Zika virus seroprevalence in blood donors from the Northeastern region of São Paulo State, Brazil, between 2015 and 2017.

OBJECTIVES: Although primarily transmitted by Aedes aegypti mosquitos, Zika virus (ZIKV) can also be transmitted by blood transfusion, due to the fact that some of the infected donors can establish asymptomatic viremia. ZIKV seroprevalence in Brazilian blood donors is unknown. The main reason for this gap in the knowledge originates from the difficulty in evaluating ZIKV humoral immunity due to antigenic cross-reactivity between the different Brazilian flaviviruses and, in particular, dengue virus (DENV). The objective of this study was to evaluate the anti-ZIKV IgG prevalence in blood donors from the Northeast region of the São Paulo State, Brazil, which experienced a ZIKV outbreak in 2016. METHODS: We evaluated the ZIKV seroprevalence using the NS1 anti-ZIKV IgG test (Euroimmun), followed by confirmation of the positive and borderline results using the Plaque Reduction Neutralization Test (PRNT). ZIKV seroprevalence was estimated by testing plasma samples collected in 2015 (before the ZIKV outbreak), 2016 (during the outbreak) and 2017 (after the outbreak). In order to investigate possible antigenic cross - reactivity between ZIKV and DENV we also included samples that were taken well before the ZIKV outbreak, in years 2010 and 2013. RESULTS: The results obtained by the Euroimmun anti-ZIKV IgG test demonstrated ZIKV seroreactivity in 2015, 2016, and 2017 with prevalences of 5.3%, 12.8% and 13.2%, respectively. The inclusion of blood donor samples from 2010 to 2013, demonstrated anti-ZIKV IgG reactivity only for 2013 (1.7%). The PRNT testing of the ZIKV positive and borderline ELISA reacting samples generated positive results only for the years of 2016 and 2017 (prevalences of 5.6% and 9.1%) which coincided with the introduction of ZIKV in our region. CONCLUSIONS: Our results estimate for the first time the ZIKV seroprevalence among Brazilian blood donors from a region with apparently extensive ZIKV circulation and which, at the same time, is highly endemic for DENV. We detected relatively low ZIKV seroprevalence in blood donors from the studied region probably due to the lower intensity of the outbreak compared to other Brazilian locations. Our study adds to the global understanding of ZIKV circulation and the herd immunity of the exposed population.

A microfluidic approach to study the effect of mechanical stress on erythrocytes in sickle cell disease.

The human red blood cell is a biconcave disc of 6-8 × 2 µm that is highly elastic. This capacity to deform enables it to stretch while circulating through narrow capillaries to ensure its main function of gas exchange. Red cell shape and deformability are altered in membrane disorders because of defects in skeletal or membrane proteins affecting protein-protein interactions. Red cell properties are also altered in other pathologies such as sickle cell disease. Sickle cell disease is a genetic hereditary disorder caused by a single point mutation in the ß-globin gene generating sickle haemoglobin (HbS). Hypoxia drives HbS polymerisation that is responsible for red cell sickling and reduced deformability. The main clinical features of sickle cell disease are vaso-occlusive crises and haemolytic anaemia. Foetal haemoglobin (HbF) inhibits HbS polymerisation and positively impacts red cell survival in the circulation but the mechanism through which it exerts this action is not fully characterized. In this study, we designed a microfluidic biochip mimicking the dimensions of human capillaries to measure the impact of repeated mechanical stress on the survival of red cells at the single cell scale under controlled pressure. We show that mechanical stress is a critical parameter underlying intravascular haemolysis in sickle cell disease and that high intracellular levels of HbF protect against lysis. The biochip is a promising tool to address red cell deformability in pathological situations and to screen for molecules positively impacting this parameter in order to improve red cell survival in the circulation.