Reinfection thresholds regulate pathogen diversity: The unusual patterns of influenza A evolution

The awareness that pathogens can adapt and evolve over relatively short time scales is changing our view of infectious disease epidemiology and control. Research on the transmission dynamics of antigenically diverse pathogens is progressing and there is increasing recognition for the need of new concepts and theories. Influenza is a favourite model system. Annual epidemics result from the progressive antigenic drift of influenza A and B viruses, and occasionally severe pandemics are caused by the emergence of novel influenza A subtypes (antigenic shift). We explore these dynamics by means of epidemiological models. Cross-immunity reflects upon the dynamics of reinfection, inducing an important threshold in transmission - the "reinfection threshold". We find our model could help explain the unusual patterns of influenza evolution by providing a simple framework where drift and shift might occur.

The interplay of diversity and lymphocyte selection as an evolutionary force in shaping lymphoid tissue.

During immune responses an hypermutation mechanism is activated that target the rearranged variable genes of immunoglobulins. This generates an enormous diversity, but decreases the initial average affinity of the response. This process has been documented from lower to higher vertebrates. The existence of a selective mechanism has been inferred only in higher vertebrates because in them (but not in lower vertebrates) the average affinity of serum antibodies (Ab) increases with time after the climax of the response (termed affinity maturation). It is now known that in higher vertebrates the mutation/selection of Ab specificities takes place in organized, transient structures named Germinal Centers (GC). It has been proposed that there the mutation/selection process has been optimized to maximize affinity maturation. This would narrow considerably the initial diversity and would increase the specificity of the Abs. If diversity is at least as important as affinity maturation, then a trade-off will be established in vertebrates as a more complex evolutionary force affecting the size, structure and life span of GCs. A theoretical analysis suggests that at least the size of GCs may be determined by such trade-off between diversity and affinity maturation.

Refining eBURST - Can we go to an F word?

Multi Locus Sequence Typing (MLST) is a "new age" typing method based upon sequencing 7 house keeping genes of a given strain and in assigning to each allele a number. The final Sequence Type(ST) of a strain is a unique 7 number code that characterizes the isolate. The algorithm used to calculate relationships between strain types is eBURST (enhanced Based Upon Related Sequence Types). The eBURST algorithm basically counts the number of different alleles between strains, creates links between STs that differ at a single allele and attempts to determine which is the "founder" ST from which all other derived. This is then used to group the STs and display their relationships. Here we propose a novel metric that takes into account the relative frequency of alleles of each gene in the population do determine the distance between STs. We consider this to be a sequel of the eBURST algorithm and propose the name fBURST.

The Tragedy of the Commons and the Public Goods Dilemma. The significance of Rivalry and Excludability in Evolutionary Biology.

Not Supplied.