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Biomedical subjects

M Langlais

Publications and source records attributed to M Langlais.

13 recordsLinked to original sources
PubMed2000

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.

Animals↗
PubMed2000

A modelling approach to vaccination and contraception programmes for rabies control in fox populations.

In a previous study, three of the authors designed a one-dimensional model to simulate the propagation of rabies within a growing fox population; the influence of various parameters on the epidemic model was studied, including oral-vaccination programmes. In this work, a two-dimensional model of a fox population having either an exponential or a logistic growth pattern was considered. Using numerical simulations, the efficiencies of two prophylactic methods (fox contraception and vaccination against rabies) were assessed, used either separately or jointly. It was concluded that far lower rates of administration are necessary to eradicate rabies, and that the undesirable side-effects of each programme disappear, when both are used together.

Animals↗
PubMed1998

Dynamics of a feline retrovirus (FeLV) in host populations with variable spatial structure.

The predictions of epidemic models are remarkably affected by the underlying assumptions concerning host population dynamics and the relation between host density and disease transmission. Furthermore, hypotheses underlying distinct models are rarely tested. Domestic cats (Felis catus) can be used to compare models and test their predictions, because cat populations show variable spatial structure that probably results in variability in the relation between density and disease transmission. Cat populations also exhibit various dynamics. We compare four epidemiological models of Feline Leukaemia Virus (FeLV). We use two different incidence terms, i.e. proportionate mixing and pseudo-mass action. Population dynamics are modelled as logistic or exponential growth. Compared with proportionate mixing, mass action incidence with logistic growth results in a threshold population size under which the virus cannot persist in the population. Exponential growth of host populations results in systems where FeLV persistence at a steady prevalence and depression of host population growth are biologically unlikely to occur. Predictions of our models account for presently available data on FeLV dynamics in various populations of cats. Thus, host population dynamics and spatial structure can be determinant parameters in parasite transmission, host population depression, and disease control.

Animals↗
PubMed1997

Modelling the feline leukemia virus (FeLV) in natural populations of cats (Felis catus).

A compartmental model was built in order to study the circulation and impact of Feline Leukemia Virus (FeLV) in populations of domestic cats. The model was tested with data from a long-term study of several feline populations. The study of stability shows that FeLV is maintained in the population with a stable equilibrium and a slight reduction of population size. Estimation of the transmission rate allows us to make a comparison with the values previously estimated in the literature. We compare the impact of mass vaccination or removal programmes in controlling FeLV infection, and conclude that vaccination is more efficient.

Animals↗
PubMed1995

Population dynamics of feline immunodeficiency virus within cat populations.

A deterministic model was constructed for studying the circulation of Feline Immunodeficiency Virus (FIV), a feline retrovirus homologous to Human Immunodeficiency Virus (HIV), within populations of domestic cats. The model has been tested with data generated by a long-term study of several natural cat populations. Simulations and a study of stability show that once introduced, the retrovirus is maintained within the population, with a stable equilibrium stage reached by both numbers of susceptible and infected individuals. An estimation of parameters indicates that the transmission rate is low and depends on the structure of the population. In addition, FIV has a low impact on the population in that the total number of cats at equilibrium when this virus is present is almost always equal to the habitat carrying capacity in the absence of the virus. Those results, in agreement with other observations, suggest that FIV originally arose in the distant past.

Animals↗
PubMed1990

Raman spectroscopic study of the effects of Ca2+, Mg2+, Zn2+, and Cd2+ ions on calf thymus DNA: binding sites and conformational changes.

The interaction of Mg2+, Ca2+, Zn2+, and Cd2+ with calf thymus DNA has been investigated by Raman spectroscopy. These spectra reveal that all of these ions, and particularly Zn2+, bind to phosphate groups of DNA, causing a slight structural change in the polynucleotide at very small metal: DNA (P) concentration ratio (ca. 1:30). This results in increased base-stacking interactions, with negligible change of the B conformation of DNA. Contrary to Zn2+ and Cd2+, which interact extensively with the nucleic bases (particularly at the N7 position of guanine), the alkaline-earth metal ions are bound almost exclusively to the phosphate groups. The affinity of both the Zn2+ and Cd2+ ions for G.C base pairs is comparable, but the Cd2+ ions interact more extensively with A.T pairs than Zn2+ ions. Interstrand cross-linking through the N3 atom of cytosine is suggested in the presence of Zn2+, but not Cd2+.

Animals↗
PubMed1988

A laser Raman spectroscopic study of the interaction of the methylmercury cation with AMP, ADP and ATP.

The interaction of the CH3Hg+ cation with adenosine 5'-monophosphate, adenosine 5'-diphosphate, and adenosine 5'-triphosphate has been studied in aqueous solution at neutral pH by laser Raman spectroscopy. Metal binding is shown to occur preferentially at the N-1 ring position of adenine, with some indication of coordination to the N-7 site and substitution of a proton on the exocyclic NH2 group of the nucleic base. Binding of the cation to phosphate groups also occurs extensively, with both the -PO2-3 and -PO-2 groups. The equilibrium constants for the binding to the phosphate groups and for N-1 coordination are approx. 70 and 600 M-1, respectively.

Adenosine Diphosphate↗
PubMed1988

A laser Raman spectroscopic study of the interaction of calf-thymus DNA with Cu(II) and Pb(II) ions: metal ion binding and DNA conformational changes.

The interaction of calf-thymus DNA with Cu(II) and Pb(II) ions has been investigated in H2O and D2O solutions at physiological pH, using laser Raman spectroscopy. The results confirm the destabilizing effect of Cu2+ ions, which are shown to bind strongly to the guanine and cytidine bases, perturbing the A-T base pairs and disrupting the double-helical structure of DNA, whose conformation is markedly altered by these interactions. Earlier claims that Pb2+ ions destabilize DNA are not supported by the present study. These ions are found to interact only weakly with the nucleic bases, binding to the N7 position of the guanine bases and also interacting with the A-T pairs. Both types of ions are found to interact with the charged phosphate groups of DNA, although these sites are preferred over the nucleic bases by Pb2+ ions.

Copper↗
PubMed1988

Large time behavior in a nonlinear age-dependent population dynamics problem with spatial diffusion.

In this work we analyze the large time behavior in a nonlinear model of population dynamics with age-dependence and spatial diffusion. We show that when t----+ infinity either the solution of our problem goes to 0 or it stabilizes to a nontrivial stationary solution. We give two typical examples where the stationary solutions can be evaluated upon solving very simple partial differential equations. As a by-product of the extinction case we find a necessary condition for a nontrivial periodic solution to exist. Numerical computations not described below show a rapid stabilization.

Aging↗