Combining experimental evolution and field population assays to study the evolution of host range breadth.

Adapting to specific hosts often involves trade-offs that limit performance on other hosts. These constraints may either lead to narrow host ranges (i.e. specialists, able to exploit only one host type) or wide host ranges often leading to lower performance on each host (i.e. generalists). Here, we combined laboratory experiments on field populations with experimental evolution to investigate the impact of adaptation to the host on host range evolution and associated performance over this range. We used the two-spotted spider mite, Tetranychus urticae, a model organism for studies on the evolution of specialization. Field mite populations were sampled on three host plant species: tomato, citrus tree and rosebay (Nerium oleander). Testing these populations in the laboratory revealed that tomato populations of mites could exploit tomato only, citrus populations could exploit citrus and tomato whereas Nerium populations could exploit all three hosts. Besides, the wider niche ranges of citrus and Nerium populations came at the cost of low performance on their non-native hosts. Experimental lines selected to live on the same three host species exhibited similar patterns of host range and relative performance. This result suggests that adaptation to a new host species may lead to wider host ranges but at the expense of decreased performance on other hosts. We conclude that experimental evolution may reliably inform on evolution in the field.

On the optimal size of marine reserves.

The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. This study examines the impact of the creation of marine protected areas, from both economic and biological perspectives. The consequences of reserve establishment on the long-run equilibrium fish biomass and fishery catch levels are evaluated. We include reserve size as control variable to maximize catch at equilibrium. A continuous time model is used to simulate the effects of reserve size on fishing catch. Fish movements between the sites is assumed to take place at a faster time scale than the variation of the stock and the change of the fleet size. We take advantage of these two time scales to derive a reduced model governing the dynamics of the total fish stock and the fishing effort. Simulation results suggest that the establishment of a protected marine reserve will always lead to an increase in total fish biomass, an optimal size of a marine reserve can achieve to maximize the catch at equilibrium.

Reproductive numbers for nonautonomous spatially distributed periodic SIS models acting on two time scales.

In this work we deal with a general class of spatially distributed periodic SIS epidemic models with two time scales. We let susceptible and infected individuals migrate between patches with periodic time dependent migration rates. The existence of two time scales in the system allows to describe certain features of the asymptotic behavior of its solutions with the help of a less dimensional, aggregated, system. We derive global reproduction numbers governing the general spatially distributed nonautonomous system through the aggregated system. We apply this result when the mass action law and the frequency dependent transmission law are considered. Comparing these global reproductive numbers to their non spatially distributed counterparts yields the following: adequate periodic migration rates allow global persistence or eradication of epidemics where locally, in absence of migrations, the contrary is expected.

The morphology of secondary-hardening carbides in a martensitic steel at the peak hardness by 3DFIM.

The morphology and composition of secondary-hardening M(2)C carbides in a complex steel under non-isothermal tempering condition has been investigated with three-dimensional field ion microscopy and atom-probe tomography. The technical set-up and the condition of investigations have been developed. We will reveal for the first time, a virtually non-biased image of the so-called secondary-hardening microstructure, consisting in a very fine dispersion of nanometer-sized needles, idiomorphs and blocky carbides. Needles precipitate with a large number density at the maximum hardness peak. We have found out that this mixture of shape could be explained by the onset of coarsening, but the role of local factors have been evidenced: variation of composition among the carbides and even local strain effects due to the precipitation of a second phase can play a role in changing the growth conditions.

Comparative study of potential transfer of natural and anthropogenic cadmium to plankton communities in the North-West African upwelling.

A Lagrangian approach based on a physical-biogeochemical modeling was used to compare the potential transfer of cadmium (Cd) from natural and anthropogenic sources to plankton communities (Cd-uptake) in the North-West African upwelling. In this region, coastal upwelling was estimated to be the main natural source of Cd while the most significant anthropogenic source for marine ecosystem is provided by phosphate industry. In our model experiment, Cd-uptake (natural or anthropogenic) in the North-West African upwelling is the result of an interplay between the Cd dispersion (by advection processes) and the simulated biological productivity. In the Moroccan waters, advection processes limit the residence time of water masses resulting in a low natural Cd-uptake by plankton communities while anthropogenic Cd-uptake is high. As expected, the situation is reversed in the Senegalo-Mauritanian upwelling where natural Cd-uptake is higher than anthropogenic Cd-uptake. Based upon an estimate of Cd sources, our modeling study shows, unexpectedly, that the anthropogenic signal of potential Cd-bioaccumulation in the Moroccan upwelling is of the same order of magnitude as the natural signal mainly present in the Senegalo-Mauritanian upwelling region. A comparison with observed Cd levels in mollusk and fishes, which shows overall agreement with our simulations, is confirming our estimates.

Dynamics of a feline virus with two transmission modes within exponentially growing host populations.

Feline panleucopenia virus (FPLV) was introduced in 1977 on Marion Island (in the southern Indian Ocean) with the aim of eradicating the cat population and provoked a huge decrease in the host population within six years. The virus can be transmitted either directly through contacts between infected and healthy cats or indirectly between a healthy cat and the contaminated environment: a specific feature of the virus is its high rate of survival outside the host. In this paper, a model was designed in order to take these two modes of transmission into account. The results showed that a mass-action incidence assumption was more appropriate than a proportionate mixing one in describing the dynamics of direct transmission. Under certain conditions the virus was able to control the host population at a low density. The indirect transmission acted as a reservoir supplying the host population with a low but sufficient density of infected individuals which allowed the virus to persist. The dynamics of the infection were more affected by the demographic parameters of the healthy hosts than by the epidemiological ones. Thus, demographic parameters should be precisely measured in field studies in order to obtain accurate predictions. The predicted results of our model were in good agreement with observations.

An unusual case of carbon monoxide poisoning.

Carbon monoxide, a gas originating from incomplete combustion of carbon-based fuels, is an important cause of human deaths. In this paper, we describe an unusual carbon monoxide poisoning in a dwelling without obvious sources of combustion gases, for which two adults had to be treated in a hyperbaric chamber. Carbon monoxide readings were taken in the house and in the neighboring homes. Methane gas and nitrogen oxide levels were also monitored in the house air. Soil samples were collected around the house and tested for hydrocarbon residues. The investigation revealed the presence of a pocket of carbon monoxide under the foundation of the house. The first readings revealed carbon monoxide levels of 500 ppm in the basement. The contamination lasted for a week. The investigation indicated that the probable source of contamination was the use of explosives at a nearby rain sewer construction site. The use of explosives in a residential area can constitute a major source of carbon monoxide for the neighboring populations. This must be investigated, and public health authorities, primary-care physicians, governmental authorities, and users and manufacturers of explosives must be made aware of this problem.

Effect of hyperchylomicronemia on the measurement of hemoglobin.

The effects of plasma triglyceride levels on the measurement of hemoglobin and other erythrocyte indices have been studied in blood samples from ten healthy controls, 11 patients with type IV hyperlipoproteinemia, and five patients with hyperchylomicronemia (type I or V). Measurements were made using erythrocytes in their own plasmas and repeated after resuspension of the cells in physiologic saline solution. Hemoglobin, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration were decreased by removal of plasma in erythrocytes from three patients with hyperchylomicronemia. It is concluded that the triglyceride contained in very-low-density lipoprotein does not affect hemoglobin measurement, while triglyceride contained in chylomicrons increased hemoglobin readings linearly.

Microbial flora associated with Candida albicans vulvovaginitis.

The relationship between vaginal microflora Candida albicans vulvovaginitis is studied. Results obtained from 340 vaginal specimens showed an increase of isolates in the absence of C albicans for all groups of microorganisms (168%), particularly for the gram-negative bacteria (226%). A high frequency of polymicrobial vaginitis is noted, as is the probable importance of anaerobic microorganisms. Finally, some special aspects of the pathogenesis of C albicans infection are discussed.

A multicenter, open comparative study of parenteral cefotaxime and ceftriaxone in the treatment of nosocomial lower respiratory tract infections.

A multicenter Canadian study enrolled 74 persons to compare low-dose cefotaxime at 1 g every 8 hr to ceftriaxone 1 g every 12 hr in patients with nosocomial pneumonia. Of 57 evaluable patients (30 cefotaxime and 27 ceftriaxone) in this preliminary report, 93% responded to therapy in both groups. Ceftriaxone patients tended to have more side effects (14.2%). This study is continuing to accrue patients to achieve 100 evaluable patients. Interim data, however, support the continued use of low-dose cefotaxime as an appropriate alternative for clinically effective and cost-effective management of nosocomially acquired pneumonia.

RP 59500, a new streptogramin highly active against recent isolates of North American staphylococci.

To assess the potential clinical utility of RP 59500, 10 investigators from separate locations in the United States and Canada each tested approximately 200 current isolates of staphylococci (Staphylococcus aureus and coagulase-negative staphylococci) by a standard protocol. RP 59500 was highly active (MIC90 < or = 2 micrograms/ml) against all strains, including those that were resistant to oxacillin, ciprofloxacin, erythromycin, and spiramycin.

Sternal wound infection after heart transplantation: incidence and results with aggressive surgical treatment.

BACKGROUND: Sternal wound infection remains a significant complication. We reviewed the incidence and the treatment of sternal wound infection after heart transplantation. METHODS: Of 226 patients who had a heart transplantation, 20 (8.8%) underwent postoperative wound debridement for superficial or deep sternal wound infection. The incidence and the survival of patients with sternal wound infection were analyzed. RESULTS: The incidence of sternal wound infection was similar among patients treated with four protocols of immunosuppressive drugs: cyclosporine and prednisone (0 of 22; 0%); cyclosporine, prednisone, and azathioprine (2 of 24; 8.3%); cyclosporine, prednisone, azathioprine, and antithymocyte globulin (15 of 139; 10.8%); and cyclosporine, prednisone, mycophenolate mofetil, and antithymocyte globulin (3 of 41; 7.3%) (p = 0.4). Six-month and 5-year survival of patients with sternal wound infection averaged 85% +/- 8% and 74% +/- 10% compared with 92% +/- 2% and 82% +/- 3% in patients without wound infection (p = 0.15). Patients with deep sternal wound infection, debridement, and reconstruction had a 5-year survival averaging 80% +/- 10%. CONCLUSIONS: The incidence of sternal wound infection remains similar between patients treated with the triple drug therapy. Surgical debridement and reconstruction can result in long-term survival after heart transplantation.

Immediate and long-term results of valve replacement for native and prosthetic valve endocarditis.

BACKGROUND: The objective of the present study was to compare current results of prosthetic valve replacement following acute infective native valve endocarditis (NVE) with that of prosthetic valve endocarditis (PVE). Prosthetic valve replacement is often necessary for acute infective endocarditis. Although valve repair and homografts have been associated with excellent outcome, homograft availability and the importance of valvular destruction often dictate prosthetic valve replacement in patients with acute bacterial endocarditis. METHODS: A retrospective analysis of the experience with prosthetic valve replacement following acute NVE and PVE between 1988 and 1998 was performed at the Montreal Heart Institute. RESULTS: Seventy-seven patients (57 men and 20 women, mean age 48 +/- 16 years) with acute infective endocarditis underwent valve replacement. Fifty patients had NVE and 27 had PVE. Four patients (8%) with NVE died within 30 days of operation and there were no hospital deaths in patients with PVE. Survival at 1, 5, and 7 years averaged 80% +/- 6%, 76% +/- 6%, and 76% +/- 6% for NVE and 70% +/- 9%, 59% +/- 10%, and 55% +/- 10% for PVE, respectively (p = 0.15). Reoperation-free survival at 1, 5, and 7 years averaged 80% +/- 6%, 76% +/- 6%, and 76% +/- 6% for NVE and 45% +/- 10%, 40% +/- 10%, and 36% +/- 9% for PVE (p = 0.003). Five-year survival for NVE averaged 75% +/- 9% following aortic valve replacement and 79% +/- 9% following mitral valve replacement. Five-year survival for PVE averaged 66% +/- 12% following aortic valve replacement and 43% +/- 19% following mitral valve replacement (p = 0.75). Nine patients underwent reoperation during follow-up: indications were prosthesis infection in 4 patients (3 mitral, 1 aortic), dehiscence of mitral prosthesis in 3, and dehiscence of aortic prosthesis in 2. CONCLUSIONS: Prosthetic valve replacement for NVE resulted in good long-term patient survival with a minimal risk of reoperation compared with patients who underwent valve replacement for PVE. In patients with PVE, those who needed reoperation had recurrent endocarditis or noninfectious periprosthetic dehiscence.

Viability assessment by dye exclusion. A fluorescent method for fungal cells.

A new fluorescent staining technique for fungi utilizes the differential affinity of dead cells for rhodamine B. A mounting medium has been devised that includes the dye. This medium allows direct processing of cells from a broth and provides optimal conditions for fluorescence intensity. Comparison with the standard methylene blue exclusion test as applied to the Candida albicans yeast phase indicates similar specificity. Various pseudohyphae and several fungi also exhibited selective uptake of the dye when killed. This technique should prove useful in studying the effect of both drugs and cells on pathogenic yeasts.

Favus: twenty indigenous cases in the province of Quebec.

Twenty indigenous cases of favus in two families residing in the province of Quebec were studied. Importantly, the disease, although active, remained undiagnosed for many years in most of the cases. The finding of active cases suggests that the disease is still endemic in regions previously described as harboring cases, namely the province of Quebec and possibly Kentucky.

Modeling of cardiac electrophysiological mechanisms: from action potential genesis to its propagation in myocardium.

The aim of the present paper is to describe the different attempts at modeling cardiac electrophysiological mechanisms, mainly at the membrane and cellular level, from action potential genesis to its propagation in myocardium. The Hodgkin and Huxley model describing the nervous action potential's theoretical reconstruction is first recalled, for it represents the basic model for a large part of cardiac action potential models. These models (Beeler and Reuter, Van Capelle and Durrer, Luo and Rudy) are then successively studied as their main applications by diverse authors. Varied approaches, like the Fitzhugh-Nagumo model (derived from the Bonhoeffer-Van der Pol model of oscillatory systems) or cellular automata models applied to the study of ventricular activation wave propagation and diseases associated with its perturbation, are then presented and discussed. Other, different approaches, such as general studies of excitable media, are evoked. This paper concludes with a critical evaluation of these different methods of electrophysiological cardiac modeling and of the main domains in which they led to significant results and in which they appear able to generate future perspectives.

Serological survey for congenital toxoplasmosis among 4,136 pregnant women.

A prospective seroepidemiological survey for latent congenital toxoplasmosis was carried out among 4,136 women and 3,787 of their offspring in and around Montreal. The indirect immunofluorescent antibody test was used to titrate specific IgG and IgM antibodies and results were standardized in international units. The prevalence of antibodies was 40-8% for the mothers and 36-4% for the babies. Mean annual seroconversion rate was 0-95%. Thus, 30 women would have been expected to acquire toxoplasmosis during pregnancy: two cases only were observed and the reasons for it are discussed. Four cases of congenital toxoplasmosis were diagnosed serologically (0-1%), none of them showed any signs of illness. Preventive treatment was administered to 12 of 52 pregnant women suspected of a recently acquired infection.

HREM, FIM and tomographic atom probe investigation of Guinier-Preston zones in an Al-1.54at% Cu alloy.

An investigation of Guinier-Preston zones in Al-1.54at% Cu alloy annealed for 30h at 100 degrees C was carried out on the same monocrystal with complementary techniques of high-resolution electron microscopy (HREM) and tomographic atom probe-field ion microscopy (TAP-FIM). HREM results show that majority of GP1 zones are monolayers 1-9nm in size. However, some GP2 zones and particles in an intermediate state of growth between GP1 and GP2 stage were also found. From TAP results it follows that GP1 zones with different Cu concentrations ranging from 40% up to 100% Cu coexist. The residual solid solution is very heterogeneous. In the vicinity of GP particles the Cu content in the matrix falls down to zero, the solid solution in other regions contains from 0.7 to 1at% Cu.

Assessment of impaired tactile sensation. A pilot study.

Three methods are compared for assessing impaired tactile sensation in vibration-exposed workers: a medical examination including traditional neurological tests and refined measures of vibrotactile perception and gap detection. Of 18 subjects only 12 were judged free of confounding factors--five forestry workers exposed to chain-saw vibration, aged 28 (SD 5) years, and seven laboratory workers not exposed to vibration, aged 36 (SD 7) years. Each method identified the same subject as suffering the most from tactile impairment, but they differed in their ranking of the severity of sensory changes. The ranking by gap detection and vibrotactile perception at low frequencies was the most consistent [Spearman rank correlation coefficient (r) = 0.90]. The clinical results, when staged according to the neurological component of vibration-induced white finger, ranked the thresholds for gap detection and low-frequency vibrotactile perception equally well (r = 0.70). In contrast, the Taylor-Pelmear staging of the clinical results poorly represented the ranking of tactile thresholds recorded for these workers (r = 0.00 and -0.20, respectively). It also appeared that improved techniques for measuring vibrotactile and gap perception thresholds can detect sensory changes in the fingers not consistently found by conventional clinical tests.