Detection of emerging diseases in occupational health: usefulness and limitations of the application of pharmacosurveillance methods to the database of the French national occupational disease surveillance and prevention network (RNV3P)

OBJECTIVE

To test data mining methods used in pharmacosurveillance in order to identify potential emerging disease-nuisance associations in the national occupational disease surveillance and prevention network (RNV3P) database.

METHODS

Proportional reporting ratios (PRR) used in pharmacosurveillance were applied to detect disproportional reporting of disease-nuisance associations which are not compensated by the national social security system.

RESULTS

The 24 785 reports of the RNV3P were grouped into 1344 different disease-nuisance associations reported more than twice, of which 422 did not give entitlement to compensation by the social security system. Among these associations, 162 were potentially emergent and generated a signal, of which eight associations involve cancer.

CONCLUSION

This work is the first stage of an exploratory investigation submitting the questions raised to experts and involving participants in the network in reflection on the hypotheses generated.

Bird migration routes and risk for pathogen dispersion into western Mediterranean wetlands

Migratory movements of wild birds likely spread zoonotic infectious agents, such as avian influenza and West Nile viruses.

Wild birds share with humans the capacity for moving fast over large distances. During migratory movements, birds carry pathogens that can be transmitted between species at breeding, wintering, and stopover places where numerous birds of various species are concentrated. We consider the area of the Camargue (southern France) as an example to highlight how ad hoc information already available on birds’ movements, abundance, and diversity can help assess the introduction and transmission risk for birdborne diseases in the western Mediterranean wetlands. Avian influenza and West Nile viruses are used as examples because birds are central to the epidemiology of these viruses.

Evidence of laboratory vector competence of Culex modestus for West Nile virus

During the past 10 years, West Nile virus (WNV) has been responsible for large and severe human outbreaks and horse epizootics through the Old and the New World. Since WNV was first isolated from field-collected mosquitoes of Culex modestus in 1964 in France, this species, which aggressively feeds on birds and mammals, is considered a putative WNV vector in Europe. We report on the first evidence on the laboratory vector competence of Cx. modestus for WNV. To assess this trait, F3 and F4 females from southern France were fed through a membrane with a strain of WNV isolated from a horse in the Camargue (Rhône River delta) in 2000. On day 14 after virus ingestion, 90% of mosquitoes displayed a disseminated infection. WNV was detected in the saliva from 2 of 5 infected mosquitoes selected for testing. These preliminary results demonstrate that Cx. modestus is capable of experimentally transmitting WNV.

Bird Species Potentially Involved in Introduction, Amplification, And Spread of West Nile Virus in A Mediterranean Wetland, The Camargue (Southern France)

West Nile virus (WNV) is a mosquito-transmitted Flavivirus with a transmission cycle involving birds as amplifying hosts. Wild birds are also believed to carry WNV over large distances and are able to introduce it into new areas during migration and dispersal. In this paper, our objective is to provide lists of birds potentially involved in the introduction, the amplification and the spread of WNV in the Camargue, a Mediterranean wetland in the south of France where several WNV outbreaks have occurred since the 1960s. Bird species were classified according to the following ecological factors: migratory status and provenance area, used biotopes, abundance and period of presence in the Camargue. The obtained lists of bird species potentially involved in the introduction, amplification and spread of WNV should prove useful to determine target species on which further studies on WNV ecology in birds could be focused.

Remote sensing based identification of environmental risk factors associated with West Nile disease in horses in Camargue, France

Geographic information system and remote sensing technologies were used to identify landscape features associated with risk of West Nile virus transmission as defined by the presence of confirmed horse cases. SPOT-4 images of Camargue area were used to generate a map of landscape categories of epidemic foci and the geographic information system was employed to determine the proportion of landscape components surrounding 10 horse case sites and 17 control sites. The spatio-temporal analysis of the cases outbreak gave the best results for a spatial window of 9 km and a temporal window of 18 days. Two clusters were identified (relative risk=3.35), both in the wet area of Camargue, near the town "Les Saintes Maries de la Mer". The first one was 4 km radius, the second 9 km. The relationships between the presence of cases and proportions of landscape categories were analyzed using generalized linear model. The best model indicated that rice fields and dry bushes, wet "sansouire" and open water were the major components of the landscape that were associated with the presence of West Nile virus cases.

Aedes aegypti survival and dengue transmission patterns in French Guiana

Field survival of Aedes aegypti females is a key parameter for estimating the dengue transmission potential of a mosquito population. The objectives of this study were to explore the dynamics of these survival rates at different times of the year in French Guiana and to analyze the results from the perspective of dengue patterns. The mosquitoes were captured, marked, released, and recaptured during four consecutive days in six houses every month, for three to 24 months, from January 1997 to December 1998. Laboratory experiments showed no effects on female survival but some effect on the survival of males. Females' daily survival in the field varied from 0.525 to 1 but was mostly between 0.8 and 0.95 during the entire year, with a mean value of 0.913. The field survival of Ae. aegypti females in French Guiana was thus in agreement with the likely transmission of dengue and the dengue endemic patterns throughout the year. On the other hand, heavy rainfalls during this time were less favorable to Ae. aegypti survival, which may explain part of the El Niño effect on dengue epidemics in French Guiana. The methods and results on Ae. aegypti survival will be implemented in a global dengue surveillance network in French Guiana.

Distribution of equine infectious anemia in horses in the north of Minas Gerais State, Brazil

The paper examines the prevalence of equine infectious anemia (EIA) in horse populations in the northern part (comprising 89 cities) of Minas Gerais State, Brazil, from January 2002 to December 2004. Data on 8,981 agar gel immunodiffusion test results from the region were used as input for a statistical and autoregressive analysis model to construct a city-level map of the distribution of EIA prevalence. The following EIA prevalence (P) levels were found: 49 cities with 0 < P < or = 0.5%, 26 with 0.5% < P < or = 1.5%, 10 with 1.5% < P < or = 5%, and 4 with 5% < P < or = 25%.

Horse-, bird-, and human-seeking behavior and seasonal abundance of mosquitoes in a West Nile virus focus of southern France

After 35 yr of disease absence, West Nile virus (family Flaviviridae, genus Flavivirus, WNV) circulation has been regularly detected in the Camargue region (southern France) since 2000. WNV was isolated from Culex modestus Ficalbi, which was considered the main vector in southern France after horse outbreaks in the 1960s. Recent WNV transmissions outside of the Cx. modestus distribution suggested the existence of other vectors. To study potential WNV vectors, horse- and bird-baited traps and human landing collections of mosquitoes were carried out weekly from May to October 2004 at two Camargue sites: one site in a wet area and the other site in a dry area, both chosen for their past history of WNV transmission. At the wet site, the most abundant species in bird-baited traps were Culex pipiens L. and Cx. modestus; both species also were found in lower proportions on horses and humans. The most abundant species in horse-baited traps and human landing collections were Aedes caspius (Pallas), Aedes vexans (Meigen), and Anopheles hyrcanus (Pallas) sensu lato; some of these species were occasionally collected with avian blood at the end of the summer. Anopheles maculipennis Meigen sensu lato was an abundant horse feeder, but it was rarely collected landing on human bait and never contained avian blood. At the dry site, Cx. pipiens was the most abundant species in bird- and horse-baited traps. The seasonal and circadian dynamics of these species are analyzed, and their potential in WNV transmission in Camargue discussed.

Horse-, bird-, and human-seeking behavior and seasonal abundance of mosquitoes in a West Nile virus focus of southern France

After 35 yr of disease absence, West Nile virus (family Flaviviridae, genus Flavivirus, WNV) circulation has been regularly detected in the Camargue region (southern France) since 2000. WNV was isolated from Culex modestus Ficalbi, which was considered the main vector in southern France after horse outbreaks in the 1960s. Recent WNV transmissions outside of the Cx. modestus distribution suggested the existence of other vectors. To study potential WNV vectors, horse- and bird-baited traps and human landing collections of mosquitoes were carried out weekly from May to October 2004 at two Camargue sites: one site in a wet area and the other site in a dry area, both chosen for their past history of WNV transmission. At the wet site, the most abundant species in bird-baited traps were Culex pipiens L. and Cx. modestus; both species also were found in lower proportions on horses and humans. The most abundant species in horse-baited traps and human landing collections were Aedes caspius (Pallas), Aedes vexans (Meigen), and Anopheles hyrcanus (Pallas) sensu lato; some of these species were occasionally collected with avian blood at the end of the summer. Anopheles maculipennis Meigen sensu lato was an abundant horse feeder, but it was rarely collected landing on human bait and never contained avian blood. At the dry site, Cx. pipiens was the most abundant species in bird- and horse-baited traps. The seasonal and circadian dynamics of these species are analyzed, and their potential in WNV transmission in Camargue discussed.

Rainfall triggered dynamics of Aedes mosquito aggressiveness

Inspired by Davidson method of estimating daily survivals of a structureless population of mosquitoes, we present a model which describes the behavior of floodwater mosquitoes in terms of emergence functions following a rainfall event, blood feeding frequency and parous stages, and survival at various stages. As a generalization of the Davidson formula, we have developed an approach for dealing with the dynamics of structured population of mosquitoes, and derived various formulas allowing assessment of demographic parameters like durations of gonotrophic cycles and (apparent) daily survivals. The method was subsequently applied to field data of floodwater mosquitoes Aedes vexans arabiensis, potential vectors of Rift Valley fever in West Africa, collected during the 2003 rainy season in Barkedji, Senegal. We found that mosquitoes emerged about 3 to 4 days following an efficient rainfall, and mosquito emergences, described by a bell shaped function, lasted for about 2 days. The mean duration of the gonotrophic cycle was 3 days and the apparent daily survival about 0.87.

Stabilization of membrane pores by packing

We present a model for pore stabilization in membranes without surface tension. Whereas an isolated pore is always unstable (since it either shrinks, tending to reseal, or grows without bound until membrane disintegration), it is shown that excluded volume interactions in a system of many pores can stabilize individual pores of a given size in a certain range of model parameters. For such a multipore membrane system, the distribution of pore size and associated pore lifetime are calculated within the mean-field approximation. We predict that, above the temperature T(m), when the effective line tension becomes negative, the membrane exhibits a dynamic sievelike porous structure.

Modelling and determination of the transmission contact rate for contagious bovine pleuropneumonia

Contagious bovine pleuropneumonia (CBPP) is a cattle respiratory disease that represents one of the major threats to cattle health and production in sub-Saharan Africa. The transmission contact rate of CBPP plays a key role in the spreading dynamics of the disease. We have developed an approach based on the combination of a SEIR model describing the spread of CBPP with the dynamic of seroconversion to determine the transmission contact rate for CBPP. This method has been subsequently applied to serological diagnostic data obtained from an experimental vaccine trial. As a result, we find that the transmission contact rates for subclinical, clinical and chronic infective states are respectively, 0.084/N, 0.45 and 0.14/N per animal per day, where N is the herd population size, and the basic reproductive number corresponding to this trial (N=28) is R0=27.

Mapping Rift Valley Fever vectors and prevalence using rainfall variations

High activity of the Rift Valley Fever (RVF) virus is related to a tremendous increase of associated mosquito vectors, which follows periods of high rainfall. Indeed, rainfall creates an ecologically humid environment that insures the proliferation of breeding sites and the development of RVF vectors. Data collected by Fontenille et al. (1998) from 1991 to 1996 in the Barkedji area in the northern Senegal are employed to discuss and quantify the incidence of rainfall upon the abundances of RVF vectors. We have constructed a non-linear mapping of vector abundances versus rainfall variations, and developed a stochastic model and a corresponding algorithm allowing on output the simulation of RVF mosquito vectors as a function of rainfall trajectories in the course of time. This stochastic mapping of vector abundance is subsequently used to assess the prevalence of RVF in a population of susceptible hosts as a consequence of rainfall.

Bubble relaxation dynamics in double-stranded DNA

This paper deals with the two-state (opening-closing of base pairs) model used to describe the fluctuation dynamics of a single bubble formation. We present an exact solution for the discrete and finite size version of the model that includes end effects and derive analytic expressions of the correlation function, survival probability, and lifetimes for the bubble relaxation dynamics. It is shown that the continuous and semi-infinite limit of the model becomes a good approximation to an exact result when aN <<1, where N is bubble size and a, the ratio of opening to closing rates of base pairs, is the control parameter of DNA melting.

Isolation of yellow fever virus from nulliparous Haemagogus (Haemagogus) janthinomys in eastern Amazonia

In 1998, an epizootic of yellow fever (YF) killed many howler monkeys (Alouatta spp.) in eastern Amazonia near the city of Altamira. An infection level with YF virus of approximately 3.6% was determined from analysis of 456 females of Haemagogus janthinomys Dyar, the main enzootic YF vector in South America. One month later, a second study of 164 females captured in the same place led to infection levels of 0.8% for parous and 2.9% for nulliparous females. These results lead to the conclusion that vertical transmission, one of the key elements in the epidemiology of YF, occurs in South America as it does in Africa.

Dispersal of spores following a persistent random walk

A model of a persistent random walk is used to describe the transport and deposition of the spore dispersal process. In this model, the spore particle flies along straight line trajectories, with constant speed v, which are interrupted by scattering, originating from interaction of spores with the field and wind variations, which randomly change its direction. To characterize the spore dispersal gradients, we have derived analytical expressions of the deposition probability epsilon (r|v) of airborne spores as a function of the distance r from the spore source in an infinite free space and in a disk of radius R with an absorbing edge that mimics an agricultural field surrounded with fields of nonhost plants and bare land. It is found in the free space that epsilon (r|v) approximately e(-alphar/l), with alpha a function of l(d)/l, where l and l(d) are the scattering and deposition mean free paths, respectively. In the disk, however, epsilon (r|v) is an infinite series of Bessel functions and, exhibits three regimes: absorbing (R<l(d)), intermediate (R=l(d)), and deposition (R>l(d)).

Influence of environment fluctuations on incoherent neutron scattering functions

In extending the conventional dynamic models, we consider a simple model to account for the environment fluctuations of particle atoms in a protein system and derive the elastic incoherent structure factor (EISF) and the incoherent scattering correlation function C(Q,t) for both the jump dynamics between sites with fluctuating site interspacing and for the diffusion inside a fluctuating sphere. We find that the EISF of the system (or the normalized elastic intensity) is equal to that in the absence of fluctuations averaged over the distribution of site interspacing or sphere radius a. The scattering correlation function is C(Q,t)= Sigma(n)<e(-lambda(n)(a)t)> psi(t), where the average is taken over the Q-dependent effective distribution of relaxation rates lambda(n)(a), and psi(t) is the correlation function of the length a. When psi(t)=1, the relaxation of C(Q,t) is exponential for the jump dynamics between sites [since lambda(n)(a) is independent of a] while it is nonexponential for diffusion inside a sphere.

Protein flexibility from the dynamical transition: a force constant analysis

A standard analysis of the scattered neutron incoherent elastic intensity measured with very good energy resolution yields elastic scans, i.e., mean-square displacements of atomic motions (in a pico to nanosecond time scale) in a sample as a function of temperature. This provides a quick way for characterizing the dynamical behavior of biological macromolecules, such behavior being correlated with biological function and activity. Elastic scans of proteins exhibit a dynamical transition at approximately 200 K, marking a cross-over in molecular fluctuations between harmonic and nonharmonic dynamical regimes. This paper presents an approach allowing analysis of the elastic scan in terms of force constants and related parameters, such as the free energy barrier DeltaG at the transition. We find that the increased protein flexibility beyond the dynamical transition is associated with DeltaG approximately equals RT and effective force constants of the order of 0.1-3 N/m. The analysis provides a set of parameters for characterizing molecular resilience and exploring relations among dynamics, function, and activity in proteins.

Incoherent neutron scattering functions for diffusion inside two concentric spheres

We consider the diffusion of a particle inside two concentric spheres as a model for diffusing motions inside and between two semipermeable subregions or sublayers of a confining region. Analytic expressions for the elastic incoherent structure factor (EISF) and the incoherent scattering correlation function, C(Q,t), are derived for this model. It is found that, as a result of interferences between regions, the EISF is a weighted coherent summation over amplitudes corresponding to subregions and the relaxation rate of C(Q,t) has a turnover behavior with a minimum at Q(m). In addition to the single exponential behavior for Q<Q(m), C(Q, t) also shows a biexponential decay as a function of time for intermediate values of Q>/=Q(m). The rate of decay at short times is related to diffusion over length scales under consideration while at long times it is given by the relaxation to equilibrium in fluctuations of population between subregions.

Entropic barriers, transition states, funnels, and exponential protein folding kinetics: a simple model

This paper presents an analytically tractable model that captures the most elementary aspect of the protein folding problem, namely that both the energy and the entropy decrease as a protein folds. In this model, the system diffuses within a sphere in the presence of an attractive spherically symmetric potential. The native state is represented by a small sphere in the center, and the remaining space is identified with unfolded states. The folding temperature, the time-dependence of the populations, and the relaxation rate are calculated, and the folding dynamics is analyzed for both golf-course and funnel-like energy landscapes. This simple model allows us to illustrate a surprising number of concepts including entropic barriers, transition states, funnels, and the origin of single exponential relaxation kinetics.

Simulations of electron transfer in the NADPH-bound catalase from Proteus mirabilis PR

Catalase-bound NADPH both prevents and reverses the accumulation of compound II, an inactive form of catalase that is generated from the normal active intermediate form (compound I) when catalase is exposed to a steady flow of hydrogen peroxide. The mechanism for the regeneration reaction is unknown although NADPH could act either as a one-electron or a two-electron donor. Recently, a reaction scheme has been proposed in which the formation of compound II from compound I generates a neighboring radical species within the protein. NADPH would then donate two electrons, one to compound II for reduction of the iron and the other to the protein free radical. In this paper, we report calculations to find the dominant electron tunneling pathways between NADPH and the heme iron in the catalase from the peroxide-resistant mutant of Proteus mirabilis. Two major tunneling pathways are found which fuse together on Ser-196. It is suggested that the sequence Gly-Ser of the loop that divides the beta 5-strand is the key element for shielding a radical amino acid.