Aphids alter host-plant nitrogen isotope fractionation

Plant sap-feeding insects and blood-feeding parasites are frequently depleted in (15)N relative to their diet. Unfortunately, most fluid-feeder/host nitrogen stable-isotope studies simply report stable-isotope signatures, but few attempt to elucidate the mechanism of isotopic trophic depletion. Here we address this deficit by investigating the nitrogen stable-isotope dynamics of a fluid-feeding herbivore-host plant system: the green peach aphid, Myzus persicae, feeding on multiple brassicaceous host plants. M. persicae was consistently more than 6‰ depleted in (15)N relative to their hosts, although aphid colonized plants were 1.5‰ to 2.0‰ enriched in (15)N relative to uncolonized control plants. Isotopic depletion of aphids relative to hosts was strongly related to host nitrogen content. We tested whether the concomitant aphid (15)N depletion and host (15)N enrichment was coupled by isotopic mass balance and determined that aphid (15)N depletion and host (15)N enrichment are uncoupled processes. We hypothesized that colonized plants would have higher nitrate reductase activity than uncolonized plants because previous studies had demonstrated that high nitrate reductase activity under substrate-limiting conditions can result in increased plant δ(15)N values. Consistent with our hypothesis, nitrate reductase activity in colonized plants was twice that of uncolonized plants. This study offers two important insights that are likely applicable to understanding nitrogen dynamics in fluid-feeder/host systems. First, isotopic separation of aphid and host depends on nitrogen availability. Second, aphid colonization alters host nitrogen metabolism and subsequently host nitrogen stable-isotope signature. Notably, this work establishes a metabolic framework for future hypothesis-driven studies focused on aphid manipulation of host nitrogen metabolism.     

Rerooting the evolutionary tree of malaria parasites

Malaria parasites (Plasmodium spp.) have plagued humans for millennia. Less well known are related parasites (Haemosporida), with diverse life cycles and dipteran vectors that infect other vertebrates. Understanding the evolution of parasite life histories, including switches between hosts and vectors, depends on knowledge of evolutionary relationships among parasite lineages. In particular, inferences concerning time of origin and trait evolution require correct placement of the root of the evolutionary tree. Phylogenetic reconstructions of the diversification of malaria parasites from DNA sequences have suffered from uncertainty concerning outgroup taxa, limited taxon sampling, and selection on genes used to assess relationships. As a result, inferred relationships among the Haemosporida have been unstable, and questions concerning evolutionary diversification and host switching remain unanswered. A recent phylogeny placed mammalian malaria parasites, as well as avian/reptilian Plasmodium, in a derived position relative to the avian parasite genera Leucocytozoon and Haemoproteus, implying that the ancestral forms lacked merogony in the blood and that their vectors were non-mosquito dipterans. Bayesian, outgroup-free phylogenetic reconstruction using relaxed molecular clocks with uncorrelated rates instead suggested that mammalian and avian/reptilian Plasmodium parasites, spread by mosquito vectors, are ancestral sister taxa, from which a variety of specialized parasite lineages with modified life histories have evolved.     

Rapid evolution of disease resistance is accompanied by functional changes in gene expression in a wild bird

Wild organisms are under increasing pressure to adapt rapidly to environmental changes. Predicting the impact of these changes on natural populations requires an understanding of the speed with which adaptive phenotypes can arise and spread, as well as of the underlying mechanisms. However, our understanding of these parameters is poor in natural populations. Here we use experimental and molecular approaches to investigate the recent emergence of resistance in eastern populations of North American house finches (Carpodacus mexicanus) to Mycoplasma galliseptum (MG), a severe conjunctivitis-causing bacterium. Two weeks following an experimental infection that took place in 2007, finches from eastern US populations with a 12-y history of exposure to MG harbored 33% lower MG loads in their conjunctivae than finches from western US populations with no prior exposure to MG. Using a cDNA microarray, we show that this phenotypic difference in resistance was associated with differences in splenic gene expression, with finches from the exposed populations up-regulating immune genes postinfection and those from the unexposed populations generally down-regulating them. The expression response of western US birds to experimental infection in 2007 was more similar to that of the eastern US birds studied in 2000, 7 y earlier in the epizootic, than to that of eastern birds in 2007. These results support the hypothesis that resistance has evolved by natural selection in the exposed populations over the 12 y of the epizootic. We hypothesize that host resistance arose and spread from standing genetic variation in the eastern US and highlight that natural selection can lead to rapid phenotypic evolution in populations when acting on such variation.     

Dual-Stage Picolinic Acid-Derived Inhibitors of Toxoplasma gondii

Toxoplasma gondii causes a prevalent human infection for which only the acute stage has an FDA-approved therapy. To find inhibitors of both the acute stage parasites and the persistent cyst stage that causes a chronic infection, we repurposed a compound library containing known inhibitors of parasitic hexokinase, the first step in the glycolysis pathway, along with a larger collection of new structural derivatives. The focused screen of 22 compounds showed a 77% hit rate (>50% multistage inhibition) and revealed a series of aminobenzamide-linked picolinic acids with submicromolar potency against both T. gondii parasite forms. Picolinic acid 23, designed from an antiparasitic benzamidobenzoic acid class with challenging ADME properties, showed 60-fold-enhanced solubility, a moderate LogD_7.4, and a 30% improvement in microsomal stability. Furthermore, isotopically labeled glucose tracing revealed that picolinic acid 23 does not function by hexokinase inhibition. Thus, we report a new probe scaffold to interrogate dual-stage inhibition of T. gondii.     

Primary Amoebic Meningoencephalitis in an Infant

Primary amoebic meningoencephalitis is rare but fatal disease encountered in immunocompetent individuals. Here, we present a case of a previously healthy 8-month-old female child, who presented with features of meningoencephalitis of 2 days’ duration. Rapidly moving trophozoites of amoeba were observed in cerebrospinal fluid, which were confirmed to be Naegleria fowleri on polymerase chain reaction. Broad-spectrum antimicrobial therapy with ceftriaxone, vancomycin, amphotericin B and acyclovir was initiated. However, the patient deteriorated and left the hospital against medical advice. The isolation of N. fowleri in this case demands for increased awareness for prompt diagnosis and management in view of its high mortality.     

Baylisascaris procyonis–Associated Meningoencephalitis in a Previously Healthy Adult,California, USA

After severe neurocognitive decline developed in an otherwise healthy 63-year-old man, brain magnetic resonance imaging showed eosinophilic meningoencephalitis and enhancing lesions. The patient tested positive for antibodies to Baylisascaris spp. roundworms, was treated with albendazole and dexamethasone, and showed improvement after 3 months. Baylisascariasis should be considered for all patients with eosinophilic meningitis.     

靶向寄生虫的核酸适配体应用研究进展

核酸适配体是人工合成的单链DNA或RNA寡核苷酸,经指数富集的配体系统进化技术体外筛选获得。核酸适配体可与病毒、细菌、寄生虫等生物体的蛋白质与其他小分子靶标进行高亲和力和特异性结合。与抗体相比,核酸适配体具有无免疫原性、制备简单、易于批量生产、便于修饰、性能稳定、价格低廉等优点,在疾病诊断和治疗领域具有重要的应用潜力。本文综述了靶向疟原虫、锥虫、利什曼原虫等寄生虫的核酸适配体的研究进展,以期为寄生虫感染的检测和防治提供新策略。     

Intestinal parasitic infection: prevalence,knowledge, attitude,and practices among schoolchildren in an urban area of Taiz city,Yemen

BackgroundIntestinal parasitic infections (IPIs) are regarded as one of the main public health problems and socio-economic issues adversely affecting the health of millions of people worldwide. Our study aimed to describe the knowledge, attitude, and practices of local urban schoolchildren in Taiz City towards intestinal parasitic infections.Methods and materialThis is a cross-sectional study conducted in Taiz, Yemen from March to May 2019. A total of 385 schoolchildren were selected using a random sampling technique from 7 primary schools. Wet-mount microscopic examination, formol-ether concentration techniques, and Lugols'' iodine were employed in parasite detection and cyst identification.ResultsOf the 385 schoolchildren examined for IPIs, 107 (27.8%) were positive for the presence of enteric parasites, some having multiple infections. The prevalence was slightly higher in males 46 (28.6%) than in females 61 (27.2%) but have no statistical difference (P = 0.77). Entamoeba histolytica/dispar was the most common infection with 16.4% of cases. A substantial percentage (40.5%) of the respondents displayed poor knowledge. The respondents also revealed inappropriate attitudes and practices that contribute to the prevalence of IPIs in the study.ConclusionsThe study revealed the prevalence of intestinal parasites among the schoolchildren in Taiz, Yemen, suggesting that IPIs remain a major public health problem. Entamoeba histolytica/dispar was the most prevalent intestinal parasites identified among the schoolchildren. Age, poor knowledge of the mode of transmission, prevention, and acquisition of IPIs, and poor habitual hygiene practices increase the risk of acquiring intestinal infections.     

广东省河源市龙川县紫市镇猫、犬、猪、鼠寄生虫感染情况调查

目的了解广东省河源市龙川县猫、犬、猪、鼠寄生虫感染情况，为人体寄生虫病防治工作提供科学依据。方法采用生理盐水直接涂片法和清水自然沉淀集卵法，检查猫、犬、猪、鼠粪便，查找寄生虫虫卵。结果调查猫、犬、猪、鼠粪便271份，检出寄生虫卵89份，寄生虫总感染率为32．84％。以猫、犬寄生虫感染率最高。寄生虫感染度以猫粪中的曼氏迭宫绦虫最高，平均每张玻片检出虫卵580个。检出寄生虫卵6种：钩虫卵、蛔虫卵、鞭虫卵、曼氏迭宫绦虫卵、长膜壳绦虫卵和姜片虫卵。猫、犬、猪、鼠各种寄生虫感染情况，以钩虫、蛔虫、鞭虫和曼氏迭宫绦虫感染多见。猪感染寄生虫种类最多。结论广东省河源市龙川县紫市镇猫、犬、猪、鼠寄生虫感染情况比较严重，以猫、犬为甚。寄生虫感染种类较多，提示当地人群也可能有同类寄生虫感染，应引起当地政府和卫生防疫部门的高度重视。     

Co-infection with Trypanosoma brucei brucei prevents experimental autoimmune encephalomyelitis in DBA/1 mice through induction of suppressor APCs

The immune system has co-evolved with the infectious agents that challenge it, and in response pathogens have developed different mechanisms to subvert host immunity. A wealth of evidence suggests that infections are important components in the development of a functional immune system, and understanding the modulation of the host immune system by pathogens may offer new therapeutic strategies in a non-infectious setting. We investigated how infection with the protozoan parasite Trypanosoma brucei brucei (Tbb) modulates the autoimmune response to recombinant myelin oligodendrocyte glycoprotein (rMOG) in DBA/1 mice. Mice harbouring a Tbb infection did not develop experimental autoimmune encephalomyelitis (EAE) induced by immunization with rMOG in CFA, an animal model for the human autoimmune disease multiple sclerosis. Additionally, mice infected with the parasite at the time of immunization or 1 week later developed less severe EAE than uninfected controls. Protected mice displayed a markedly diminished rMOG-specific proliferation and IFNgamma production in lymph node cells and had correspondingly low titres of serum anti-rMOG IgG. Antigen-presenting cells (APCs) from spleens of Tbb-infected mice presented rMOG less efficiently to rMOG-specific T cells in vitro than did splenic APCs from uninfected mice and could also inhibit antigen-specific proliferation in control in vitro cultures. This suppressive effect is at least in part due to increased release of IL-10. Transfer of splenic APCs from Tbb-infected mice into mice immunized with rMOG-CFA 7 days previously abrogated disease significantly. These findings indicate that infections can prevent autoimmunity and that APCs might be used as immunomodulants.