Structural evolution of an immune evasion determinant shapes pathogen host tropism.

Modern infectious disease outbreaks often involve changes in host tropism, the preferential adaptation of pathogens to specific hosts. The Lyme disease-causing bacterium Borrelia burgdorferi (Bb) is an ideal model to investigate the molecular mechanisms of host tropism, because different variants of these tick-transmitted bacteria are distinctly maintained in rodents or bird reservoir hosts. To survive in hosts and escape complement-mediated immune clearance, Bb produces the outer surface protein CspZ that binds the complement inhibitor factor H (FH) to facilitate bacterial dissemination in vertebrates. Despite high sequence conservation, CspZ variants differ in human FH-binding ability. Together with the FH polymorphisms between vertebrate hosts, these findings suggest that minor sequence variation in this bacterial outer surface protein may confer dramatic differences in host-specific, FH-binding-mediated infectivity. We tested this hypothesis by determining the crystal structure of the CspZ-human FH complex, and identifying minor variation localized in the FH-binding interface yielding bird and rodent FH-specific binding activity that impacts infectivity. Swapping the divergent region in the FH-binding interface between rodent- and bird-associated CspZ variants alters the ability to promote rodent- and bird-specific early-onset dissemination. We further linked these loops and respective host-specific, complement-dependent phenotypes with distinct CspZ phylogenetic lineages, elucidating evolutionary mechanisms driving host tropism emergence. Our multidisciplinary work provides a novel molecular basis for how a single, short protein motif could greatly modulate pathogen host tropism.

Role of Anopheles Mosquitoes in Cache Valley Virus Lineage Displacement, New York, USA.

Cache Valley virus (CVV) is a mosquitoborne virus that infects livestock and humans. We report results of surveillance for CVV in New York, USA, during 2000-2016; full-genome analysis of selected CVV isolates from sheep, horse, humans, and mosquitoes from New York and Canada; and phenotypic characterization of selected strains. We calculated infection rates by using the maximum-likelihood estimation method by year, region, month, and mosquito species. The highest maximum-likelihood estimations were for Anopheles spp. mosquitoes. Our phylogenetic analysis identified 2 lineages and found evidence of segment reassortment. Furthermore, our data suggest displacement of CVV lineage 1 by lineage 2 in New York and Canada. Finally, we showed increased vector competence of An. quadrimaculatus mosquitoes for lineage 2 strains of CVV compared with lineage 1 strains.

Cellular and immunological mechanisms influence host-adapted phenotypes in a vector-borne microparasite.

Predicting pathogen emergence and spillover risk requires understanding the determinants of a pathogens' host range and the traits involved in host competence. While host competence is often considered a fixed species-specific trait, it may be variable if pathogens diversify across hosts. Balancing selection can lead to maintenance of pathogen polymorphisms (multiple-niche-polymorphism; MNP). The causative agent of Lyme disease, Borrelia burgdorferi (Bb), provides a model to study the evolution of host adaptation, as some Bb strains defined by their outer surface protein C (ospC) genotype, are widespread in white-footed mice and others are associated with non-rodent vertebrates (e.g. birds). To identify the mechanisms underlying potential strain × host adaptation, we infected American robins and white-footed mice, with three Bb strains of different ospC genotypes. Bb burdens varied by strain in a host-dependent fashion, and strain persistence in hosts largely corresponded to Bb survival at early infection stages and with transmission to larvae (i.e. fitness). Early survival phenotypes are associated with cell adhesion, complement evasion and/or inflammatory and antibody-mediated removal of Bb, suggesting directional selective pressure for host adaptation and the potential role of MNP in maintaining OspC diversity. Our findings will guide future investigations to inform eco-evolutionary models of host adaptation for microparasites.

Reliability of routine anthropometric measurements to estimate body composition in term infants.

BACKGROUND: Birth weight percentiles provide limited information on qualitative infant growth. Body composition provides estimates of fat mass, fat-free mass, and body fat percentage (adiposity). We sought to implement assessment of body composition at birth into clinical practice using a validated anthropometric equation and to evaluate measurement reliability. METHODS: Body composition was incorporated into newborn nursery admission procedure. Body fat percentage derived from skinfold measurements performed by clinical nurses were compared to a historical database of similar measurements performed on newborns by experienced research staff. Body Mass Index (BMI) and Ponderal Index (PI) were used as surrogates for adiposity. Comparison of correlations between groups assessed measurement reliability. P < 0.05 was considered significant. RESULTS: Nine hundred and ninety-one infants had body composition evaluated. Correlations were similar between BMI and %BF for measurements performed by research and clinical nurses (r2 = 0.82 versus r2 = 0.80; P = 0.142 for the difference between correlation coefficients) demonstrating good reliability. Similar results were found using PI (r2 = 0.58 versus r2 0.53; P = 0.105). CONCLUSIONS: Body composition can be assessed at birth using a validated anthropometric equation. Measurements performed by clinical RNs were found to be reliable, allowing for a qualitative measure of growth beyond birth weight. IMPACT: Assessment of neonatal body composition at birth can be implemented into routine clinical practice using an anthropometric equation to estimate fat free-mass, fat mass, and percentage body fat. It provides a detailed, reproducible protocol to incorporate into routine practice. Assessment of fat mass, fat-free mass, and adiposity at birth allows for a qualitative measure of intrauterine growth beyond birth weight. Routine assessment of body composition provides a foundation for longitudinal follow-up of metabolic health in infancy and childhood.

Aedes albopictus saliva contains a richer microbial community than the midgut.

BACKGROUND: Past findings demonstrate that arthropods can egest midgut microbiota into the host skin leading to dual colonization of the vertebrate host with pathogens and saliva microbiome. A knowledge gap exists on how the saliva microbiome interacts with the pathogen in the saliva. To fill this gap, we need to first define the microbial composition of mosquito saliva. METHODS: The current study aimed at analyzing and comparing the microbial profile of Aedes albopictus saliva and midgut as well as assessing the impact of Zika virus (ZIKV) infection on the midgut and saliva microbial composition. Colony-reared Ae. albopictus strains were either exposed to ZIKV infectious or noninfectious bloodmeal. At 14 ays postinfection, the 16S V3-V4 hypervariable rRNA region was amplified from midgut and saliva samples and sequenced on an Illumina MiSeq platform. The relative abundance and diversity of midgut and saliva microbial taxa were assessed. RESULTS: We observed a richer microbial community in the saliva compared with the midgut, yet some of the microbial taxa were common in the midgut and saliva. ZIKV infection did not impact the microbial diversity of midgut or saliva. Further, we identified Elizabethkingia spp. in the Ae. albopictus saliva. CONCLUSIONS: This study provides insights into the microbial community of the Ae. albopictus saliva as well as the influence of ZIKV infection on the microbial composition of its midgut and saliva. The identification of Elizabethkingia spp., an emerging pathogen of global health significance, in Ae. albopictus saliva is of medical importance. Future studies to assess the interactions between Ae. albopictus saliva microbiome and ZIKV could lead to novel strategies for developing transmission barrier tools.

Maintenance of a host-specific minority mutation in the West Nile virus NS3.

West Nile virus (WNV), the most prevalent arthropod-borne virus (arbovirus) in the United States, is maintained in a cycle between Culex spp. mosquitoes and birds. Arboviruses exist within hosts and vectors as a diverse set of closely related genotypes. In theory, this genetic diversity can facilitate adaptation to distinct environments during host cycling, yet host-specific fitness of minority genotypes has not been assessed. Utilizing WNV deep-sequencing data, we previously identified a naturally occurring, mosquito-biased substitution, NS3 P319L. Using both cell culture and experimental infection in natural hosts, we demonstrated that this substitution confers attenuation in vertebrate hosts and increased transmissibility by mosquitoes. Biochemical assays demonstrated temperature-sensitive ATPase activity consistent with host-specific phenotypes. Together these data confirm the maintenance of host-specific minority variants in arbovirus mutant swarms, suggest a unique role for NS3 in viral fitness, and demonstrate that intrahost sequence data can inform mechanisms of host-specific adaptation.

Phylogenomic Diversity Elucidates Mechanistic Insights into Lyme Borreliae-Host Association.

Host association-the selective adaptation of pathogens to specific host species-evolves through constant interactions between host and pathogens, leaving a lot yet to be discovered on immunological mechanisms and genomic determinants. The causative agents of Lyme disease (LD) are spirochete bacteria composed of multiple species of the Borrelia burgdorferi sensu lato complex, including B. burgdorferi (Bb), the main LD pathogen in North America-a useful model for the study of mechanisms underlying host-pathogen association. Host adaptation requires pathogens' ability to evade host immune responses, such as complement, the first-line innate immune defense mechanism. We tested the hypothesis that different host-adapted phenotypes among Bb strains are linked to polymorphic loci that confer complement evasion traits in a host-specific manner. We first examined the survivability of 20 Bb strains in sera in vitro and/or bloodstream and tissues in vivo from rodent and avian LD models. Three groups of complement-dependent host-association phenotypes emerged. We analyzed complement-evasion genes, identified a priori among all strains and sequenced and compared genomes for individual strains representing each phenotype. The evolutionary history of ospC loci is correlated with host-specific complement-evasion phenotypes, while comparative genomics suggests that several gene families and loci are potentially involved in host association. This multidisciplinary work provides novel insights into the functional evolution of host-adapted phenotypes, building a foundation for further investigation of the immunological and genomic determinants of host association. IMPORTANCE Host association is the phenotype that is commonly found in many pathogens that preferential survive in particular hosts. The Lyme disease (LD)-causing agent, B. burgdorferi (Bb), is an ideal model to study host association, as Bb is mainly maintained in nature through rodent and avian hosts. A widespread yet untested concept posits that host association in Bb strains is linked to Bb functional genetic variation conferring evasion to complement, an innate defense mechanism in vertebrate sera. Here, we tested this concept by grouping 20 Bb strains into three complement-dependent host-association phenotypes based on their survivability in sera and/or bloodstream and distal tissues in rodent and avian LD models. Phylogenomic analysis of these strains further correlated several gene families and loci, including ospC, with host-specific complement-evasion phenotypes. Such multifaceted studies thus pave the road to further identify the determinants of host association, providing mechanistic insights into host-pathogen interaction.

Acute Liver Failure due to Miliary Liver Metastasis.

Acute liver failure (ALF) is a medical emergency with high mortality. Accurate etiological diagnosis, intensive liver support, and liver transplantation are critical for the management of these patients. Malignant infiltration of the liver uncommonly results in ALF. Diffuse infiltration can be missed by imaging, particularly in early stages, and biopsy is often required to clinch the diagnosis. We report a case of ALF due to diffuse liver metastasis.

Corrigendum: Zika Virus Infection Results in Biochemical Changes Associated With RNA Editing, Inflammatory and Antiviral Responses in Aedes albopictus.

[This corrects the article DOI: 10.3389/fmicb.2020.559035.].

Vector Competence of Aedes albopictus Populations from the Northeastern United States for Chikungunya, Dengue, and Zika Viruses.

The Asian tiger mosquito (Aedes albopictus) is an important vector of a number of arboviruses, including Zika (ZIKV), dengue (DENV), and chikungunya (CHIKV) viruses, and has recently expanded its range in the eastern United States to southern New England and New York. Given the recent establishment and proliferation of Ae. albopictus in this region and the increasing amount of international travel between the United States and endemic countries, there is a need to elucidate the public health risk posed by this mosquito species in the Northeast. Accordingly, we evaluated the competence of four Ae. albopictus populations from Connecticut and New York, for two strains each of ZIKV, DENV serotype 2 (DENV-2), and CHIKV, currently circulating in the Americas, to evaluate the local transmission risk by this vector. We found that local Ae. albopictus populations are susceptible to infection by all three viruses but are most capable of transmitting CHIKV. Variation in competence was observed for ZIKV and CHIKV, driven by the virus strains and mosquito population, whereas competence was more homogeneous for the DENV-2 strains under evaluation. These results suggest that under optimal circumstances, Ae. albopictus could support localized transmission of these viruses and emphasize the importance of maintaining mosquito surveillance and control programs to suppress Ae. albopictus populations and limit further range expansion of this species.

Zika Virus Infection Results in Biochemical Changes Associated With RNA Editing, Inflammatory and Antiviral Responses in Aedes albopictus.

Rapid and significant range expansion of both the Zika virus (ZIKV) and its Aedes vector species has resulted in the declaration of ZIKV as a global health threat. Successful transmission of ZIKV by its vector requires a complex series of interactions between these entities including the establishment, replication and dissemination of the virus within the mosquito. The metabolic conditions within the mosquito tissues play a critical role in mediating the crucial processes of viral infection and replication and represent targets for prevention of virus transmission. In this study, we carried out a comprehensive metabolomic phenotyping of ZIKV infected and uninfected Ae. albopictus by untargeted analysis of primary metabolites, lipids and biogenic amines. We performed a comparative metabolomic study of infection state with the aim of understanding the biochemical changes resulting from the interaction between the ZIKV and its vector. We have demonstrated that ZIKV infection results in changes to the cellular metabolic environment including a significant enrichment of inosine and pseudo-uridine (Ψ) levels which may be associated with RNA editing activity. In addition, infected mosquitoes demonstrate a hypoglycemic phenotype and show significant increases in the abundance of metabolites such as prostaglandin H2, leukotriene D4 and protoporphyrinogen IX which are associated with antiviral activity. These provide a basis for understanding the biochemical response to ZIKV infection and pathology in the vector. Future mechanistic studies targeting these ZIKV infection responsive metabolites and their associated biosynthetic pathways can provide inroads to identification of mosquito antiviral responses with infection blocking potential.

Subcutaneous daidzein administration enhances recovery of skilled ladder rung walking performance following stroke in rats.

Stroke is a devastating event which can result in permanent disability. Due to the lack of treatments available for use after stroke, compounds which work to limit cell loss, reduce behavioral deficits, and enhance recovery of function are needed. The isoflavone daidzein has been demonstrated to be neuroprotective when fed to rats beginning prior to stroke. Herein, we tested whether subcutaneous delivery of daidzein beginning at the time of stroke reduced injury and/or enhanced functional recovery over 14 days after stroke. Baseline performance on the skilled ladder rung walking task was recorded immediately before stroke (Day 0). Rats then underwent a unilateral permanent middle cerebral artery occlusion and received a subcutaneous minipump containing either daidzein dissolved in vehicle or vehicle alone. Performance on the skilled ladder rung walking task was recorded again on Day +3, Day +7, and Day +14 post-stroke. Rats were then euthanized and brains were collected for lesion volume analysis. The numbers of slight and deep forelimb slips on the task were recorded for 3 trials for each rat per day. Rats treated with daidzein exhibited fewer deep slips over the course of the experiment than rats which received only vehicle (p<0.05). No difference was detected in total forelimb slips or slight slips (p>0.05). Lesion volume was not different between groups (p>0.05). No differences were found in weight between groups during the study (p>0.05).