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BIOLOGICAL SCIENCES / POPULATION BIOLOGY
Globalization and the population structure of Toxoplasma gondii
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*Division of Parasitic Diseases, Centers for Disease Control and Prevention, 4770 Buford Highway, Chamblee, GA 30341; Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 12735 Twinbrook Parkway, Rockville, MD 20852; and **Animal Parasitic Diseases Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705
Edited by Francisco J. Ayala, University of California, Irvine, CA, and approved May 30, 2006 (received for review February 21, 2006)
Toxoplasma gondii is a protozoan parasite that infects nearly all mammal and bird species worldwide. Usually asymptomatic, toxoplasmosis can be severe and even fatal to many hosts, including people. Elucidating the contribution of genetic variation among parasites to patterns of disease transmission and manifestations has been the goal of many studies. Focusing on the geographic component of this variation, we show that most genotypes are locale-specific, but some are found across continents and are closely related to each other, indicating a recent radiation of a pandemic genotype. Furthermore, we show that the geographic structure of T. gondii is extraordinary in having one population that is found in all continents except South America, whereas other populations are generally confined to South America, and yet another population is found worldwide. Our evidence suggests that South American and Eurasian populations have evolved separately until recently, when ships populated by rats, mice, and cats provided T. gondii with unprecedented migration opportunities, probably during the transatlantic slave trade. Our results explain several enigmatic features of the population structure of T. gondii and demonstrate how pervasive, prompt, and elusive the impact of human globalization is on nature.
evolutionary history | migration | pandemic genotype | protozoan parasite | trade
Present address: Department of Biomedical Sciences, Grand Valley State University, 218 Padnos Hall, 1 Campus Drive, Allendale, MI 49401.
¶D.H.G. and E.R.D. contributed equally to this work.
||Present address: Department of Microbiology and Immunology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1019.
Author contributions: T.L. and J.P.D. designed research; T.L., P.L.M., D.H.G., E.R.D., and J.P.D. performed research; T.L. and P.L.M. analyzed data; and T.L. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
To whom correspondence should be addressed: at the present address: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 12735 Twinbrook Parkway, Room 2W13A, Rockville, MD 20852. E-mail: tlehmann{at}niaid.nih.gov
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