Transfusion-transmitted Babesiosis Research Articles

Transmission risk evaluation of transfusion blood containing low-density Babesia microti.

Babesia is a unique apicomplexan parasite that specifically invades and proliferates in red blood cells and can be transmitted via blood transfusion, resulting in transfusion-transmitted babesiosis. However, detecting Babesia in blood before transfusion has not received enough attention, and the risk of transfusing blood containing a low density of Babesia microti (B. microti) is unclear, possibly threatening public health and wellness. This study aimed to determine the lower detection limit of B. microti in blood and to evaluate the transmission risk of blood transfusion containing low-density B. microti. Infected BALB/c mouse models were established by transfusing infected whole blood with different infection rates and densities of B. microti. Microscopic examination, nested Polymerase Chain Reaction (nested PCR), and an enzyme-linked immunosorbent assay (ELISA) were used to evaluate the infection status of the mouse models. Meanwhile, the nested PCR detection limit of B. microti was obtained using pure B. microti DNA samples with serial concentrations and whole blood samples with different densities of B. microti-infected red blood cells. Thereafter, whole mouse blood with a B. microti density lower than that of the nested PCR detection limit and human blood samples infected with B. microti were transfused into healthy mice to assess the transmission risk in mouse models. The infection status of these mice was evaluated through microscopic examination, nested PCR tests, and ELISA. The mice inoculated with different densities of B. microti reached the peak infection rate on different days. Overall, the higher the blood B. microti density was, the earlier the peak infection rate was reached. The levels of specific antibodies against B. microti in the blood of the infected mice increased sharply during the first 30 days of infection, reaching a peak level at 60 days post-infection, and maintaining a high level thereafter. The nested PCR detection limits of B. microti DNA and parasite density were 3 fg and 5.48 parasites/μL, respectively. The whole blood containing an extremely low density of B. microti and human blood samples infected with B. microti could infect mice, confirming the transmission risk of transfusing blood with low-density B. microti. Whole blood containing extremely low density of B. microti poses a high transmission risk when transfused between mice and mice or human and mice, suggesting that Babesia detection should be considered by governments, hospitals, and disease prevention and control centers as a mandatory test before blood donation or transfusion.

Protective efficacy and correlates of immunity of immunodominant recombinant Babesia microti antigens.

Babesia microti, an intraerythrocytic apicomplexan parasite, is the primary causative agent of human babesiosis and an emerging threat to public health in the United States and elsewhere. An effective vaccine against B. microti would reduce disease severity in acute babesiosis patients and shorten the parasitemic period in asymptomatic individuals, thereby minimizing the risk of transfusion-transmitted babesiosis. Here we report on immunogenicity, protective efficacy, and correlates of immunity following immunization with four immunodominant recombinantly produced B. microti antigens-Serine Reactive Antigen 1 (SERA1), Maltese Cross Form Related Protein 1 (MCFRP1), Piroplasm β-Strand Domain 1 (PiβS1), and Babesia microti Alpha Helical Cell Surface Protein 1 (BAHCS1)-delivered subcutaneously in Montanide ISA 51/CpG adjuvant in three doses to BALB/c mice. Following B. microti parasite challenge, BAHCS1 led to the highest reduction in peak parasitemia (67.8%), followed by SERA1 (44.8%) and MCFRP1 (41.9%); PiβS1 (27.6%) had minimal protective effect. All four B. microti antigens induced high ELISA total IgG and each isotype; however, antibody levels did not directly correlate with anti-parasitic activity in mice. Increased prechallenge levels of some cell populations including follicular helper T cells (TFH) and memory B cells, along with a set of six cytokines [IL-1α, IL-2, IL-3, IL-6, IL-12(p40), and G-CSF] that belong to both innate and adaptive immune responses, were generally associated with protective immunity. Our results indicate that mechanisms driving recombinant B. microti antigen-induced immunity are complex and multifactorial. We think that BAHCS1 warrants further evaluation in preclinical studies.

Molecular Screening of Blood Donors for Babesia in Tyrol, Austria

Introduction: Babesia is a tick-borne intraerythrocytic parasite that is globally ubiquitous, yet understudied. Several species of Babesia have been shown to be transfusion-transmissible. Babesia has been reported in blood donors, animals, and ticks in the Tyrol (Western Austria), and regional cases of human babesiosis have been described. We sought to characterize the risk of Babesia to the local blood supply. Methods: Prospective molecular testing was performed on blood donors who presented to regional, mobile blood collection drives in the Tyrol, Austria (27 May to October 4, 2021). Testing was conducted using the cobas^® Babesia assay (Roche Molecular Systems, Inc.), a commercial PCR assay approved for blood donor screening that is capable of detecting the 4 primary species causing human babesiosis (i.e., B. microti, B. divergens, B. duncani, and B. venatorum). A confirmatory algorithm to manage initial PCR-reactive samples was developed, as were procedures for donor and product management. Results: A total of 7,972 donors were enrolled and screened; 4,311 (54.1%) were male, with a median age of 47 years (IQR = 34–55). No positive cases of Babesia were detected, corresponding with an overall prevalence of 0.00% (95% CI: 0.00%, 0.05%). Discussion: The findings suggest that the prevalence of Babesia is low in Austrian blood donors residing in the Tyrol, even during months of peak tick exposure. Although one cannot conclude the absence of Babesia in this population given the limited sample size, the findings suggest that the regional risk of transfusion-transmitted babesiosis is low.

Babesia blood testing: the first-year experience.

Babesia is an intraerythrocytic parasite responsible for hundreds of cases of transfusion-transmitted babesiosis in the past 50 years. In May of 2020, blood testing for Babesia was implemented at the American Red Cross (ARC) for all donations in endemic areas of the northeastern and midwestern regions of the United States. Between May 2020 and May 2021, 1,816,669 donations from 13 states and DC were tested for Babesia by the ARC. Testing was performed in pools of 16 whole blood lysates using a licensed nucleic acid test (NAT) targeting Babesia 18S rRNA. Reactive donations were tested for B. microti antibody by immunoglobulin G immunofluorescence. Suspected cases of transfusion-transmitted babesiosis (TTB) were investigated if reported. The first 13 months of Babesia screening identified 365 NAT-reactive donations. Antibodies for B. microti were detected in 79% (287) of reactive donations; negative serology samples were prevalent between May and July. Follow-up donations were collected from 142 donors, and 86% (122), collected up to 74 days after index, remained NAT reactive. Reactive donations were mainly collected in MA (77), CT (68), NY (49), NJ (47), and PA (44), but were identified in all states except Delaware. Most reactive blood donors were male (65%) aged between 40 and 80 years. Since the beginning of Babesia testing, no case of TTB was identified. The absence of TTB cases since implementation of Babesia screening for blood donations collected in endemic areas suggests testing is an effective strategy to eliminate TTB.

Preventing Transfusion-Transmitted Babesiosis.

Babesia are tick-borne intra-erythrocytic parasites and the causative agents of babesiosis. Babesia, which are readily transfusion transmissible, gained recognition as a major risk to the blood supply, particularly in the United States (US), where Babesia microti is endemic. Many of those infected with Babesia remain asymptomatic and parasitemia may persist for months or even years following infection, such that seemingly healthy blood donors are unaware of their infection. By contrast, transfusion recipients are at high risk of severe babesiosis, accounting for the high morbidity and mortality (~19%) observed in transfusion-transmitted babesiosis (TTB). An increase in cases of tick-borne babesiosis and TTB prompted over a decade-long investment in blood donor surveillance, research, and assay development to quantify and contend with TTB. This culminated in the adoption of regional blood donor testing in the US. We describe the evolution of the response to TTB in the US and offer some insight into the risk of TTB in other countries. Not only has this response advanced blood safety, it has accelerated the development of novel serological and molecular assays that may be applied broadly, affording insight into the global epidemiology and immunopathogenesis of human babesiosis.

Risk of transfusion-transmitted Babesia microti in Canada.

Babesia microti has gained a foothold in Canada as tick vectors become established in broader geographic areas. B. microti infection is associated with mild or no symptoms in healthy individuals but is transfusion-transmissible and can be fatal in immunocompromised individuals. This is the first estimate of clinically significant transfusion-transmitted babesiosis (TTB) risk in Canada. The proportion of B. microti-antibody (AB)/nucleic acid amplification test (NAT)-positive whole blood donations was estimated at 5.5% of the proportion of the general population with reported Lyme Disease (also tick-borne) based on US data. Monte Carlo simulation estimated the number and proportion of infectious red cell units for three scenarios: base, localized incidence (risk in Manitoba only), and donor study informed (prevalence from donor data). The model simulated 1,029,800 donations repeated 100,000 times for each. In the base scenario 0.5 (0.01, 1.75), B. microti-NAT-positive donations would be expected per year, with 0.08 (0, 0.38) recipients suffering clinically significant TTB (1 every 12.5 years). In the localized incidence scenario, there were 0.21(0, 0.7) B. microti-NAT-positive donations, with 0.04 (0, 0.14) recipient infections (about 1 every 25 years). In the donor study informed scenario, there were 4.6 (0.3, 15.8) B. microti-NAT-positive donations expected, and 0.81 (0.05, 3.14) clinically significant TTB cases per year. The likelihood of clinically relevant TTB is low. Testing would have very little utility in Canada at this time. Ongoing pathogen surveillance in tick vectors is important as B. microti prevalence appears to be slowly increasing in Canada.

Educational Case: A Case of Transfusion-Transmitted Babesiosis: Diagnostic Perspectives Across the Clinical Laboratory

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, see http://journals.sagepub.com/doi/10.1177/2374289517715040.1

2247 Transfusion Associated Babesiosis: An Uncommon Cause of Acute Liver Failure

INTRODUCTION: Babesiosis is a zoonotic disease caused by obligate intracellular protozoa that reproduce in erythrocytes. We present a case of transfusion-transmitted babesiosis (TTB) leading to acute liver failure (ALF). Whereas mild liver chemistry abnormalities are common in babesiosis, to the authors’ knowledge this is the first case of TTB directly leading to ALF. CASE DESCRIPTION/METHODS: A 79-year-old man from New Jersey with end stage renal disease presented with two weeks of flu-like illness and was found to have profound liver function abnormalities consistent with ALF. Six weeks prior the patient was hospitalized for a diverticular bleed at which time he received multiple packed red blood cell transfusions and recovered to his baseline health. At that time, liver chemistries were normal. On arrival, he was afebrile and normotensive. He was oriented but lethargic. Skin exam notable for pallor. His abdomen was benign. Initial investigations revealed AST 3497 IU/L, ALT 2719 IU/L, ALP 259 IU/L, TB 5.2mg/dl, DB 3.6mg/dl. INR was 4.1, Hgb 8.7g/dL, and fibrinogen 252mg/dl. LDH 2003 IU/L with haptoglobin < 8.0mg/dl. Peripheral smear revealed ring-shaped intra-erythrocytic trophozoites (Figure 1). Babesia microti PCR was positive. Atovaquone and azithromycin were started and exchange transfusion performed. Fevers and worsening encephalopathy progressed despite directed treatment. Multi-system organ failure developed and care was withdrawn. Further testing determined our patient was a recipient of babesia microti contaminated transfusion. DISCUSSION: Babesiosis is a world-wide emerging disease caused by intra-erythrocytic protozoa that are transmitted primarily through Ixodes ticks but also through blood transfusion. TTB is often severe in presentation with a mortality rate of approximately 20%. Marked hemolytic anemia, disseminated intravascular coagulation, and adult respiratory distress syndrome may develop. Case series have established that patients with babesiosis exhibit abnormal liver chemistries with median values notable for ALT of 59 IU/L and AST 79 IU/L. A literature review reveals just one published case of babesiosis presenting as ALF, and no such cases when babesia is transmitted through transfusion. Babesiosis should be considered in the differential diagnosis of ALF in patients living in or having recently travelled to an endemic area or who have recently received transfusions. In such patients, we recommend performing blood smear to prevent delay in treatment.

Babesia: Prevention for the Blood Supply

Exposure to blood, whether through blood transfusion, organ transplantation, or even pregnancy (mother to fetus), can transmit infectious disease. Blood suppliers routinely test donated blood for a variety of infectious pathogens and screening for Babesia spp. occurs in endemic areas of the United States. People living in areas of endemicity are not allowed to donate blood if they have a history of babesiosis. Transmission of Babesia microti through red blood cell blood transfusion is a serious, although rare, public health threat for which these preventive measures are necessary. The first case of transfusion-transmitted babesiosis in the United States occurred in 1979, and the incidence has increased. The National Healthcare Safety Network Hemovigilance Module tracks transfusion-transmitted infections (TTI). In a reporting period ending December, 2016, the most frequently reported TTI involving red blood cell units was for Babesia spp. in 16 of 24 reported infections.

Persistence of Babesia microti Infection in Humans.

Persistent infection is a characteristic feature of babesiosis, a worldwide, emerging tick-borne disease caused by members of the genus Babesia. Persistence of Babesia infection in reservoir hosts increases the probability of survival and transmission of these pathogens. Laboratory tools to detect Babesia in red blood cells include microscopic detection using peripheral blood smears, nucleic acid detection (polymerase chain reaction and transcription mediated amplification), antigen detection, and antibody detection. Babesia microti, the major cause of human babesiosis, can asymptomatically infect immunocompetent individuals for up to two years. Chronically infected blood donors may transmit the pathogen to another person through blood transfusion. Transfusion-transmitted babesiosis causes severe complications and death in about a fifth of cases. Immunocompromised patients, including those with asplenia, HIV/AIDS, malignancy, or on immunosuppressive drugs, often experience severe disease that may relapse up to two years later despite anti-Babesia therapy. Persistent Babesia infection is promoted by Babesia immune evasive strategies and impaired host immune mechanisms. The health burden of persistent and recrudescent babesiosis can be minimized by development of novel therapeutic measures, such as new anti-parasitic drugs or drug combinations, improved anti-parasitic drug duration strategies, or immunoglobulin preparations; and novel preventive approaches, including early detection methods, tick-avoidance, and blood donor screening.

Heavy parasitemia in babesiosis treated without adjunctive red cell exchange

Babesiosis is a tick-borne infectious disease caused by the protozoa Babesia but transplacental, and transfusion transmission may occur. While most infections are asymptomatic, rarely, it can present with a severe, life-threatening illness. Treatment is primarily with antibiotics, but red cell exchange (RCE) has been used in more severe cases which are characterized by high-grade parasitemia, evidence of severe hemolysis and or multi-organ failure. A threshold parasite level of 10% has arbitrarily been applied as an indication for RCE; however, this threshold is not evidence-based.We report on three cases of severe babesiosis in which we considered the use of RCE on the basis of a parasite level greater than 10%, but the procedure was not performed. We deferred RCE on account of the good clinical state of the patient and the absence of end-organ failure. All patients were followed daily until discharge. Two of these patients had been splenectomized, and each received a single unit of red blood cells during the hospitalization. The third patient had a long history of refractory lymphoma and was pancytopenic requiring multiple transfusions during the years before the diagnosis of babesiosis. She had transfusion-transmitted babesiosis from a red blood cell transfused 46 days prior to diagnosis. All three patients responded well to antibiotics, and none expired. This small case series suggests that requests for RCE solely on the basis of an arbitrary level of parasitemia should be questioned and the clinical state and evidence of end-organ failure considered in the decision to perform RCE.

Characteristics of transfusion-transmitted Babesia microti, American Red Cross 2010-2017.

Babesia microti, a red blood cell (RBC) parasite transmitted naturally to vertebrate hosts by ixodid ticks, is endemic to the northeastern and upper midwestern United States, with the geographic range of infected ticks expanding. B. microti is a blood safety issue with >200 transfusion-transmissions reported. The American Red Cross's Hemovigilance program investigated hospital-reported transfusion-transmitted babesiosis (TTB) cases. Follow-up samples from involved donors were tested for B. microti antibodies and parasite DNA, the latter by real-time polymerase chain reaction (PCR). Test-positive donors were permanently deferred from future donations. B. microti-positive donors were implicated in 77 of 143 suspect TTB cases investigated from 2010 through 2017. In four cases, two positive donors were identified for a total of 81 positive donors. In three cases, a RBC unit was split and components transfused multiple times to the same pediatric recipient. RBCs were the transmitting product in all cases. At follow-up, all involved donors were antibody positive; 25 donors were also PCR positive. Positive donations were collected throughout the year, peaking in the summer. Most donors (78) were resident of, or traveled to (2), an endemic state. One donor resided in a non-endemic state without relevant travel history. One fatality listed babesia as a contributing factor. No implicated donation was screened by an investigational protocol. Babesiosis remains a blood safety issue. Prior to FDA-licensed screening test availability and final FDA Guidance, blood collectors in endemic states investigationally tested none, a portion, or all collections. Future expanded testing will reduce the frequency of TTB cases.

Transfusion-Transmitted Infections Reported to the National Healthcare Safety Network Hemovigilance Module.

Transfusion-transmitted infections (TTIs) can be severe and result in death. Transfusion-transmitted viral pathogen transmission has been substantially reduced, whereas sepsis due to bacterial contamination of platelets and transfusion-transmitted babesiosis may occur more frequently. Quantifying the burden of TTI is important to develop targeted interventions. From January 1, 2010, to December 31, 2016, health care facilities participating in the National Healthcare Safety Network Hemovigilance Module monitored transfusion recipients for evidence of TTI and recorded the total number of units transfused. Facilities use standard criteria to report TTIs. Incidence rates of TTIs, including for bacterial contamination of platelets and transfusion-transmitted babesiosis, are presented. One hundred ninety-five facilities reported 111 TTIs and 7.9 million transfused components to the National Healthcare Safety Network Hemovigilance Module. Of these 111 reports, 54 met inclusion criteria. The most frequently reported pathogens were Babesia spp in RBCs (16/23, 70%) and Staphylococcus aureus in platelets (12/30, 40%). There were 1.95 (26 apheresis, 4 whole blood derived) TTIs per 100 000 transfused platelet units and 0.53 TTI per 100 000 transfused RBC components, compared to 0.68 TTI per 100 000 all transfused components. Bacterial contamination of platelets and transfusion-transmitted babesiosis were the most frequently reported TTIs. Interventions that reduce the burden of bacterial contamination of platelets, particularly collected by apheresis, and Babesia transmission through RBC transfusion would reduce transfusion recipient morbidity and mortality. These analyses demonstrate the value and importance of facility participation in national recipient hemovigilance using standard reporting criteria.

Transfusion-Transmitted Babesiosis.

Babesiosis is most commonly caused by Babesia microti and is transmitted via the bite of an infected Ixodes spp tick. However, Babesia is also transmitted via blood transfusion. In the United States, the first case of transfusion-transmitted babesiosis was recognized in 1979, and in recent years, the incidence has rapidly increased. Because most of the infected blood donors do not experience any symptoms, they pose a significant risk to the blood supply. Donor deferral for a history of babesiosis is currently performed but is ineffective. In March 2018, the FDA licensed a DNA PCR and antibody assay that were used in tandem in pivotal trials for screening blood donors for B microti; with other assays still being evaluated under investigational new drug protocols. Blood donation screening is essential to reducing the risk of transfusion-transmitted babesiosis, which is why blood centers collecting in geographic regions of highest risk have been testing since approximately 2010. Investigational NAT assays of higher sensitivity are pending FDA review. Further, in July 2018, the FDA issued a draft guidance for reducing the risk of transfusion-transmitted babesiosis. Release of the final guidance may be postponed until sensitivities and specificities of all current and potential strategies have been properly evaluated.

Transfusion-transmitted babesiosis: one state's experience

The risk for tickborne exposure to Babesia microti infection exists statewide in Massachusetts. Broad exposure complicates investigations of transfusion-transmitted babesiosis (TTB). We summarize 8 years of the epidemiology of TTB and highlight the role of public health in prevention and control. Cases of babesiosis are routinely reported to the Massachusetts Department of Public Health. These are investigated to determine whether they meet the surveillance case definition and to identify whether they were potentially transfusion transmitted. Frequencies from 2009 to 2016 are described and incidence rates calculated using population denominators from the US census. Changes over time were analyzed using simple linear regression. From 2009 to 2016, there were 2578 cases of babesiosis reported; of these, 45 (1.7%) were transfusion transmitted. Of the 45 cases of TTB, 15 (33%) received blood products from two or more suppliers. In 11 TTB cases, the Department of Public Health was notified first, who in turn notified the appropriate blood provider. In 2009, the crude rate of reported babesiosis was 1.2 per 100,000 population and increased significantly through 2016 to 7.8 per 100,000 population (p = 0.006). The number of blood donors reported with laboratory evidence of B. microti infection increased from 19 in 2012 to 78 in 2016; at the same time, the number of TTB cases decreased from six to three. TTB remains a major challenge, and blood donor screening strategies are currently in the process of implementation. While population and environmental changes facilitate increases in babesiosis, donor screening has the potential to eliminate TTB.

Assessing the risk of Babesia to the United States blood supply using a risk-based decision-making approach: Report of AABB's Ad Hoc Babesia Policy Working Group (original report).

Recognizing the increasing threat of transfusion-transmitted babesiosis to the US blood supply, the AABB Board of Directors tasked an Ad Hoc Babesia Policy Working Group (the Working Group) to use the Alliance of Blood Operators' risk-based decision-making (RBDM) framework to assess the risks and benefits of introducing Babesia donation testing in the United States. The regional nature of the Babesia microti risk added complexity to the RBDM assessment because of the unique operational and financial considerations for operators and hospitals located in endemic states. Therefore, the assessment considered safety, product availability, sector sustainability, and technology availability. After assessing safety risk, economic and operational impact, reimbursement equity, ethical considerations, and stakeholder feedback from two consultations, the Working Group concluded that a regional approach to donor screening in endemic states was appropriate because it applied the intervention where the risk was highest and appropriately allocated cost to the risk. Nucleic acid testing using a ribosomal RNA template was the recommended intervention because it was the most cost-effective, resulted in no wasted units, and captured similar numbers of infections as antibody plus DNA-based polymerase chain reaction. The current model for blood reimbursement was maintained but AABB was encouraged to facilitate collection of data to identify threats to sector sustainability in endemic states. Babesia expansion was acknowledged with a mechanism to regularly reevaluate what are "endemic states." Finally, given that public awareness of the Babesia threat is the first line of defense, AABB should work with appropriate agencies for general education about the health risk from B. microti.

A pilot serosurvey of Babesia microti in Chinese blood donors.

Babesia spp. are tick-borne, intraerythrocytic protozoan parasites, several of which are transfusion-transmissible. Transfusion-transmitted babesiosis poses serious risk to a diverse patient population, including neonates, patients aged >50 years, the asplenic and the immunocompromised that are over-represented among transfusion recipients. Despite reports of B. microti and B. venatorum in People's Republic of China (PRC), no surveillance of blood donors for Babesia has previously been undertaken. We sought to determine the rates of B. microti seroreactivity in a sample of blood donors in the PRC. A pilot serosurvey was conducted of community blood donors (n = 1000) who donated July-August 2016 at Mudanjiang Blood Center (Heilongjiang Province) using indirect fluorescent antibody testing for antibodies against B. microti. The slides were prepared using B. microti-infected hamster blood. Samples that were initially positive to a titre of 64 were subjected to repeat IFA testing. Final seroreactivity was based on repeat reactivity to ≥64. A total of 1000 individual donor samples were evaluated, comprising 888 whole blood and 112 platelet donations. Thirteen of 1000 (1·3%) donors were seroreactive for B. microti [8 (0·8%) and five (0·05%) at titres of 64 and 128, respectively]. Our preliminary findings support the need for expanded Babesia surveillance in Chinese blood donors, replete with molecular evaluation, to evaluate the risk to the blood supply.

Transfusion-transmitted and community-acquired babesiosis in New York, 2004 to 2015.

Babesiosis is a potentially life-threatening zoonotic infection most frequently caused by the intraerythrocytic parasite Babesia microti. The pathogen is usually tickborne, but may also be transfusion or vertically transmitted. Healthy persons, including blood donors, may be asymptomatic and unaware they are infected. Immunocompromised patients are at increased risk for symptomatic disease. All reported community-acquired babesiosis cases in New York from 2004 to 2015 were evaluated, enumerated, and characterized. All potential transfusion-transmitted babesiosis (TTB) cases reported through one or more of three public health surveillance systems were investigated to determine the likelihood of transfusion transmission. In addition, host-seeking ticks were actively collected in public parks and other likely sites of human exposure to B.microti. From 2004 to 2015, a total of 3799 cases of babesiosis were found; 55 (1.4%) of these were linked to transfusion. The incidence of both community-acquired babesiosis and TTB increased significantly during the 12-year study period. The geographic range of both ticks and tickborne infections also expanded. Among TTB cases, 95% of recipients had at least one risk factor for symptomatic disease. Implicated donors resided in five states, including in 10 New York counties. More than half of implicated donors resided in counties known to be B.microti endemic. The increasing incidence of TTB correlated with increases in community-acquired babesiosis and infection of ticks with B.microti. Surveillance of ticks and community-acquired cases may aid identification of emerging areas at risk for Babesia transfusion transmission.

Screening of patient blood samples for babesiosis using enzymatic assays

Human babesiosis is an emerging tick-borne disease in the United States and Europe. Transmitted by Ixodes ticks, the causative agent Babesia microti is an intraerythrocytic parasite that causes mild to deadly disease. Transmission of B. microti can also occur by transfusion of infected blood and blood products resulting in transfusion-transmitted babesiosis (TTB), which carries a high risk of fatality. To effectively manage this rise in B. microti infections, better screening tools are needed, which require minimal manipulation of the samples before testing. To this end, we tested two enzymatic assays, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), for efficacy in diagnosis of babesiosis. The results show that AST and ALT activity is significantly higher in the plasma of B. microti-infected patients. Moreover, statistical analysis revealed that these assays have high sensitivity and positive predictive values, which highlights their usefulness as diagnostics for babesiosis. These standardized enzymatic assays can be used to perform high-throughput, large-scale screens of blood and blood products before they are certified safe for transfusion.

Inactivation of Babesia microti in red blood cells and platelet concentrates.

With an increasing number of recognized transfusion-transmitted (TT) babesiosis cases, Babesia microti is the most frequently TT parasite in the United States. We evaluated the inactivation of B. microti in red blood cells (RBCs) prepared in Optisol (AS-5) using amustaline and glutathione (GSH) and in platelet components (PCs) in 100% plasma using amotosalen and low-energy ultraviolet A (UVA) light. Individual RBCs and apheresis PCs were spiked with B. microti-infected hamster RBCs (iRBCs) to a final concentration of 106 iRBCs/mL and treated with the respective inactivation systems according to the manufacturer's instruction. Samples were collected before (control) and after (test) each treatment. Dilutions of the control samples to 10-6 were inoculated into hamsters, while the test samples were inoculated neat or at 10-1 dilution. At 3 and 5 weeks postinoculation, hamsters were evaluated for B. microti infection by microscopic observation of blood smears and 50% infectivity titers (ID50 ) were determined. Log reduction was calculated as control log ID50 minus test log ID50 . Parasitemia was detected in hamsters injected with as low as 100,000-fold diluted control samples, while no parasites were detectable in the blood smears of any hamsters receiving neat test samples. Mean log reduction was more than 5 log/mL by amustaline/GSH for RBCs and more than 4.5 log/mL by amotosalen/UVA for PCs. B. microti was inactivated to the limit of detection in RBCs and PCs after the respective inactivation treatment. Complete inactivation of B. microti was achieved in this animal infectivity model, and pathogen reduction treatment inhibited transmission of infection.