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The peritrophic matrix of blood-feeding insects is a chitinous structure that forms a protective barrier against oral pathogens and abrasive particles1. Tsetse flies transmit Trypanosoma brucei, which is the parasite that causes human sleeping sickness and is also partially responsible for animal trypanosomiasis in Sub-Saharan Africa. For this parasite to establish an infection in flies, it must first colonize the area between the peritrophic matrix and gut epithelium called the ectoperitrophic space. Although unproven, it is generally accepted that trypanosomes reach the ectoperitrophic space by penetrating the peritrophic matrix in the anterior midgut2,3,4. Here, we revisited this event using fluorescence- and electron-microscopy methodologies. We show that trypanosomes penetrate the ectoperitrophic space in which the newly made peritrophic matrix is synthesized by the proventriculus. Our model describes how these proventriculus-colonizing parasites can either migrate to the ectoperitrophic space or become trapped within peritrophic matrix layers to form cyst-like bodies that are passively pushed along the gut as the matrix gets remodelled. Furthermore, early proventricular colonization seems to be promoted by factors in trypanosome-infected blood that cause higher salivary gland infections and potentially increase parasite transmission.

International audience; The single-celled parasite Trypanosoma brucei is transmitted by hematophagous tsetse flies. Life cycle progression from mammalian bloodstream form to tsetse midgut form and, subsequently, infective salivary gland form depends on complex developmental steps and migration within different fly tissues. As the parasite colonizes the glucose-poor insect midgut, ATP production is thought to depend on activation of mitochondrial amino acid catabolism via oxidative phosphorylation (OXPHOS). This process involves respiratory chain complexes and F1Fo-ATP synthase and requires protein subunits of these complexes that are encoded in the parasite's mitochondrial DNA (kDNA). Here, we show that progressive loss of kDNA-encoded functions correlates with a decreasing ability to initiate and complete development in the tsetse. First, parasites with a mutated F1Fo-ATP synthase with reduced capacity for OXPHOS can initiate differentiation from bloodstream to insect form, but they are unable to proliferate in vitro. Unexpectedly, these cells can still colonize the tsetse midgut. However, these parasites exhibit a motility defect and are severely impaired in colonizing or migrating to subsequent tsetse tissues. Second, parasites with a fully disrupted F1Fo-ATP synthase complex that is completely unable to produce ATP by OXPHOS can still differentiate to the first insect stage in vitro but die within a few days and cannot establish a midgut infection in vivo. Third, parasites lacking kDNA entirely can initiate differentiation but die soon after. Together, these scenarios suggest that efficient ATP production via OXPHOS is not essential for initial colonization of the tsetse vector but is required to power trypanosome migration within the fly. IMPORTANCE African trypanosomes cause disease in humans and their livestock and are transmitted by tsetse flies. The insect ingests these parasites with its blood meal, but to be transmitted to another mammal, the trypanosome must undergo complex development within the tsetse fly and migrate from the insect's gut to its salivary glands. Crucially, the parasite must switch from a sugar-based diet while in the mammal to a diet based primarily on amino acids when it develops in the insect. Here, we show that efficient energy production by an organelle called the mitochondrion is critical for the trypanosome's ability to swim and to migrate through the tsetse fly. Surprisingly, trypanosomes with impaired mitochondrial energy production are only mildly compromised in their ability to colonize the tsetse fly midgut. Our study adds a new perspective to the emerging view that infection of tsetse flies by trypanosomes is more complex than previously thought.

The single-celled parasite Trypanosoma brucei causes sleeping sickness in humans and nagana in livestock and is transmitted by hematophagous tsetse flies. Lifecycle progression from mammalian bloodstream form to tsetse midgut form and, subsequently, infective salivary gland form depends on complex developmental steps and migration within different fly tissues. As the parasite colonises the glucose-poor insect midgut, its ATP production is thought to depend on activation of mitochondrial amino acid catabolism via oxidative phosphorylation. This process involves respiratory chain complexes and the F1FO-ATP synthase, and it requires protein subunits of these complexes that are encoded in the parasite’s mitochondrial DNA (kinetoplast or kDNA). Here we show that a progressive loss of kDNA-encoded functions correlates with an increasingly impaired ability of T. brucei to initiate and complete its development in the tsetse. First, parasites with a mutated F1FO-ATP synthase with a reduced capacity for oxidative phosphorylation can initiate differentiation from bloodstream to insect form, but they are unable to proliferate in vitro. Unexpectedly, these cells can still colonise the tsetse midgut. However, these parasites exhibit a motility defect and are severely impaired in colonising or migrating to subsequent tsetse tissues. Second, parasites with a fully disrupted F1FO-ATP synthase complex that is completely unable to produce ATP by oxidative phosphorylation can still differentiate to the first insect stage in vitro but die within a few days and cannot establish a midgut infection in vivo. Third, mutant parasites lacking kDNA entirely can initiate differentiation but die within 24 h. Together, these three scenarios show that efficient ATP production via oxidative phosphorylation is not essential for initial colonisation of the tsetse vector, but it is required to power trypanosome migration within the fly.

Microbiota within mosquitoes influence nutrition, immunity, fecundity, and the capacity to transmit pathogens. Despite their importance, we have a limited understanding of host-microbiota interactions, especially at the cellular level. It is evident bacterial symbionts that are localized within the midgut also infect other organs within the mosquito; however, the route these symbionts take to colonize other tissues is unknown. Here, utilizing the gentamicin protection assay, we showed that the bacterial symbionts Cedecea and Serratia have the capacity to invade and reside intracellularly within mosquito cells. Symbiotic bacteria were found within a vacuole and bacterial replication was observed in mosquito cell by transmission electron microscopy, indicating bacteria were adapted to the intracellular milieu. Using gene silencing, we determined that bacteria exploited host factors, including actin and integrin receptors, to actively invade mosquito cells. As microbiota can affect pathogens within mosquitoes, we examined the influence of intracellular symbionts on Zika virus (ZIKV) infection. Mosquito cells harbouring intracellular bacteria had significantly less ZIKV compared to uninfected cells or cells exposed to non-invasive bacteria. Intracellular bacteria were observed to substantially upregulate the Toll and IMD innate immune pathways, providing a possible mechanism mediating these anti-viral effects. Examining mono-axenically infected mosquitoes using transmission electron and fluorescent microscopy revealed that bacteria occupied an intracellular niche in vivo. Our results provided evidence that bacteria that associate with the midgut of mosquitoes have intracellular lifestyles which likely have implications for mosquito biology and pathogen infection. This study expands our understanding of host-microbiota interactions in mosquitoes, which is important as symbiont microbes are being exploited for vector control strategies.

Background Phlebotomus (Larroussius) guggisbergi is among the confirmed vectors for cutaneous leishmaniasis (CL) transmission in Kenya. This scarring and stigmatizing form of leishmaniasis accounts for over one million annual cases worldwide. Most recent CL epidemics in Kenya have been reported in Gilgil, Nakuru County, where the disease has become a public health issue. However, little is known about the factors that drive its transmission. Here, we sought to determine the occurrence, distribution and host blood feeding preference of the vectors, and to identify Leishmania species and infection rates in sandflies using molecular techniques. This information could lead to a better understanding of the disease transmission and improvement of control strategies in the area. Methodology/ Principal findings An entomological survey of sandflies using CDC light traps was conducted for one week per month in April 2016, and in June and July 2017 from five villages of Gilgil, Nakuru county; Jaica, Sogonoi, Utut, Gitare and Njeru. Sandflies were identified to species level using morphological keys and further verified by PCR analysis of cytochrome c oxidase subunit I (COI) gene. Midguts of female sandflies found to harbour Leishmania were ruptured and the isolated parasites cultured in Novy-MacNeal-Nicolle (NNN) media overlaid with Schneider’s insect media to identify the species. Leishmania parasite screening and identification in 198 randomly selected Phlebotomus females and parasite cultures was done by PCR-RFLP analysis of ITS1 gene, nested kDNA-PCR and real-time PCR-HRM followed by sequencing. Bloodmeal source identification was done by real-time PCR-HRM of the vertebrate cytochrome-b gene. A total of 729 sandflies (males: n = 310; females: n = 419) were collected from Utut (36.6%), Jaica (24.3%), Sogonoi (34.4%), Njeru (4.5%), and Gitare (0.1%). These were found to consist of nine species: three Phlebotomus spp. and six Sergentomyia spp. Ph. guggisbergi was the most abundant species (75.4%, n = 550) followed by Ph. saevus sensu lato (11.3%, n = 82). Sandfly species distribution across the villages was found to be significantly different (p, Author summary Leishmaniases are diseases caused by Leishmania parasites and transmitted through the bites of infected female sandflies during blood feeding. In Kenya, two main forms of the disease exist; visceral (VL) and cutaneous leishmaniasis (CL). Most recent CL epidemics in Kenya have been reported in Gilgil, Nakuru county, where the disease has become a public health problem. However, little is known about the factors that drive its transmission in the area. In this study, we investigated the occurrence, distribution, host preference and Leishmania infection rates in sandflies collected from Gilgil using molecular tools. This could lead to a better understanding of the disease and improvement of control strategies in the area. Our results revealed a high infection rate of L. tropica in two sandfly species (Ph. guggisbergi and Ph. saevus s.l.), which may indicate a high circulation level of this parasite in the area. However, we also identified L. major infection from Ph. guggisbergi species by PCR. Analysis of sandfly bloodmeal sources showed that Ph. guggisbergi fed on a diverse range of vertebrates including goats, rock hyraxes, rabbits, wild pigs and rodents whereas Ph. saevus s.l. fed mainly on humans. The potential of Ph. guggisbergi as a vector of L. major and whether other vertebrate hosts play a role in maintaining Leishmania parasites in this CL endemic area needs further investigation.

Background In the Kingdom of Saudi Arabia (KSA), Leishmania major and L. tropica are the main causative agents of Old World cutaneous leishmaniasis (CL). The national CL treatment regimen consists of topical 1% clotrimazole/2% fusidic acid cream followed by 1–2 courses of intralesional sodium stibogluconate (SSG); however, treatment efficacy is highly variable and the reasons for this are not well understood. In this study, we present a complete epidemiological map of CL and determined the efficacy of the standard CL treatment regime in several endemic regions of KSA. Results Overall, three quarters of patients in all CL-endemic areas studied responded satisfactorily to the current treatment regime, with the remaining requiring only an extra course of SSG. The majority of unresponsive cases were infected with L. tropica. Furthermore, the development of secondary infections (SI) around or within the CL lesion significantly favoured the treatment response of L. major patients but had no effect on L. tropica cases. Conclusions The response of CL patients to a national treatment protocol appears to depend on several factors, including Leishmania parasite species, geographical location and occurrences of SI. Our findings suggest there is a need to implement alternative CL treatment protocols based on these parameters. Electronic supplementary material The online version of this article (10.1186/s13071-019-3453-4) contains supplementary material, which is available to authorized users.

The peritrophic matrix (PM) of haematophagus insects is a chitinous structure that surrounds the bloodmeal, forming a protective barrier against oral pathogens and abrasive particles. To establish an infection in the tsetse midgut,Trypanosoma bruceimust colonise the ectoperitrophic space (ES), located between the PM and gut epithelium. Although unproven, it is generally accepted that trypanosomes reach the ES by directly penetrating the PM in the anterior midgut. Here we revisited this event by employing novel fluorescence and electron microscopy methodologies and found that instead, trypanosomes reach the ES via the newly secreted PM in the tsetse proventriculus. Within this model, parasites colonising the proventriculus can either migrate to the ES or become trapped within PM layers forming cysts that move along the entire gut as the PM gets remodelled. Early proventricular colonisation appears to be promoted by unidentified factors in trypanosome-infected blood, resulting in higher salivary gland infections and potentially increasing parasite transmission.

African trypanosomes are vector-borne hemoparasites of humans and animals. In the mammal, parasites evade the immune response through antigenic variation. Periodic switching of the variant surface glycoprotein (VSG) coat covering their cell surface allows sequential expansion of serologically distinct parasite clones. Trypanosome genomes contain many hundreds of VSG genes, subject to rapid changes in nucleotide sequence, copy number, and chromosomal position. Thus, analyzing, or even quantifying, VSG diversity over space and time presents an enormous challenge to conventional techniques. Indeed, previous population genomic studies have overlooked this vital aspect of pathogen biology for lack of analytical tools. Here we present a method for analyzing population-scale VSG diversity in Trypanosoma congolense from deep sequencing data. Previously, we suggested that T. congolense VSGs segregate into defined “phylotypes” that do not recombine. In our data set comprising 41 T. congolense genome sequences from across Africa, these phylotypes are universal and exhaustive. Screening sequence contigs with diagnostic protein motifs accurately quantifies relative phylotype frequencies, providing a metric of VSG diversity, called the “variant antigen profile.” We applied our metric to VSG expression in the tsetse fly, showing that certain, rare VSG phylotypes may be preferentially expressed in infective, metacyclic-stage parasites. Hence, variant antigen profiling accurately and rapidly determines the T. congolense VSG gene and transcript repertoire from sequence data, without need for manual curation or highly contiguous sequences. It offers a tractable approach to measuring VSG diversity across strains and during infections, which is imperative to understanding the host–parasite interaction at population and individual scales.