Acknowledgments We thank Robert Hunter for coordinating the blood bank investigation, Anne Kjemtrump and Barbara Herwaldt for their expertise and advice in the clinical and epidemiological aspects of babesiosis, Marianna Wilson and David E. Dassey for their thoughtful review, and the laboratory staff at CDC for their as- sistance with testing and conﬁrmation. Ms Ngo is an epidemiologist and Dr Civen is a medical epi- demiologist with the vector-borne disease unit of the Acute Com- municable Disease Control program of the Los Angeles County Department of Public Health. Their research interests include the surveillance and epidemiology of vector-borne diseases affecting Los Angeles County. References 1. Leiby DA. Babesiosis and blood transfusion: ﬂying under the radar. Vox Sang. 2006;90:157–65. DOI: 10.1111/j.1423-0410 .2006.00740.x 2. Conrad PA, Kjemtrup AM, Carreno RA, Thomford J, Wainwright K, Eberhard M, et al. Description of Babesia duncani n.sp. (Api- complexa: Babesiidae) from humans and its differentiation from other piroplasms. Int J Parasitol. 2006;36:779–89. DOI: 10.1016/j. ijpara.2006.03.008 3. Herwaldt BL, de Bruyn G, Pieniazek NJ, Homer M, Lofy KH, Slemenda SB, et al. Babesia divergens–like infection, Washington State. Emerg Infect Dis. 2004;10:622–9. 4. Leiby DA, Chung AP, Gill JE, Houghton RL, Persing DH, Badon S, et al. Demonstrable parasitemia among Connecticut blood donors with antibodies to Babesia microti. Transfusion. 2005;45:1804–10. DOI: 10.1111/j.1537-2995.2005.00609.x Babesiosis Acquired through Blood Transfusion 5. Maine Center for Disease Control and Prevention. Reportable infec- tious diseases in Maine, 2006 Summary [cited 2008 May 20]. Avail- able from http://www.maine.gov/dhhs/boh/newpubs.htm 6. Rhode Island Department of Health. Health topics: babesiosis [cited 2008 May 20]. Available from http://www.health.state.ri.us/topics/ babesiosis.php 7. McQuiston JH, Childs JE, Chamberland ME, Tabor E. Transmis- sion of tick-borne agents of disease by blood transfusion: a review of known and potential risks in the United States. Transfusion. 2000;40:274–84. DOI: 10.1046/j.1537-2995.2000.40030274.x 8. Krause PJ, Spielman A, Telford SR, Sikand VJ, McKay K, Chris- tianson D, et al. Persistent parasitemia after acute babesiosis. N Engl J Med. 1998;339:160–5. DOI: 10.1056/NEJM199807163390304 9. Wormser GP, Dattwyler RJ, Shapiro ED, Halperin JJ, Steere AC, Klempner MS, et al. The clinical assessment, treatment, and pre- vention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006;43:1089–134. DOI: 10.1086/508667 10. Kjemtrup AM, Lee B, Fritz CL, Evans C, Chervenak M, Con- rad PA. Investigation of transfusion transmission of a WA1-type babesial parasite to a premature infant in California. Transfusion. 2002;42:1482–7. DOI: 10.1046/j.1537-2995.2002.00245.x 11. Yao J. Infections transmitted from use of blood products. Presented at: Infectious Diseases Society of America 45th Annual Meeting; October 5, 2007; San Diego, CA, USA. Address for correspondence: Van Ngo, Los Angeles County Department of Public Health, 313 N Figueroa Ave #212, Los Angeles, CA 90012, USA; email: vngo@ph.lacounty.gov The opinions expressed by authors contributing to this journal do not necessarily reﬂect the opinions of the Centers for Disease Con- trol and Prevention or the institutions with which the authors are afﬁliated. etymologia Babesia [bə-be′ ze-ə] A genus of protozoa of the order Piroplasmida, named for Victor Babès (1854–1926), a Romanian bacteriologist who discovered a parasitic sporozoon in ticks in 1885. The parasites occur within the erythrocytes of various vertebrates and cause babesiosis, a tick-borne infection of domestic animals and humans. Babès was also a coauthor of the ﬁrst text on bacteriology (Bacteria and Their Role in the Anatomy and Pathological Histology of Contagious Diseases, with French scientist A.V. Cornil); the ﬁrst to demonstrate the presence of tuberculous bacilli in the urine of infected patients; a founder of serum therapy; and the ﬁrst to introduce rabies vaccination to Romania. Sources: Dorland’s illustrated medical dictionary, 31st edition. Philadelphia: Saunders; 2007; www.whonamedit.com; www.ici.ro/ romania/en/stiinta/babes.html Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 15, No. 5, May 2009 787