John C. Carlson

A Simulation Model of African Anopheles Ecology and Population Dynamics for the Analysis of Malaria Transmission.

BackgroundMalaria is one of the oldest and deadliest infectious diseases in humans. Many mathematical models of malaria have been developed during the past century, and applied to potential interventions. However, malaria remains uncontrolled and is increasing in many areas, as are vector and parasite resistance to insecticides and drugs.MethodsThis study presents a simulation model of African malaria vectors. This individual-based model incorporates current knowledge of the mechanisms underlying Anopheles population dynamics and their relations to the environment. One of its main strengths is that it is based on both biological and environmental variables.ResultsThe model made it possible to structure existing knowledge, assembled in a comprehensive review of the literature, and also pointed out important aspects of basic Anopheles biology about which knowledge is lacking. One simulation showed several patterns similar to those seen in the field, and made it possible to examine different analyses and hypotheses for these patterns; sensitivity analyses on temperature, moisture, predation and preliminary investigations of nutrient competition were also conducted.ConclusionsAlthough based on some mathematical formulae and parameters, this new tool has been developed in order to be as explicit as possible, transparent in use, close to reality and amenable to direct use by field workers. It allows a better understanding of the mechanisms underlying Anopheles population dynamics in general and also a better understanding of the dynamics in specific local geographic environments. It points out many important areas for new investigations that will be critical to effective, efficient, sustainable interventions.

Field assessments in western Kenya link malaria vectors to environmentally disturbed habitats during the dry season

BackgroundNumerous malaria epidemics have occurred in western Kenya, with increasing frequency over the past 20 years. A variety of hypotheses on the etiology of these epidemics have been put forth, with different implications for surveillance and control. We investigated the ecological and socioeconomic factors promoting highland malaria vectors in the dry season after the 2002 epidemic.MethodsInvestigations were conducted in Kisii District during the dry season. Aquatic habitats in were surveyed for presence of malaria vectors. Brick-making pits were further investigated for co-associations of larval densities with emergent vegetation, habitat age, and predator diversity. Indoor spray catches were completed in houses near aquatic habitats. Participatory rural appraisals (PRAs) were conducted with 147 community members.ResultsThe most abundant habitat type containing Anopheles larvae was brick-making pits. Vegetation and habitat age were positively associated with predator diversity, and negatively associated with mosquito density. Indoor spray catches found that houses close to brick-making sites had malaria vectors, whereas those next to swamps did not. PRAs revealed that brick-making has grown rapidly in highland swamps due to a variety of socioeconomic pressures in the region.ConclusionBrick-making, an important economic activity, also generates dry season habitats for malaria vectors in western Kenya. Specifically, functional brick making pits contain less that 50% as many predator taxa and greater than 50% more mosquito larvae when compared with nearby abandoned brick making pits. Further evaluations of these disturbed, man-made habitats in the wet season may provide information important for malaria surveillance and control.

Cockroach exposure independent of sensitization status and association with hospitalizations for asthma in inner-city children

BACKGROUND Children with asthma living in urban environments experience disproportionately high asthma hospitalization rates. Excessive exposure to perennial allergens, including cockroach and house dust mite (HDM), have been implicated, but data are limited. OBJECTIVE To examine the relation between cockroach and HDM exposure and measures of asthma morbidity and health care utilization. METHODS Participants included 86 atopic asthmatic children living in New Orleans, Louisiana. Sensitization status was determined by means of serum specific IgE testing, and vacuum dust samples were collected for allergen analysis. Logistic regression analysis was used to assess the odds of persistent wheezing, emergency department visits, and asthma hospitalization in those with high vs low levels of allergen exposure. RESULTS Approximately 44% and 40% of children were exposed to Bla g 1 levels greater than 2 U/g and HDM levels greater than 2 μg/g, respectively, and 24% reported at least 1 hospitalization in the previous 4 months. The median Bla g 1 level was significantly higher in the homes of children hospitalized compared with those with no hospital admissions (7.2 vs 0.8 U/g). In multivariable models, the odds of hospitalization were significantly higher in children exposed to Bla g 1 levels greater than 2 U/g (adjusted odds ratio, 4.2; 95% confidence interval, 1.24-14.17), independent of sensitization status. Exposure to HDMs was not associated with any measure of morbidity. CONCLUSIONS Exposure to cockroach allergen was strongly associated with increased hospitalization in children with asthma. This effect cannot be explained entirely by IgE-mediated inflammation. Controlled interventional trials are needed to determine whether isolated cockroach abatement improves asthma control.

Being ready to treat Ebola virus disease patients.

As the outbreak of Ebola virus disease (EVD) in West Africa continues, clinical preparedness is needed in countries at risk for EVD (e.g., United States) and more fully equipped and supported clinical teams in those countries with epidemic spread of EVD in Africa. Clinical staff must approach the patient with a very deliberate focus on providing effective care while assuring personal safety. To do this, both individual health care providers and health systems must improve EVD care. Although formal guidance toward these goals exists from the World Health Organization, Medecin Sans Frontières, the Centers for Disease Control and Prevention, and other groups, some of the most critical lessons come from personal experience. In this narrative, clinicians deployed by the World Health Organization into a wide range of clinical settings in West Africa distill key, practical considerations for working safely and effectively with patients with EVD.

Diversity Cascades and Malaria Vectors

ABSTRACT The interactions between predator diversity and primary consumer abundance can include direct effects and indirect, cascading effects. Understanding these effects on immature Anopheles mosquitoes is important in sub-Saharan Africa, where most cases of malaria occur. Aquatic predators and immature mosquitoes were collected from shallow pools of varying age previously excavated by brickmakers in the western highlands of Kenya. Path analysis showed an indirect negative effect of habitat age on An. gambiae (Giles, 1902) mediated by effects on predator diversity. Disturbance resets habitats to an earlier successional stage, diminishing predator diversity and increasing An. gambiae populations. The increase in vector abundance as a result of reduced predator diversity highlights the public health value in conserving native insect diversity.

A single intervention for cockroach control reduces cockroach exposure and asthma morbidity in children

Background Exposure to cockroaches is an important asthma trigger, particularly for children with asthma living in inner cities. Integrated pest management is the recommended approach to cockroach abatement; however, it is costly and difficult to implement. The impact of reducing cockroach exposure on asthma outcomes is not known. Objective We sought to test the use of a single intervention, insecticidal bait, to reduce cockroach exposure in the home of children with asthma in New Orleans and to examine the impact of cockroach reduction on asthma outcomes. Methods One hundred two children aged 5 to 17 years with moderate to severe asthma were enrolled in a 12‐month randomized controlled trial testing the use of insecticidal bait on cockroach counts and asthma morbidity. Homes were visited 6 times and asthma symptoms were assessed every 2 months. Results After adjustment, intervention homes had significantly fewer cockroaches than did control homes (mean change in cockroaches trapped, 13.14; 95% CI, 6.88‐19.39; P < .01). Children in control homes had more asthma symptoms and unscheduled health care utilization in the previous 2 weeks (1.82, 95% CI, 0.14‐3.50, P = .03; 1.17, 95% CI, 0.11‐2.24, P = .03, respectively) and a higher proportion of children with FEV1 of less than 80% predicted (odds ratio, 5.74; 95% CI, 1.60‐20.57; P = .01) compared with children living in intervention homes. Conclusions Previous research has demonstrated improvement in asthma health outcomes using multifaceted interventions. The strategic placement of insecticidal bait, which is inexpensive, has low toxicity, and is widely available, resulted in sustained cockroach elimination over 12 months and was associated with improved asthma outcomes. This single intervention may be an alternative to multifaceted interventions currently recommended to improve asthma morbidity.

Colonization of abandoned swimming pools by larval mosquitoes and their predators following Hurricane Katrina

ABSTRACT Thousands of flooded swimming pools were abandoned in New Orleans following Hurricane Katrina and provided a natural experiment to examine colonization of a novel aquatic habitat by mosquito larvae and their aquatic predators. We conducted a randomized survey of flooded swimming pools in two neighborhoods in January 2006 and found that 64% contained mosquito larvae, 92% contained predatory invertebrates, and 47% contained fishes. We collected 12,379 immature mosquitoes representing five species, primarily Culiseta inornata, and secondarily, the arboviral vector Culex quinquefasciatus. Dragonfly nymphs in the families Aeshnidae and Libellulidae were the most common predatory invertebrates collected among a total of 32 non-mosquito invertebrate species. Eleven species of fishes were collected, with Gambusia affinis accounting for 76% of the catch. Diversity of fishes in swimming pools was positively correlated with proximity to a levee breach and the fish assemblage found in swimming pools was similar to that found along shorelines of Lake Pontchartrain and drainage canals that flooded the study area. Mosquito larvae were rare or absent from pools containing fishes; however, path analysis indicated that the presence of top predators or abundant competitors may somewhat mitigate the effect of Gambusia affinis on mosquito presence.

The Relationship Between a Specific IgE Level and Asthma Outcomes: Results from the 2005-2006 National Health and Nutrition Examination Survey

BACKGROUND Allergen exposure is associated with increased specific IgE (sIgE), and allergen exposure plus sensitization is predictive of asthma outcomes. However, it is not known if sIgE is predictive of asthma outcomes in the absence of exposure data. OBJECTIVE To investigate whether IgE to indoor allergens is predictive of and has a dose-response relationship with asthma emergency department (ED) visits and wheeze. METHODS In the 2005-2006 National Health and Nutrition Examination Survey, 351 children and 390 adults reported current asthma. Continuous sIgE to 9 indoor allergens were considered. Asthma morbidity in the past year was measured by wheezing. Health care utilization was defined as any asthma ED visits in the past year. RESULTS Analyses were adjusted for race, age, education, poverty index ratio and (in adults) tobacco use. In children, ED visits were associated with cockroach (odds ratio [OR] 1.5 [95% CI, 1.1-2 .1), rat (OR 1.9 [95% CI, 1.2-2.8]), and Aspergillus (OR 1.6 [95% CI, 1.001-2.60]). Continuous Aspergillus (OR 1.5 [95% CI, 1.04-2.1), Alternaria (OR 1.4 [95% CI, 1.1-1.6]), and total IgE (OR 1.2 [95% CI, 1.1-1.4]) were associated with wheeze in children. Adult ED visits were associated with sIgE for dust mites (Dermatophagoides pteronyssinus OR 1.6 [95% CI, 1.3-2.1]; Dermatophagoides farinae OR 1.6 [95% CI, 1.3-1.9]), total IgE (OR 1.4 [95% CI, 1.04- 1.9]), and the sum of sIgEs (OR 1.6 [95% CI, 1.2-2.2]). CONCLUSIONS Sensitization to particular indoor environmental allergens was found to be a risk factor for wheeze and asthma ED visits. These outcomes increased as the concentration of sIgE to these allergens increased.

Nesting Bird “Host Funnel” Increases Mosquito-Bird Contact Rate

ABSTRACT Increases in vector-host contact rates can enhance arbovirus transmission intensity. We investigated weekly fluctuations in contact rates between mosquitoes and nesting birds using the recently described Nest Mosquito Trap (NMT). The number of mosquitoes per nestling increased from <1 mosquito per trap night to 36.2 in the final 2 wk of the nesting season. Our evidence suggests the coincidence of the end of the avian nesting season and increasing mosquito abundances may have caused a “host funnel,” concentrating host-seeking mosquitoes to the few remaining nestlings. The relative abundance of mosquitoes collected by the NMT suggests that significantly more Aedes albopictus (Skuse) and Culex pipiens (L.) /restuans (Theobald) sought nesting bird bloodmeals than were predicted by their relative abundances in CO2-baited Centers for Disease Control and Prevention light and gravid traps. Culex salinarius (Coquillett) and Culex erraticus Dyar and Knab were collected in NMTs in proportion to their relative abundances in the generic traps. Temporal host funnels and nesting bird host specificity may enhance arbovirus amplification and explain observed West Nile virus and St. Louis encephalitis virus amplification periods.

Asthma severity, not asthma control, is worse in atopic compared with nonatopic adolescents with asthma

BACKGROUND The effects of atopic and nonatopic asthma phenotypes on asthma morbidity are unclear. Moreover, asthma morbidity in patients without atopy might be mediated by immunoglobulin E (IgE). OBJECTIVE To determine differences in morbidity in patients with asthma with and without atopy in a population of inner-city adolescents with asthma and to assess the impact of total IgE (tIgE) in this population. METHODS Data were obtained from 546 inner-city adolescents in the Asthma Control Evaluation study. A positive skin prick test reaction to 14 aeroallergens and specific IgE to 5 aeroallergens determined atopic status. High (≥75th percentile) and low (≤25th percentile) tIgE levels were categorized. Asthma control (Asthma Control Test) and asthma severity (Composite Asthma Severity Index [CASI]) were measured at multiple time points over 1 year. Fractional exhaled nitric oxide (FeNO) and measurements of morbidity also were collected. Multivariable and repeated measures analyses modeled the relation between atopic status and morbidity. RESULTS Baseline CASI scores increased 0.90 point (P < .05) and FeNO increased 0.85 natural logarithmic unit (P < .001) in participants with vs without atopy. Repeated measures analyses showed consistent results. Participants without atopy and increased tIgE had FeNO 0.73 natural log unit higher (P < .01) than low tIgE and a nonsignificant increase in CASI. The CASI score and FeNO levels were higher for high than for low tIgE in participants with atopy. CONCLUSION In this population, participants with atopic asthma had worse asthma severity and higher FeNO compared with those with nonatopic asthma, but no difference in control. In all participants, higher tIgE indicated worse severity and higher FeNO. In this population, asthma severity and FeNO might be mediated by IgE in the 2 asthma phenotypes.