Modelling of predator-prey trophic interactions. Part I: two trophic levels.

A class of lumped parameter models to describe the local dynamics in a controlled environment of a two-trophic chain is considered. The class is characterized by a trophic function (functional response of predator to the abundance of prey) depending on the ratio of prey biomass x and a linear function of predator biomass y: f(qx/[(1-rho)k + rhoy]), where q is the efficiency of the predation process, k is a reference biomass, and rho (0 < or = rho < or = 1) specifies the predation model. The trophic function is defined only by some properties determining its shape. A stability analysis of the models has been performed by taking the parameters q and rho as bifurcation parameters: the regions in the (rho,q) plane of existence and stability of nonnegative equilibrium states and limit cycles are determined. This analysis shows that the behaviour of the models is qualitatively similar for 0 < or = rho < 1 (in particular the null state is always a saddle point), while the value rho=1 gives rise to some kind of structural instability of the system (in particular the null state becomes an attractor for sufficiently high predation efficiency).

Human health improvement in Sub-Saharan Africa through integrated management of arthropod transmitted diseases and natural resources.

A concept of an ecosystem approach to human health improvement in Sub-Saharan Africa is presented here. Three factors mainly affect the physical condition of the human body: the abiotic environment, vector-transmitted diseases, and natural resources. Our concept relies on ecological principles embedded in a social context and identifies three sets of subsystems for study and management: human disease subsystems, natural resource subsystems, and decision-support subsystems. To control human diseases and to secure food from resource subsystems including livestock or crops, integrated preventive approaches are preferred over exclusively curative and sectorial approaches. Environmental sustainability - the basis for managing matter and water flows - contributes to a healthy human environment and constitutes the basis for social sustainability. For planning and implementation of the human health improvement scheme, participatory decision-support subsystems adapted to the local conditions need to be designed through institutional arrangements. The applicability of this scheme is demonstrated in urban and rural Ethiopia.

[Gram positive microorganisms in urinary tract infections: epidemiology and therapy]. / I microrganismi Gram-positivi nelle infezioni urinarie: epidemiologia e note di terapia.

Urinary tract infections are the most frequent hospital acquired infections and represent one of the major problem in general practice. The predominant causative agents are enteric gram-negative bacteria. Nevertheless, the importance of gram-positive bacteria, particularly Staphylococcus aureus and Enterococcus, has progressively increased especially in nosocomial urinary tract infections. Such an increase is probably related to the indiscriminate use of beta-lactam antibiotics or to the growing number of susceptible patients (surgical procedures, immunodeficiency, ecc.) The therapeutic approach of community and hospital infections is different: while in the first case treatment is usually not difficult, the therapy for nosocomial urinary tract infections should be based on the results of antibiotic susceptibility tests since a multiantibiotic resistant microorganism is often involved.