Swine populations worldwide are sporadically infected by influenza viruses from humans and birds leading to geographically heterogeneous swine influenza virus populations that pose epizootic and pandemic threats.

A novel compartment model identifies the impact of malaria strain diversity on biogeographic drug resistance patterns, supported by empirical evidence.

Mathematical modeling shows that local populations of the malaria parasite self-organize into a limited number of transient but distinct strains through competition for hosts in immunity space.

Each dengue serotype contains moderate antigenic diversity, and population immunity drives clade turnover in a hyperendemic population.

Deleterious mutations slow down flu's antigenic evolution, make it more punctuated in nature, and reduce the virus's genetic diversity.

Despite the virus' error prone polymerase, influenza virus antigenic evolution is rare, even in previously immune hosts, virus replication occurs before producing new antibodies.

An analysis of influenza viruses from naturally infected people suggests a tight transmission bottleneck and little positive selection within hosts.

The longer duration of seasonal influenza virus infection in young children may provide opportunities for within-host evolution as a result of maintenance of genetic diversity through mutation-selection balance.

The first comprehensive analysis of antigenic switching in the malaria-causing parasite Plasmodium falciparum provides new insights into the process that prevents individuals from acquiring immunity to the disease.

Vaccination has the potential to decrease swine influenza diversification by restricting influenza virus co-infections and reassortment events in pigs.