STUDIES IN SEARCH OF A SUITABLE EXPERIMENTAL INSECT MODEL FOR XENODIAGNOSIS OF HOSTS WITH CHAGAS' DISEASE 3 - ON THE INTERACTION OF VECTOR SPECIES AND PARASITE STRAIN IN THE REACTION OF BUGS TO INFECTION BY TRYPANOSOMA CRUZI* Alina Perlowagora-Szumlewicz** Carlos Alberto Muller** Carlos José de Carvalho Moreira** PERLOWAGORA-SZUMLEWICZ, A. et al. Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease. 3 - On the interaction of vector species and parasite strain in the reaction of bugs to infection by Trypanosoma cruzi. Rev. Saúde públ., S. Paulo, 22:390-400, 1988. ABSTRACT: The reaction of nine vector species of Chagas' disease to infection by seven different Trypanosoma cruzi strains; Berenice, Y, FL, CL, S. Felipe, Colombiana and Gávea, are examined and compared. On the basis of the insects' ability to establish and maintain the infection, vector species could be divided into two distinct groups which differ in their reaction to an acute infection by T. cruzi. While the proportion of positive bugs was found to be low in Triatoma infestans and Triatoma dimidiata it was high, ranging from 96.9% to 100% in the group of wild (Rhodnius neglectus, Triatoma rubrovaria)and essentially sylvatic vectors in process of adaptation to human dwellings, maintained under control follow- ing successful insecticidal elimination of Triatoma infestans (Panstrongylus megistus, Triatoma sordida and Triatoma pseudomaculata). An intermediate position is held by Triatoma brasiliensis and Rhodnius prolixus. This latter has been found to interchange between domestic and sylvatic environments. The most important finding is the strikingly good reaction between each species of the sylvatic bugs and prac- tically all T. cruzi strains herein studied, thus indicating that the factors responsible for the excellent reac- tion of P.megistus to infection by Y strain, as previously reported also come into operation in the reaction of the same vector species to acute infections by five of the remaining T.cruzi strains. Comparison or data reported by other investigators with those herein described form the basis of the discussion of Dipetalo- gaster maximus as regards its superiority as a xenodiagnostic agent. UNITERMS: Trypanosomiasis, South American, diagnosis. Insect vectors, parasitology. Host-pa- rasite, relations. Triatoma, parasitology. Panstrongylus, parasitology. Rhodnius, parasitology. Trypano- soma cruzi. INTRODUCTION their reaction to Y strain of Trypanosoma cruzi. Studies reported by the authors'15,16 in 1982 The fact that P.megistus proved to be and 1987 were beginning to uncover an efficient in evaluating the infectivity potential extraordinary variety of vector species of T.cruzi Y strain from acute14 as from (Panstrongylus megistus, Rhodnius neglectus, chronic16infections, seemed to us a major step in Triatoma sordida, Triatoma pseudomaculata, upgrading the efficiency of xenodiagnosis in Triatoma rubrovaria), which are being field surveys***. However, the reaction of this identified as successful xenodiagnostic agents. vector to infection by other strains and/or All cited species, these considered, at the isolates of T.cruzi raised questions which must start of our laboratory colonies (1973), be| answered before the vector can be completely wild (Triatoma rubrovaria, recommended for general use in experimental Rhodnius neglectus), as well as those essentially and natural infections. If all or some of the sylvatic (Panstrongylus megistus, Triatoma factors responsible for the excellent reaction of sordida, Triatoma pseudomaculata) were this vector to infection by Y strain are not superior to domiciliated Triatoma infestans, operating in the reaction to infection by other Triatoma dimidiata and Rhodnius prolixus in strains, then the role of this vector as a * Supported in part by the National Council of Research(CNPq). Proc. 403773/82 — PIDE V. Presented at the Annual Meeting on Basic Research ín Chagas' Disease. Caxambu, Brazil, 1987. ** Laboratory of Vectors of Chagas' Disease. Department of Entomology. Oswaldo Cruz Institute Foundation (FIOCRUZ). Estr. da Covanca, 56, Jacarepaguá — 22700 — Rio de Janeiro, RJ — Brazil. *** Unpublished experiments. xenodiagnostic agent would be of limited from guinea-pigs closely resemble the parasites usefulness. Doubt would also be cast on the of other T.cruzi strains. proposed general role of xenodiagnosis to Triatominae used: The domiciliated detect infections by T.cruzi. T. infestans, T. dimidiata and R. prolixus, Since the initial guidelines for the study of T .sordida, T. pseudomaculata, T.brasiliensis, xenodiagnosis in chronic infection by Y strain P.megistus, all essentially sylvatic but some like were drawn up from findings in acute infections T. sordida and P.megistus in process of by this strain, the responsiveness of nine vector adaptation to human dwellings, in areas species to acute infections with seven different maintained under control following insecticidal strains of T.cruzi were first studied. Results elimination of T.infestans, as stated by Barreto4 obtained are described. The animals which and Forattini et al.5; T.rubrovaria and survived the acute infections formed the group R.neglectus considered completely wild bugs of donors in xenodiagnosis of chronic although, the latter tends to colonize human infections, results of which will be reported in a homes in areas of intensive agricultural and forthcoming paper, the 4th of this series. cattle breeding activities as reported by Forattini et al.6 and by Silveira et al.17. The origin and history of these bugs, reared MATERIAL AND METHODS under ambient conditions was described previously (1982)15. Their life history Protozoa: Six well known strains of T.cruzi parameters of major importance were reported and one "cruzi like" parasite isolated in 1977 by Perlowagora-Szumlewicz13,14. by the senior author from naturally infected Mammalian hosts: 42 guinea-pigs weighing adults P.megistus collected in Gávea, Rio de from 300 to 350gr were divided in seven equal Janeiro (Brazil), were used throughout the groups of six. All groups but one were experiments. inoculated ip with 0.2-0.3ml of infected mouse T.cruzi Y strain isolated in S. Paulo (Brazil) blood containing parasite numbers ranging in 1950 from a human infection was obtained from 10.2 x 104 to 10.8 x 104. Since mice from "Centro de Pesquisas René Rachou, inoculated with "Gávea" isolate only Fundação Oswaldo Cruz (FIOCRUZ)", Belo occasionally showed single parasites in the Horizonte, MG, (Brazil) in 1974, and since then peripheral circulation, the infection has been maintained in this laboratory by syringe induced through an inoculation of 1.0ml. (10.1 passage. x 104 parasites) of a saline suspension of the gut Five other strains obtained in 1981 from the from infected P.megistus. Dept. of Protozoology of "Instituto Oswaldo All guinea-pigs developed parasitemia which Cruz" of "FIOCRUZ" are: "Berenice" reached its peak between 21 and 36 days after isolated in 1962 in "Belo Horizonte, MG", inoculation of "Berenice", "Y", "FL" and Brazil from the first human case of Chagas' "CL". In hosts harboring "São Felipe" or disease; "São Felipe" isolated in "São Felipe, "Colombiana" it peaked within a period of 26- Bahia", (Brazil) in 1974; "Colombiana" 68 days, in the group of guinea-pigs infected isolated in 1962 in "Belo Horizonte, MG", with the "Gávea" isolate it reached the highest "FL" and "CL" both isolated in 1963 from level between the 35th and 76th day after naturally infected bugs collected in " Rio inoculation. Grande do Sul" (Brazil) "Gávea" a T.cruzi Batches of bugs fed on infected animals: The like parasite isolated from naturally infected scheme followed was essentially this described adult P.megistus collected in "Gávea" area of in 1982 with one major addition "Rio de Janeiro" (Brazil) in 1977. There was (Perlowagora-Szumlewicz & Müller15). While difficulty in establishing an overt parasitemia in previously the reaction of nine different vector infected mice, which only occasionally showed species to infection by Y strain was studied, the one parasite in wet films of tail blood. herein described experiments were extended to Therefore this isolate has been maintained by the responsiveness of the same nine vector feeding triatomid bugs on infected mice and species to experimental infections produced by inoculating their feaces or suspensions of the seven different strains. digestive tract ip into clean mice and Groups of 54 clean fourth instar nymphs of guinea-pigs. These latter,in contrast to the each of the nine vector species, starved since former, developed long lasting parasitemia and their transition from the third stage, were fed in like mice harbored the infection until death due batches of nine specimens on groups of six to aging. Parasites found in Giemsa stained guinea-pigs each, previously infected with one dried films of bug feaces or peripheral blood of the seven different strains of T.cruzi. The number of bugs of all nine species, used in summarized in Table 2. The reasons for xenodiagnosis of six guinea-pigs infected with centering our attention on specimens with heavy infections had been described in detail in the same strain was 486 (54 x 9). The total 16 number of specimens of all nine species fed on our recent paper . all seven groups of guinea-pigs (six per group), From the analysis of overalls seen in Table 1, each infected with a different strain of T.cruzi it is obvious that although feeding of bugs from was 3402 (486