Mammalian cell invasion assays, using metacyclic trypomastigotes of Trypanosoma cruzi G and CL strains, showed that the CL strain enters target cells in several-fold higher numbers as compared with the G strain. Analysis of expression of surface glycoproteins in metacyclic forms of the two strains by iodination, immunoprecipitation and FACS, revealed that gp90, undetectable in the CL strain, is one of the major surface molecules in the G strain, that expression of gp82 is comparable in both strains and that gp35/50 is expressed at lower levels in the CL strain. Purified gp90 and gp35/50 bound more efficiently than gp82 to cultured HeLa cells. However, the intensity of the Ca2+ response triggered in HeLa cells by gp82 was significantly higher than that induced by gp35/50 or gp90. Most of the Ca2+ signalling activity of the metacyclic extract towards HeLa cells was due to gp82 and was inhibitable by gp82-specific monoclonal antibody 3F6. Ca2+ mobilization was also triggered in metacyclic trypomastigotes by host-cell components; it was mainly gp82-mediated and more intense in the CL than in the G strain. We propose that expression of gp90 and gp35/50 at high levels impairs binding of metacyclic forms to host cells through productive gp82-mediated interaction, which leads to the target-cell and parasite Ca2+ mobilization required for invasion. Analysis of metacyclic forms of eight additional T. cruzi strains corroborated the inverse correlation between infectivity and expression of gp90 and gp35/50.

/pdf/infectivity-of-trypanosoma-cruzi-strains-is-associated-with-3rsia04kf0.pdf

Infectivity of Trypanosoma cruzi strains is associated with differential expression of surface glycoproteins with differential Ca2+ signalling activity

https://mmbr.asm.org/content/mmbr/44/1/140.full.pdf

Biology and physiology of the lower Trypanosomatidae.

Trypanosomatid parasites are fairly common in the latex, phloem, fruit sap, seed albumen, and even in the nectar, of many plant families. They are transmitted to the plants in the saliva of phytophagous hemipterous bugs (Insecta). Morphologically, plant trypanosomatids have no special characteristic, except perhaps a very twisted cell body. Most occur in plants as promastigotes and a few as choanomastigotes. It is still controversial whether or not they are pathogenic in lactiferous plants or fruit, but it is certain that the phloem parasites are pathogenic in coconut palms and coffee bushes. In these plants, they cause lethal diseases responsible for the destruction of many plantations in Central and South America, but fortunately nowhere else in the world. Probably more than one genus of Trypanosomatidae is represented among the plant parasites. The most important is certainly Phytomonas, but Leptomonas, Crithidia and Herpetomonas may also be present. The distinction between them is difficult and only recently have molecular markers become available to help in their identification. At present, Phytomonas can be identified by DNA hybridization with a specific probe (SL3') complementary to a sequence of the mini-exon or spliced leader gene. The development of a polymerase chain reaction coupled to SL3' hybridization has facilitated the detection of Phytomonas in plants. The phylogeny of Phytomonas is still being worked out. For the moment it can only be said that the genus is very close to Herpetomonas.

Phytomonas and other trypanosomatid parasites of plants and fruit.

This article considers how specificity patterns are shaped during the course of parasite evolution. Parasites are first and foremost specific to site, or microhabitat; host ranges are far more subject to change than is microhabitat. Specificity results from a number of convergent phenomena starting with habits (microhabitat and feeding styles) of free-living progenitors and the way in which the parasitic association arises (e.g., passive oral contamination as opposed to intrusive entry). These bias the types of interaction parasites have with the host, and, through this, the way specificity develops. Host ecology acts as an external factor affecting specificity and predominates in parasites that interact minimally with the hosts physiological and immune systems. Coevolutionary factors are more important in parasites that feed on host tissues or occur in extraintestinal sites. Here, parasites must present the right cues, and respond appropriately to the host defense system. The ability to generalize these cues and responses across host boundaries may act as a constraint on host range. The functional role of the host in the parasite life history also affects the degree of specificity; thus, parasites may act as host generalists in hosts that act as trophic channels to the final host. The role of competition in determining specificity is difficult to assess. However, competition has been reported to influence microhabitat and host distribution through interactive site selection and/or competitive seclusion.

Evolutionary factors influencing the nature of parasite specificity

Immunity to blood parasites of animals and man.

SYNOPSIS

The insectivorous bug Zelus leucogrammus (Perty, 1834) (Hemiptera, Reduviidae) was found to harbor several species of trypanosomatids of the genera Leptomonas, Crithidia, Herpetomonas and Blastocrithidia. However, laboratory bred nymphs given sterile food were infected only by Blastocrithidia, the other flagellates appearing in their intestinal tract when they were fed on other insects.



The Blastocrithidia was thought to belong to a single species and to be a parasite proper of Z. leucogrammus (and possibly other Hemiptera), producing luxuriant infections in the intestinal tract of the bugs captured in nature and spreading easily among isolated populations through cannibalism and ingestion of cysts; it was also abundant in the genital tract of gravid females but transovarian transmission was not proved. This Blastocrithidia experimentally infected Triatoma infestans and is very close to B. triatomae Cerisola, del Prado, Rohwedder and Bozzini, 1971.



The other trypanosomatids, never numerous in naturally infected Z. leucogrammus, are acquired by the bug from many different insects, chiefly Diptera, on which it was seen to feed. Herpetomonas muscarum and C. luciliae, the common trypanosomatids among several muscoid Diptera, were isolated both from flies and from the bugs fed on them.

Maria P. Deane

Papers

Trypanosomatidae Isolated from Zelus leucogrammus (Perty, 1834) (Hemiptera, Reduviidae), with a Discussion on Flagellates of Insectivorous Bugs

Lack of protection against Trypanosoma cruzi by multiple doses of T. lewisi culture forms. A discussion on some strains of "lewisi".