Jonathan Swinton

Gonococcal infection and human fertility in sub-Saharan Africa

An analysis is presented of the influence of Neisseria gonorrhoeae on hum an population growth in regions of sub-Saharan Africa where gonococcal infections are prevalent in sexually active adults. Combining epidemiological and demographic data within the framework of a mathematical model, we show that gonorrhoea has a major impact on fertility and, concomitantly, on net population growth in areas with a high prevalence of untreated infections. Specifically, a 20% prevalence in sexually active adults is predicted to induce a 50% reduction in net population growth. Model predictions are in good agreement with observed data from Uganda, and the sensitivity of the prediction to various complications, such as heterogeneity in sexual behaviour, is assessed. The analysis suggests that the predicted increase in fertility arising from expanded sexually transmitted disease (std) control programmes in Africa to help combat the spread of hum an immunodeficiency viruses (HIV-1 and HIV-2) will help to offset the predicted demographic impact of aids in the worst afflicted areas. In other areas the rise in fertility associated with effective std control will need to be countered by the linkage of std control programmes with family planning initiatives.

Stability of travelling pulse solutions to a laser equation

Abstract The stability of travelling pulse solutions to a partial differential equation modelling a laser system is determined through a simple robust part-numerical method not previously applied to such a system. The agreement with the results of a full blown numerical simulation is complete for all the cases examined.

The stability of homoclinic pulses: a generalisation of Evans's method

Abstract Evanss method provides a stability analysis for pulse-like solutions of partial differential equations which is particularly well suited to numerical implementation. The original formulation was only applicable to pulses corresponding to orbits homoclinic to a fixed point with an unstable manifold of dimension exactly one. This paper extends the method of Evans by removing this restriction on the dimension of the unstable manifold. I also show how to apply the method to heteroclinic orbits.

Dynamic interaction between Leishmania infection in mice and Th1-type CD4+ T-cells: complexity in outcome without a requirement for Th2-type responses

The interaction between Leishmania parasites and Th1 cells is investigated using a simple mathematical model of immunological responses and parasite population growth within the host. The model generates patterns of resistance and susceptibility to infection that mirror observed trends in experimental infections of mice and of humans exposed to infection in areas of endemic transmission. The heterogeneity in outcome predicted by the model can arise either through differences in the values of the parameters that characterize the genetic background of the host or as a consequence of differences in the size of the infecting inoculum of the parasite. Detailed analyses of equilibrium states and of the time course of infection within a host suggest that a limitation in the availability of precursor T‐cells, as a consequence of high levels of recruitment into the activated pool, may play a signficant role in the progression of infection in susceptible hosts. A brief discussion is presented of the implications of model prediction for therapeutic intervention.

Complex Outcomes in Mouse Leishmaniasis: A Model for the Dynamics of the TH1 Response

The interaction between Leishmania parasites and Th1 cells is investigated using a simple mathematical model of immunological responses and parasite population growth within the host. The model generates patterns of resistance and susceptibility to infection that mirror observed trends in experimental infections of mice and humans exposed to infection in areas of endemic transmission. The heterogeneity in outcome predicted by the model can arise either through differences in the values of the parameters that characterize the genetic background of the host or as a consequence of differences in the size of the infecting inoculum of the parasite. Detailed analyses of equilibrium states and of the time course of infection within a host suggest that a limitation in the availability of precursor T cells, as a consequence of high levels of recruitment into the activated pool, may play a significant role in the progression of infection in susceptible hosts.