LEARNING OBJECTIVES
1. Discuss the advances of blood donor viral-transmitted disease testing in the U.S. 2. Describe the Zika virus in terms of demographics, disease transmission, and current donor testing. 3. Describe hepatitis E virus in terms of demographics, disease transmission, and current donor testing. 4. Describe Babesia infection in terms of demographics, disease transmission, and current donor testing.
For more than 75 years, blood banks and transfusion centers have been dramatically increasing the safety of blood transfusions. Through better donor and donation screening, automation of laboratory testing, and commercial introduction of pathogen reduction technology for blood components, the risk of transfusion-transmitted viral infections in the United States has been reduced to nearly zero today.1 Transfusion medicine professionals have perfected the art of staying keenly focused on safety while simultaneously adapting to new methods, requirements, challenges, and best practices.
This review is primarily focused on recent advances relating to laboratory screening of whole blood donations for transfusion-transmissible pathogens. It is important, however, to mention the fundamental and continuing need for blood banks to apply appropriate donor questioning and testing (e.g., blood pressure, hematocrit, body temperature) prior to collection.
In addition, blood banks, hospital transfusion centers, and other healthcare professionals overseeing transfusions must adopt rigorous quality systems as part of a coordinated hemovigilance program covering the whole transfusion chain—from blood collection centers to blood banks to the transfusion itself. These quality systems and best practices are the foundations that allow the technical advances to shine. Without them, the contribution of advanced technologies will be compromised.2
In the U.S., donated blood is tested for infectious disease according to guidance issued by the Food and Drug Administration (FDA). The blood is tested by both immunoassays (IA) and nucleic acid tests (NAT) for the viruses HIV-1, HIV-2, HBV, and HCV. Testing for some infectious agents uses only NAT-based assays (West Nile Virus) or uses only immunoassays (HTLV-I and II, syphilis). A limited number of donations are screened for cytomegalovirus (CMV) antibodies to meet the needs of a select subset of patients for CMV-negative blood products in any particular region.
In recent years, blood testing has become increasingly concentrated in large laboratories located near airports to better manage blood specimen transportation and permit efficient use of multiple testing instruments and computerized systems for identification and test result management, enabling faster donation-to-result turnaround time. Commercial automated instrumentation is used to perform high-throughput testing of the plasma or serum portion of donations. Results of the testing are communicated back to the collection center, and if the testing is negative, the blood or blood fractions/components are released for transfusion. This combination of sensitive testing technology, automation to improve efficiency and reduce the likelihood of human error, and quality systems has now reduced the possibility of viral transfusion-transmitted infections (TTIs) to about one transfusion per million in the U.S.3
Collections of platelets obtained from apheresis are tested for bacterial contamination by culture, normally started within 24 hours of collection. In contrast, whole blood-derived platelets are typically tested with immunoassays.
Like other viral outbreaks before it, the recent Zika virus outbreak has demonstrated the importance of researchers, healthcare experts, governments, and industry working together on epidemiological surveillance, biological research, development, and implementation of tests that use the most advanced screening technologies. These are all essential to tracking and controlling the spread of the disease, and they serve as models for addressing future threats.
Zika virus (ZIKV) was unknown in the Americas until May 2015.4 It was first identified in 1947 in a rhesus monkey in the Zika forest of Uganda5 and it is transmitted by Aedes mosquitos. The virus is closely related to other viruses in the family Flaviviridae such as West Nile, dengue, and yellow fever. Sporadic cases in Africa and Asia were reported before an outbreak occurred in Micronesia in 2007. The virus spread to French Polynesia and New Caledonia in the Pacific Ocean.6 It may have entered Brazil in 2014. The first locally transmitted cases were reported in that nation’s northeastern region in 2015.7 The World Health Organization declared the outbreak a global public health emergency on February 1, 2016.
ZIKV infections are often asymptomatic. In the early incubation period, blood donors may feel well enough to donate.8 In contrast to related arboviruses, ZIKV infection carries a risk of microcephaly, fetal loss, and additional adverse outcomes in babies born to mothers infected during pregnancy.9 There is also growing evidence of risk for Guillain-Barré Syndrome in infected adults,10 although that appears to occur at low incidence.
Dedicated manufacturing steps in plasma fractionation—such as solvent-detergent, caprylate or heat treatment and nanofiltration—have the capacity to destroy or eliminate pathogens with Flaviviridae characteristics.11 But experts are still investigating whether the virus is transmissible through whole blood transfusion. This past summer, blood banks in suspected endemic areas (Puerto Rico, Hawaii, and Florida and other Southern states) began using investigational NAT tests to screen whole blood and blood products for Zika virus. Two NAT blood donor screening assays have been approved by the U.S. FDA under an Investigational New Drug (IND) application.
On August 26, 2016, the FDA revised its initial guidance, advising testing for Zika virus in all donated blood and blood components in the U.S. The revised FDA guidance does not apply to source plasma, which is used for further manufacture of plasma-derived products. Viral inactivation and removal methods that are currently used to clear viruses in the manufacturing process for plasma-derived products are sufficient to reduce the risk of the transmission of Zika virus.11
Experts continue to investigate many aspects of Zika infection; among other questions, they are seeking answers to the following:
Hepatitis E virus (HEV) has been known as a transfusion-transmissible agent since the early 2000s, and TTI of HEV has been documented in several countries.12 Though usually a self-limiting illness, in susceptible populations HEV infection can cause serious disease including fulminant hepatitis and death. Transfusion recipients who have compromised immune systems (e.g., cancer patients undergoing chemotherapy) or patients with pre-existing liver damage are at risk. Pregnant women are also at elevated risk for severe disease.
Active infection for HEV, as analyzed using NAT testing for viral RNA, is found at varying frequencies in donor populations around the world. A recent study has shown that HEV RNA appears to be relatively rare in the U.S. donor population.13 Presently the only countries screening donors for HEV RNA are Japan (in Hokkaido), Spain, and Ireland.14 There have been recent discussions at transfusion safety expert meetings and in published editorials discussing comprehensive HEV RNA screening of donated blood.15 Consideration has also been given to maintaining HEV RNA-screened blood and blood fractions in quantities sufficient for recipients at risk, such as the immunosuppressed.
Babesiosis is caused by protozoan parasites that replicate within red blood cells (intraerythrocytic parasites). It is transmitted to humans by Ixodid ticks taking a blood meal. Humans are an incidental host; the usual hosts of the ticks are primarily rodents, and often the white-footed mouse.
In the U.S., infection by Babesia microti has been considered an emerging infectious disease, with an increasing number of cases reported annually.16 Most infections occur in the Northeast and upper Midwest states, which is the normal geographical range of Ixodes scapularis. The incidence of infection outside of these regions is lower but not unknown, and often caused by other species (Babesia duncani or Babesia divergens).
Outside of the U.S., human infections caused by Babesia venatorum have been documented. Infections can be asymptomatic; thus donors can be unaware of an infection and pass normal screening. Babesia is the most frequent infectious cause of transfusion-transmitted mortality in the U.S.17 Between 1979 and 2009, more than 159 transfusion infections, resulting in multiple deaths, have been recorded.18
Investigational tests are currently being used in the U.S. to screen blood donors for Babesia using NAT and immunodiagnostic technology.16 This screening is currently localized to those areas endemic for Ixodes ticks and cover a portion of blood donations.
Huge strides in interdicting infected blood donations have greatly improved the safety of the blood supply in the U.S. There is no doubt that in the next 75 years, scientific advances will reduce the residual risk even further.
Sam Rose, PhD, serves as director of medical affairs at Grifols, S.A.
Jeff Linnen, PhD, serves as associate vice president of product development at Hologic, Inc.
Grifols and Hologic are long-standing partners in the development of Procleix blood screening products, including the Procleix Zika Virus Assay.
Although there is no FDA-licensed test for Zika virus, testing for Zika became available through two* separate Investigational New Drug (IND) applications for blood collected in Puerto Rico and mainland United States. The tests became available on April 3, 2016 (Roche Molecular Systems, Inc.), and June 20, 2016 (Hologic, Inc./Grifols):
*as of September 12, 2016
