Recent Expansion of Toxoplasma Through Enhanced Oral Transmission

Science  17 Jan 2003:
Vol. 299, Issue 5605, pp. 414-416
DOI: 10.1126/science.1078035

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The global predominance of three clonalToxoplasma gondii lineages suggests that they are endowed with an exceptional trait responsible for their current parasitism of nearly all warm-blooded vertebrates. Genetic polymorphism analyses indicate that these clonal lineages emerged within the last 10,000 years after a single genetic cross. Comparison with ancient strains (∼1 million years) suggests that the success of the clonal lineages resulted from the concurrent acquisition of direct oral infectivity. This key adaptation circumvented sexual recombination, simultaneously promoting transmission through successive hosts, hence leading to clonal expansion. Thus, changes in complex life cycles can occur rapidly and can profoundly influence pathogenicity.

  • * These authors contributed equally to this work.

  • To whom correspondence should be addressed. E-mail: sibley{at}

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