Temporal dynamics of the egg bank of Aedes aegypti (Diptera: Culicidae) in the winter-spring transition in a temperate region.

In temperate regions, the populations of Aedes aegypti (L.) (Diptera: Culicidae) remain in the egg stage during the winter. In Buenos Aires, Argentina, a temperate region in the southern limit of Ae. aegypti distribution, the start of the next reproductive season and the rate of increase of the adult population depend on the egg bank that remains after the winter. This study aimed to analyze the mortality, field-hatching, and survival of eggs exposed to field conditions representative of those that occur in nature. In addition, the post-exposure hatching response of the eggs was assessed. Four egg batches were exposed to natural conditions starting in mid-winter and were recovered progressively after 3, 6, 9, and 12 weeks. One egg batch (initial control) was not exposed in the field and remained under laboratory conditions. After the exposure period, the recovered intact, collapsed, and hatched eggs were counted. Intact eggs were immersed three times in the laboratory to study their hatching response. Progressive increases in the proportion of lost (presumably by predation), dead, and hatched eggs in successive egg batches were recorded. Field-hatching was recorded from late winter onwards. The first hatchings occurred in conditions probably not favorable to complete development into reproductive adults. A progressive decrease in live eggs was observed, with 51% of the recovered eggs alive after 12 weeks of exposure. In the laboratory, the hatching response in the first immersion was low for the initial control and for the eggs exposed for 3 weeks, and increased for successive cohorts. The results confirm that the survival of Ae. aegypti eggs in the winter-spring transition ensures persistence throughout the next favorable season in Buenos Aires City. The observed inhibition to hatch of the first batches might relate to a photoperiod-induced diapause, as observed in previous studies.

Increased size and energy reserves in diapausing eggs of temperate Aedes aegypti populations.

Many insects overwinter in diapause, a pre-programmed anticipated response to unfavorable environmental conditions, often induced by a short-day photoperiod. Diapause involves morphological changes and increased energy stores required for metabolic demands during winter. In diapausing mosquito eggs, the accumulation of lipids plays an important role, because these molecules are the primary fuel consumed during embryogenesis and pharate larvae metabolism, and have a key role in egg desiccation resistance. The supposed inability of the mosquito Aedes aegypti to lay diapausing eggs has been recently challenged by a study on a temperate population, which showed that the inhibition of egg hatching in response to short days is possible in this species. Thus, the aim of the present study was to assess the effects of parental photoperiod on embryonic diapause-related traits, such as the triglyceride content and size of eggs laid, of two populations whose localities of origin differ in their winter length. Two colonies were maintained for each population: one under a Short-Day Photoperiod (SD: 10 h:14 h - Light:Dark) and the other under a Long-Day Photoperiod (LD: 14 h:10 h - Light:Dark). The eggs obtained from each combination of population and light treatment were used for size measurement (length, width and volume) and for the quantification of triglyceride content. Egg size showed differences between photoperiod treatments, with larger width and volume in eggs from the SD treatment. Remarkably, eggs from the SD treatment accumulated twice as many triglycerides as those from the LD treatment. Also, the eggs derived from the population having the longer winter accumulated larger amounts of triglycerides. The higher lipid content is probably contributing to a better survival during the cold season in both populations. The photoperiod-induced response in egg size and amount of triglycerides observed in this study support the hypothesis that the Ae. aegypti populations studied are able to lay diapausing eggs, a fact that provides physiological bases for the further expansion of this species to colder regions.

Comparative Study on the Thermal Performance of Three Aedes aegypti (Diptera: Culicidae) Populations From Argentina.

The distribution of Aedes aegypti (L.) (Diptera: Culicidae) is expanding towards colder regions, which could be aided by an adaptation of the immature stages to the local thermal conditions. This study aimed to assess the developmental success at different temperatures in three populations of Ae. aegypti located across a climate gradient in Argentina. Survival to the adult stage, development time, and wing length at 14, 18.5 and 24°C were compared among three populations of Argentina: Resistencia in the subtropical region, and Buenos Aires and San Bernardo in the temperate region. Survival was similar between populations and equal to or higher than 69%, and increased at higher temperatures within the studied range. Development times were similar between populations. A negative effect of temperature was observed and the reduction of development time at increasing temperatures was stronger for males than for females. Wing lengths were negatively affected by increasing temperatures, and the reduction of wing length was stronger for females than for males. Also, the reduction of wing lengths with temperature was stronger for San Bernardo and Resistencia than for Buenos Aires, and differences between sexes were larger for Resistencia than for Buenos Aires or San Bernardo. Although the results do not evidence differences in survival and development time between temperate and tropical populations, the three populations have a higher tolerance to low temperatures than the populations from other regions.

Effect of Parental Photoperiod on Body Size and Developmental Time of Aedes aegypti (Diptera: Culicidae) in Buenos Aires City.

Many insects use photoperiod as a signal to anticipate upcoming unfavorable conditions. Photoperiod sensitivity may be a relevant factor in Aedes (Stegomyia) aegypti (L.) populations at the cool margins of the species' range, where winter conditions have a strong effect on population dynamics. In this study, we evaluated the effect of parental photoperiod on preimaginal survival and developmental time, and on wing length for the first generation of Ae. aegypti from a temperate region (Buenos Aires City, Argentina). Our experiment started with eggs from parents exposed to short-day (SD; 10:14 [L:D]) or long-day (LD; 14:10 [L:D]) photoperiods during their entire life span. Eggs were stored under the same photoperiod (SD or LD) as their parents for 91 d, until immersion. After hatching, larvae were reared until adult emergence in thermal baths at one of two constant temperatures (17 or 23°C), at a photoperiod of 12:12 (L:D) h and fed ad libitum. Survival from larva I to adult emergence was not affected either by parental photoperiod or rearing temperature. At a rearing temperature of 23°C, female offspring from the SD parental photoperiod developed faster and had shorter wings compared with those from the LD parental photoperiod. No effect of parental photoperiod was observed on female offspring reared at 17°C. In male offspring, parental photoperiod had no effect on developmental time and wing length, independently of the rearing temperature. Results indicate that the parental photoperiod may affect some offspring traits. This effect may be a characteristic of Ae. aegypti populations in temperate regions to deal with the winter conditions.

Delayed mortality effects of cold fronts during the winter season on Aedes aegypti in a temperate region.

The expansion of the invasive mosquito Aedes aegypti L. (Diptera: Culicidae) towards temperate regions in the Americas is causing concern because of its public health implications. As for other insects, the distribution limits of Ae. aegypti have been suggested to be related to minimum temperatures and to be controlled mainly by cold tolerance. The aim of this study was to assess the daily mortality of immature stages of Ae. aegypti under natural winter conditions in Buenos Aires, Argentina, in relation to preceding thermal conditions. The experiment was performed outdoors, and one cohort of larvae was started each week for 16 weeks, and reared up to the emergence of the adults. Three times a week, larvae, pupae and emerged adults were counted, and these data were used to calculate the daily mortality of larvae, pupae and adults and to analyze their relationship with thermal conditions. The results showed that mortality was generally low, with a few peaks of high mortality after cold front events. The mortality of pupae and larvae showed a higher correlation with the cooling degree hours of previous days than with the minimum, maximum or mean temperatures. Pupae and adults showed to be more vulnerable to low temperatures than larvae. A delay in mortality was observed in relation to the low temperature events, with a proportion of individuals dying in a later stage after the end of the cold front. These results suggest that thermal conditions during cold fronts in Buenos Aires are close to the tolerance limit of the local Ae. aegypti population. The wide range of responses of different individuals suggests that low winter temperatures may constitute a selective force, leading the population to a higher tolerance to low temperatures, which might favor the further expansion of this species towards colder regions.

Effects of Constant and Fluctuating Low Temperatures on the Development of Aedes aegypti (Diptera: Culicidae) from a Temperate Region.

Most studies of the effects of low temperature on the development of immature stages of Aedes aegypti (L.) have been performed at constant temperatures in the laboratory, which may not accurately reflect the variable environmental conditions in the field. Thus, the aim of this study was to assess the effect of constant temperatures (CT) and fluctuating low temperatures (FT) on the fitness of Ae. aegypti of Buenos Aires, Argentina. Three CT treatments (12, 14, and 16°C) and three FT treatments (12, 14, and 16°C ± 4°C) were performed and then survival, development time, and size of adults analyzed for each treatment. The immature stages completed development in all the treatments, with an average survival of 88% at 16°C, 85% at 14°C, and 22% at 12°C, and showed no differences between the CT and FT treatments. Development times were similar between the CT and FT treatments at 16°C (average ± SD: 22.7 ± 2.0 d) and at 14°C (average ± SD: 30.5 ± 2.5 d), whereas at 12°C, they lasted longer under CT (average ± SD: 46.6 ± 5.1 d) than under FT (average ± SD: 37 ± 6.5 d). The sizes of the adults at 12 and 14°C were similar but larger than those at 16°C, and showed no differences between the CT and FT treatments. Compared to populations of other geographical regions assessed in previous studies, the shorter development times and the high survival at 14 and 16°C, and the ability to complete development at 12°C, a fact not previously reported, suggest that the Ae. aegypti population of Buenos Aires city has a higher tolerance to these conditions.

Adaptation to temperate climates: Evidence of photoperiod-induced embryonic dormancy in Aedes aegypti in South America.

Dormancy is a developmental arrest in arthropods, in response to unfavorable conditions in temporally varying environments. In Aedes aegypti, the supposed inability of eggs to inhibit hatching has been used to explain the restriction of this species to tropical and subtropical regions. However, the geographic range of Ae. aegypti is constantly expanding towards temperate regions. Thus, the aim of the present study was to assess the ability of Ae. aegypti individuals from a temperate region (Buenos Aires City, Argentina) to enter photoperiod induced dormancy. To this end, we exposed both the parental generation and the eggs to short-day (SD: 10L:14D) and long-day (LD: 14L:10D) photoperiods, and studied the temporal variation in egg hatching. The experiment consisted of 28 treatment combinations of three factors: parental photoperiod (SD or LD), egg storage photoperiod (SD or LD), and age of eggs (14, 28, 42, 56, 70, 91, and 112 days). The results showed a lower hatching response with the SD parental photoperiod, and a trend to higher hatching with longer egg storage time in all photoperiod treatment combinations. The egg storage photoperiod showed no effect on egg hatching. In both parental photoperiod treatments, egg replicates of most ages from different females showed a large variability, with some replicates with lowest hatching response and others with highest hatching response. Our results show the ability of Ae. aegypti to inhibit egg hatching in response to a short-day photoperiod, which could allow the further expansion of this species to regions with colder winters.

Ischiocrural Strength May Be a Better Prognostic Marker Than Quadriceps Strength in COPD.

It is well known that chronic obstructive pulmonary disease (COPD) patients present with muscle dysfunction that may not correlate with the degree of severity of airflow obstruction. Historically, the strength deficit of the knee extensor musculature (quadriceps) has been described as an independent factor of mortality in COPD. We present the results of a retrospective study with longitudinal follow-up of 60 patients with severe COPD followed for 7 years. During follow-up 22 patients died, mainly of respiratory cause. We have observed that the strength of knee flexor muscles (ischiocrural) and dominant handgrip were independent predictors of mortality in severe COPD patients. However, knee extensor strength (quadriceps) was not an independent predictor of mortality. This is the first study which highlights the importance of knee flexor musculature as a prognostic factor in COPD.

Effects of scarcity and excess of larval food on life history traits of Aedes aegypti (Diptera: Culicidae).

Few studies have assessed the effects of food scarcity or excess on the life history traits of Aedes aegypti (L.) (Diptera: Culicidae) independently from larval density. We assessed immature survival, development time, and adult size in relation to food availability. We reared cohorts of 30 Ae. aegypti larvae from newly hatched to adult emergence with different food availability. Food conditions were kept constant by transferring larvae each day to a new food solution. Immature development was completed by some individuals in all treatments. The shortest development time, the largest adults, and the highest survival were observed at intermediate food levels. The most important effects of food scarcity were an extension in development time, a decrease in the size of adults, and a slight decrease in survival, while the most important effects of food excess were an important decrease in survival and a slight decrease in the size of adults. The variability in development time and adult size within sex and treatment increased at decreasing food availability. The results suggest that although the studied population has adapted to a wide range of food availabilities, both scarcity and excess of food have important negative impacts on fitness.

Safety of Rehabilitation Program for COPD Patients / Seguridad de un programa de rehabilitación para pacientes con EPOC

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Egg Hatching and Survival of Immature Stages of Aedes aegypti (Diptera: Culicidae) Under Natural Temperature Conditions During the Cold Season in Buenos Aires, Argentina.

In temperate regions, the seasonal dynamics of Aedes aegypti (L.) (Diptera: Culicidae) is mainly influenced by temperature. It is assumed that, during the winter season, the population remains as eggs and that the development and population growth of surviving eggs begin during the following spring. The aim of the current study was to assess egg hatching of Ae. aegypti during the winter in Buenos Aires city (Argentina), and analyze the survival of immature stages. The experiments consisted of immersing eggs and studying the development of immature stages of cohorts from June and September under natural temperature conditions. The proportion of hatched eggs was compared between weeks of immersion and related to environmental variables. Survival was compared among cohorts and the development rate was related to the mean temperature during development. The results showed that, with few exceptions, egg hatching was over 45% during the winter period. The proportion of hatched eggs was positively associated with immersion temperature, pre-immersion temperature and photoperiod. The immature stages completed the development during the cold season, with a trend toward increased survival of late-hatching cohorts. Survival was 30% at 13.2 °C and above 90% at 20 °C, whereas the development time at low temperatures was 49.4 d at 13.2 °C and 17.7 d at 20 °C. The high hatching and survival compared with other studies suggest that the local population might be adapting to winter conditions. The anticipated emergence of adults would be adaptive if they are able to reproduce successfully in the early spring.

Improvement in walking abilities in transfemoral amputees with a distal weight bearing implant.

BACKGROUND: The ability to walk with a prosthesis is the main objective of rehabilitation following amputation, and distance and speed of walking achieved are considered determining factors in amputees' perception of quality-of-life. OBJECTIVES: To assess walking abilities and improvement in gait distance and speed parameters in patients undergoing transfemoral amputation with a femoral implant that allows distal support of the residuum. STUDY DESIGN: Experimental before-and-after study. METHODS: Ten transfemoral amputation patients received a titanium implant that allowed distal weight bearing of the residuum within the socket. The post-intervention follow-up period was 14 months. We evaluated the functionality using a 2-min walk test and the physiological cost index. RESULTS: The etiology of amputation was traumatic in six patients (60%). The mean 2-min walk test score was 98.4 ± 19.5 m prior to the femoral implant and 122.5 ± 26.1 m at 14 months ( p < 0.008), representing an improvement of 24.5%. The mean gait speed prior to the femoral implant was 0.82 ± 0.16 and 1.02 ± 0.21 m/s at 14 months ( p < 0.008). The physiological cost index showed no differences ( p < 0.55). CONCLUSION: The results of this study show an improvement in the distance walked and gait speed in amputees 14 months after having received a femoral implant. Clinical relevance This article provides additional insight into the use of a femoral implant that allows distal support of the residuum to improve walking abilities and gait distance and speed parameters in patients undergoing transfemoral amputation, mainly those of vascular origin.

Effectiveness of a tailored implementation programme to improve recognition, diagnosis and treatment of anxiety and depression in general practice: a cluster randomised controlled trial.

BACKGROUND: Anxiety and depression are not always diagnosed and treated in primary care as has been recommended. A tailored implementation programme, which addresses key barriers for change by targeted interventions, may help to remedy this. METHODS: The effectiveness of an individually tailored implementation programme, additional to standardised training and feedback on the recognition and treatment of patients with anxiety or depression in general practice, was examined in a cluster randomised controlled trial. Participants were 46 general practitioners (GPs) from 23 general practices (12 intervention, 11 control) and 444 patients aged 18 years or older (198 intervention, 246 control) who screened positive on the extended Kessler 10. In the control group, GPs received a 1-day training in guidelines for recognition and stepped treatment for anxiety and depression. Ten months after the training session, GPs received feedback on their performance over the preceding 6 months. In the intervention group, GPs received the same training and feedback as those in the control condition; in addition, they were offered support, tailored to perceived local barriers to change. The support was delivered in the format of peer group supervisions and personalised telephone consultations. Data were based on an audit of patient records and patient surveys at baseline and after 3 and 6 months. RESULTS: The tailored implementation programme led to recognition of a higher proportion of patients presenting with anxiety and depression (42% versus 31%; odds ratio (OR) = 1.60; 95% CI: 1.01-2.53), more consultations after recognition (IRR = 1.78; 95% CI: 1.14-2.78) and did not lead to more prescription of antidepressants (OR = 1.07; 95% CI: 0.52-2.19) or referral to specialist mental health services (OR = 1.62; 95% CI: 0.72-3.64). Patients in the intervention group reported better accessibility of care (effect size (ES) = 0.4; p < 0.05) and provision of information and advice (ES = 0.5; p < 0.05). CONCLUSIONS: A tailored implementation programme may enhance the recognition and treatment of patients with anxiety or depression. Further development and evaluation of the programme is warranted to determine its cost-effectiveness. TRAIL REGISTRATION: Dutch Trial Register identifier NTR1912 .

A model for the development of Aedes (Stegomyia) aegypti as a function of the available food.

We discuss the preimaginal development of the mosquito Aedes aegypti from the point of view of the statistics of developmental times and the final body-size of the pupae and adults. We begin the discussion studying existing models in relation to published data for the mosquito. The data suggest a developmental process that is described by exponentially distributed random times. The existing data show as well that the idea of cohorts emerging synchronously is verified only in optimal situations created at the laboratory but it is not verified in field experiments. We propose a model in which immature individuals progress in successive stages, all of them with exponentially distributed times, according to two different rates (one food-dependent and the other food-independent). This phenomenological model, coupled with a general model for growing, can explain the existing observations and new results produced in this work. The emerging picture is that the development of the larvae proceeds through a sequence of steps. Some of the steps depend on the available food. While food is in abundance, all steps can be thought as having equal duration, but when food is scarce, those steps that depend on food take considerably longer times. For insufficient levels of food, increase in larval mortality sets in. As a consequence of the smaller rates, the average pupation time increases and the cohort disperses in time. Dispersion, as measured by standard deviation, becomes a quadratic function of the average time indicating that cohort dispersion responds to the same causes than delays in pupation and adult emergence. During the whole developmental process the larva grows monotonically, initially at an exponential rate but later at decreasing rates, approaching a final body-size. Growth is stopped by maturation when it is already slow. As a consequence of this process, there is a slight bias favoring small individuals: Small individuals are born before larger individuals, although the tendency is very weak.

The longitudinal prediction of costs due to health care uptake and productivity losses in a cohort of employees with and without depression or anxiety.

OBJECTIVE: To examine how various predictors and subgroups of respondents contribute to the prediction of health care and productivity costs in a cohort of employees. METHODS: We selected 1548 employed people from a cohort study with and without depressive and anxiety symptoms or disorders. Prediction rules, using the RuleFit program, were applied to identify predictors and subgroups of respondents, and to predict estimations of subsequent 1-year health care and productivity costs. RESULTS: Symptom severity and diagnosis of depression and anxiety were the most important predictors of health care costs. Depressive symptom severity was the most important predictor for productivity costs. Several demographic, social, and work predictors did not predict economic costs. CONCLUSIONS: Our data suggest that from a business perspective it can be beneficial to offer interventions aimed at prevention of depression and anxiety.

Modeling the cost-effectiveness of health care systems for alcohol use disorders: how implementation of eHealth interventions improves cost-effectiveness.

BACKGROUND: Informing policy decisions about the cost-effectiveness of health care systems (ie, packages of clinical interventions) is probably best done using a modeling approach. To this end, an alcohol model (ALCMOD) was developed. OBJECTIVE: The aim of ALCMOD is to estimate the cost-effectiveness of competing health care systems in curbing alcohol use at the national level. This is illustrated for scenarios where new eHealth technologies for alcohol use disorders are introduced in the Dutch health care system. METHOD: ALCMOD assesses short-term (12-month) incremental cost-effectiveness in terms of reductions in disease burden, that is, disability adjusted life years (DALYs) and health care budget impacts. RESULTS: Introduction of new eHealth technologies would substantially increase the cost-effectiveness of the Dutch health care system for alcohol use disorders: every euro spent under the current system returns a value of about the same size (€1.08, ie, a "surplus" of 8 euro cents) while the new health care system offers much better returns on investment, that is, every euro spent generates €1.62 in health-related value. CONCLUSION: Based on the best available evidence, ALCMOD's computations suggest that implementation of new eHealth technologies would make the Dutch health care system more cost-effective. This type of information may help (1) to identify opportunities for system innovation, (2) to set agendas for further research, and (3) to inform policy decisions about resource allocation.

Cold season mortality and hatching behavior of Aedes aegypti L. (Diptera: Culicidae) eggs in Buenos Aires City, Argentina.

In temperate regions, populations of Aedes aegypti survive the cold season in the egg stage. In the present work, we studied the cold-season mortality of Ae. aegypti eggs and their subsequent hatching pattern in Buenos Aires city. Eggs were exposed during the winter season (three months) in three neighborhoods located along a gradient of distance toward the Río de la Plata River, coincident with a gradient of activity of Ae. aegypti. Results showed mortalities lower (30.6%) than those from tropical regions during the dry season. Significant differences were detected among the egg mortalities of each site with a maximum value at the site nearest the Río de la Plata River (50%), and a minimum value at the most continental site (9%). Post-experimental hatching response of eggs differed between sites, with the highest proportion of hatched eggs during the first immersion in the site nearest to the river and the lowest proportion in the most continental site. The hatching proportion also differed between age classes, with older (early-laid) eggs hatching later than new (late-laid) ones. Our results provide the first information of Ae. aegypti egg mortality in temperate South America and support the hypothesis that differences in egg mortality are associated with abundance patterns of Ae. aegypti in Buenos Aires city.