Control of tsetse flies and trypanosomes using molecular genetics

Gut microbiota metagenomics and mediation of phenol degradation in Bactrocera minax (Diptera, Tephritidae)

BACKGROUND

Gut microbiota mediating insect-plant interactions have many manifestations, either by provisioning missing nutrients, or by overcoming plant defensive reactions. However, the mechanism by which gut microbiota empower insects to survive by overcoming a variety of plant secondary metabolites remains largely unknown. Bactrocera minax larvae develop in immature citrus fruits, which present numerous phenolic compounds that challenge the larvae. To explore the role of gut microbes in host use and adaptability, we uncovered the mechanisms of phenol degradation by gut microbes using metagenomic and metatranscriptomic analyses, and verified the degradation ability of isolated and cultured bacteria. Research on this subject can help develop potential strain for the environmental friendly pest management operations.

RESULTS

We demonstrated the ability of gut microbes in B. minax larvae to degrade phenols in unripe citrus. After antibiotic treatment, coniferyl alcohol and coumaric aldehyde significantly reduced the survival rate, body length and body weight of the larvae. The metagenomic and metatranscriptomic analyses in B. minax provided evidence for the presence of genes in bacteria and the related pathway involved in phenol degradation. Among them, Enterococcus faecalis and Serratia marcescens, isolated from the gut of B. minax larvae, played critical roles in phenol degradation. Furthermore, supplementation of E. faecalis and S. marcescens in artificial diets containing coniferyl alcohol and coumaric aldehyde increased the survival rate of larvae.

CONCLUSION

In summary, our results provided the first comprehensive analysis of gut bacterial communities by high-throughput sequencing and elucidated the role of bacteria in phenol degradation in B. minax, which shed light on the mechanism underlying specialist insect adaption to host secondary metabolites via gut bacteria. © 2024 Society of Chemical Industry.

Tsetse Flies Infected with Trypanosomes in Three Active Human African Trypanosomiasis Foci of the Republic of Congo

INTRODUCTION

Human African trypanosomiasis (HAT) is a neglected tropical disease still endemic in the Republic of Congo. Despite the continuous detection of HAT cases in the country, there is still not enough data on trypanosome infections in tsetse flies, trypanosome species and tsetse flies' species distribution in endemic foci. The present study was intended to fill this gap and improve understanding of trypanosome circulation in three active foci in the centre and south of Congo.

METHODS

Pyramid traps were set in various places in villages to collect tsetse flies both during the rainy and dry seasons. Once collected, tsetse flies were identified using morphological keys. DNA extracted from flies was processed by PCR for species identification and for detection of trypanosome presence. A second PCR was run for different trypanosome species identification.

RESULTS

A total of 1291 tsetse flies were collected. The average apparent density of flies per day was 0.043 in Mpouya, 0.73 in Ngabé and 2.79 in Loudima. Glossina fuscipes quazensis was the predominant tsetse fly collected in Ngabé and Mpouya, while Glossina palpalis palpalis was the only tsetse fly found in Loudima. A total of 224 (17.7%) flies were detected infected by trypanosomes; 100 (7.91%) by Trypanosoma congolense savannah, 22 (1.74%) by Trypanosoma congolense forest, 15 (1.19%) by Trypanosoma vivax, 83 (6.56%) by Trypanosoma brucei (s.l.) and 2 (0.16%) undetermined species. No T Trypanosoma brucei gambiense was found. A total of 57 co-infections between T. brucei (s.l.) and T. congolense savannah or T. brucei (s.l.) and T. congolense forest were found only in G. p. palpalis. Loudima recorded the highest number of infected tsetse flies.

CONCLUSION

The study provided updated information on the distribution of tsetse fly populations as well as on Trypanosoma species circulating in tsetse flies in the different active HAT foci in Congo. These data suggested a high risk of potential transmission of animal trypanosomes in these foci, thus stressing the need for active surveillance in this endemic area.

Overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors

This article presents an overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors. It first briefly summarises some of the disease-causing pathogens vectored by insects and emphasises the need for innovative control methods to counter the threat of resistance by both the vector insect to pesticides and the pathogens to therapeutic drugs. Subsequently, the state of art of paratransgenesis is described, which is a particularly ingenious method currently under development in many important vector insects that could provide an additional powerful tool for use in integrated pest control programmes. The requirements and recent advances of the paratransgenesis technique are detailed and an overview is given of the microorganisms selected for genetic modification, the effector molecules to be expressed and the environmental spread of the transgenic bacteria into wild insect populations. The results of experimental models of paratransgenesis developed with triatomines, mosquitoes, sandflies and tsetse flies are analysed. Finally, the regulatory and safety rules to be satisfied for the successful environmental release of the genetically engineered organisms produced in paratransgenesis are considered.

Apparent density, trypanosome infection rates and host preference of tsetse flies in the sleeping sickness endemic focus of northwestern Uganda

Background

African trypanosomiasis, caused by protozoa of the genus Trypanosoma and transmitted by the tsetse fly, is a serious parasitic disease of humans and animals. Reliable data on the vector distribution, feeding preference and the trypanosome species they carry is pertinent to planning sustainable control strategies.

Methodology

We deployed 109 biconical traps in 10 villages in two districts of northwestern Uganda to obtain information on the apparent density, trypanosome infection status and blood meal sources of tsetse flies. A subset (272) of the collected samples was analyzed for detection of trypanosomes species and sub-species using a nested PCR protocol based on primers amplifying the Internal Transcribed Spacer (ITS) region of ribosomal DNA. 34 blood-engorged adult tsetse midguts were analyzed for blood meal sources by sequencing of the mitochondrial cytochrome c oxidase 1 (COI) and cytochrome b (cytb) genes.

Results

We captured a total of 622 Glossina fuscipes fuscipes tsetse flies (269 males and 353 females) in the two districts with apparent density (AD) ranging from 0.6 to 3.7 flies/trap/day (FTD). 10.7% (29/272) of the flies were infected with one or more trypanosome species. Infection rate was not significantly associated with district of origin (Generalized linear model (GLM), χ² = 0.018, P = 0.895, df = 1, n = 272) and sex of the fly (χ2 = 1.723, P = 0.189, df = 1, n = 272). However, trypanosome infection was highly significantly associated with the fly’s age based on wing fray category (χ² = 22.374, P < 0.001, df = 1, n = 272), being higher among the very old than the young tsetse. Nested PCR revealed several species of trypanosomes: T. vivax (6.62%), T. congolense (2.57%), T. brucei and T. simiae each at 0.73%. Blood meal analyses revealed five principal vertebrate hosts, namely, cattle (Bos taurus), humans (Homo sapiens), Nile monitor lizard (Varanus niloticus), African mud turtle (Pelusios chapini) and the African Savanna elephant (Loxodonta africana).

Conclusion

We found an infection rate of 10.8% in the tsetse sampled, with all infections attributed to trypanosome species that are causative agents for AAT. However, more verification of this finding using large-scale passive and active screening of human and tsetse samples should be done. Cattle and humans appear to be the most important tsetse hosts in the region and should be considered in the design of control interventions.

Review on trypanosomiasis and their prevalence in some country on the Red Sea

Trypanosomiasis is a protozoan infection affecting both human and animals in almost all parts of the world. It can affect a very large range of domestic and wild hosts including camelids, equines, cattle, buffaloes, sheep, goats, pigs, dogs and other carnivores, deer, gazelles and elephants. This review paper was designed to address the effect of this economically important disease in countries on the Red Sea, especially in Egypt, Sudan, Somalia, and Saudi Arabia during the period 2010 to 2020. The prevalence of trypanosomiasis is different between these countries due to different types of diagnostic methods (Giemsa-stained blood smears, Hematocrit centrifugation, Serological test, and molecular analysis PCR) used and differential distribution of vector (Tse tse) flies. In current review, retrospective studies of published literature on distribution and prevalence of Trypanosoma evansi infection in the Red Sea Countries was conducted [Google Scholar and PubMed were used to retrieve the published literature from 2000-2020. A total of 77 published articles met the eligibility criteria and were reviewed. A total of 16 reports have been reported on the prevalence and distribution of Trypnosoma evansi infection in the Red Sea Countries have been from 2010-2020]. According to the published literature, we can say that trypanosomiasis in camels are more prevalent in Sudan than in other countries, followed by 17% and 51.78% in both clinical and non-clinical cases. Hence, the reliable diagnostic tests should be used for rapid treatment or control of the disease as if not treated appropriately in early-stage, can lead to death of the camels.

Prevalence and associated risk factors of bovine trypanosomosis in tsetse suppression and non-suppression areas of South Omo Zone, Southwestern Ethiopia

A cross-sectional study aimed to elucidate the prevalence of bovine trypanosomosis and its potential risk factors was conducted in tsetse suppression and non-suppression areas of South Omo Zone, Southern Ethiopia from November 2018- May 2019. A total of 1284 blood samples from local zebu cattle (642 each in dry and wet season) were examined by using buffy coat technique and thin blood smear method. The overall prevalence was 11.05 % with 14.33 % in dry and 7.78 % in wet season. According to multiple logistic regression analysis of tsetse suppression areas, higher prevalence in female than male (OR = 0.48, 95 % CI: 0.27, 0.83), in poor (OR = 3.25, 95 % CI: 1.26, 11.09) and medium (OR = 2.07, 95 % CI: 0.74, 7.37) than good body conditioned animals was recorded. Moreover, tethered animals (OR = 2.07, 95 % CI: 1.06, 3.92) were more likely to be infected than communal grazers and also higher prevalence in dry season than wet season (OR = 0.52, 95 % CI: 0.30, 0.87). Similarly, in tsetse non-suppression areas, higher prevalence in female than male (OR = 0.48, 95 % CI: 0.27, 0.85) and in wet season (OR = 0.41, 95 % CI: 0.23, 0.7) than dry season was recorded. Trypanosoma congolense and Trypanosoma vivax were found in cattle with the former more prevalent in both areas. Overall pooled mean packed cell volume (PCV) of parasitaemic animals (23.57 ± 3.13) was significantly lower than aparasitaemic animals (27.80 ± 4.95). Similarly, parasitaemic animals from tsetse suppression areas and tsetse non-suppression areas had significantly lower mean PCV than their aparasitaemic counterparts. Mean PCV of T. congolense (23.59 ± 3.22) infected animals was not different (P > 0.05) from T. vivax infected animals (23.26 ± 3.31). It was also indicated that the probability of anaemic animals to be parasitaemic was significantly higher (P < 0.05) than non-anaemic animals in both areas. In conclusion, the prevalence of trypanosomosis revealed its endemicity which bottlenecked the livestock production and productivity in the study area despite of tsetse suppression activities. Therefore, integrated parasite and vector control approach should be undertaken to curve the disease.

Trypanosome prevalence in pigs and tsetse flies from selected areas of Jomoro district of the western region of Ghana

Detection of trypanosomes in tsetse or domestic livestock is a basic requirement for epidemiological studies as well as for planning and implementing control measures against tsetse and trypanosomiasis. This epidemiological study aimed at assessing the prevalence of trypanosomes in pigs and tsetse flies in the Jomoro district of the western region of Ghana using molecular techniques. Blood was collected from pigs and biconical traps were used to collect tsetse flies. DNA was isolated from 300 pig blood samples and 300 flies for trypanosome detection and identification by PCR. Packed Cell Volume (PCV) of blood samples from 300 pigs was measured using a micro-haematocrit reader. Glossina palpalis palpalis was the only tsetse species found in the area with fly apparent density of 18.4 fly/trap/day. An overall prevalence of trypanosomes in the study area was 4.3% and 0.8% in pigs and tsetse flies respectively. Mixed infection with Trypanosoma (T.) congolense forest and T. vivax was most prevalent 46.2% followed by single infection of T. vivax 15.4%, T. congolense and a mixed infection of T. congolense, T. vivax and T. brucei sl. were the least with 7.7% each. There were no significant differences in trypanosome prevalence among different age groups and between both sexes of the studied pigs (p > 0.05). Trypanosome prevalence was lower in healthy looking 1.9% than the sick looking 20%, pigs (P < 0.05). Mean PCV of parasitaemic pigs 29.3% was significantly lower than that of aparasitaemic pigs 37.8%. Two out of the five species-specific primers used could not identify any trypanosome species from the total blood samples examined. This could possibly mean that those species are not found in the present study area. These results provide useful background information for further study and justification to extend tsetse control to the Jomoro district.

Role of plants in the transmission of Asaia sp., which potentially inhibit the Plasmodium sporogenic cycle in Anopheles mosquitoes

Biological control against malaria and its transmission is currently a considerable challenge. Plant-associated bacteria of the genus Asaia are frequently found in nectarivorous arthropods, they thought to have a natural indirect action on the development of plasmodium in mosquitoes. However, virtually nothing is known about its natural cycle. Here, we show the role of nectar-producing plants in the hosting and dissemination of Asaia. We isolated Asaia strains from wild mosquitoes and flowers in Senegal and demonstrated the transmission of the bacteria from infected mosquitoes to sterile flowers and then to 26.6% of noninfected mosquitoes through nectar feeding. Thus, nectar-producing plants may naturally acquire Asaia and then colonize Anopheles mosquitoes through food-borne contamination. Finally, Asaia may play an indirect role in the reduction in the vectorial capacity of Anopheles mosquitoes in a natural environment (due to Plasmodium-antagonistic capacities of Asaia) and be used in the development of tools for Asaia-based paratransgenetic malaria control.

Screening for Small Molecule Modulators of Trypanosoma brucei Hsp70 Chaperone Activity Based upon Alcyonarian Coral-Derived Natural Products

The Trypanosoma brucei Hsp70/J-protein machinery plays an essential role in survival, differentiation, and pathogenesis of the protozoan parasite, and is an emerging target against African Trypanosomiasis. This study evaluated a set of small molecules, inspired by the malonganenones and nuttingins, as modulators of the chaperone activity of the cytosolic heat inducible T. brucei Hsp70 and constitutive TbHsp70.4 proteins. The compounds were assessed for cytotoxicity on both the bloodstream form of T. b. brucei parasites and a mammalian cell line. The compounds were then investigated for their modulatory effect on the aggregation suppression and ATPase activities of the TbHsp70 proteins. A structure-activity relationship for the malonganenone-class of alkaloids is proposed based upon these results.

Molecular identification of Wolbachia and Sodalis glossinidius in the midgut of Glossina fuscipes quanzensis from the Democratic Republic of Congo

During the last 30 years, investigations on the microbiome of different tsetse species have generated substantial data on the bacterial flora of these cyclical vectors of African trypanosomes, with the overarching goal of improving the control of trypanosomiases. It is in this context that the presence of Wolbachia and Sodalis glossinidius was studied in wild populations of Glossina fuscipes quanzensis from the Democratic Republic of Congo. Tsetse flies were captured with pyramidal traps. Of the 700 Glossina f. quanzensis captured, 360 were dissected and their midguts collected and analyzed. Sodalis glossinidius and Wolbachia were identified by PCR. The Wolbachia-positive samples were genetically characterized with five molecular markers. PCR revealed 84.78% and 15.55% midguts infected by Wolbachia and S. glossinidius, respectively. The infection rates varied according to capture sites. Of the five molecular markers used to characterize Wolbachia, only the fructose bis-phosphate aldolase gene was amplified for about 60% of midguts previously found with Wolbachia infections. The sequencing results confirmed the presence of Wolbachia and revealed the presence of S. glossinidius in the midgut of Glossina f. quanzensis. A low level of midguts were naturally co-infected by both bacteria. The data generated in this study open a framework for investigations aimed at understanding the contribution of these symbiotic microorganisms to the vectorial competence of Glossina fuscipes quanzensis.

Combining paratransgenesis with SIT: impact of ionizing radiation on the DNA copy number of Sodalis glossinidius in tsetse flies

Background

Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of the causative agents of African Trypanosomosis, which has been identified as a neglected tropical disease in both humans and animals in many regions of sub-Saharan Africa. The sterile insect technique (SIT) has shown to be a powerful method to manage tsetse fly populations when used in the frame of an area-wide integrated pest management (AW-IPM) program. To date, the release of sterile males to manage tsetse fly populations has only been implemented in areas to reduce transmission of animal African Trypanosomosis (AAT). The implementation of the SIT in areas with Human African Trypanosomosis (HAT) would require additional measures to eliminate the potential risk associated with the release of sterile males that require blood meals to survive and hence, might contribute to disease transmission. Paratransgenesis offers the potential to develop tsetse flies that are refractory to trypanosome infection by modifying their associated bacteria (Sodalis glossinidius) here after referred to as Sodalis. Here we assessed the feasibility of combining the paratransgenesis approach with SIT by analyzing the impact of ionizing radiation on the copy number of Sodalis and the vectorial capacity of sterilized tsetse males.

Results

Adult Glossina morsitans morsitans that emerged from puparia irradiated on day 22 post larviposition did not show a significant decline in Sodalis copy number as compared with non-irradiated flies. Conversely, the Sodalis copy number was significantly reduced in adults that emerged from puparia irradiated on day 29 post larviposition and in adults irradiated on day 7 post emergence. Moreover, irradiating 22-day old puparia reduced the copy number of Wolbachia and Wigglesworthia in emerged adults as compared with non-irradiated controls, but the radiation treatment had no significant impact on the vectorial competence of the flies.

Conclusion

Although the radiation treatment significantly reduced the copy number of some tsetse fly symbionts, the copy number of Sodalis recovered with time in flies irradiated as 22-day old puparia. This recovery offers the opportunity to combine a paratransgenesis approach – using modified Sodalis to produce males refractory to trypanosome infection – with the release of sterile males to minimize the risk of disease transmission, especially in HAT endemic areas. Moreover, irradiation did not increase the vector competence of the flies for trypanosomes.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1283-8) contains supplementary material, which is available to authorized users.

Diversity and phylogenetic relationships of Glossina populations in Nigeria and the Cameroonian border region

Background

Tsetse flies are vectors of trypanosomes, parasites that cause devastating disease in humans and livestock. In the course of vector control programmes it is necessary to know about the Glossina species present in the study area, the population dynamics and the genetic exchange between tsetse fly populations.

Results

To achieve an overview of the tsetse fly diversity in Nigeria and at the Nigeria-Cameroon border, tsetse flies were trapped and collected between February and March 2014 and December 2016. Species diversity was determined morphologically and by analysis of Cytochrome C Oxidase SU1 (COI) gene sequences. Internal transcribed spacer-1 (ITS-1) sequences were compared to analyse variations within populations. The most dominant species were G. m. submorsitans, G. tachinoides and G. p. palpalis. In Yankari Game Reserve and Kainji Lake National Park, G. submorsitans and G. tachinoides were most frequent, whereas in Old Oyo National Park and Ijah Gwari G. p. palpalis was the dominant species. Interestingly, four unidentified species were recorded during the survey, for which no information on COI or ITS-1 sequences exists. G. p. palpalis populations showed a segregation in two clusters along the Cameroon-Nigerian border.

Conclusions

The improved understanding of the tsetse populations in Nigeria will support decisions on the scale in which vector control is likely to be more effective. In order to understand in more detail how isolated these populations are, it is recommended that further studies on gene flow be carried out using other markers, including microsatellites.

Genetic Differentiation of Glossina pallidipes Tsetse Flies in Southern Kenya

The tsetse fly Glossina pallidipes, the major vector of the parasite that causes animal African trypanosomiasis in Kenya, has been subject to intense control measures with only limited success. The G. pallidipes population dynamics and dispersal patterns that underlie limited success in vector control campaigns remain unresolved, and knowledge on genetic connectivity can provide insights, and thereby improve control and monitoring efforts. We therefore investigated the population structure and estimated migration and demographic parameters in G. pallidipes using genotypic data from 11 microsatellite loci scored in 250 tsetse flies collected from eight localities in Kenya. Clustering analysis identified two genetically distinct eastern and western clusters (mean between-cluster F ST = 0.202) separated by the Great Rift Valley. We also found evidence of admixture and migration between the eastern and western clusters, isolation by distance, and a widespread signal of inbreeding. We detected differences in population dynamics and dispersal patterns between the western and eastern clusters. These included lower genetic diversity (allelic richness; 7.48 versus 10.99), higher relatedness (percent related individuals; 21.4% versus 9.1%), and greater genetic differentiation (mean within-cluster F ST; 0.183 versus 0.018) in the western than the eastern cluster. Findings are consistent with the presence of smaller, less well-connected populations in Western relative to eastern Kenya. These data suggest that recent anthropogenic influences such as land use changes and vector control programs have influenced population dynamics in G. pallidipes in Kenya, and that vector control efforts should include some region-specific strategies to effectively control this disease vector.

Culturable epiphytic bacteria isolated from Teleogryllus occipitalus crickets metabolize insecticides

The development of insecticide resistance is attributed to evolutionary changes in pest insect genomes, such as alteration of drug target sites, upregulation of degrading enzymes, and enhancement of drug excretion. Beyond these well-known mechanisms, symbiotic bacteria may confer insecticide resistance to host crickets. The current study was designed to screen all possible culturable bacterial groups found living in and on the bodies of Teleogryllus occipitalis crickets. We recovered 263 visible bacterial colonies and cultured them individually. After identifying the colonies based on morphology and phylogenetic analysis, we shortlisted 55 bacterial strains belonging to 28 genera. Of these 55 bacterial strains, 18 degraded at least 50% of the original amount of 400 mg/L chlorpyrifos (CP) after 24 hr of coculture. Six of these strains degraded more than 70% of the original amount of 400 mg/L CP. Three strains had antagonistic effects on Bacillus thuringiensis growth. Additionally, the ability of the isolates to degrade glyphosate, phoxim, and esfenvalerate was assessed. We also detected extracellular hydrolase enzyme activities in these isolates. We propose that epiphytic bacterial strains play multiple roles in cricket biology, one of which contributes to chemical and biological pesticide resistance.

Tsetse fly evolution, genetics and the trypanosomiases - A review

This reviews work published since 2007. Relative efforts devoted to the agents of African trypanosomiasis and their tsetse fly vectors are given by the numbers of PubMed accessions. In the last 10 years PubMed citations number 3457 for Trypanosoma brucei and 769 for Glossina. The development of simple sequence repeats and single nucleotide polymorphisms afford much higher resolution of Glossina and Trypanosoma population structures than heretofore. Even greater resolution is offered by partial and whole genome sequencing. Reproduction in T. brucei sensu lato is principally clonal although genetic recombination in tsetse salivary glands has been demonstrated in T. b. brucei and T. b. rhodesiense but not in T. b. gambiense. In the past decade most genetic attention was given to the chief human African trypanosomiasis vectors in subgenus Nemorhina e.g., Glossina f. fuscipes, G. p. palpalis, and G. p. gambiense. The chief interest in Nemorhina population genetics seemed to be finding vector populations sufficiently isolated to enable efficient and long-lasting suppression. To this end estimates were made of gene flow, derived from F_ST and its analogues, and Ne, the size of a hypothetical population equivalent to that under study. Genetic drift was greater, gene flow and Ne typically lesser in savannah inhabiting tsetse (subgenus Glossina) than in riverine forms (Nemorhina). Population stabilities were examined by sequential sampling and genotypic analysis of nuclear and mitochondrial genomes in both groups and found to be stable. Gene frequencies estimated in sequential samplings differed by drift and allowed estimates of effective population numbers that were greater for Nemorhina spp than Glossina spp. Prospects are examined of genetic methods of vector control. The tsetse long generation time (c. 50 d) is a major contraindication to any suggested genetic method of tsetse population manipulation. Ecological and modelling research convincingly show that conventional methods of targeted insecticide applications and traps/targets can achieve cost-effective reduction in tsetse densities.

Temporal genetic differentiation in Glossina pallidipes tsetse fly populations in Kenya

BACKGROUND

Glossina pallidipes is a major vector of both Human and Animal African Trypanosomiasis (HAT and AAT) in Kenya. The disease imposes economic burden on endemic regions in Kenya, including south-western Kenya, which has undergone intense but unsuccessful tsetse fly control measures. We genotyped 387 G. pallidipes flies at 13 microsatellite markers to evaluate levels of temporal genetic variation in two regions that have been subjected to intensive eradication campaigns from the 1960s to the 1980s. One of the regions, Nguruman Escarpment, has been subject to habitat alteration due to human activities, while the other, Ruma National Park, has not. In addition, Nguruman Escarpment is impacted by the movement of grazing animals into the area from neighboring regions during the drought season. We collected our samples from three geographically close sampling sites for each of the two regions. Samples were collected between the years 2003 and 2015, spanning ~96 tsetse fly generations.

RESULTS

We established that allelic richness averaged 3.49 and 3.63, and temporal Ne estimates averaged 594 in Nguruman Escarpment and 1120 in Ruma National Park. This suggests that genetic diversity is similar to what was found in previous studies of G. pallidipes in Uganda and Kenya, implying that we could not detect a reduction in genetic diversity following the extensive control efforts during the 1960s to the 1980s. However, we did find differences in temporal patterns of genetic variation between the two regions, indicated by clustering analysis, pairwise FST, and Fisher's exact tests for changes in allele and genotype frequencies. In Nguruman Escarpment, findings indicated differentiation among samples collected in different years, and evidence of local genetic bottlenecks in two locations previous to 2003, and between 2009 and 2015. In contrast, there was no consistent evidence of differentiation among samples collected in different years, and no evidence of local genetic bottlenecks in Ruma National Park.

CONCLUSION

Our findings suggest that, despite extensive control measures especially between the 1960s and the 1980s, tsetse flies in these regions persist with levels of genetic diversity similar to that found in populations that did not experience extensive control measures. Our findings also indicate temporal genetic differentiation in Nguruman Escarpment detected at a scale of > 80 generations, and no similar temporal differentiation in Ruma National Park. The different level of temporal differentiation between the two regions indicates that genetic drift is stronger in Nugruman Escarpment, for as-yet unknown reasons, which may include differences in land management. This suggests land management may have an impact on G. pallidipes population genetics, and reinforces the importance of long term monitoring of vector populations in estimates of parameters needed to model and plan effective species-specific control measures.

Hsp70/J-protein machinery from Glossina morsitans morsitans, vector of African trypanosomiasis

Tsetse flies (Glossina spp.) are the sole vectors of the protozoan parasites of the genus Trypanosoma, the causative agents of African Trypanosomiasis. Species of Glossina differ in vector competence and Glossina morsitans morsitans is associated with transmission of Trypanosoma brucei rhodesiense, which causes an acute and often fatal form of African Trypanosomiasis. Heat shock proteins are evolutionarily conserved proteins that play critical roles in proteostasis. The activity of heat shock protein 70 (Hsp70) is regulated by interactions with its J-protein (Hsp40) co-chaperones. Inhibition of these interactions are emerging as potential therapeutic targets. The assembly and annotation of the G. m. morsitans genome provided a platform to identify and characterize the Hsp70s and J-proteins, and carry out an evolutionary comparison to its well-studied eukaryotic counterparts, Drosophila melanogaster and Homo sapiens, as well as Stomoxys calcitrans, a comparator species. In our study, we identified 9 putative Hsp70 proteins and 37 putative J-proteins in G. m. morsitans. Phylogenetic analyses revealed three evolutionarily distinct groups of Hsp70s, with a closer relationship to orthologues from its blood-feeding dipteran relative Stomoxys calcitrans. G. m. morsitans also lacked the high number of heat inducible Hsp70s found in D. melanogaster. The potential localisations, functions, domain organisations and Hsp70/J-protein partnerships were also identified. A greater understanding of the heat shock 70 (Hsp70) and J-protein (Hsp40) families in G. m. morsitans could enhance our understanding of the cell biology of the tsetse fly.

Patterns of tsetse abundance and trypanosome infection rates among habitats of surveyed villages in Maasai steppe of northern Tanzania

Background

Changes of land cover modify the characteristics of habitat, host-vector interaction and consequently infection rates of disease causing agents. In this paper, we report variations in tsetse distribution patterns, abundance and infection rates in relation to habitat types and age in the Maasai Steppe of northern Tanzania. In Africa, Tsetse-transmitted trypanosomiasis negatively impacted human life where about 40 million people are at risk of contracting the disease with dramatic socio-economical consequences, for instance, loss of livestock, animal productivity, and manpower.

Methods

We trapped tsetse flies in dry and wet seasons between October 2014 and May 2015 in selected habitats across four villages: Emboreet, Loiborsireet, Kimotorok and Oltukai adjacent to protected areas. Data collected include number and species of tsetse flies caught in baited traps, PCR identification of trypanosome species and extraction of monitored Normalized Difference Vegetation Index (NDVI) data from Moderate Resolution Imaging Spectrometer (MODIS).

Results

Our findings demonstrate the variation of tsetse fly species abundance and infection rates among habitats in surveyed villages in relation to NDVI and host abundance. Results have shown higher tsetse fly abundance in Acacia-swampy ecotone and riverine habitats for Emboreet and other villages, respectively. Tsetse abundance was inconsistent among habitats in different villages. Emboreet was highly infested with Glossina swynnertoni (68%) in ecotone and swampy habitats followed by G. morsitans (28%) and G. pallidipes (4%) in riverine habitat. In the remaining villages, the dominant tsetse fly species by 95% was G. pallidipes in all habitats. Trypanosoma vivax was the most prevalent species in all infected flies (95%) with few observations of co-infections (with T. congolense or T. brucei).

Conclusions

The findings of this study provide a framework to mapping hotspots of tsetse infestation and trypanosomiasis infection and enhance the communities to plan for effective control of trypanosomiasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-017-0340-0) contains supplementary material, which is available to authorized users.

Genetic diversity of Glossina fuscipes fuscipes along the shores of Lake Victoria in Tanzania and Kenya: implications for management

BACKGROUND

Tsetse flies (Diptera: Glossinidae) are sole vectors for trypanosomiasis, which affect human health and livestock productivity in Africa. Little is known about the genetic diversity of Glossina fuscipes fuscipes, which is an important species in Tanzania and Kenya. The main objective of the study was to provide baseline data to determine the genetic variability and divergence of G. f. fuscipes in the Lake Victoria basin of Tanzania and Kenya in order to guide future vector control efforts in the region.

FINDINGS

Two hundred and seventy five G. f. fuscipes from 8 sites along the shores of Lake Victoria were screened for genetic polymorphisms at 19 microsatellite loci. Samples were collected from two sites in Kenya and six sites in Tanzania. Four of the Tanzanian sites were located in the Rorya district, on the eastern shores of Lake Victoria, while the other two sites were from Ukerewe and Bukoba districts from the southern and western Lake Victoria shores, respectively. Four genetically distinct allopatric clusters were revealed by microsatellite analysis, which sorted the sampling sites according to geography, with sites separated by as little as ~65 km belonging to distinct genetic clusters, while samples located within ~35 km from each other group in the same cluster.

CONCLUSION

Our results suggest that there is ongoing genetic admixture within sampling sites located ~35 km from each other, while sites located ~65 km apart are genetically isolated from each other. Similar patterns emerged from a parallel study on G. f. fuscipes analyzed from the Lake Victoria Uganda shores. From a control perspective these results suggest that for sites within the same genetic cluster, control efforts should be carried out in a coordinated fashion in order to avoid re-invasions. Future work should focus on better quantifying the extent and spatial patterns of the observed genetic discontinuities of the G. f. fuscipes populations along the Tanzanian shores. This will aid in their control by providing guidelines on the geographical extent of the area to be treated at the same time.

Determinants of Human African Trypanosomiasis Elimination via Paratransgenesis

Human African trypanosomiasis (HAT), transmitted by tsetse flies, has historically infected hundreds of thousands of individuals annually in sub-Saharan Africa. Over the last decade, concerted control efforts have reduced reported cases to below 10,000 annually, bringing complete elimination within reach. A potential technology to eliminate HAT involves rendering the flies resistant to trypanosome infection. This approach can be achieved through the introduction of transgenic Sodalis symbiotic bacteria that have been modified to produce a trypanocide, and propagated via Wolbachia symbionts, which confer a reproductive advantage to the paratransgenic tsetse. However, the population dynamics of these symbionts within tsetse flies have not yet been evaluated. Specifically, the key factors that determine the effectiveness of paratransgenesis have yet to be quantified. To identify the impact of these determinants on T.b. gambiense and T.b. rhodesiense transmission, we developed a mathematical model of trypanosome transmission that incorporates tsetse and symbiont population dynamics. We found that fecundity and mortality penalties associated with Wolbachia or recombinant Sodalis colonization, probabilities of vertical transmission, and tsetse migration rates are fundamental to the feasibility of HAT elimination. For example, we determined that HAT elimination could be sustained over 25 years when Wolbachia colonization minimally impacted fecundity or mortality, and when the probability of recombinant Sodalis vertical transmission exceeded 99.9%. We also found that for a narrow range of recombinant Sodalis vertical transmission probability (99.9–90.6% for T.b. gambiense and 99.9–85.8% for T.b. rhodesiense), cumulative HAT incidence was reduced between 30% and 1% for T.b. gambiense and between 21% and 3% for T.b. rhodesiense, although elimination was not predicted. Our findings indicate that fitness and mortality penalties associated with paratransgenic symbionts, as well as tsetse migration rates, are instrumental to HAT elimination, and should be a key focus in the development of paratransgenic symbionts.

Human African trypanosomiasis, also known as sleeping sickness, is a parasitic disease transmitted by tsetse flies in sub-Saharan Africa. The disease leads to death if not treated. Recent control efforts have reduced the burden of disease from hundreds of thousands of cases per year to fewer than 10,000 cases annually. A potential strategy to completely eliminate sleeping sickness involves genetically modifying the symbiotic bacteria, which are vertically transmitted from mother to offspring, in order to investigate which factors are most important for the successful elimination of human African trypanosomiasis. We found that sleeping sickness was eliminated only when the genetically modified symbionts were successfully transmitted from mother to offspring, and did not reduce fertility or increase mortality in tsetse. We additionally identified tsetse migration rate as an important factor for sleeping sickness elimination.

Characterization and pharmacological analysis of two adipokinetic hormone receptor variants of the tsetse fly, Glossina morsitans morsitans

Adipokinetic hormones (AKH) are well known regulators of energy metabolism in insects. These neuropeptides are produced in the corpora cardiaca and perform their hormonal function by interacting with specific G protein-coupled receptors (GPCRs) at the cell membranes of target tissues, mainly the fat body. Here, we investigated the sequences, spatial and temporal distributions, and pharmacology of AKH neuropeptides and receptors in the tsetse fly, Glossina morsitans morsitans. The open reading frames of two splice variants of the Glomo-akh receptor (Glomo-akhr) gene and of the AKH neuropeptide encoding genes, gmmhrth and gmmakh, were cloned. Both tsetse AKHR isoforms show strong sequence conservation when compared to other insect AKHRs. Glomo-AKH prepropeptides also have the typical architecture of AKH precursors. In an in vitro Ca(2+) mobilization assay, Glomo-AKH neuropeptides activated each receptor isoform up to nanomolar concentrations. We identified structural features of tsetse AKH neuropeptides essential for receptor activation in vitro. Gene expression profiles suggest a function for AKH signaling in regulating Glossina energy metabolism, where AKH peptides are released from the corpora cardiaca and activate receptors mainly expressed in the fat body. This analysis of the ligand-receptor coupling, expression, and pharmacology of the two Glomo-AKHR variants facilitates further elucidation of the function of AKH in G. m. morsitans.

Genome-Wide Comparative Analysis of Chemosensory Gene Families in Five Tsetse Fly Species

For decades, odour-baited traps have been used for control of tsetse flies (Diptera; Glossinidae), vectors of African trypanosomes. However, differential responses to known attractants have been reported in different Glossina species, hindering establishment of a universal vector control tool. Availability of full genome sequences of five Glossina species offers an opportunity to compare their chemosensory repertoire and enhance our understanding of their biology in relation to chemosensation. Here, we identified and annotated the major chemosensory gene families in Glossina. We identified a total of 118, 115, 124, and 123 chemosensory genes in Glossina austeni, G. brevipalpis, G. f. fuscipes, G. pallidipes, respectively, relative to 127 reported in G. m. morsitans. Our results show that tsetse fly genomes have fewer chemosensory genes when compared to other dipterans such as Musca domestica (n>393), Drosophila melanogaster (n = 246) and Anopheles gambiae (n>247). We also found that Glossina chemosensory genes are dispersed across distantly located scaffolds in their respective genomes, in contrast to other insects like D. melanogaster whose genes occur in clusters. Further, Glossina appears to be devoid of sugar receptors and to have expanded CO₂ associated receptors, potentially reflecting Glossina's obligate hematophagy and the need to detect hosts that may be out of sight. We also identified, in all species, homologs of Ir84a; a Drosophila-specific ionotropic receptor that promotes male courtship suggesting that this is a conserved trait in tsetse flies. Notably, our selection analysis revealed that a total of four gene loci (Gr21a, GluRIIA, Gr28b, and Obp83a) were under positive selection, which confers fitness advantage to species. These findings provide a platform for studies to further define the language of communication of tsetse with their environment, and influence development of novel approaches for control.

Chemical sensing is crucial to survival of tsetse flies; the sole cyclical vectors of African trypanosomes that cause the neglected zoonotic tropical disease sleeping sickness in humans. For many years, vector control has been used to mitigate trypanosome infections among rural populations of sub-Saharan Africa. Nevertheless, development of an all-inclusive strategy to control tsetse flies using odour-baited traps has been limited by disparate responses to the odors exhibited by various tsetse species. In this study, proteins that are putatively involved in chemical sensing were identified and compared among five tsetse species and their close relatives with an aim of enhancing our knowledge on tsetse olfaction. Our findings suggest that the chemosensory genes are conserved across tsetse fly species despite their documented differential responses in odours. We found no species-specific sequence variations among the five species to suggest that differential response to odours is due to loss or gain of genes. It could therefore be hypothesized that the observed differences emerge during the downstream processing of odour molecules involving post translational modification of the chemosensory proteins. We thus recommend functional studies on the identified proteins to determine their roles and molecular interactions.

Trypanosoma Infection Rates in Glossina Species in Mtito Andei Division, Makueni County, Kenya

African Animal Trypanosomiasis (AAT) transmitted cyclically by tsetse fly (Glossina spp.) is a major obstacle to livestock production in the tropical parts of Africa. The objective of this study was to determine the infection rates of trypanosomes in Glossina species in Mtito Andei Division, Makueni County, Kenya. Tsetse fly species, G. longipennis and G. pallidipes, were trapped and DNA was isolated from their dissected internal organs (proboscis, salivary glands, and midguts). The DNA was then subjected to a nested PCR assay using internal transcribed spacer primers and individual trypanosome species were identified following agarose gel electrophoresis. Out of the 117 flies trapped in the area 39 (33.3%) were teneral while 78 (67%) were nonteneral. G. pallidipes constituted the largest percentage of 58% while G. longipennis were 42%. The overall trypanosomes infection rate in all nonteneral Glossina spp. was 11.53% with G. longipennis recording the highest infection rate of 23.08% while G. pallidipes had an infection rate of 5.77%. T. vivax was the most infectious (10.26%) compared to T. congolense (1.28%). Mean apparent densities were strongly positively correlated with infection rates (r = 0.95) confirming the importance of this parameter as an indicator of AAT transmission risk.

Heterogeneity in the prevalence and intensity of bovine trypanosomiasis in the districts of Amuru and Nwoya, Northern Uganda

Background

Livestock trypanosomiasis, transmitted mainly by tsetse flies of the genus Glossina is a major constraint to livestock health and productivity in the sub-Saharan Africa. Knowledge of the prevalence and intensity of trypanosomiasis is important in understanding the epidemiology of the disease. The objectives of this study were to (a) assess the prevalence and intensity of trypanosome infections in cattle, and (b) to investigate the reasons for the heterogeneity of the disease in the tsetse infested districts of Amuru and Nwoya, northern Uganda.

Methods

A cross-sectional study was conducted from September, 2011 to January, 2012. Blood samples were collected from 816 cattle following jugular vein puncture, and screened for trypanosomes by HCT and ITS-PCR. A Pearson chi-squared test and logistic regression analyses were performed to determine the association between location, age, sex, and prevalence of trypanosome infections.

Results

Out of the 816 blood samples examined, 178 (22 %) and 338 (41 %) tested positive for trypanosomiasis by HCT and ITS-PCR, respectively. Trypanosoma vivax infection accounted for 77 % of infections detected by ITS-PCR, T. congolense (16 %), T. brucei s.l (4 %) and mixed (T. vivax/ T. congolense/T.brucei) infections (3 %). The risk of trypanosome infection was significantly associated with cattle age (χ²  = 220.4, df = 3, P < 0.001). The highest proportions of infected animals were adult males (26.7 %) and the least infected were the less than one year old calves (2.0 %). In addition, the risk of trypanosome infection was significantly associated with sex (χ² = 16.64, df = 1, P < 0.001), and males had a significantly higher prevalence of infections (26.8 %) than females (14.6 %).

Conclusion

Our results indicate that the prevalence and intensity of trypanosome infections are highly heterogeneous being associated with cattle age, location and sex.

Phenolics-rich fraction of Khaya senegalensis stem bark: antitrypanosomal activity and amelioration of some parasite-induced pathological changes

CONTEXT

The stem bark of Khaya senegalensis A. Juss (Meliaceae) is currently used for the treatment of trypanosomiasis by traditional practitioners in Nigeria.

OBJECTIVES

The present study investigated the anti-Trypanosoma brucei brucei activity of phenolics-rich fraction of K. senegalensis (pfks) and its ameliorative effects on trypanosome-induced pathological changes.

MATERIALS AND METHODS

The fraction was initially analyzed by gas chromatography-mass spectrometry (GC-MS). A 60 min time course experiment was conducted with various concentrations of the fraction using a 96-well microtiter plate technique and was further used to treat T. brucei infected rats at 100, 200 and 300 mg/kg body weight (BW). Indices of anemia as well as hepatic and renal functions were analyzed in all experimental animals at the end of the experiment.

RESULTS

The GC-MS analysis of the pfks revealed that the most abundant phytochemicals are phloroglucinol (40.56%) and 3,4-(dihydroxyphenyl) acetic acid (41.76%). The fraction showed a concentration dependent in vitro antitrypanosomal activity. Interestingly, the fraction completely eliminated the parasites from the bloodstream of infected rats without relapse during the experimental period at the dose of 300 mg/kg BW and also kept the parasites consistently lower at 100 and 200 mg/kg BW than that was recorded in the untreated infected rats. Furthermore, the severity of T. brucei-induced anemia and hepatic damage was significantly (p < 0.05) ameliorated in the 300 mg/kg BW treatment group whereas the parasite-induced renal damage was significantly (p < 0.05) ameliorated in all treatment groups.

CONCLUSION

Data from this study may suggest that phenolics play an important role in the antitrypanosomal activity of K. senegalensis.

Population dynamics of Glossina palpalis gambiensis symbionts, Sodalis glossinidius, and Wigglesworthia glossinidia, throughout host-fly development

The tsetse fly (Diptera: Glossinidae), the vector of trypanosomes causing human and animal trypanosomiasis, harbors symbiotic microorganisms including the primary symbiont Wigglesworthia glossinidia, involved in the fly's nutrition and fertility, and the secondary symbiont Sodalis glossinidius, involved in the trypanosome establishment in the fly's midgut. Both symbionts are maternally transmitted to the intrauterine progeny through the fly's milk gland secretions. In this study, we investigated the population dynamics of these symbionts during fly development. Wigglesworthia and Sodalis densities were estimated using quantitative PCR performed on Glossina palpalis gambiensis at different developmental stages. The results showed that the density of the primary Wigglesworthia symbiont was higher than that of Sodalis for all host developmental stages. Sodalis densities remained constant in pupae, but increased significantly in adult flies. The opposite situation was observed for Wigglesworthia, whose density increased in pupae and remained constant during the female adult stage. Moreover, Wigglesworthia density increased significantly during the transition from the pupal to the teneral stage, while mating had a contradictory effect depending on the age of the fly. Finally, tsetse fly colonization by both symbionts appears as a continuous and adaptive process throughout the insect's development. Last, the study demonstrated both symbionts of G. p. gambiensis, the vector of the chronic form of human African trypanosomiasis, to be permanent inhabitants of the colony flies throughout their life span. This was expected for the primary symbiont, Wigglesworthia, but not necessarily for the secondary symbiont, S. glossinidius, whose permanent presence is not required for the fly's survival. This result is of importance as Sodalis could be involved in the tsetse fly vector competence and may constitute a target in the frame of sleeping sickness fighting strategies.

The population structure of Glossina fuscipes fuscipes in the Lake Victoria basin in Uganda: implications for vector control

Background

Glossina fuscipes fuscipes is the primary vector of trypanosomiasis in humans and livestock in Uganda. The Lake Victoria basin has been targeted for tsetse eradication using a rolling carpet initiative, from west to east, with four operational blocks (3 in Uganda and 1 in Kenya), under a Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). We screened tsetse flies from the three Ugandan PATTEC blocks for genetic diversity at 15 microsatellite loci from continental and offshore populations to provide empirical data to support this initiative.

Methods

We collected tsetse samples from 11 sites across the Lake Victoria basin in Uganda. We performed genetic analyses on 409 of the collected tsetse flies and added data collected for 278 individuals in a previous study. The flies were screened across 15 microsatellite loci and the resulting data were used to assess the temporal stability of populations, to analyze patterns of genetic exchange and structuring, to estimate dispersal rates and evaluate the sex bias in dispersal, as well as to estimate demographic parameters (N_E and N_C).

Results

We found that tsetse populations in this region were stable over 4-16 generations and belong to 4 genetic clusters. Two genetic clusters (1 and 2) corresponded approximately to PATTEC blocks 1 and 2, while the other two (3 and 4) fell within PATTEC block 3. Island populations grouped into the same genetic clusters as neighboring mainland sites, suggesting presence of gene flow between these sites. There was no evidence of the stretch of water separating islands from the mainland forming a significant barrier to dispersal. Dispersal rates ranged from 2.5 km per generation in cluster 1 to 14 km per generation in clusters 3 and 4. We found evidence of male-biased dispersal. Few breeders are successfully dispersing over large distances. Effective population size estimates were low (33–310 individuals), while census size estimates ranged from 1200 (cluster 1) to 4100 (clusters 3 and 4). We present here a novel technique that adapts an existing census size estimation method to sampling without replacement, the scheme used in sampling tsetse flies.

Conclusion

Our study suggests that different control strategies should be implemented for the three PATTEC blocks and that, given the high potential for re-invasion from island sites, mainland and offshore sites in each block should be targeted at the same time.

Microbial communities associated with the larval gut and eggs of the Western corn rootworm

BACKGROUND

The western corn rootworm (WCR) is one of the economically most important pests of maize. A better understanding of microbial communities associated with guts and eggs of the WCR is required in order to develop new pest control strategies, and to assess the potential role of the WCR in the dissemination of microorganisms, e.g., mycotoxin-producing fungi.

METHODOLOGY/PRINCIPAL FINDINGS

Total community (TC) DNA was extracted from maize rhizosphere, WCR eggs, and guts of larvae feeding on maize roots grown in three different soil types. Denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene and ITS fragments, PCR-amplified from TC DNA, were used to investigate the fungal and bacterial communities, respectively. Microorganisms in the WCR gut were not influenced by the soil type. Dominant fungal populations in the gut were affiliated to Fusarium spp., while Wolbachia was the most abundant bacterial genus. Identical ribosomal sequences from gut and egg samples confirmed a transovarial transmission of Wolbachia sp. Betaproteobacterial DGGE indicated a stable association of Herbaspirillum sp. with the WCR gut. Dominant egg-associated microorganisms were the bacterium Wolbachia sp. and the fungus Mortierella gamsii.

CONCLUSION/SIGNIFICANCE

The soil type-independent composition of the microbial communities in the WCR gut and the dominance of only a few microbial populations suggested either a highly selective environment in the gut lumen or a high abundance of intracellular microorganisms in the gut epithelium. The dominance of Fusarium species in the guts indicated WCR larvae as vectors of mycotoxin-producing fungi. The stable association of Herbaspirillum sp. with WCR gut systems and the absence of corresponding sequences in WCR eggs suggested that this bacterium was postnatally acquired from the environment. The present study provided new insights into the microbial communities associated with larval guts and eggs of the WCR. However, their biological role remains to be explored.

Endosymbiotic bacteria in insects: their diversity and culturability

Many animals and plants possess symbiotic microorganisms inside their body, wherein intimate interactions occur between the partners. The Insecta, often rated as the most diverse animal group, show various types of endosymbiotic associations, ranging from obligate mutualism to facultative parasitism. Although technological advancements in culture-independent molecular techniques, such as quantitative PCR, molecular phylogeny and in situ hybridization, as well as genomic and metagenomic analyses, have allowed us to directly observe endosymbiotic associations in vivo, the molecular mechanisms underlying insect-microbe interactions are not well understood, because most of these insect endosymbionts are neither culturable nor genetically manipulatable. However, recent studies have succeeded in the isolation of several facultative symbionts by using insect cell lines or axenic media, revolutionizing studies of insect endosymbiosis. This article reviews the amazing diversity of bacterial endosymbiosis in insects, focusing on several model systems with culturable endosymbionts, which provide a new perspective towards understanding how intimate symbiotic associations may have evolved and how they are maintained within insects.

Options for the delivery of anti-pathogen molecules in arthropod vectors

Blood feeding arthropods are responsible for the transmission of a large array of medically important infectious agents that include viruses, bacteria, protozoan parasites and helminths. The recent development of transgenic and paratransgenic technologies have enabled supplementing the immune system of these arthropod vectors with anti-pathogen effector molecules in view of compromising their vector competence for these microbial agents. The characteristics of the selected anti-pathogen compound will largely determine the efficacy and specificity of this approach. Low specificity will generally result in bystander effects, likely having a direct or indirect fitness cost for the arthropod. In contrast, the use of highly specific compounds from the adaptive immune system of vertebrates such as antibody derived fragments is more likely to enable highly specific effects without conferring a selective disadvantage to the (para)transgenic arthropods. Here, Nanobodies® are excellent candidates to increase the immune competence of arthropods. Moreover they were shown to exert a novel type of anti-pathogen activity that uniquely depends on their small size.

Senna occidentalis leaf extract possesses antitrypanosomal activity and ameliorates the trypanosome-induced anemia and organ damage

The in vitro and in vivo antitrypanosomal effects of the ethanol extract of Senna occidentalis leaf were investigated. The crude extract exhibited an in vitro activity against Trypanosoma brucei brucei as it completely eliminated parasites’ motility within 10 minutes postincubation with 6.66 mg/ml of effective extract concentration. The extract was further used to treat experimentally T. brucei brucei infected rats at concentrations of 100 and 200 mg/kg body weight, beginning on day 5 post infections (p.i.). At the termination of the experiment on Day 11 p.i., the extract significantly (P < 0.05) kept the parasitemia lower than was recorded in the infected untreated rats. All the infected animals developed anemia, the severity of which was significantly (P < 0.05) ameliorated by the extract treatment. The infection caused significant (P < 0.05) increases in serum alanine and aspartate aminotransferases as well as serum urea and creatinine levels. However, treatment of infected animals with the extract significantly (P < 0.05) prevented the trypanosome-induced increase in these biochemical indices. Furthermore, the T. brucei infection caused hepatomegaly and splenomegaly that were significantly (P < 0.05) ameliorated by the extract administration. It was concluded that orally administered ethanol extract of S. occidentalis leaf possessed anti-T. brucei brucei activity and could ameliorate the disease-induced anemia and organ damage.

Pathogenic mechanisms of Trypanosoma evansi infections

Insect-borne diseases exact a high public health burden and have a devastating impact on livestock and agriculture. To date, control has proved to be exceedingly difficult. One such disease that has plagued sub-Saharan Africa is caused by the protozoan African trypanosomes (Trypanosoma species) and transmitted by tsetse flies (Diptera: Glossinidae). This presentation describes Trypanosoma evansi (T. evansi) which causes the disease known as trypanosomosis (Surra) or trypanosomiasis in which several attempts have being made to unravel the clinical pathogenic mechanisms in T. evansi infections, yielding various reports which have implicated hemolysis associated to decrease in life span of erythrocytes and extensive erythrophagocytosis being among those that enjoy prominence. T. evansi generates Adenosine Triphosphate (ATP) from glucose catabolism which is required for the parasite motility and survival. Oxidation of the erythrocytes induces oxidative stress due to free radical generation. Lipid peroxidation of the erythrocytes causes membrane injury, osmotic fragility and destruction of the red blood cell (RBC) making anemia a hallmark of the pathology of T. evansi infections.

Polyandry is a common event in wild populations of the Tsetse fly Glossina fuscipes fuscipes and may impact population reduction measures

BACKGROUND

Glossina fuscipes fuscipes is the main vector of human and animal trypanosomiasis in Africa, particularly in Uganda. Attempts to control/eradicate this species using biological methods require knowledge of its reproductive biology. An important aspect is the number of times a female mates in the wild as this influences the effective population size and may constitute a critical factor in determining the success of control methods. To date, polyandry in G.f. fuscipes has not been investigated in the laboratory or in the wild. Interest in assessing the presence of remating in Ugandan populations is driven by the fact that eradication of this species is at the planning stage in this country.

METHODOLOGY/PRINCIPAL FINDINGS

Two well established populations, Kabukanga in the West and Buvuma Island in Lake Victoria, were sampled to assess the presence and frequency of female remating. Six informative microsatellite loci were used to estimate the number of matings per female by genotyping sperm preserved in the female spermathecae. The direct count of the minimum number of males that transferred sperm to the spermathecae was compared to Maximum Likelihood and Bayesian probability estimates. The three estimates provided evidence that remating is common in the populations but the frequency is substantially different: 57% in Kabukanga and 33% in Buvuma.

CONCLUSIONS/SIGNIFICANCE

The presence of remating, with females maintaining sperm from different mates, may constitute a critical factor in cases of re-infestation of cleared areas and/or of residual populations. Remating may enhance the reproductive potential of re-invading propagules in terms of their effective population size. We suggest that population age structure may influence remating frequency. Considering the seasonal demographic changes that this fly undergoes during the dry and wet seasons, control programmes based on SIT should release large numbers of sterile males, even in residual surviving target populations, in the dry season.

The diversity of insect-bacteria interactions and its applications for disease control

Prokaryotic microorganisms are widespread in all environments on Earth, establishing diverse interactions with many eukaryotic taxa, including insects. These associations may be symbiotic, pathogenic and vectoring. Independently of the type of interaction, each association starts with the adhesion of the microorganism to the host, entry and "invasion" of the host, then progresses to establishment and dissemination within the host, by avoiding host immune responses, and concludes with transmission back to the environment or to a new host. Advances in genomics and genetics have allowed the dissection of these processes and provided important information on the elements driving the shaping of the members of each association. Furthermore, many mechanisms involved in the establishment of the associations have been scrutinised, along with the development of new methods for the management of insect populations.

Tracking the feeding patterns of tsetse flies (Glossina genus) by analysis of bloodmeals using mitochondrial cytochromes genes

Tsetse flies are notoriously difficult to observe in nature, particularly when populations densities are low. It is therefore difficult to observe them on their hosts in nature; hence their vertebrate species can very often only be determined indirectly by analysis of their gut contents. This knowledge is a critical component of the information on which control tactics can be developed. The objective of this study was to determine the sources of tsetse bloodmeals, hence investigate their feeding preferences. We used mitochondrial cytochrome c oxidase 1 (COI) and cytochrome b (cytb) gene sequences for identification of tsetse fly blood meals, in order to provide a foundation for rational decisions to guide control of trypanosomiasis, and their vectors. Glossina swynnertoni were sampled from Serengeti (Tanzania) and G. pallidipes from Kenya (Nguruman and Busia), and Uganda. Sequences were used to query public databases, and the percentage identities obtained used to identify hosts. An initial assay showed that the feeds were from single sources. Hosts identified from blood fed flies collected in Serengeti ecosystem, included buffaloes (25/40), giraffes (8/40), warthogs (3/40), elephants (3/40) and one spotted hyena. In Nguruman, where G. pallidipes flies were analyzed, the feeds were from elephants (6/13) and warthogs (5/13), while buffaloes and baboons accounted for one bloodmeal each. Only cattle blood was detected in flies caught in Busia and Uganda. Out of four flies tested in Mbita Point, Suba District in western Kenya, one had fed on cattle, the other three on the Nile monitor lizard. These results demonstrate that cattle will form an integral part of a control strategy for trypanosomiasis in Busia and Uganda, while different approaches are required for Serengeti and Nguruman ecosystems, where wildlife abound and are the major component of the tsetse fly food source.

Salivary gland hypertrophy viruses: a novel group of insect pathogenic viruses

Salivary gland hypertrophy viruses (SGHVs) are a unique, unclassified group of entomopathogenic, double-stranded DNA viruses that have been reported from three genera of Diptera. These viruses replicate in nuclei of salivary gland cells in adult flies, inducing gland enlargement with little obvious external disease symptoms. Viral infection inhibits reproduction by suppressing vitellogenesis, causing testicular aberrations, and/or disrupting mating behavior. Historical and present research findings support a recent proposal of a new virus family, the Hytrosaviridae. This review describes the discovery and prevalence of different SGHVs, summarizes their biochemical characterization and taxonomy, compares morphological and histopathological properties, and details transmission routes and the influence of infection on host biology and reproduction. In addition, the potential use of SGHVs as sterilizing agents for house fly control and the deleterious impact of SGHVs on colonized tsetse flies reared for sterile insect technique are discussed.

Phylogeography and population structure of Glossina fuscipes fuscipes in Uganda: implications for control of tsetse

Background

Glossina fuscipes fuscipes, a riverine species of tsetse, is the main vector of both human and animal trypanosomiasis in Uganda. Successful implementation of vector control will require establishing an appropriate geographical scale for these activities. Population genetics can help to resolve this issue by characterizing the extent of linkage among apparently isolated groups of tsetse.

Methodology/Principal Findings

We conducted genetic analyses on mitochondrial and microsatellite data accumulated from approximately 1000 individual tsetse captured in Uganda and neighboring regions of Kenya and Sudan. Phylogeographic analyses suggested that the largest scale genetic structure in G. f. fuscipes arose from an historical event that divided two divergent mitochondrial lineages. These lineages are currently partitioned to northern and southern Uganda and co-occur only in a narrow zone of contact extending across central Uganda. Bayesian assignment tests, which provided evidence for admixture between northern and southern flies at the zone of contact and evidence for northerly gene flow across the zone of contact, indicated that this structure may be impermanent. On the other hand, microsatellite structure within the southern lineage indicated that gene flow is currently limited between populations in western and southeastern Uganda. Within regions, the average F_ST between populations separated by less than 100 km was less than ∼0.1. Significant tests of isolation by distance suggested that gene flow is ongoing between neighboring populations and that island populations are not uniformly more isolated than mainland populations.

Conclusions/Significance

Despite the presence of population structure arising from historical colonization events, our results have revealed strong signals of current gene flow within regions that should be accounted for when planning tsetse control in Uganda. Populations in southeastern Uganda appeared to receive little gene flow from populations in western or northern Uganda, supporting the feasibility of area wide control in the Lake Victoria region by the Pan African Tsetse and Trypanosomiasis Eradication Campaign.

Glossina fuscipes fuscipes is the most common species of tsetse in Uganda, where it transmits human sleeping sickness and nagana, a related disease of cattle. A consortium of African countries dedicated to controlling these diseases is poised to begin area wide control of tsetse, but a critical question remains: What is the most appropriate geographical scale for these activities? To address this question, we used population genetics to determine the extent of linkage between populations of tsetse confined to discrete patches of riverine habitat. Our results suggest that Uganda was colonized by two distinct lineages of G. f. fuscipes, which now co-occur only in a narrow band across central Uganda. Evidence for interbreeding at the zone of contact and movement of genes from the south to the north suggest that this historical genetic structure may dissolve in the future. At smaller scales, we have demonstrated that exchange of genes among neighboring populations via dispersal is at equilibrium with the differentiating force of genetic drift. Our results highlight the need for investment in vector control programs that account for the linkage observed among tsetse populations. Given its genetic isolation and its location at the far edge of G. fuscipes' range, the Lake Victoria region appears to be an appropriate target for area wide control.

Synthetic nonamer peptides derived from insect defensin mediate the killing of African trypanosomes in axenic culture

Synthetic antimicrobial 9-mer peptides (designated as peptides A and B) designed on the basis of insect defensins and their effects on the growth of African trypanosomes were examined using two isolates of Trypanosoma congolense, IL1180 and IL3338, and two isolates of Trypanosoma brucei brucei, ILTat1.1and GUTat 3.1, under axenic culture conditions. Both peptides inhibited the growth of all bloodstream form (BSF) trypanosomes at 200-400 microg/mL in the complete growth medium, with peptide A being more potent than peptide B. In addition, these peptides exhibited efficient killing at 5-20 microg/mL on BSF trypanosomes suspended in phosphate-buffered saline, whereas procyclic insect forms in the same medium were more refractory to the killing. Electron microscopy revealed that the peptides induced severe defects in the cell membrane integrity of the parasites. The insect defensin-based peptides up to either 200 or 400 microg/mL showed no cell killing or growth inhibition on NIH3T3 murine fibroblasts. The results suggest that the design of suitable synthetic insect defensin-based 9-mer peptides might provide potential novel trypanocidal drugs.

Bacteria of the genus Asaia: a potential paratransgenic weapon against malaria

Symbiotic bacteria have been proposed as tools for control of insect-borne diseases. Primary requirements for such symbionts are dominance, prevalence and stability within the insect body. Most of the bacterial symbionts described to date in Anopheles mosquitoes, the vector of malaria in humans, have lacked these features. We describe an alpha-Proteobacterium of the genus Asaia, which stably associates with several Anopheles species and dominates within the body of An. stephensi. Asaia exhibits all the required ecological characteristics making it the best candidate, available to date, for the development ofa paratransgenic approach for manipulation of mosquito vector competence. Key features of Asaia are: (i) dominance within the mosquito-associated microflora, as shown by clone prevalence in 16S rRNA gene libraries and quantitative real time Polymerase Chain Reaction (qRT-PCR); (ii) cultivability in cell-free media; (iii) ease of transformation with foreign DNA and iv) wide distribution in the larvae and adult mosquito body, as revealed by transmission electron microscopy, and in situ-hybridization experiments. Using a green fluorescent protein (GFP)-tagged Asaia strain, it has been possible to show that it effectively colonizes all mosquito body organs necessary for malaria parasite development and transmission, including female gut and salivary glands. Asaia was also found to massively colonize the larval gut and the male reproductive system of adult mosquitoes. Moreover, mating experiments showed an additional key feature necessary for symbiotic control, the high transmission potential of the symbiont to progeny by multiple mechanisms. Asaia is capable of horizontal infection through an oral route during feeding both in preadult and adult stages and through a venereal pattern during mating in adults. Furthermore, Asaia is vertically transmitted from mother to progeny indicating that it could quickly spread in natural mosquito populations.

N-acetyl D-glucosamine stimulates growth in procyclic forms of Trypanosoma brucei by inducing a metabolic shift

The lectin-inhibitory sugars D-glucosamine (GlcN) and N-acetyl D-glucosamine (GlcNAc) are known to enhance susceptibility of the tsetse fly vector to infection with Trypanosoma brucei. GlcNAc also stimulates trypanosome growth in vitro in the absence of any factor derived from the fly. Here, we show that GlcNAc cannot be used as a direct energy source, nor is it internalized by trypanosomes. It does, however, inhibit glucose uptake by binding to the hexose transporter. Deprivation of D-glucose leads to a switch from a metabolism based predominantly on substrate level phosphorylation of D-glucose to a more efficient one based mainly on oxidative phosphorylation using L-proline. Procyclic form trypanosomes grow faster and to higher density in D-glucose-depleted medium than in D-glucose-rich medium. The ability of trypanosomes to use L-proline as an energy source can be regulated depending upon the availability of D-glucose and here we show that this regulation is a graded response to D-glucose availability and determined by the overall metabolic state of the cell. It appears, therefore, that the growth stimulatory effect of GlcNAc in vitro relates to the switch from D-glucose to L-proline metabolism. In tsetse flies, however, it seems probable that the effect of GlcNAc is independent of this switch as pre-adaptation to growth in proline had no effect on tsetse infection rate.

Genomic resources for invertebrate vectors of human pathogens, and the role of VectorBase

High-throughput genome sequencing techniques have now reached vector biology with an emphasis on those species that are vectors of human pathogens. The first mosquito to be sequenced was Anopheles gambiae, the vector for Plasmodium parasites that cause malaria. Further mosquitoes have followed: Aedes aegypti (yellow fever and dengue fever vector) and Culex pipiens (lymphatic filariasis and West Nile fever). Species that are currently in sequencing include the body louse Pediculus humanus (Typhus vector), the triatomine Rhodnius prolixus (Chagas disease vector) and the tick Ixodes scapularis (Lyme disease vector). The motivations for sequencing vector genomes are to further understand vector biology, with an eye on developing new control strategies (for example novel chemical attractants or repellents) or understanding the limitations of current strategies (for example the mechanism of insecticide resistance); to analyse the mechanisms driving their evolution; and to perform an exhaustive analysis of the gene repertory. The proliferation of genomic data creates the need for efficient and accessible storage. We present VectorBase, a genomic resource centre that is both involved in the annotation of vector genomes and act as a portal for access to the genomic information (http://www.vectorbase.org).

Insect-microbe mutualism without vertical transmission: a stinkbug acquires a beneficial gut symbiont from the environment every generation

The broad-headed bug Riptortus clavatus (Heteroptera: Alydidae) possesses a number of crypts at a posterior midgut region, which house a dense population of a bacterial symbiont belonging to the genus Burkholderia. Although the symbiont is highly prevalent (95 to 100%) in the host populations, the symbiont phylogeny did not reflect the host systematics at all. In order to understand the mechanisms underlying the promiscuous host-symbiont relationship despite the specific and prevalent association, we investigated the transmission mode and the fitness effects of the Burkholderia symbiont in R. clavatus. Inspection of eggs and a series of rearing experiments revealed that the symbiont is not vertically transmitted but is environmentally acquired by nymphal insects. The Burkholderia symbiont was present in the soil of the insect habitat, and a culture strain of the symbiont was successfully isolated from the insect midgut. Rearing experiments by using sterilized soybean bottles demonstrated that the cultured symbiont is able to establish a normal and efficient infection in the host insect, and the symbiont infection significantly improves the host fitness. These results indicated that R. clavatus postnatally acquires symbiont of a beneficial nature from the environment every generation, uncovering a previously unknown pathway through which a highly specific insect-microbe association is maintained. We suggest that the stinkbug-Burkholderia relationship may be regarded as an insect analogue of the well-known symbioses between plants and soil-associated microbes, such as legume-Rhizobium and alder-Frankia relationships, and we discuss the evolutionary relevance of the mutualistic but promiscuous insect-microbe association.

Bacterial symbionts in the hepatopancreas of isopods: diversity and environmental transmission

The midgut glands (hepatopancreas) of terrestrial isopods contain bacterial symbionts. We analysed the phylogenetic diversity of hepatopancreatic bacteria in isopod species from various suborders colonizing marine, semiterrestrial, terrestrial and freshwater habitats. Hepatopancreatic bacteria were absent in the marine isopod Idotea balthica (Valvifera). The symbiotic bacteria present in the midgut glands of the freshwater isopod Asellus aquaticus (Asellota) were closely related to members of the proteobacterial genera Rhodobacter, Burkholderia, Aeromonas or Rickettsiella, but differed markedly between populations. By contrast, species of the suborder Oniscidea were consistently colonized by the same phylotypes of hepatopancreatic bacteria. While symbionts in the semiterrestrial isopod Ligia oceanica (Oniscidea) were close relatives of Pseudomonas sp. (Gammaproteobacteria), individuals of the terrestrial isopod Oniscus asellus (Oniscidea) harboured either 'Candidatus Hepatoplasma crinochetorum' (Mollicutes) or 'Candidatus Hepatincola porcellionum' (Rickettsiales), previously described as symbionts of another terrestrial isopod, Porcellio scaber. These two uncultivated bacterial taxa were consistently present in each population of six and three different species of terrestrial isopods, respectively, collected in different geographical locations. However, infection rates of individuals within a population ranged between 10% and 100%, rendering vertical transmission unlikely. Rather, feeding experiments suggest that 'Candidatus Hepatoplasma crinochetorum' is environmentally transmitted to the progeny.

Interspecific transfer of bacterial endosymbionts between tsetse fly species: infection establishment and effect on host fitness

Tsetse flies (Glossina spp.) can harbor up to three distinct species of endosymbiotic bacteria that exhibit unique modes of transmission and evolutionary histories with their host. Two mutualist enterics, Wigglesworthia and Sodalis, are transmitted maternally to tsetse flies' intrauterine larvae. The third symbiont, from the genus Wolbachia, parasitizes developing oocytes. In this study, we determined that Sodalis isolates from several tsetse fly species are virtually identical based on a phylogenetic analysis of their ftsZ gene sequences. Furthermore, restriction fragment-length polymorphism analysis revealed little variation in the genomes of Sodalis isolates from tsetse fly species within different subgenera (Glossina fuscipes fuscipes and Glossina morsitans morsitans). We also examined the impact on host fitness of transinfecting G. fuscipes fuscipes and G. morsitans morsitans flies with reciprocal Sodalis strains. Tsetse flies cleared of their native Sodalis symbionts were successfully repopulated with the Sodalis species isolated from a different tsetse fly species. These transinfected flies effectively transmitted the novel symbionts to their offspring and experienced no detrimental fitness effects compared to their wild-type counterparts, as measured by longevity and fecundity. Quantitative PCR analysis revealed that transinfected flies maintained their Sodalis populations at densities comparable to those in flies harboring native symbionts. Our ability to transinfect tsetse flies is indicative of Sodalis ' recent evolutionary history with its tsetse fly host and demonstrates that this procedure may be used as a means of streamlining future paratransgenesis experiments.

Schistosoma mansoni: DNA microarray gene expression profiling during the miracidium-to-mother sporocyst transformation

For the human blood fluke, Schistosoma mansoni, the developmental period that constitutes the transition from miracidium to sporocyst within the molluscan host involves major alterations in morphology and physiology. Although the genetic basis for this transformation process is not well understood, it is likely to be accompanied by changes in gene expression. In an effort to reveal genes involved in this process, we performed a DNA microarray analysis of expressed mRNAs between miracidial and 4 d old in vitro-cultured mother sporocyst stages of S. mansoni. Fluorescently labeled, dsDNA targets were synthesized from miracidia and sporocyst total RNA and hybridized to oligonucleotide DNA microarrays containing 7335 S. mansoni sequences. Fluorescence intensity ratios were statistically compared between five biologically replicated experiments to identify particular transcripts that displayed stage-associated expression within miracidial and sporocyst mRNA populations. A total of 361 sequences showed stage-associated expression in miracidia, while 273 probes displayed sporocyst-associated expression. Differentially expressed mRNAs were annotated with gene ontology terminology based on BLAST homology using high throughput gene ontology functional annotation toolkit (HT-GO-FAT) and clustered using the GOblet GO browser software. A subset of genes displaying stage-associated expression by microarray analyses was verified utilizing real-time quantitative PCR. The use of DNA microarrays for the profiling of gene expression in early-developing S. mansoni larvae provides a starting point for expanding our understanding of the genes that may be involved in the establishment of parasitism and maintenance of infection in these important life cycle stages.

Extrachromosomal DNA of the symbiont Sodalis glossinidius

The extrachromosomal DNA of Sodalis glossinidius from two tsetse fly species was sequenced and contained four circular elements: three plasmids, pSG1 (82 kb), pSG2 (27 kb), and pSG4 (11 kb), and a bacteriophage-like pSG3 (19 kb) element. The information suggests S. glossinidius is evolving towards an obligate association with tsetse flies.

Tick, fly, and mosquito control—Lessons from the past, solutions for the future

In order to continue to produce livestock in a sustainable fashion, it is suggested that what was used in the past will continue to form the mainstay of future control. For the foreseeable future, we must conserve what we have, and use it in combination with all the principles of integrated pest management, namely strategic and focussed treatments of animals, environmental control of breeding sites, disease management (including the principles of enzootic stability), and resistant breeds. Whilst new technologies, such as the development of vaccines both against the insect pest in some cases or the disease they transmit in others, and genetic engineering hold out some hope for the future; these are not sufficiently well advanced to permit wholesale application.

A case for a Glossina genome project

Given the medical and agricultural significance of Glossina, knowledge of the genomic aspects of the vector and vector-pathogen interactions are a high priority. In preparation for a full genome sequence initiative, an extensive set of expressed sequence tags (ESTs) has been generated from tissue-specific normalized libraries. In addition, bacterial artificial chromosome (BAC) libraries are being constructed, and information on the genome structure and size from different species has been obtained. An international consortium is now in place to further efforts to lead to a full genome project.