Science  12 Jul 2013:
Vol. 341, Issue 6142, pp. 116

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  1. Weak Immune System Toughens Malaria Parasite

    Virulence boost.

    Researchers saw parasite evolution in immunocompromised mice.


    The arms race between pathogens and their host can heat up even if the host is a wimp. An experimental evolution study in mice has found that malaria parasites infecting rodents with weakened immune systems evolve increased virulence.

    Andrew Read and Victoria Barclay of Pennsylvania State University, University Park, tested this by first giving a pair of mice antibodies that disabled a key immune molecule, the CD4 receptor, and then infecting them with a mouse malaria parasite. Then, each week for 21 weeks, they infected a new pair of immunocompromised mice with parasites taken from the immunocompromised mice infected the week before. Finally, to compare the virulence of each week's parasites, they infected healthy mice with the pathogens; parasites from week 21 grew faster and caused more anemia and weight loss than parasites from week 10, Read reported last month at Evolution 2013 in Snowbird, Utah.

    Read is concerned that the rise in number of HIV-infected and other immunocompromised people might hasten the evolution of pathogens into deadlier forms. Although Read's mouse experiment "is a very elegant and sobering study," says Daniel Bolnick, an evolutionary biologist at the University of Texas, Austin, "we certainly can't take it for granted that biological patterns in mice can be extrapolated to humans."