and São Paulo (H Lent & AV Martins 1940 Rev Entomol 11: 887-886, O Tavares 1971 Rev Soc Bras Med Trop v. 5, JC Filho1979 Rev Bras Malar D trop XXXI: 579-585, DNC Bento et al. 1992 Rev Soc Bras Med Trop 25: 51-58). R. prolixus have been found colonizing both sylvatic and artificial environments. In the forests this species has been mainly associated with birds although itcan also be found in other sylvatic ecotopes such as burrows of armadillos. The presence of R. prolixus in human dwellings were reported in the states of Goiás, Minas Gerais and Pernambuco by AC Silveira et al. (1984 Rev Brasil Malariol D Trop 36: 15-312). It is important to emphasize that these were scattered reports and no more studies about R. prolixus in those areas have been published.

R. prolixus found in Teresópolis seemed very well adapted to that environment since adults, nymphs and even eggs could be found. It is known that triatomines specially Rhodnius are well adapted to different palm trees (L Diotaiuti et al. 1984 Rev Brasil Malariol D Trop 36: 11-14, 1984 Mem Inst Oswaldo Cruz 79: 293-301, Bento et al. loc.cit.), but this is the first report on Rhodnius colonizing Pteridophyta. The inhabitants of the border of the forest did not recognize the bugs and no Chagas' disease records have been found, suggesting that only a sylvatic transmission cycle is taking place in this area and that R. prolixus is directly associated with the maintenance of the parasite among wild animals. The species was probably introduced in the area through migrants and we do not know if R. prolixus is spread through all the county or is just initiating the colonization. In any case, further studies are necessary in order to follow up the colonization of R. prolixus in Teresópolis.

+Corresponding author. Fax: +55-21-280-1589
Received 25 April 1997
Accepted 15 January 1998


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