Correction: Vector mapping and bloodmeal metabarcoding demonstrate risk of urban Chagas disease transmission in Caracas, Venezuela.

[This corrects the article DOI: 10.1371/journal.pntd.0010613.].

Vector mapping and bloodmeal metabarcoding demonstrate risk of urban Chagas disease transmission in Caracas, Venezuela.

Chagas disease is a significant public health risk in rural and semi-rural areas of Venezuela. Triatomine infection by the aetiological agent Trypanosoma cruzi is also observed in the Metropolitan District of Caracas (MDC), where foodborne T. cruzi outbreaks occasionally occur but active vector-to-human transmission (infection during triatomine bloodmeal) is considered absent. Citizen science-based domiciliary triatomine collection carried out between 2007 and 2013 in the MDC has advanced understanding of urban T. cruzi prevalence patterns and represents an important public awareness-building tool. The present study reports on the extension of this triatomine collection program from 2014 to 2019 and uses mitochondrial metabarcoding to assess feeding behavior in a subset of specimens. The combined, thirteen-year dataset (n = 4872) shows a high rate of T. cruzi infection (75.2%) and a predominance of Panstrongylus geniculatus (99.01%) among triatomines collected in domiciliary areas by MDC inhabitants. Collection also involved nymphal stages of P. geniculatus in 18 of 32 MDC parishes. Other collected species included Triatoma nigromaculata, Triatoma maculata, Rhodnius prolixus, and Panstrongylus rufotuberculatus. Liquid intestinal content indicative of bloodmeal was observed in 53.4% of analyzed specimens. Dissection pools representing 108 such visually blooded P. geniculatus specimens predominantly tested positive for human cytochrome b DNA (22 of 24 pools). Additional bloodmeal sources detected via metabarcoding analysis included key sylvatic T. cruzi reservoirs (opossum and armadillo), rodents, and various other synanthropic and domesticated animals. Results suggest a porous sylvatic-domiciliary transmission interface and ongoing adaptation of P. geniculatus to the urban ecotope. Although P. geniculatus defecation traits greatly limit the possibility of active T. cruzi transmission for any individual biting event, the cumulation of this low risk across a vast metropolitan population warrants further investigation. Efforts to prevent triatomine contact with human food sources also clearly require greater attention to protect Venezuela's capital from Chagas disease.

Fractal analysis reveals functional unit of ventilation in the lung.

Ventilation is inhomogeneous in the lungs across species. It has been hypothesized that ventilation inhomogeneity is largely determined by the design of the airway branching network. Because exchange of gases at the alveolar barrier is more efficient when gas concentrations are evenly distributed at subacinar length scales, it is assumed that a 'functional unit' of ventilation exists within the lung periphery, where gas concentration becomes uniform. On the other hand, because the morphology of pulmonary airways and alveoli, and the distribution of inhaled fluorescent particles show self-similar fractal properties over a wide range of length scales, it has been predicted that fractal dimension of ventilation approaches unity within an internally homogeneous functional unit of ventilation. However, the existence of such a functional unit has never been demonstrated experimentally due to lack of in situ gas concentration measurements of sufficient spatial resolution in the periphery of a complex bifurcating network. Here, using energy-subtractive synchrotron radiation tomography, we measured the distribution of an inert gas (Xe) in the in vivo rabbit lung during Xe wash-in breathing manoeuvres. The effects of convective flow rate, diffusion and cardiac motion were also assessed. Fractal analysis of resulting gas concentration and tissue density maps revealed that fractal dimension was always smaller for Xe than for tissue density, and that only for the gas, a length scale existed where fractal dimension approached unity. The length scale where this occurred was seen to correspond to that of a rabbit acinus, the terminal structure comprising only alveolated airways. KEY POINTS: Gas ventilation is inhomogeneous in the lung of many species. However, it is not known down to what length scales this inhomogeneity persists. It is generally assumed that ventilation becomes homogeneous at subacinar length scales, beyond the spatial resolution of commonly available imaging techniques, hence this has not been demonstrated experimentally. Here we measured the distribution of inhaled Xe gas in the rabbit lung using synchrotron radiation energy-subtractive imaging and used fractal analysis to show that ventilation becomes internally uniform within regions about the size of rabbit lung acini.

A simulation study of diffusion-convection interaction and its effect on multiple breath washout indices.

Experimental studies of acinar ventilation heterogeneity (Sacin) derived from the multiple breath washout have shown the potential of Sacin to pick up structural change in lung disease. Recent Sacin data suggest that even when intra-acinar structure is unaltered, the combination of convection, diffusion and number of acini fed by patent terminal bronchioles can modify Sacin. We show here how Sacin is affected by structural features such as the secondary alveolar septa, intra-acinar ramification and number of ventilated acini. The simulations also predict relationships between respective alterations in Sacin and washout indices such as lung clearance index (LCI) and alveolar mixing efficiency (AME). This was verified experimentally, with highly significant correlations between Sacin and LCI (r = +0.85;p < 0.001) and between Sacin and AME (r = - 0.92; p < 0.001). We have shown how acinar ventilation heterogeneity can be affected by a reduction of number of ventilated acini, a change in overall alveolization or in intra-acinar alveolization pattern, via their impact on the balance between convection and diffusion at acinar level.

Acinar and conductive ventilation heterogeneity in severe CF lung disease: back to the model.

Severe convective ventilation heterogeneity occurring in CF lung disease requires a modified method to determine acinar and conductive components of ventilation heterogeneity from normalized phase III slope (Sn) curves. Modified Sacin* and Scond* (as opposed to standard Sacin and Scond) are proposed and interpreted on the basis of 2 conceptual mechanisms: (a) flow asynchrony between two convection-dependent units with a different specific ventilation, but with an identical acinus inside each unit (generating an identical diffusion-convection-dependent portion of Sn); (b) different specific ventilation (without any flow asynchrony) between two convection-dependent units with the worst ventilated unit containing an abnormal acinus generating the greatest diffusion-convection-dependent portion of Sn. In CF patients with an abnormal lung clearance index (LCI), Scond* (but not Scond) and Sacin* were significant contributors to LCI (ß(Scond*)=0.70; ß(Sacin*)=0.49; P<0.001 for both). Mechanism (a) can entirely account for experimental Scond* values, while mechanism (b) implies that experimental Sacin* values are likely dominated by peripheral ventilation heterogeneity in the best ventilated portions of the lung.

Consensus statement for inert gas washout measurement using multiple- and single- breath tests.

Inert gas washout tests, performed using the single- or multiple-breath washout technique, were first described over 60 years ago. As measures of ventilation distribution inhomogeneity, they offer complementary information to standard lung function tests, such as spirometry, as well as improved feasibility across wider age ranges and improved sensitivity in the detection of early lung damage. These benefits have led to a resurgence of interest in these techniques from manufacturers, clinicians and researchers, yet detailed guidelines for washout equipment specifications, test performance and analysis are lacking. This manuscript provides recommendations about these aspects, applicable to both the paediatric and adult testing environment, whilst outlining the important principles that are essential for the reader to understand. These recommendations are evidence based, where possible, but in many places represent expert opinion from a working group with a large collective experience in the techniques discussed. Finally, the important issues that remain unanswered are highlighted. By addressing these important issues and directing future research, the hope is to facilitate the incorporation of these promising tests into routine clinical practice.

Lung clearance index in adult cystic fibrosis patients: the role of convection-dependent lung units.

We investigated the extent of convective ventilation heterogeneity contributing to the observed lung clearance index values in adult cystic fibrosis patients, as the result of two simulated scenarios, either 1) a fixed part of the lungs becoming increasingly less compliant, or 2) an increasingly greater part of the lung being less compliant. In 25 cystic fibrosis patients and 25 matched controls, we computed the lung clearance index and also quantified curvilinearity of the washout concentration curve, where curvilinearity is equal to 0 (linear in semilog plot) reflects homogeneous ventilation and curvilinearity equal to 1 corresponds to the presence of an infinitesimally slowly emptying lung unit. In the cystic fibrosis group (forced expiratory volume in 1 s 27-100% predicted), lung clearance index and curvilinearity average±sd values were 10.3±2.3 and 0.57±0.13, respectively, and were significantly different from control values (6.2±0.4 and 0.18±0.07; both p<0.001); lung clearance index and curvilinearity were also correlated (R = 0.67; p<0.001). The average curvilinearity value in the cystic fibrosis group was found to be compatible with a cumulative volume of underventilated lung of 40-50%, depending on the simulation scenario considered. The degree of washout curvilinearity observed here indicates that a major determinant of the abnormal lung clearance index values observed in adult cystic fibrosis patients is ventilation heterogeneity generated between convection-dependent lung units, while the remainder of lung clearance index abnormality with respect to normal controls potentially represents the small airways within these lung zones.

Ventilation heterogeneity in the acinar and conductive zones of the normal ageing lung.

RATIONALE: Small airways function studies in lung disease have used three promising multiple breath washout (MBW) derived indices: indices of ventilation heterogeneity in the acinar (S(acin)) and conductive (S(cond)) lung zones, and the lung clearance index (LCI). Since peripheral lung structure is known to change with age, ventilation heterogeneity is expected to be affected too. However, the age dependence of the MBW indices of ventilation heterogeneity in the normal lung is unknown. OBJECTIVES: The authors systematically investigated S(acin), S(cond) or LCI as a function of age, testing also the robustness of these relationships across two laboratories. METHODS: MBW tests were performed by never-smokers (50% men) in the age range 25-65 years, with data gathered across two laboratories (n=120 and n=60). For comparison with the literature, the phase III slopes from classical single breath washout tests were also acquired in one group (n=120). MEASUREMENTS AND MAIN RESULTS: All three MBW indices consistently increased with age, representing a steady worsening of ventilation heterogeneity in the age range 25-65. Age explained 7-16% of the variability in S(acin) and S(cond) and 36% of the variability in LCI. There was a small but significant gender difference only for S(acin). Classical single breath washout phase III slopes also showed age dependencies, with gender effects depending on the normalisation method used. CONCLUSIONS: With respect to the clinical response, age is a small but consistent effect that needs to be factored in when using the MBW indices for the detection of small airways abnormality in disease.

Relationships between the lung clearance index and conductive and acinar ventilation heterogeneity.

The lung clearance index (LCI) derived from a multiple breath washout test has regained considerable popularity in recent years, alternatively being promoted as an early detection tool or a marker of small airways function. In this study, we systematically investigated the link between LCI and indexes of acinar and conductive airways ventilation heterogeneity (Sacin, Scond) to assess potential contributions from both lung zones. Relationships were examined in 55 normal subjects after provocation, where only Scond is known to be markedly increased, and in 55 asthma patients after bronchodilation, in whom both Scond and Sacin ranged between normal and abnormal. LCI was correlated to Scond in both groups (R = 0.37-0.43; P < 0.01 for both); in the asthma group, LCI was also tightly correlated to Sacin (R = 0.70; P < 0.001). Potential mechanisms operational at various levels of the bronchial tree were identified by considering washout curvilinearity in addition to LCI to distinguish specific ventilation and dead space effects (also illustrated by simple 2-compartment model simulations). Although the asthma data clearly demonstrate that LCI can reflect very peripheral ventilation heterogeneities, the normal provocation data also convincingly show that LCI increases may be the exclusive result of far more proximal ventilation heterogeneities. Because LCI potentially includes heterogeneities at all length scales, it is suggested that ventilation imaging in combination with LCI measurement at the mouth could identify the scale of relevant ventilation heterogeneities. In the meantime, interpretations of LCI results in the clinic based on washout curves collected at the mouth should be handled with caution.

Gas mixing in the airways and airspaces.

Basic physical concepts of diffusion, convection, and dispersion pertaining to gas transport in the human airways are reviewed. Their incorporation into quantitative models of gas mixing is presented, also illustrating the crucial interaction of gas transport equations with the model geometry. Model simulations are confronted with the available experimental gas mixing indices such as the phase III slope obtained in normal human lungs, with some pertinent examples in laboratory animals and in human lung disease. The use of inert gases with differing diffusion coefficients and their associated phase III slope provides invaluable experimental information on gas mixing in the lungs, with the concept of the diffusion front playing a central role. Sources of inter- and intraregional ventilation heterogeneity can be related to the location of the diffusion front, which offers the possibility to distinguish between ventilation heterogeneity proximal to the diffusion front (driven by convection between lung units larger than acini) and more peripheral ventilation heterogeneity (driven by diffusion-convection interaction mainly within the acinus). While specific ventilation distribution and flow asynchrony co-act to generate convection-dependent ventilation heterogeneity, local structural asymmetry of the acinar air spaces is sufficient to generate diffusion-convection-dependent ventilation heterogeneity. The remaining hiatus in our understanding of ventilation heterogeneity in the human lung is described, together with some potential perspectives for its investigation.

Enfermedad de chagas sistémico en fase aguda por transmisión oral: diagnóstico integral de un caso autopsiado / Acute phase of systemic chagas disease due to oral transmission: integral diagnosis of an autopsied case

Se presenta el primer caso autopsiado en Venezuela con enfermedad de Chagas por transmisión oral. Se trata de una joven de 24 años de edad con 8 semanas de embarazo quien contrajo la enfermedad conjuntamente con 71 niños y 14 adultos, la mayoría integrantes de la comunidad escolar “Rómulo Monasterios” en la localidad de Chichiriviche de la costa Vargas, donde ocurrió el segundo brote agudo de enfermedad de Chagas por transmisión oral registrado en Venezuela. El diagnóstico epidemiológico, clínico, serológico y parasitológico en sangre y líquido pleural extraídos en vida, fueron confirmados con los hallazgos histopatológicos y moleculares (PCR) de los tejidos. Se plantearon las características peculiares del caso así como algunos aspectos de la transmisión oral, ampliamente estudiados en nuestro país en animales de experimentación.

This first autopsy case with Chagas disease by oral transmissions in Venezuela is presented. This is a 24 year old girl with 8 weeks of pregnancy who contracted the disease together with 71 and 14 adults, the majority members of the school community “Romulo Monasterios” in the town of Vargas State, where occurred the second acute Chagas disease outbreak by oral transmission in Venezuela.The epidemiological, clinical, serological and parasitological diagnosis in the blood and pleural fluid extracted in life, were confirmed with the histopathology and molecular (PCR) finding in the tissues, Special features of the case are shown, as well as, some aspects of oral transmission widely studied in our country in experimental animals.