Donor Screening for Emerging Infectious Diseases: An Update

By Naomi Greer and Laurie Munk

The past year has seen significant progress in the collection and preliminary analysis of data on efforts to screen blood donors for exposure to emerging infectious diseases. Three experts provided updates on four such diseases in session 5104-S, “TTD-I: Emerging Infectious Diseases.”

What Have We Learned from Chagas’ Disease Testing?

First to speak was Susan L. Stramer, PhD, from the American Red Cross (ARC). She reviewed the latest information on Chagas’ disease prevalence, which indicates one in 30,000 donors in the United States is antibody positive. Although Chagas’ disease is mostly an imported disease in the US and Canada, some Trypanosoma cruzi infections may be autochthonous.

Of the 11 species of triatomine bugs in the US, seven have been shown to be infected with T. cruzi at rates varying between 5 and 100 percent. Infection rates also vary within mammalian reservoirs.

Stramer identified several challenges related to Chagas’ disease screening:

·          No “gold standard” exists for testing.

·          Identification of transfusion recipients who have developed Chagas’ disease is slow.

·          Donor questioning needs to be detailed.

Changes to Donor Screening Policies May Be Needed for Babesiosis, Malaria

David A. Leiby, PhD, from ARC and George Washington University, shared current thinking about babesiosis and malaria, and suggested that some changes to donor screening policies may be warranted.

Babesia and Plasmodium — the agents of babesiosis and malaria, respectively — are closely related, but donor screening policies for the parasites differ. While there is a lifetime deferral for history of babesiosis, there is a one- to three-year deferral for risk and no lifetime deferral for a history of malaria. No screening tests currently exist for either parasite.

Despite the different donor screening policies, neither Babesia nor Plasmodium species are commonly transmitted through transfusions. The first case of transfusion-transmitted B. microti, the primary agent of babesiosis in the US, was reported this year in Europe, but fewer than 10 cases are reported annually worldwide. Also, fewer than five cases of transfusion-transmitted malaria have been reported since 1998. “This raises a blood safety versus availability issue,” Leiby said.

Leiby offered a preview of the results of a study conducted by ARC that examined malaria-     deferred donors. The study found that EIA testing of 3,229 donors who were not deferred on the basis of screening questions revealed 11 repeat-reactive donations. The study will be presented in greater detail at a session on Monday, (5330-TC-I) “Emerging or Neglected Parasites.”

One implication of the study, Leiby noted, is that the donor screening process is not detecting all donors who test positive. The significance of long-term antibody titers in some donors remains unclear. Challenges ahead include determining whether these donors are partially immune, whether the persistent titers have any relationship to transfusion transmission and whether retention of such donors is advisable.

According to Leiby, some of the problems could be addressed by eliminating travel-related screening questions and deferring all donors who have had a history of malaria. He also noted that tests should be implemented to ensure blood safety. Ideally, they would include a nucleic acid test for Babesia as well as a multiplex test that could identify and defer chronic carriers of Babesia and detect all species of Plasmodium.

The Growing Global Impact of Dengue Viruses

The risk to the blood supply posed by dengue viruses was addressed by Lyle Petersen, MD, MPH, from the Centers for Disease Control and Prevention.

The global impact of dengue is significant, putting 2.5 billion people at risk. Every year, there are 50 million to 100 million new dengue cases reported, according to the World Health Organization, and 25,000 people die as a result of the virus.

In the Americas, the number of cases of dengue — which is related to West Nile virus — has spiked in recent years, with the latest figures reaching epidemic proportions. Despite the recent increase in reported cases, there has been only one case of transfusion-transmitted dengue infection, which occurred in Singapore.

A number of studies have been conducted during the past several years to test donations for the presence of dengue. Petersen shared the results from the most recent study (conducted by ARC and published in the latest TRANSFUSION Abstract Supplement), which found 12 dengue-infected donors among 16,521 donors tested in Puerto Rico — or a prevalence rate of 0.07 percent. This finding underscores the concern that components collected in areas where dengue fever is endemic may be transfused in the US and that screening measures should be considered.


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