Studies on Trypanosoma rangeli Tejera, 1920: IX. Course of infection in different stages of Rhodnius prolixus

Abstract

Frequent individual observations od different stages of Rhodnius prolixus exposed to Trypanosoma rangeli, revealed a higher susceptibility to infection in the bugs exposed during the two first instars. The mortality rate in infected bugs was significantly higher than in controls, indicating that the parasite was responsible for the majority of deaths. An analysis of the mortality distribution, per instar, is presented. Statistical analysis of deaths among the different infected instars, showed that T. rangeli produces its pathological effect in any stage of R. prolixus independently of its susceptibility to the parasite. The survival to adult decreased in all the infected instar bugs. A significant longer time to reach the adult stage was observed in the infected bugs when compared with controls, excepting for specimens exposed in the third instar. The epidemiological significance of the present results is discussed.

A standardizable protocol for infection of Rhodnius prolixus with Trypanosoma rangeli, which mimics natural infections and reveals physiological effects of infection upon the insect

“…Only 13% of the insects infected orally that presented parasites in the intestinal tract had parasites infecting their salivary glands. This is in accordance with previously reported infection rates ranging between 2% and 50% (Añez et al, 1987;Groot, 1954;Hecker et al, 1990;Marinkelle, 1968;Tobie, 1965Tobie, , 1970. The mechanisms that prevent the passage of the parasite from the lumen of the midgut to the .…”

“…At present, investigation of this area is hindered by non-standardization of inoculation procedures, and by limited information available in studies concerning the sizes of parasite inocula used, in addition to the environmental conditions under which published assays were developed. These considerations, and the relevance of laboratory studies to understand natural infections, are of prime importance as T. rangeli does not always invade the haemocoel in the natural course of infection and natural infection rates can be low as 2% (Añez et al, 1987;Hecker et al, 1990;Tobie, 1965Tobie, , 1970. Therefore, the present work initially compared different infection methods in order to establish a procedure that could mimic natural infections.…”

What is the ‘true’ effect ofTrypanosoma rangelion its triatomine bug vector?

“…However, results reported in the literature regarding insect stage are conflicting. There are just two published studies by the same group (Añez et al , ), hence with bugs from the same colony and the same T. rangeli strain, comparing the mortality of insects infected with T. rangeli at each stage, and no significant difference in mortality between stages was reported in either study. They did observe, however, that T. rangeli dose seemed to affect insect mortality.…”

“…Two studies reported augmented negative effects in inoculated insects (Watkins, unpublished doctoral dissertation, Koerich et al ) that were not observed in orally infected insects in the same experiment, suggesting problems stemming from the parasite injection procedure. Additionally, many studies that employed the oral infection technique did not take into account the quantity of blood consumed by each insect in the infective meal (Grewal , Tobie , Gómez , Añez , Añez et al ). Complete engorgement is required to initiate and execute molting in triatomines (Wigglesworth ), and thus it is possible that molting problems could have been associated with small blood meals instead of or in addition to T. rangeli infection.…”

Developmental and reproductive patterns of Triatoma brasiliensis infected with Trypanosoma cruzi under laboratory conditions

“…cruzi, unlike Trypanosoma rangeli, has been established to be harmful to mammals, mainly humans. In contrast, it seems to only be sub-pathogenic to the triatomines (Schaub 1988(Schaub , 1989a(Schaub , 1992(Schaub , 1994, whereas T. rangeli is pathogenic to its triatomine vectors (Grewal 1957, Añez 1984, Añez et al 1987. T. cruzi requires synergistic stressors, such as starvation or other environmental factors, to cause actual harm to the triatomines (Schaub 1992).…”