Günter A. Schaub

Plasma nitrite reflects constitutive nitric oxide synthase activity in mammals

Changes in plasma nitrite concentration in the human forearm circulation have recently been shown to reflect acute changes in endothelial nitric oxide synthase (eNOS)-activity. Whether basal plasma nitrite is a general marker of constitutive NOS-activity in vivo is yet unclear. Due to the rapid metabolism of nitrite in blood and the difficulties in its analytical determination literature data on levels of nitrite in mammals are largely inconsistent. We hypothesized that constitutive NOS-activity in the circulatory system is relatively uniform throughout the mammalian kingdom. If true, this should result in comparable systemic plasma nitrite levels in different species. Using three different analytical approaches we determined plasma nitrite concentration to be in a nanomolar range in a variety of species: humans (305 +/- 23 nmol/l), monkeys (367 +/- 62 nmol/l), minipigs (319 +/- 24 nmol/l), dogs (305 +/- 50 nmol/l), rabbits (502 +/- 21 nmol/l), guinea pigs (412 +/- 44 nmol/l), rats (191 +/- 43 nmol/l), and mice (457 +/- 51 nmol/l). Application of different NOS-inhibitors in humans, minipigs, and dogs decreased NOS-activity and thereby increased vascular resistance. This was accompanied by a significant, up to 80%, decrease in plasma nitrite concentration. A comparison of plasma nitrite concentrations between eNOS(-/-) and NOS-inhibited wild-type mice revealed that 70 +/- 5% of plasma nitrite is derived from eNOS. These results provide evidence for a uniform constitutive vascular NOS-activity across mammalian species.

The Development of Trypanosoma cruzi in Triatominae

Trypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects. These insects ingest an enormous amount of blood, with ingestion followed very rapidly by a strong diuresis, slow digestion and occasionally long periods of starvation. Resulting changes in the intestinal environment induce the development of dominant stages of T. cruzi--epimastigotes and metacyclic trypomastigotes--and can be correlated with the appearance of specific developmental stages--spheromastigotes and giant cells--which otherwise are only rarely seen. Here, Astrid Kollien and Günter Schaub outline recent research on these developmental steps of T. cruzi in the vector, and the effects of different compounds acting against the parasite in the vector.

Triatominae–Trypanosoma cruzi/T. rangeli: Vector–parasite interactions

Of the currently known 140 species in the family Reduviidae, subfamily Triatominae, those which are most important as vectors of the aetiologic agent of Chagas disease, Trypanosoma cruzi, belong to the tribes Triatomini and Rhodniini. The latter not only transmit T. cruzi but also Trypanosoma rangeli, which is considered apathogenic for the mammalian host but can be pathogenic for the vectors. Using different molecular methods, two main lineages of T. cruzi have been classified, T. cruzi I and T. cruzi II. Within T. cruzi II, five subdivisions are recognized, T. cruzi IIa-IIe, according to the variability of the ribosomal subunits 24Salpha rRNA and 18S rRNA. In T. rangeli, differences in the organization of the kinetoplast DNA separate two forms denoted T. rangeli KP1+ and KP1-, although differences in the intergenic mini-exon gene and of the small subunit rRNA (SSU rRNA) suggest four subpopulations denoted T. rangeli A, B, C and D. The interactions of these subpopulations of the trypanosomes with different species and populations of Triatominae determine the epidemiology of the human-infecting trypanosomes in Latin America. Often, specific subpopulations of the trypanosomes are transmitted by specific vectors in a particular geographic area. Studies centered on trypanosome-triatomine interaction may allow identification of co-evolutionary processes, which, in turn, could consolidate hypotheses of the evolution and the distribution of T. cruzi/T. rangeli-vectors in America, and they may help to identify the mechanisms that either facilitate or impede the transmission of the parasites in different vector species. Such mechanisms seem to involve intestinal bacteria, especially the symbionts which are needed by the triatomines to complete nymphal development and to produce eggs. Development of the symbionts is regulated by the vector. T. cruzi and T. rangeli interfere with this system and induce the production of antibacterial substances. Whereas T. cruzi is only subpathogenic for the insect host, T. rangeli strongly affects species of the genus Rhodnius and this pathogenicity seems based on a reduction of the number of symbionts.

IL-12-Independent IFN-γ Production by T Cells in Experimental Chagas’ Disease Is Mediated by IL-18

IL-12p35-deficient (IL-12p35−/−) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas’ disease. Delayed immune responses were observed in mutant mice, although comparable IFN-γ and TNF-α blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4+ T cells as the cellular source for IL-12-independent IFN-γ production. IL-18 was induced in IL-12p35−/− mice and was responsible for IFN-γ production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-γ production in experimental Chagas’ disease that is T cell and IL-18 dependent.

Monitoring of putative vectors of bluetongue virus serotype 8, Germany.

To identify the vectors of bluetongue virus (BTV) in Germany, we monitored Culicoides spp. biting midges during April 2007–May 2008. Molecular characterization of batches of midges that tested positive for BTV suggests C. obsoletus sensu stricto as a relevant vector of bluetongue disease in central Europe.

Interactions between intestinal compounds of triatomines and Trypanosoma cruzi

Triatomine bugs are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease, a devastating disease that disables and leads to the death of many people in Latin America. In this review, factors from the insect vector are described, including digestive enzymes, hemolysins, agglutinins, microbiota and especially antimicrobial factors, which are potentially involved in regulating the development of T. cruzi in the gut. Differential regulation of parasite populations shows that some triatomine defense reactions discriminate not only between molecular signals specific for trypanosome infections but also between different strains of T. cruzi.

Modes of association of Trypanosoma cruzi with the intestinal tract of the vector Triatoma infestans

The interface between Trypanosoma cruzi and two regions of the intestinal tract of reduviid bugs, the small intestine and the rectum, was investigated by electron microscopy. The mode of association of the trypanosomes with the midgut surface differs fundamentally from that in the rectum, the preferred site of colonisation by T. cruzi. The parasites caused no detrimental changes in the extracellular membrane layers, microvilli or epithelial cells. Parasites resided mainly at the border of the gut contents, also regularly showing parasite-parasite interdigitations. In regions in which the extracellular membrane layers were absent or only weakly developed, trypanosome bodies or flagella occasionally could be found inserted shallowly between the tips of the microvilli. Since there were usually no ultrastructural modifications of the cell body and/or flagellum associated with attachment, there is apparently no strong attachment of the flagellates to the wall of the midgut. In the rectal lumen the flagellates also interdigitated with each other and on the rectal wall T. cruzi was intimately attached to the rectal cuticle lining. At the attachment site flagella were enlarged and sometimes contained electron-dense, hemidesmosome-like material beneath the plasma membrane.

Scanning electron microscopic studies ofTrypanosoma cruzi in the rectum of its vectorTriatoma infestans

The cuticular surface of the rectum ofTriatoma infestans and its colonization by aTrypanosoma cruzi strain originating from the same locality as the bugs were studied by scanning electron microscopy at different weeks post infectionem. On the basis of the cuticular folding, the rectum can be subdivided into five regions. The rectal gland has the finest structure and the region anterior to the anus the deepest folds.Try. cruzi always prefers to colonize the rectal gland, while the other regions are colonized in varying densities. Most of the flagellates are epimastigotes (long and short), except in the region at the entrance of the midgut, where trypomastigotes predominate.

Repeated introduction of Aedes albopictus into Germany, July to October 2012

During a small-scale surveillance project to identify possible routes of entry for invasive mosquitoes into Germany, 14 adult Aedes (Stegomyia) albopictus (Skuse) were discovered between July and October 2012. They were trapped at three different service stations in Bavaria and Baden-Wuerttemberg located along two motorways that connect Germany with southern Europe. This indicates regular introduction of A. albopictus into Germany and highlights the need for a continuous surveillance and control programme.

Pathogenicity of trypanosomatids on insects

More and more effects of trypanosomatids on insects have been recognized in the past few years. Here, Günter A. Schaub reviews such effects, classifying the flagellates according to the intensity of the effects on the insect host into pathogenic, subpathogenic and apathogenic trypanosomatids. He emphasizes that subpathogenic trypanosomatids which cause only minor effects under optimal conditions might act synergistically with natural stressors, thereby being an important regulatory factor in insect populations.