Key Source Habitats and Potential Dispersal of Triatoma infestans Populations in Northwestern Argentina: Implications for Vector Control

Background

Triatoma infestans —the principal vector of the infection that causes Chagas disease— defies elimination efforts in the Gran Chaco region. This study identifies the types of human-made or -used structures that are key sources of these bugs in the initial stages of house reinfestation after an insecticide spraying campaign.

Methodology and Principal Findings

We measured demographic and blood-feeding parameters at two geographic scales in 11 rural communities in Figueroa, northwest Argentina. Of 1,297 sites searched in spring, 279 (21.5%) were infested. Bug abundance per site and female fecundity differed significantly among habitat types (ecotopes) and were highly aggregated. Domiciles (human sleeping quarters) had maximum infestation prevalence (38.7%), human-feeding bugs and total egg production, with submaximal values for other demographic and blood-feeding attributes. Taken collectively peridomestic sites were three times more often infested than domiciles. Chicken coops had greater bug abundance, blood-feeding rates, engorgement status, and female fecundity than pig and goat corrals. The host-feeding patterns were spatially structured yet there was strong evidence of active dispersal of late-stage bugs between ecotopes. Two flight indices predicted that female fliers were more likely to originate from kitchens and domiciles, rejecting our initial hypothesis that goat and pig corrals would dominate.

Conclusions and Significance

Chicken coops and domiciles were key source habitats fueling rapid house reinfestation. Focusing control efforts on ecotopes with human-fed bugs (domiciles, storerooms, goat corrals) would neither eliminate the substantial contributions to bug population growth from kitchens, chicken coops, and pig corrals nor stop dispersal of adult female bugs from kitchens. Rather, comprehensive control of the linked network of ecotopes is required to prevent feeding on humans, bug population growth, and bug dispersal simultaneously. Our study illustrates a demographic approach that may be applied to other regions and triatomine species for the design of innovative, improved vector control strategies.     

Domestic Animal Hosts Strongly Influence Human-Feeding Rates of the Chagas Disease Vector Triatoma infestans in Argentina

Background

The host species composition in a household and their relative availability affect the host-feeding choices of blood-sucking insects and parasite transmission risks. We investigated four hypotheses regarding factors that affect blood-feeding rates, proportion of human-fed bugs (human blood index), and daily human-feeding rates of Triatoma infestans, the main vector of Chagas disease.

Methods

A cross-sectional survey collected triatomines in human sleeping quarters (domiciles) of 49 of 270 rural houses in northwestern Argentina. We developed an improved way of estimating the human-feeding rate of domestic T. infestans populations. We fitted generalized linear mixed-effects models to a global model with six explanatory variables (chicken blood index, dog blood index, bug stage, numbers of human residents, bug abundance, and maximum temperature during the night preceding bug catch) and three response variables (daily blood-feeding rate, human blood index, and daily human-feeding rate). Coefficients were estimated via multimodel inference with model averaging.

Findings

Median blood-feeding intervals per late-stage bug were 4.1 days, with large variations among households. The main bloodmeal sources were humans (68%), chickens (22%), and dogs (9%). Blood-feeding rates decreased with increases in the chicken blood index. Both the human blood index and daily human-feeding rate decreased substantially with increasing proportions of chicken- or dog-fed bugs, or the presence of chickens indoors. Improved calculations estimated the mean daily human-feeding rate per late-stage bug at 0.231 (95% confidence interval, 0.157–0.305).

Conclusions and Significance

Based on the changing availability of chickens in domiciles during spring-summer and the much larger infectivity of dogs compared with humans, we infer that the net effects of chickens in the presence of transmission-competent hosts may be more adequately described by zoopotentiation than by zooprophylaxis. Domestic animals in domiciles profoundly affect the host-feeding choices, human-vector contact rates and parasite transmission predicted by a model based on these estimates.     

A Pilot Study of Diffusion-Weighted MRI in Patients Undergoing Neoadjuvant Chemoradiation for Pancreatic Cancer

PURPOSE: In the current study we examined the ability of diffusion MRI (dMRI) to predict pathologic response in pancreatic cancer patients receiving neoadjuvant chemoradiation. METHODS: We performed a prospective pilot study of dMRI in patients with resectable pancreatic cancer. Patients underwent dMRI prior to neoadjuvant chemoradiation. Surgical specimens were graded according to the percent tumor cell destruction. Apparent diffusion coefficient (ADC) maps were used to generate whole-tumor derived ADC histogram distributions and mean ADC values. The primary objective of the study was to correlate ADC parameters with pathologic and CT response. RESULTS: Ten of the 12 patients enrolled on the study completed chemoradiation and had surgery. Three were found to be unresectable at the time of surgery and no specimen was obtained. Out of the 7 patients who underwent pancreaticoduodenectomy, 3 had a grade III histopathologic response (> 90% tumor cell destruction), 2 had a grade IIB response (51% to 90% tumor cell destruction), 1 had a grade IIA response (11% to 50% tumor cell destruction), and 1 had a grade I response (> 90% viable tumor). Median survival for patients with a grade III response, grade I-II response, and unresectable disease were 25.6, 18.7, and 6.1 months, respectively. There was a significant correlation between pre-treatment mean tumor ADC values and the amount of tumor cell destruction after chemoradiation with a Pearson correlation coefficient of 0.94 (P = .001). Mean pre-treatment ADC was 161 × 10^− 5 mm²/s (n = 3) in responding patients (> 90% tumor cell destruction) compared to 125 × 10^− 5 mm²/s (n = 4) in non-responding patients (> 10% viable tumor). CT imaging showed no significant change in tumor size in responders or non-responders. CONCLUSIONS: dMRI may be useful to predict response to chemoradiation in pancreatic cancer. In our study, tumors with a low ADC mean value at baseline responded poorly to standard chemoradiation and would be candidates for intensified therapy.     

NCI Workshop Report: Clinical and Computational Requirements for Correlating Imaging Phenotypes with Genomics Signatures

The National Cancer Institute (NCI) Cancer Imaging Program organized two related workshops on June 26–27, 2013, entitled “Correlating Imaging Phenotypes with Genomics Signatures Research” and “Scalable Computational Resources as Required for Imaging-Genomics Decision Support Systems.” The first workshop focused on clinical and scientific requirements, exploring our knowledge of phenotypic characteristics of cancer biological properties to determine whether the field is sufficiently advanced to correlate with imaging phenotypes that underpin genomics and clinical outcomes, and exploring new scientific methods to extract phenotypic features from medical images and relate them to genomics analyses. The second workshop focused on computational methods that explore informatics and computational requirements to extract phenotypic features from medical images and relate them to genomics analyses and improve the accessibility and speed of dissemination of existing NIH resources. These workshops linked clinical and scientific requirements of currently known phenotypic and genotypic cancer biology characteristics with imaging phenotypes that underpin genomics and clinical outcomes. The group generated a set of recommendations to NCI leadership and the research community that encourage and support development of the emerging radiogenomics research field to address short-and longer-term goals in cancer research.     

Maternal cardiovascular disease after twin pregnancies complicated by hypertensive disorders of pregnancy: a population-based cohort study

Background:People whose singleton pregnancy is affected by hypertensive disorders of pregnancy (HDP) are at risk of future cardiovascular disease. It is unclear, however, whether this association can be extrapolated to twin pregnancies. We aimed to compare the association between HDP and future cardiovascular disease after twin and singleton pregnancies.Methods:We conducted a population-based retrospective cohort study that included nulliparous people in Ontario, Canada, 1992–2017. We compared the future risk of cardiovascular disease among pregnant people from the following 4 groups: those who delivered a singleton without HDP (referent) and with HDP, and those who delivered twins either with or without HDP.Results:The populations of the 4 groups were as follows: 1 431 651 pregnant people in the singleton birth without HDP group; 98 631 singleton birth with HDP; 21 046 twin birth without HDP; and 4283 twin birth with HDP. The median duration of follow-up was 13 (interquartile range 7–20) years. The incidence rate of cardiovascular disease was lowest among those with a singleton or twin birth without HDP (0.72 and 0.74 per 1000 person-years, respectively). Compared with people with a singleton birth without HDP, the risk of cardiovascular disease was highest among those with a singleton birth and HDP (1.47 per 1000 person-years; adjusted hazard ratio [HR] 1.81 [95% confidence interval (CI) 1.72–1.90]), followed by people with a twin pregnancy and HDP (1.07 per 1000 person-years; adjusted HR 1.36 [95% CI 1.04–1.77]). The risk of the primary outcome after a twin pregnancy with HDP was lower than that after a singleton pregnancy with HDP (adjusted HR 0.74 [95% CI 0.57–0.97]), when compared directly.Interpretation:In a twin pregnancy, HDP are weaker risk factors for postpartum cardiovascular disease than in a singleton pregnancy.

Cardiovascular disease has been shown to be the leading cause of death among women.^1–3 Classic risk factors for cardiovascular disease include obesity, diabetes mellitus, hypertension and family history of cardiovascular disease. ³ More recently, an association has been established between a history of hypertensive disorders of pregnancy (HDP) — gestational hypertension and pre-eclampsia — and future risk of cardiovascular disease.^1,4–11 Consequently, some recommend using a history of HDP for cardiovascular disease risk stratification in women.^3,12The leading hypothesis for the pathogenesis of HDP is that it results from abnormal placentation due to impaired trophoblast invasion,^13–16 resulting in reduced placental perfusion.^17–19 This, in turn, leads to abnormal secretion of the angiogenic factors soluble FMS-like tyrosine kinase 1 (sFlt1) and soluble endoglin (sEng),²⁰ which induce endothelial dysfunction and the clinical manifestations of HDP.^19,21–24 The mechanisms underlying the association between HDP and future cardiovascular disease are under debate.²⁵ One hypothesis is that HDP are merely a marker of underlying subclinical or clinical vascular risk factors that predispose a person to both HDP and future cardiovascular disease.A person who is pregnant with twins is at about 3–4 times higher risk of HDP than a person with a singleton pregnancy,^26–33 with rates of 14% and 5%, respectively.³⁴ The higher risk of HDP in twin pregnancies may be due to higher circulating sFlt1 and sEng owing to greater placental mass in twin pregnancies, ^35–37 and less related to the classic vascular risk factors for HDP in a singleton pregnancy. Therefore, a logical question is whether the established higher risk of future cardiovascular disease after singleton pregnancies with HDP also occurs in twin pregnancies with HDP. Limited data are available to answer this question.³⁸ In the current study, we aimed to test the hypothesis that the association between HDP and future cardiovascular disease is less pronounced in twin versus singleton pregnancies.     

Perturbation of the Intermolecular Contact Regions (Molecular Surface) of Hemoglobin S by Intramolecular, Low-O2-Affinity-Inducing Central Cavity Cross-Bridges

The general assumption among researchers on hemoglobin is that the intramolecular central cavity cross-bridging of Hb does not result in any generalized perturbations at the protein surface. A corollary of this is that central cavity cross-bridges are unlikely to influence the polymerization of deoxy HbS, since polymerization is a protein surface phenomenon involving the participation of multiple protein surface amino acid residues. In an attempt to evaluate this experimentally, we have introduced two low-O₂-affinity-inducing central cavity cross-bridges into HbS, ββ-sebacyl [between the two Lys-82(β) residues] and αα-fumaryl [between the two Lys-99(α) residues], and investigated their influence on the polymerization of the deoxy protein. The O₂ affinities of the cross-bridged HbS exhibited sensitivity toward the buffer ions and pH in a cross-link-specific fashion. The modulation of the O₂ affinity of these cross-bridged HbS in the presence of allosteric effectors, DPG and L-35, is also very distinct, reflecting the differences in the conformational features these two cross-bridges induce within the central cavity at the respective effector-binding domains. In addition, the αα-fumaryl cross bridge inhibited the polymerization, reflecting the perturbation of the microenvironment of one or more intermolecular contact residues, protein surface residues, as a consequence of the central cavity cross-bridge. On the other hand, the ββ-sebacyl cross-bridge exerted a slight potentiating effect on the polymerization of HbS. This reflects the fact that the perturbations at the protein surface are limited and favor polymerization. The results presented demonstrate that the structural changes induced by the central cavity cross-bridges are very specific and not simply restricted to the sites of modification, but are propagated to distant sites/domains, both within and outside the central cavity. It is conceivable that other surface regions that are not involved in the polymerization could also experience similar structural/conformational consequences. These results should be taken into consideration in designing intramolecularly cross-bridged asymmetric hybrid HbS for mapping the contribution of the intermolecular contact residues in the cis and trans dimers of deoxy HbS during polymerization.     

Quantification of Bacterial Groups within Human Fecal Flora by Oligonucleotide Probe Hybridization

To investigate the population structure of the predominant phylogenetic groups within the human adult fecal microbiota, a new oligonucleotide probe designated S-G-Clept-1240-a-A-18 was designed, validated, and used with a set of five 16S rRNA-targeted oligonucleotide probes. Application of the six probes to fecal samples from 27 human adults showed additivity of 70% of the total 16S rRNA detected by the bacterial domain probe. The Bacteroides group-specific probe accounted for 37% ± 16% of the total rRNA, while the enteric group probe accounted for less than 1%. Clostridium leptum subgroup and Clostridium coccoides group-specific probes accounted for 16% ± 7% and 14% ± 6%, respectively, while Bifidobacterium and Lactobacillus groups made up less than 2%.     

Sulfate-Reducing Bacteria Methylate Mercury at Variable Rates in Pure Culture and in Marine Sediments

Differences in methylmercury (CH₃Hg) production normalized to the sulfate reduction rate (SRR) in various species of sulfate-reducing bacteria (SRB) were quantified in pure cultures and in marine sediment slurries in order to determine if SRB strains which differ phylogenetically methylate mercury (Hg) at similar rates. Cultures representing five genera of the SRB (Desulfovibrio desulfuricans, Desulfobulbus propionicus, Desulfococcus multivorans, Desulfobacter sp. strain BG-8, and Desulfobacterium sp. strain BG-33) were grown in a strictly anoxic, minimal medium that received a dose of inorganic Hg 120 h after inoculation. The mercury methylation rates (MMR) normalized per cell were up to 3 orders of magnitude higher in pure cultures of members of SRB groups capable of acetate utilization (e.g., the family Desulfobacteriaceae) than in pure cultures of members of groups that are not able to use acetate (e.g., the family Desulfovibrionaceae). Little or no Hg methylation was observed in cultures of Desulfobacterium or Desulfovibrio strains in the absence of sulfate, indicating that Hg methylation was coupled to respiration in these strains. Mercury methylation, sulfate reduction, and the identities of sulfate-reducing bacteria in marine sediment slurries were also studied. Sulfate-reducing consortia were identified by using group-specific oligonucleotide probes that targeted the 16S rRNA molecule. Acetate-amended slurries, which were dominated by members of the Desulfobacterium and Desulfobacter groups, exhibited a pronounced ability to methylate Hg when the MMR were normalized to the SRR, while lactate-amended and control slurries had normalized MMR that were not statistically different. Collectively, the results of pure-culture and amended-sediment experiments suggest that members of the family Desulfobacteriaceae have a greater potential to methylate Hg than members of the family Desulfovibrionaceae have when the MMR are normalized to the SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in marine sediments that are rich in organic matter and dissolved sulfide rapid CH₃Hg accumulation is coupled to rapid sulfate reduction. The observations described above have broad implications for understanding the control of CH₃Hg formation and for developing remediation strategies for Hg-contaminated sediments.     

Single-Step Purification of Two Functional Human Apolipoprotein E Variants Hyperexpressed inEscherichia coli

We have cloned, from total human liver RNA, the cDNA encoding apolipoprotein E3 (apoE3). Site-directed mutagenesis was used to obtain the cDNA encoding the apoE4 isoform, a major variant of this apolipoprotein in man. These two cDNAs were subcloned into the procaryotic expression vector pAHRS. A polyhistidine tag was added at the NH₂-termini of the recombinant proteins (apoE3 and apoE4) to enable rapid purification. The resulting plasmids (pAHRS-apoE3 and pAHRS-apoE4) were introduced into theEscherichia colistrain BL21(DE3). Recombinant strains were grown at 37°C in a Luria and Bertani medium and the addition of isopropyl β-thiogalactoside resulted in the expression of large amounts of apoE protein (40.5 kDa), representing at least 15% of cellular proteins. The recombinant apoE isoforms were purified, under denaturating conditions, in one step by affinity chromatography on a Ni-chelated agarose column, yielding to about 20 mg of 96% pure protein per liter of culture. Compared to plasma apoE3 purified from human very low density lipoproteins, the two renatured recombinant apoE isoforms have the same secondary structure content, as revealed by circular dichroism measurement. Moreover, the recombinant apoE3 isoform shares similar properties for the association with lipids, compared to the human protein, indicating that the addition of the amino-terminal polyhistidine peptide does not influence the structure and the lipid binding properties of this recombinant apoE isoform. No differences in the secondary structure of recombinant apoE4 were detected, whereas this isoform presents specific reactivity with lipids. This simple and rapid procedure for the expression and the purification of functional recombinant apoE should therefore enable structural and physiological studies requiring large amounts of these apolipoproteins.     

Differing roles of mitochondrial nitric oxide synthase in cardiomyocytes and urothelial cells

The existence of mitochondrial nitric oxide (NO) synthase (mtNOS) has been controversial since it was first reported in 1995. We have addressed this issue by making direct microsensor measurements of NO production in the mitochondria isolated from mouse hearts. Mitochondrial NO production was stimulated by Ca2+ and inhibited by blocking electrogenic Ca2+ uptake or by using NOS antagonists. Cardiac mtNOS was identified as the neuronal isoform by the absence of NO production in the mitochondria of mice lacking the neuronal but not the endothelial or inducible isoforms. In cardiomyocytes from dystrophin-deficient (mdx) mice, elevated intracellular Ca2+, increased mitochondrial NO production, slower oxidative phosphorylation, and decreased ATP production were detected. Inhibition of mtNOS increased contractility in mdx but not in wild-type cardiomyocytes, indicating that mtNOS may protect the cells from overcontracting. mtNOS was also implicated in radiation-induced cell damage. In irradiated rat/mouse urinary bladders, we have evidence that mitochondrially produced NO damages the urothelial "umbrella" cells that line the bladder lumen. This damage disrupts the permeability barrier thereby creating the potential to develop radiation cystitis. RT-PCR and Southern blot analyses indicate that mtNOS is restricted to the umbrella cells, which scanning electron micrographs show are selectively damaged by radiation. Simultaneous microsensor measurements demonstrate that radiation increases NO and peroxynitrite (ONOO-) production in these cells, which can be prevented by transfection with manganese superoxide dismutase (MnSOD) or instillation of NOS antagonists during irradiation or irradiation of bladders devoid of mtNOS. These studies demonstrate that mtNOS is in the cardiomyocytes and urothelial cells, that it is derived from the neuronal isoform, and that it can be either protective or detrimental.