THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER Vol. 24, No. 13
Tuesday, March 29, 2005
A. Provided by Sharon Wallace, Division of Outbreak Investigation, Maryland Department of
Health and Mental Hygiene.
17 outbreaks were reported to DHMH during MMWR Week 12(March 20 – March 26):
12 Gastroenteritis Outbreaks
9 outbreaks of GASTROENTERITIS associated with Nursing Homes in Baltimore Co., Calvert Co., Baltimore City,
Wicomico Co., Allegany Co., and Howard Co.
1 outbreak of FOODBORNE GASTROENTERITIS associated with a Restaurant in Prince Georges Co.
2 outbreaks of FOODBORNE GASTROENTERITIS associated with Private Halls in Anne Arundel Co.
5 Respiratory Outbreaks
4 outbreaks of INFLUENZA-LIKE ILLNESS/PNEUMONIA associated with Nursing Homes in Prince George's Co., and
Montgomery
Co., 1 cluster of PERTUSSIS associated with a Private Home in Baltimore Co.
B. The Johns Hopkins Hospital, Department of Pathology, Information provided by,
Kathleen Burns, M.D., Ph. D
A Clinical Case (Adapted from the Electronic Patient Record)
A 77-year-old woman with type II diabetes, hypertension, and hypothyroidism was in her usual
state of health until approximately two weeks prior to admission. She was visiting Florida at the time and
began there to experience chills, fatigue and generalized weakness. Prior to this trip, she had been visiting a
vacation home in Nantucket sporadically over the summer. She shortened her trip due to her symptoms and
returned home to Doysletown, Pennsylvania. At Doylestown Hospital she was noted to have fevers to 102.8oC,
a BUN and creatinine of 54 and 2, a total bilirubin of 5.9, platelet count 33,000 and a hemoglobin of 9.1. A
peripheral smear was examined, and she was referred two days after Babesia diagnosis was made for
management of complications at The Johns Hopkins Hospital in September of 2004.
The Peripheral Smear
A peripheral blood smear photograph illustrating Babesia microti ring forms without the pathoneumonic. Maltese cross formations. In laboratory proficiency
testing, these are commonly misdiagnosed as malaria.
Babesiosis
Babesia parasites, most commonly Babesia microti, are transmitted to humans by bites from the
northeastern deer tick Ixodes scapularis (also called Ixodes dammini) or the western United Stated Ixodes
pacificus. When symptomatic, sequelae range from mild very vague complaints, to florid parasitemia
involving up to 85% of red cells in the immunecompromised. End organ complications include respiratory
failure with pulmonary edema and renal failure. Long-term asymptomatic Babesia carrier states have been
described in vertebrates, including people.
The “intraerythrocytic bacteria”, as they were called, were originally described by Babes in the late
1800s in cattle 1, and the first human infections were described in the 1950s. Babesia sporozoites enter RBCs
via the complement C3b receptor after complexing with C3 in the serum 2. The sexual phase of the organism
takes place in the tick, while reproduction by asexual formation of merozoites and trophozoites occurs in
human RBCs. Like similarly transmitted infections, Babesiosis can be contracted iatrogenically by blood
transfusion 3-7. An excellent review of Babesiosis with two case reports is published by Setty et al. 8.
In the Eye of the Beholder?
Babesia in peripheral smears are sometimes overlooked, and without reliably seeing Maltese cross
formations, even a fairly experienced observer can easily mistake it for malaria. It can otherwise be
distinguished from Plasmodium species clinically by the absence of travel history outside the United States,
and morphologically by pleomorphism of the ring forms or presence of small rings with central palor, lack of
hemozoin deposits, and lack of stages other than the ring form.
More objective means of detection include PCR-based assays, indirect immunoflourescence assays
(IFAs), and enzyme-linked immunosorbent assays (ELISAs), although wide-scale screening applications for
currently available tests in populations with low pretest probability (i.e., a blood donor population) seem
prohibitively expensive and problematic. A recent study by Homer et al. 9 extrapolate from traditional
approaches for identifying assay target antigens, however, and suggest that newly-discovered Babesia antigens
might prove useful in identifying low grade symptomatic or asymptomatic carriers. Instead of relying on host
antibody targets in advanced infections where many types of killed microbe epitopes may be exposed, their
rationale identifies antigens shed from living microbes. Homer et al. infected severe combined
immunodeficiency (SCID) mice with Babesia and took only their sera (cleared of cellular debris and intact
parasites) for target identification. This sera enriched in shed microbial products was used to elicit an antibody
response from immunocompetent mice, whose antisera were collected for a Babesia genomic expression
library screen. Several of the putative Babesia gene products identified contain signature sequences of secreted
proteins, suggesting that this approach is successful. I imagine the clever principle of this screen may have
applicability for diagnostic test development in the setting of many types of infection, and would make
interesting reading for the Newsletter audience this week.
References;
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Babes V. Sur l’hemoglobinurie bacterienne boeuf. Comptes Rendus de Acad Sci III 1888;107:692-4.
Ward PA, Jack RM. The entry process of Babesia merozoites into red cells. Am J Pathol 1981;102(1):109-13.
Wittner M, Rowin KS, Tanowitz HB, et al. Successful chemotherapy of transfusion babesiosis. Ann Intern Med
1982;96(5):601-4.
Mintz ED, Anderson JF, Cable RG, Hadler JL. Transfusion-transmitted babesiosis: a case report from a new
endemic area. Transfusion 1991;31(4):365-8.
Herwaldt BL, Kjemtrup AM, Conrad PA, et al. Transfusion-transmitted babesiosis in Washington State: first
reported case caused by a WA1-type parasite. J Infect Dis 1997;175(5):1259-62.
Perdrizet GA, Olson NH, Krause PJ, Banever GT, Spielman A, Cable RG. Babesiosis in a renal transplant recipient
acquired through blood transfusion. Transplantation 2000;70(1):205-8.
Kain KC, Jassoum SB, Fong IW, Hannach B. Transfusion-transmitted babesiosis in Ontario: first reported case in
Canada. Cmaj 2001;164(12):1721-3.
Setty S, Khalil Z, Schori P, Azar M, Ferrieri P. Babesiosis. Two atypical cases from Minnesota and a review. Am J
Clin Pathol 2003;120(4):554-9.
Homer MJ, Lodes MJ, Reynolds LD, et al. Identification and characterization of putative secreted antigens from
Babesia microti. J Clin Microbiol 2003;41(2):723-9.