Consequences of reducing pertussis transmission - A minimal model.

Since the 1980s there as been an increase in the occurrence of pertussis cases in developed countries, as well as a shift towards the higher age groups. This resurgence follows 30 years of intense mass vaccination, and has been attributed primarily to three factors: (1) more effective diagnosis of the disease; (2) waning of vaccine-induced immunity; and (3) loss of vaccine efficacy due to the emergence of new Bordetella pertussis strains. Mathematical models provide valuable insight into hypotheses plausibility. Here we consider that exposure to B. pertussis through natural infection or vaccination induces an immune response that prevents severe disease but does not fully prevent mild infections. We consider that immunity wanes, making these protective effects temporary. Analysis shows that the highest incidence of disease is expected to occur at intermediate transmission intensities, suggesting that the pertussis resurgence may be induced solely by a reduction in transmission independently of vaccination. These results seem to be in concordance with findings for malaria and may be more generally applicable to diseases where immunity has a limited effect on transmission of infection and a greater effect on severity of disease. The mechanism also requires that these effects wane over time. Applicability of the pertussis model framework to malaria will be further investigated.

Evolution of a Conjugative Plasmid.

Conjugative plasmids can mediate gene transfer between bacterial taxa in diverse environments. What happens when a plasmid arrives to a new bacterial cell? Is the plasmid-bacteria adaptation that may have occurred in previous bacterial cells usefull in the new strain?

Aurélien Mazurie, Samuel Bottani and Massimo Vergassola (2005) An evolutionary and functional assessment of regulatory network motifs. Genome Biology 6:R35

You can grab the paper at: http://genomebiology.com/2005/6/4/R35