The genomic basis of host and vector specificity in non-pathogenic trypanosomatids

The ability of trypanosome parasites to survive and sustain infections is dependent on diverse and intricate immune evasion mechanisms. Pathogenic trypanosomes often have broad host niches that preclude identification of host specific adaptations. In contrast, some non-pathogenic species of the genus Trypanosoma have highly specific hosts and vectors. Trypanosoma theileri, a non-pathogenic parasite of bovines, has a predicted surface protein architecture that likely aids survival in its mammalian host, distinct from the dominant variant surface glycoprotein coat of pathogenic African trypanosomes. In both species, their surface proteins are encoded by genes which account for ~10% of their genome. A non-pathogenic parasite of sheep, Trypanosoma melophagium, is transmitted by the sheep ked and is closely related to T. theileri. To explore host and vector specificity between these closely related species, we sequenced the T. melophagium genome and transcriptome and an annotated draft genome was assembled. T. melophagium was compared to 43 kinetoplastid genomes, including T. theileri. T. melophagium and T. theileri have an AT biased genome, the greatest bias of publicly available trypanosomatids. This trend may result from selection acting to decrease the genome nucleotide cost. The T. melophagium genome is 6.3Mb smaller than T. theileri and large families of proteins, characteristic of the predicted surface of T. theileri, were found to be absent or greatly reduced in T. melophagium. Instead, T. melophagium has modestly expanded protein families associated with the avoidance of complement-mediated lysis. The genome of T. melophagium contains core genes required for development, glycolysis, RNA interference, and meiotic exchange, each being shared with T. theileri. Comparisons between T. melophagium and T. theileri provide insight into the specific adaptations of these related trypanosomatids to their distinct mammalian hosts and arthropod vectors.

Vector Specificity of Arbovirus Transmission

More than 25% of human infectious diseases are vector-borne diseases (VBDs). These diseases, caused by pathogens shared between animals and humans, are a growing threat to global health with more than 2.5 million annual deaths. Mosquitoes and ticks are the main vectors of arboviruses including flaviviruses, which greatly affect humans. However, all tick or mosquito species are not able to transmit all viruses, suggesting important molecular mechanisms regulating viral infection, dissemination, and transmission by vectors. Despite the large distribution of arthropods (mosquitoes and ticks) and arboviruses, only a few pairings of arthropods (family, genus, and population) and viruses (family, genus, and genotype) successfully transmit. Here, we review the factors that might limit pathogen transmission: internal (vector genetics, immune responses, microbiome including insect-specific viruses, and coinfections) and external, either biotic (adult and larvae nutrition) or abiotic (temperature, chemicals, and altitude). This review will demonstrate the dynamic nature and complexity of virus–vector interactions to help in designing appropriate practices in surveillance and prevention to reduce VBD threats.

DNA Multi-Marker Genotyping and CIAS Morphometric Phenotyping of Fasciola gigantica-Sized Flukes from Ecuador, with an Analysis of the Radix Absence in the New World and the Evolutionary Lymnaeid Snail Vector Filter

Fascioliasis is a disease caused by Fasciola hepatica worldwide transmitted by lymnaeid snails mainly of the Galba/Fossaria group and F. gigantica restricted to parts of Africa and Asia and transmitted by Radix lymnaeids. Concern has recently risen regarding the high pathogenicity and human infection capacity of F. gigantica. Abnormally big-sized fasciolids were found infecting sheep in Ecuador, the only South American country where F. gigantica has been reported. Their phenotypic comparison with F. hepatica infecting sheep from Peru, Bolivia and Spain, and F. gigantica from Egypt and Vietnam demonstrated the Ecuadorian fasciolids to have size-linked parameters of F. gigantica. Genotyping of these big-sized fasciolids by rDNA ITS-2 and ITS-1 and mtDNA cox1 and nad1 and their comparison with other countries proved the big-sized fasciolids to belong to F. hepatica. Neither heterozygotic ITS position differentiated the two species, and no introgressed fragments and heteroplasmic positions in mtDNA were found. The haplotype diversity indicates introductions mainly from other South American countries, Europe and North America. Big-sized fasciolids from Ecuador and USA are considered to be consequences of F.gigantica introductions by past livestock importations. The vector specificity filter due to Radix absence should act as driving force in the evolution in such lineages.

Vector Specificity of the Relapsing Fever Spirochete Borrelia hermsii (Spirochaetales: Borreliaceae) for the Tick Ornithodoros hermsi (Acari: Argasidae) Involves Persistent Infection of the Salivary Glands

The relapsing fever spirochetes Borrelia hermsii and Borrelia turicatae are each maintained and transmitted in nature by their specific tick vectors, Ornithodoros hermsi Wheeler (Acari: Argasidae) and Ornithodoros turicata (Duges), respectively. The basis for this spirochete and vector specificity is not known, but persistent colonization of spirochetes in the tick’s salivary glands is presumed to be essential for transmission by these long-lived ticks that feed in only minutes on their warm-blooded hosts. To examine this hypothesis further, cohorts of O. hermsi and O. turicata were infected with B. hermsii and examined 7–260 d later for infection in their midgut, salivary glands, and synganglion. While the midgut from all ticks of both species at all time points examined were infected with spirochetes, the salivary glands of only O. hermsi remained persistently infected. The salivary glands of O. turicata were susceptible to an early transient infection. However, no spirochetes were observed in these tissues beyond the first 32 d after acquisition. Ticks of both species were fed on mice 112 d after they acquired spirochetes and only those mice fed upon by O. hermsi became infected. Thus, the vector competency for B. hermsii displayed by O. hermsi but not O. turicata lies, in part, in the persistent infection of the salivary glands of the former but not the latter species of tick. The genetic and biochemical mechanisms supporting this spirochete and vector specificity remain to be identified.

Brevipalpus Species Vectoring Citrus Leprosis Virus (Cilevirus and Dichorhavirus)

Citrus leprosis (CL) is one of the most devastating viral diseases of orchards, and industries correspondingly invest highly in the management and control of the virus vector. In Brazil, the disease is caused most predominantly by the citrus leprosis virus C (CiLV-C, Kitaviridae: Cilevirus), and also by citrus leprosis virus N (CiLV-N, Rhabdoviridae: Dichorhavirus). Both viruses are transmitted by false spider mites and at least three different species, Brevipalpus yothersi Baker, B. papayensis Baker, and B. phoenicis (Geijskes) sensu stricto, have been reported in citrus orchards. The main goal of this study was to evaluate the capacity of three Brevipalpus species to transmit citrus leprosis virus (cytoplasmic and nuclear types). The capacity of false spider mites to acquire the virus was accomplished using RT–PCR and the ability to inoculation the virus to host plants (common bean and sweet orange) was assessed via viral transmission assays. Common beans infested with B. yothersi and B. papayensis showed symptoms of CiLV-C in 87.5 and 17% of the plants assessed, respectively. In sweet orange, B. yothersi was exclusively able to inoculate CiLV-C, and around 83% of samples were symptomatic. Host plants infected with CiLV-N showed symptoms only when infested with B. phoenicis sensu stricto (s.s.). All the Brevipalpus species (Acari: Tenuipalpidae) were able to acquire both viruses (CiLV-C and CiLV-N), but not infect plants. These results suggest the existence of virus-vector specificity in the leprosis pathosystem, and this information will be critical for enhancing our further understanding of epidemiological features and disease management.

Spondweni virus causes fetal harm in a mouse model of vertical transmission and is transmitted by Aedes aegypti mosquitoes

Spondweni virus (SPONV) is the most closely related known flavivirus to Zika virus (ZIKV). Its pathogenic potential and vector specificity have not been well defined. SPONV has been found predominantly in Africa, but was recently detected in a pool of Culex quinquefasciatus mosquitoes in Haiti. Here we show that SPONV can cause significant fetal harm, including demise, comparable to ZIKV, in a mouse model of vertical transmission. Following maternal inoculation, we detected infectious SPONV in placentas and fetuses, along with significant fetal and placental histopathology, together indicating vertical transmission. To test vector competence, we exposed Aedes aegypti and Culex quinquefasciatus mosquitoes to SPONV-infected bloodmeals. Aedes aegypti could efficiently transmit SPONV, whereas Culex quinquefasciatus could not. Our results suggest that SPONV has the same features that made ZIKV a public health risk.

The Bacteriome of Bat Flies (Nycteribiidae) from the Malagasy Region: a Community Shaped by Host Ecology, Bacterial Transmission Mode, and Host-Vector Specificity

ABSTRACTThe Nycteribiidae are obligate blood-sucking Diptera (Hippoboscoidea) flies that parasitize bats. Depending on species, these wingless flies exhibit either high specialism or generalism toward their hosts, which may in turn have important consequences in terms of their associated microbial community structure. Bats have been hypothesized to be reservoirs of numerous infectious agents, some of which have recently emerged in human populations. Thus, bat flies may be important in the epidemiology and transmission of some of these bat-borne infectious diseases, acting either directly as arthropod vectors or indirectly by shaping pathogen communities among bat populations. In addition, bat flies commonly have associations with heritable bacterial endosymbionts that inhabit insect cells and depend on maternal transmission through egg cytoplasm to ensure their transmission. Some of these heritable bacteria are likely obligate mutualists required to support bat fly development, but others are facultative symbionts with unknown effects. Here, we present bacterial community profiles that were obtained from seven bat fly species, representing five genera, parasitizing bats from the Malagasy region. The observed bacterial diversity includesRickettsia,Wolbachia, and severalArsenophonus-like organisms, as well as other members of theEnterobacterialesand a widespread association ofBartonellabacteria from bat flies of all five genera. Using the well-described host specificity of these flies and data on community structure from selected bacterial taxa with either vertical or horizontal transmission, we show that host/vector specificity and transmission mode are important drivers of bacterial community structure.