Hospedeiros vertebrados são eficientes reservatórios para a transmissão do Trypanosoma rangeli ao inseto vetor

Abstract

Triatomines are insects that live primitively in the wild in association with nests of rodents, birds and marsupials. Besides the blood spoliation they cause, triatomines can transmit protozoans such as Trypanosoma cruzi and Trypanosoma rangeli. T. rangeli does not harm humans, although it might induce many pathogenic effects to the insect vector. Little is known about the development of T. rangeli inside their vertebrate host, since the infectivity is generally low and parasites tend to disappear from blood circulation. Transmission of the parasite occurs during the insect bite, but the mechanisms by which the insects acquire the infection from a very small number of circulating parasites in the vertebrate host are still unknown. In this work, we initially evaluated the possibility of T. rangeli transmission between insects via hemolymphagy behavior and during the blood feeding in an uninfected vertebrate host. Our results have shown, that during our experiments, the insects did not perform hemolymphagy behavior, without any detection of T. rangeli transmission even when infected insects were kept together with uninfected ones during a long period of fast. However, when uninfected nymphs were simultaneously fed together with infected nymphs in a same uninfected host, they presented infection rates higher than 60%. The number of parasites released from R. prolixus nymphs saliva during feeding was estimated using Neubauer chamber counts and qPCR. Although variations were found between insects, the average number of parasites in the salivary glands was highly reduced after a blood meal. Transmission rates to mice via the bite of infected nymphs were very high, reaching around 90%. We also observed a high capacity of these mice in transmiting the parasite to other uninfected nymphs even 30 days after they were infected. A Choachi strain maintained in LIT culture for a longer period showed a decrease in its capacity of being transmitted from infected mice to uninfected nymphs. Furthermore, the parasite load of nymphs which did get infected in these experiments was also lower. The number of parasites in both the blood of infected mice and in the anterior midgut of recently fed nymphs in these animals were not high enough to be detected via Neubauer chamber counting. Despite the low parasite load in the blood circulation of mammal host, the high infection rates found in nymphs blood fed in these mice, even in those holding older infections, strongly suggest the existence of a development cycle of T. rangeli in it mammal host.