Schematic depiction of population bottlenecks during the life cycle of <i>Trypanosoma brucei</i>.

The relative population size is shown on the y-axis. When trypanosomes are taken up by a tsetse fly, the population collapses during the adaptation to the midgut (A) and recovers thereafter. Only a few trypanosomes at a time are presumed to migrate to the salivary glands (B). Migration might take place during a defined period [6] or continuously [8]. Long epimastigote forms can reach the salivary glands where they deposit the short epimastigote forms that colonise the epithelia and give rise to metacyclic forms. During a blood meal, metacyclic forms are injected into a mammalian host. The injection and the relocation of trypanosomes from the site of injection into the bloodstream may reduce its number (C). In the mammalian host, the trypanosome population is periodically reduced in size owing to the adaptive immune response and to the differentiation of long slender bloodstream forms into non-dividing short stumpy forms (D).</p

Diversity and frequency of tagged trypanosomes in three experiments.

The bars in each chart represent the 8 tags. Frequency is shown on a log scale ranging from 0.01–100 per cent with dominant tags (>5%) highlighted in black. Tsetse flies were infected with procyclic trypanosomes with an even distribution of the tags. Three flies (A, B, and C) had infected midguts (mg) and salivary glands (sg). These flies each infected one mouse whose parasitaemia was monitored over a period of 2–3 months. Since the mice are immunocompetent, antigenic variation occurs, with each peak of parasitaemia containing trypanosomes expressing new VSGs compared to the preceding peaks. Five blood samples were taken from each mouse for analysis of the tags (indicated by large diamonds in the right panel) after 1, 2, 3, and 4 weeks and at the end of the experiment after 7–10 weeks. Flies D and E were infected on mouse C 18 and 30 days after infection (indicated with the grey arrows in the right panel). Midguts were dissected after 12 days (ID12) and 10 days (ID10). The number of sequences obtained from each sample is shown in Figure S2A.</p

Population size through the life cycle of <i>T. brucei</i> based on data from this study.

A: establishment of infection in the fly midgut following a blood meal; B: trypanosomes migrating to the salivary glands; C: establishment of infection in the mammal following fly transmission; D: fluctuations in parasite numbers in the mammalian bloodstream. Numbers in boxes refer to minimum numbers of trypanosomes surviving the transition between different tissues and hosts. The asterisk depicts the possibility that there might be waves of migration of a few parasites at a time from the midgut to the salivary glands.</p

Agrochemicals against Malaria, Sleeping Sickness, Leishmaniasis and Chagas Disease

<div><p>In tropical regions, protozoan parasites can cause severe diseases with malaria, leishmaniasis, sleeping sickness, and Chagas disease standing in the forefront. Many of the drugs currently being used to treat these diseases have been developed more than 50 years ago and can cause severe adverse effects. Above all, resistance to existing drugs is widespread and has become a serious problem threatening the success of control measures. In order to identify new antiprotozoal agents, more than 600 commercial agrochemicals have been tested on the pathogens causing the above mentioned diseases. For all of the pathogens, compounds were identified with similar or even higher activities than the currently used drugs in applied <em>in vitro</em> assays. Furthermore, <em>in vivo</em> activity was observed for the fungicide/oomyceticide azoxystrobin, and the insecticide hydramethylnon in the <em>Plasmodium berghei</em> mouse model, and for the oomyceticide zoxamide in the <em>Trypanosoma brucei rhodesiense</em> STIB900 mouse model, respectively.</p> </div

Diversity index (Simpson's index).

Diversity index (Simpson's index).</p

<i>In vitro</i> activity of the top 10 most active commercial agrochemicals on <i>P. falciparum</i> NF54 strain.

<p>The IC₅₀ values are the means of two independent assays; the individual values vary by less than a factor of 2.</p

Cloning procedure and generation of tagged trypanosomes.

A. Cloned procyclic trypanosomes were passaged through a tsetse fly and a mouse and bloodstream forms were triggered to differentiate to procyclic forms in vitro. The plasmids piTag 1–8 were then transfected separately into T. brucei. Cloned stable transformants containing each of the eight tags were isolated. B. Construction of the plasmid piTag. Eight different 40mers were integrated into the plasmid upstream of the procyclin promoter. Expression of the neomycin resistance gene (NeoR) in trypanosomes is controlled by the EP1 procyclin promoter and 5′ untranslated region (UTR) and the last 19 bases of the 3′ untranslated region and intergenic region (IGR) of EP2 procyclin. The linearised plasmid integrates into an rDNA spacer in the genome. Tags were amplified from genomic DNA by nested PCR.</p

Top 10 most active commercial agrochemicals on <i>T. b. rhodesiense</i>.

<p>The IC₅₀ values are the means of two independent assays; the individual values vary by less than a factor of 2.</p

Top 10 most active commercial agrochemicals on <i>T. cruzi</i>.

<p>The IC₅₀ values are the means of two independent assays; the individual values vary by less than a factor of 2.</p

Most active commercial agrochemicals on <i>L. donovani</i>.

<p>The IC₅₀ values are the means of two independent assays; the individual values vary by less than a factor of 2.</p