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Study Confirms: Transmission of Mosquito-Borne Viruses via Blood Transfusion is Probable

Using nucleic acid amplification testing (NAAT), researchers analyzed archived blood donor samples collected during and after the 2014 epidemic of Chikungunya virus in Puerto Rico, and found that as many as 2 percent of the samples tested positive for Chikungunya RNA.
The study findings, which will be published in the July issue of the journal Emerging Infectious Diseases, echoed those of earlier reports on the presence of the mosquito-borne virus in blood donors in Puerto Rico and on other Caribbean islands. At present, it has not been proved that Chikungunya is transmissible via blood transfusion; however, this may be only due to the difficulty in differentiating between blood-exposure and other modes of viral transmission. Indeed, it is believed that “transfusion transmission is probable, given previous instances of laboratory-acquired infections and infection of healthcare workers by blood exposures,” according to the authors of the Emerging Infectious Diseases paper.
“This work has several important implications for Chikungunya virus, as well as other arbovirus epidemics, including Zika virus,” study co-author Graham Simmons, senior investigator, Blood Systems Research Institute told the Contagion. “Arboviruses can cause massive epidemics and these are associated with high frequencies of virus positive blood donations. Further research is critical to understand the rates of transmission by transfusion of infected blood components and consequent clinical disease, which will establish the need for donor screening, as well as pathogen inactivation of blood components. Vigilance for additional arboviruses that may be emerging and impact blood safety is also important.”
In all, Dr. Simmons and his team tested 1,668 minipools of donor samples and found that 1 was positive for Dengue virus RNA, and 161 (9.7 percent) were positive for Chikungunya RNA, which indicates a minimum detectable infection rate of 0.6 percent. Because individual donations comprising reactive minipools were not archived for further testing, the researchers used a published algorithm to estimate the proportion of donations that would contain detectable levels of Chikungunya RNA and estimated minipool-NAAT detectable viremia at 0.65 percent for the overall season, with an upper limit of 0.93 percent. They reported that the highest estimated proportion of detectable RNA-positive donations was during September and October 2014 (1.34 percent and 1.31 percent, respectively), which represented a “slightly delayed peak when compared with suspected and confirmed clinical cases reported in Puerto Rico,” they noted. Interestingly, the median viral load of the 161 reactive minipools was 550 copies/mL.
The authors also tested 3,007 individual donor samples collected in Puerto Rico from September through November 2014 for Chikungunya RNA and identified 56 confirmed positive donations; individual donation NAAT yields ranged from 1.7 percent to 2.1 percent. Only 21 (37.5 percent) of the 56 positive specimens were reactive when tested for Chikungunya RNA, meaning that 35 (62.5 percent) of them would probably have been missed by routine minipool-NAAT. The authors noted that “several donations with high viremias were negative for IgM and IgG, which suggested that donors were in the peak phase of acute infection and highlights the risk for transfusion transmission.” 
“Our study demonstrated a general risk in terms of high levels of Chikungunya virus in a significant percentage of blood donors,” Dr. Simmons said. “Because of this, we are now conducting a study in Brazil to ascertain the rates of actual transfusion transmission of Chikungunya virus coupled with determining outcomes of infection in recipients. The results of this study, which should be available in about one year, will guide decisions on the need for donor screening. In the interim the implementation of an FDA-mandated policy requiring a 28-day deferral from donation following travel to countries with active Zika virus transmission will also provide safety from transfusion transmission of Chikungunya and Dengue virus in the US.” 
Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.
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