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

Abstract

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 following 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 practically all T. cruzi strains herein studied, thus indicating that the factors responsible for the excellent reaction 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 Dipetalogaster maximus as regards its superiority as a xenodiagnostic agent.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 4 - The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks

“…Additional data, from xenodiagnosis in hosts infected with different parasite stocks, have established the generality of diverse infectivity rates among sylvatic and domestic bugs exposed to acute infections by seven parasite stocks: "Berenice", "Y", "FL", "CL", "São Felipe", "Colombiana" and "Gávea", as reported by Perlowagora-Szumlewicz et al 25 (1988).…”

“…Consequently, the varying interpretations have lead to divergent opinions. Thus, comments concerning the diversity of bug responsiveness to infection by T. cruzi is a matter of interpretability rather than of substance, because apparently all record the poor performance of the parasite in the domestic T. infestans, as compared with that found by Ryckman 27 ; Little et al 17 in the wild T. protracta, or in the wild D. maximus, as stated by Barreto et al 5 , and also in the six essentially sylvatic species utilized by us in previous studies 23,24,25 .…”

“…Of the 42 guinea-pigs used in the previous study 25 , only 33 recovered from the acute infection that lasted from 57 to 67 days after inoculation of "Berenice", "Y", "FL" "CL" and "Colombiana", and from 145 to 190 days after infection with "São Felipe" and "Gávea" stock.…”

“…Rather than repeat the mode of infection of the animal hosts with the seven parasite stocks and the process of using the former in feeding several thousand noninfected bugs of different species, utilized thereafter in xenodiagnosis of acute Chagas' disease, the reader is referred to the paper 25 published in 1988, in which the xenodiagnostic test applied to the hosts, which survived the acute infection and remained in the chronic phase of the disease is described.…”

“…Although research on the vector parasite relationship, as illustrated by data from xenodiagnosis, has been under way in our laboratory for several years, it is still necessary to emphasize the consistency of the observation regarding the superiority of sylvatic vectors for xenodiagnostic purposes as stressed in the two recent papers 24,25 . The fact that this phenomenon is remarkably stable and easy to reproduce leads to the belief that the differences recorded between the groups of sylvatic and domestic vectors are valid, even though the nature of the reaction with regard to the biotope of the vector is not yet understood.…”