Prevention of Transfusion-Transmitted Malaria and Chagas Disease in Non-Endemic Countries: An 8-Year Study of Seroprevalence Among Donors at Risk in Tuscany (Central Italy)

Vector-borne parasites might be transmitted through transfusion, notably <i>Plasmodium</i> spp. and <i>Trypanosoma cruzi</i>. Prevention strategies include blood donor screening, deferral, and blood unit treatment by pathogen inactivation methods. At the end of 2015, in line with European guidelines, Italian legislation introduced a questionnaire to identify donors at risk and their screening by serological methods. In early 2016, the Laboratory of Parasitology at Pisa University Hospital started the serological analysis of donors at risk, referring to Transfusion Services located in northwestern Tuscany. The aim of the present study was to describe the prevalence of seropositive donors observed during 8 years of screening. Donors at risk of transmitting malaria were screened by ELISA (Enzyme Linked Immunosorbent Assay). The DRG ELISA kit was employed until 2020, when it was substituted by the Euroimmun ELISA kit based on the results of a comparative evaluation of available commercial kits. Seropositive donors were offered the possibility of <i>Plasmodium</i> DNA testing by Loop-Mediated AMPlification (LAMP) to exclude current infection. Donors at risk of transmitting Chagas disease were screened by ICT employing recombinant antigen until 2021, when it was substituted by ELISA employing lysate antigen because of its higher accuracy. Seropositive donors were further tested by CLIA, and WB was performed in case of discordant results, according to WHO guidelines for diagnosis of chronic Chagas disease. A total of 3754 donors were tested for anti-<i>Plasmodium</i> antibodies, revealing a 6.8% (95% CI = 6.1-7.7%) seroprevalence. Seropositivity was higher among donors from Sub-Saharan Africa (42.9%; 95% CI = 36.1-49.9%) and Southeast Asia (10.6%; 95% CI = 6.7-16.4%). A lower seropositivity was observed when employing Euroimmun ELISA (4.8; 95% CI = 3.8-5.9%) than DRG ELISA (8.2%; 95% CI = 7.1-9.3%). Seropositivity dropped to 3.6% (95% CI = 2.4-5.6) in 2020, likely because of travel restrictions during the COVID-19 pandemic. None of the tested seropositive donors (n = 20) tested positive for <i>Plasmodium</i> DNA LAMP testing. A high proportion of seroreversion was observed after one year of testing. Among 4285 donors tested for anti-<i>T. cruzi</i> antibodies seroprevalence was 0.7% (95% CI = 0.5-1.1%), a higher value than what was observed in a recent national survey. All seropositive donors were born in Europe or Latin America. Seropositivity was apparently lower with ELISA (0.5%, 95% CI = 0.2-1.2%) than ICT (0.8%, 95% CI = 0.6-1.2%), possibly due to ELISA's higher specificity, although the difference is not significant. No confirmed cases of chronic Chagas disease were identified. The study emphasizes the importance of defining the serological test employed for screening and the need to confirm seropositive results with further testing. The high seroreversion observed in the study suggests repeating seropositive donor screening after a year to minimize deferral and blood unit loss.