Karine Chalvet-Monfray

Rift Valley fever in West Africa: the role of space in endemicity.

Rift Valley fever is an endemic vector‐borne disease in West Africa, which mainly affects domestic ruminants and occasionally humans. The aetiological mechanisms of its endemicity remain under debate. We used a simple spatially explicit model to assess the possibility of endemicity without wild animals providing a permanent virus reservoir. Our model takes into account the vertical transmission in some mosquito species, the rainfall‐driven emergence of their eggs and local and distant contacts because of herd migration. Endemicity without such a permanent virus reservoir would be impossible in a single site except when there is a strictly periodic rainfall pattern; but it would be possible when there are herd movements and sufficient inter‐site variability in rainfall, which drives mosquito emergence.

A two-patch model of Gambian sleeping sickness: application to vector control strategies in a village and plantations.

A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two patches: the village and the plantations. The number of equilibrium points depends on two summary parameters: gr the proportion removed among human infectives, and R0, the basic reproduction number. The origin is stable for R0 <1 and unstable for R0 >1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insentive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.

The surface electrocardiogram in domestic ferrets.

OBJECTIVESnThe two goals of the current study were to evaluate the surface electrocardiogram for significant differences observed between two different recumbency positions and suggest normal surface electrocardiographic values in those positions for the clinically normal domestic pet ferret (Mustela putorius furo).nnnANIMALS, MATERIALS AND METHODSnSurface electrocardiograms were recorded using six standard limb leads from 80 apparently healthy domestic pet ferrets. Each was anesthetized with a combination of ketamine and diazepam. Electrocardiograms were recorded in two different recumbency positions (right lateral and sternal recumbency). The data were analyzed retrospectively and the values were compared statistically for the two different recumbency positions, for age and for gender.nnnRESULTSnSignificant differences were observed between recumbency recording positions for the following values: mean electrical axis, P wave amplitude, R wave amplitude in leads I and II and Q (or S) wave amplitude in lead I. Clinical relevance for P and Q wave amplitude differences was interpreted with caution. Heart rate was markedly higher in younger ferrets. No differences were observed between males and females.nnnCONCLUSIONSnRecumbency position significantly affects ECG recordings in the ferret. The values obtained are suggested as normal surface electrocardiographic values for the domestic pet ferret, in similar recumbency recording positions and under ketamine diazepam sedation.

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.

Time-delay dynamics for contagious bovine pleuropneumonia.

Modelling of contagious disease usually employs compartmental SEIR-like models where the waiting times in respective compartments are exponentially distributed. In this paper, we are interested in investigating how the distributions of sojourn times in infective compartments affect the dynamics and persistence of the contagious bovine pleuropneumonia, a chronic respiratory disease of cattle. Two kinds of extreme distributions of the sojourn times are considered: a Dirac delta-function and truncated Gaussian function leading to a model with (non-constant) delay and the classical exponential distribution that stands for a model without delay. Expressions of the basic reproductive numbers are derived and dynamical behaviours are discussed for the three models. It is found that the spreading of disease exhibits wave-like oscillations for the time-delay dynamics. In contrast, the disease appears to last longer when the spreading is described by the classical dynamics without delay. Subsequently, the time-delay dynamics turns out to be more appropriate for the description of an experimental epidemic of CBPP.

Modelling based method for pharmacokinetic hypotheses test

The aim of this work is to propose methods to test mechanism of synergy of toxic agents in bees. A synergy between prochloraz, an imidazole fungicide, and deltamethrin, a pyrethroid insecticide, was demonstrated experimentally. The hypothesis is that prochloraz modifies the penetration or the metabolism of deltamethrin. This hypothesis is tested using a pharmacokinetic box model. A previous experimental work showed that bee instantaneous mortalities were higher, from the time t1 to the time t2 after spraying, in groups sprayed with deltamethrin at dose D0 in the presence of prochloraz (Δ+P) than in those sprayed with deltamethrin alone at a dose α time as high (αΔ). We postulate that accrued mortality is proportional to the cumulated internal deltamethrin (ID2). ID2 of treatment (Δ+P) had to be greater than ID2 of treatment (αΔ) during the period from t1 to t2 so that the hypothesis would be consistent with the experimental data. The limit, for which the hypothesis is conceivable, is the ID2(αΔ) = ID2(Δ+P) curve. We study, in particular, the asymptotic behaviour of the limit curve when different parameters of the kinetic model tend to 0 or ∞. These limits allow to verify quickly and easily whether a mechanism is conceivable or not As the limits are calculated with algebraic values, the test can be used for other synergies.

Synergy Between Deltamethrin and Prochloraz in Bees: Different Mechanisms of Action Tested by Modeling

Abstract The aim of this work was to propose methods to test mechanisms of synergistic effects of toxic agents in bees. We assumed that the fungicide prochloraz acts synergistically on deltamethrin by increasing the penetration of deltamethrin and/or inhibiting the oxidative metabolism of deltamethrin. These hypotheses were tested by using a pharmacokinetic box model. A previous experimental work showed that there was a synergy between deltamethrin and prochloraz in bees, and allowed to compare the effects of the treatment with 0.25 g ha−1 deltamethrin in the presence of 25 g ha−1 (Δ0.25 + P) prochloraz and the treatment with 1 g ha−1 deltamethrin alone (Δ1). We postulated that cumulated mortality was proportional to the cumulated internal deltamethrin (ID 2). To be consistent with the experimental data, ID 2 of treatment (Δ0.25 + P) had to be greater than ID 2 of treatment (Δ1) during the period from 2 to 8 hours. We studied in the most favourable conditions if the different hypotheses could be consisten...