Judy Moore, B.S.

Part 1 of this article appeared in the February 2018 issue and discussed a ranking system created by the AABB to prioritize emerging infectious diseases (EIDs) based on their risk to the blood supply. Three were ranked in the red category which indicated highest priority. They are human variant Creutzfeldt-Jakob disease (vCJD), Dengue viruses (DENV), and Babesia species. 

vCJD is a transmissible spongiform encephalopathy (TSE) caused by a prion. It has a long incubation phase and is 100% fatal. There are no treatments available to reverse the disease nor are there laboratory tests to screen donor blood or detect infection. Diagnosis is based on symptoms or autopsy. Donor screening is based on whether there is a family history of vCJD or if the donor traveled or resided in the UK and Europe where the majority of cases have been reported. These situations would indefinitely defer the donor. A diagnostic test, however, could be forthcoming. A recent study reports being able to detect asymptomatic carriers of the prion using “plasminogen-bead capture and protein misfolding cyclic amplification (PMCA) technologies” with >99% specificity.1 

Dengue viruses (DENV) are flaviviruses transmitted by Aedes mosquitoes. Although typically found outside of the United States, there are some endemic regions in Texas along the border with Mexico and there have been outbreaks in Hawaii, Texas, and Puerto Rico. The virus can cause subclinical symptoms or it can cause a feverish disease with pain and rash and can progress into a hemorrhagic disorder which has a high mortality rate. It was placed in the red category for multiple reasons: the high incidence of asymptomatic infections accompanied by viremia, the detection of viral RNA in blood donors from endemic areas, the ability to cause epidemics, and the presence of the mosquito vector in the US. There are currently no donor questions regarding Dengue risk nor is there a blood screening test. However, there is a travel deferral based on travel to malaria endemic regions which overlap with DENV endemic areas. The deferral would at least capture some of the potentially DENV infected donors.2 

Babesia species are protozoa that infect red blood cells. They are transmitted by the Ixodes tick and are found in the eastern United States. There are over 100 species of Babesia although only a few are considered pathogenic in humans. Babesia microti is responsible for most of the cases of babesiosis in the U.S.3 The disease can be mild or it can be severe and fatal in immunocompromised individuals by causing hemolysis, DIC, and eventually organ failure. The incubation period can be 1-6 weeks after a tick bite and there have been over 70 cases of transfusion-transmitted cases of B. microti in the United States.2 (Another study states there have been 159 cases of transfusion-transmitted cases in the U.S.)4 There is no blood donor screening test, but like vCJD, that could be changing. In a 2012-2014 study, the American Red Cross screened and removed 335 positive B. microti donor samples from 89,153 screened samples. The screening assay used PCR to detect B. microti DNA and arrayed fluorescence immunoassays (AFIA) to detect antibodies. Positive samples were followed up with quantitative PCR testing and infectivity testing. During the same study period, there were 14 probable cases of transfusion-transmitted babesiosis from 253,031 unscreened donor samples and zero cases from the screened samples. This indicates that the screening assays can successfully reduce the transmission risk of B. microti from blood transfusions.4 This would be superior to the current practice of simply deferring a donor based on a questionnaire which is considered ineffective.4,5 

Prioritizing EID threats among the dozens of EIDs can help policy makers decide where to allocate limited time and resources and how to prepare to meet an increased threat.6 Lou Katz, chief medical officer of America’s Blood Centers, suggests a zero-risk model cannot be achieved because it would require unlimited resources which is not reality. Risk-assessment must be used to make decisions in blood banking.5 The numerous blood suppliers throughout the country have different degrees of risk and different donor populations. The appropriation of time and money will depend on the unique circumstances of that entity as well as complying with law. For the foreseeable future, blood products will be needed so the risk of transfusion-transmitted infectious diseases is not likely to vanish, but it can be reduced by recognizing potential threats and preparing for them with current knowledge and abilities. 

1. Bougard D, Brandel JP, Belondrade M, et al. Detection of prions in the plasma of presymptomatic and symptomatic patients with variant Creutzfeldt-Jakob disease. Sci. Transl. Med. 2016;8:370ra182. 
2. Stramer SL, Hollinger FB, Katz LM, et al. Emerging infectious disease agents and their potential threat to transfusion safety. Transfusion 2009;49:1S-29S. 
3. Centers for disease control and prevention. Parasites-babesiosis. https://www.cdc.gov/parasites/babesiosis/biology.html; March 2, 2017. 
4. Moritz ED, Winton CS, Tonnetti L, et al. Screening for Babesia microti in the U.S. blood supply. N Engl J Med 2016;375:2236-45. 
5. Fusco L. Maintaining the safety of the blood supply against the threat of emerging transfusion-transmitted diseases. AABB News 2017;19:012-7. 
6. Brookes VJ, Del Rio Vilas VJ, Ward MP. Disease prioritization: what is the state of the art? Epidemiol. Infect. 2015;143:2911-22.