Pathogenicity and virulence of African trypanosomes: From laboratory models to clinically relevant hosts.

African trypanosomes are vector-borne protozoa, which cause significant human and animal disease across sub-Saharan Africa, and animal disease across Asia and South America. In humans, infection is caused by variants of Trypanosoma brucei, and is characterized by varying rate of progression to neurological disease, caused by parasites exiting the vasculature and entering the brain. Animal disease is caused by multiple species of trypanosome, primarily T. congolense, T. vivax, and T. brucei. These trypanosomes also infect multiple species of mammalian host, and this complexity of trypanosome and host diversity is reflected in the spectrum of severity of disease in animal trypanosomiasis, ranging from hyperacute infections associated with mortality to long-term chronic infections, and is also a main reason why designing interventions for animal trypanosomiasis is so challenging. In this review, we will provide an overview of the current understanding of trypanosome determinants of infection progression and severity, covering laboratory models of disease, as well as human and livestock disease. We will also highlight gaps in knowledge and capabilities, which represent opportunities to both further our fundamental understanding of how trypanosomes cause disease, as well as facilitating the development of the novel interventions that are so badly needed to reduce the burden of disease caused by these important pathogens.

Extracellular release of two peptidases dominates generation of the trypanosome quorum-sensing signal.

Trypanosomes causing African sleeping sickness use quorum-sensing (QS) to generate transmission-competent stumpy forms in mammalian hosts. This density-dependent process is signalled by oligopeptides that stimulate the signal transduction pathway leading to stumpy formation. Here, using mass spectrometry analysis, we identify peptidases released by trypanosomes and, for 12 peptidases, confirm their extracellular delivery. Thereafter, we determine the contribution of each peptidase to QS signal production using systematic inducible overexpression in vivo, and confirm this activity operates through the physiological QS signalling pathway. Gene knockout of the QS-active peptidases identifies two enzymes, oligopeptidase B and metallocarboxypeptidase 1, that significantly reduce QS when ablated individually. Further, combinatorial gene knockout of both peptidases confirms their dominance in the generation of the QS signal, with peptidase release of oligopeptidase B mediated via an unconventional protein secretion pathway. This work identifies how the QS signal driving trypanosome virulence and transmission is generated in mammalian hosts.

Concurrent Schistosoma mansoni and Schistosoma haematobium infections in a peri-urban community along the Weija dam in Ghana: A wake up call for effective National Control Programme.

Globally over 200 million people are infected with schistosomiasis, and approximately 80% are caused by just two of five species, Schistosoma haematobium and Schitosoma mansoni that are broadly distributed, and often overlap across sub-Saharan Africa. Like most neglected tropical diseases, mortality is low (an estimated 200,000 deaths annually) and morbidity is considerably high and probably underestimated. Surprisingly, little attention has been given to co-infection with these two species. We have studied co-infection with S. mansoni and S. haematobium in a peri-urban community in Ghana, one of the most highly endemic countries for schistosomiasis. We collected and examined snails of the two intermediate host species from the reservoir adjacent to the community. We also used microscopical examination of stool and urine samples to determine the level of concurrent S. mansoni and S. haematobium infections in school and administered questionnaires to assess water contact activities that predispose pupils to infections Examination of the snail hosts revealed that 0.7% (7/896) of Bulinus truncatus and 1.7% (14/780) of Biomphalaria pfeifferi snails were found to be hosting cercariae morphologically consistent with that of S. haematobium and S. mansoni respectively. The overall prevalence values for urogenital and intestinal schistosomiasis were 66.8% (135/202) and 90.1% (163/181) respectively. Only 50 of 181 schistosome-infected pupils had single-species infections and the remaining 131 pupils presented concurrent infections. Among the 131 infected with both species were 50 individuals having only S. mansoni eggs in stool and S. haematobium eggs in urine (conventional presentation). Eighty-one children (81) had eggs of both species in either urine and/or stool (ectopic presentation). From these 81, 63 had eggs of both species in urine, 6 had both species in stool, and 12 had eggs of both species present in both urine and stool. A comparatively large number of individuals from the concurrent infected group presented high and moderate infection intensities than the single infected groups. The overwhelmingly high prevalence of concurrent infections indicates further study of co-infection is needed, and points to a need call for a holistic disease control plan so Ghana can be part of nations to achieve the WHO roadmap target for schistosomiasis control by 2020.

Oligopeptide Signaling through TbGPR89 Drives Trypanosome Quorum Sensing.

Trypanosome parasites control their virulence and spread by using quorum sensing (QS) to generate transmissible "stumpy forms" in their host bloodstream. However, the QS signal "stumpy induction factor" (SIF) and its reception mechanism are unknown. Although trypanosomes lack G protein-coupled receptor signaling, we have identified a surface GPR89-family protein that regulates stumpy formation. TbGPR89 is expressed on bloodstream "slender form" trypanosomes, which receive the SIF signal, and when ectopically expressed, TbGPR89 drives stumpy formation in a SIF-pathway-dependent process. Structural modeling of TbGPR89 predicts unexpected similarity to oligopeptide transporters (POT), and when expressed in bacteria, TbGPR89 transports oligopeptides. Conversely, expression of an E. coli POT in trypanosomes drives parasite differentiation, and oligopeptides promote stumpy formation in vitro. Furthermore, the expression of secreted trypanosome oligopeptidases generates a paracrine signal that accelerates stumpy formation in vivo. Peptidase-generated oligopeptide QS signals being received through TbGPR89 provides a mechanism for both trypanosome SIF production and reception.

In Vitro Assessment of Anthelmintic Activities of Rauwolfia vomitoria (Apocynaceae) Stem Bark and Roots against Parasitic Stages of Schistosoma mansoni and Cytotoxic Study.

Schistosomiasis is a Neglected Tropical Diseases which can be prevented with mass deworming chemotherapy. The reliance on a single drug, praziquantel, is a motivation for the search of novel antischistosomal compounds. This study investigated the anthelmintic activity of the stem bark and roots of Rauwolfia vomitoria against two life stages of Schistosoma mansoni. Both plant parts were found to be active against cercariae and adult worms. Within 2 h of exposure all cercariae were killed at a concentration range of 62.5-1000 µg/mL and 250-1000 µg/mL of R. vomitoria stem bark and roots, respectively. The LC50 values determined for the stem bark after 1 and 2 h of exposure were 207.4 and 61.18 µg/mL, respectively. All adult worms exposed to the concentrations range of 250-1000 µg/mL for both plant parts died within 120 h of incubation. The cytotoxic effects against HepG2 and Chang liver cell assessed using MTT assay method indicated that both plant extracts which were inhibitory to the proliferation of cell lines with IC50 > 20 µg/mL appear to be safe. This report provides the first evidence of in vitro schistosomicidal potency of R. vomitoria with the stem bark being moderately, but relatively, more active and selective against schistosome parasites. This suggests the presence of promising medicinal constituent(s).