Plasma mEV levels in Ghanain malaria patients with low parasitaemia are higher than those of healthy controls, raising the potential for parasite markers in mEVs as diagnostic targets

Samuel Antwi-Baffour; Memory Malibha-Pinchbeck; Dan Stratton; Samireh Jorfi; Sigrun Lange; Jameel Inal

doi:10.1080/20013078.2019.1697124

Plasma mEV levels in Ghanain malaria patients with low parasitaemia are higher than those of healthy controls, raising the potential for parasite markers in mEVs as diagnostic targets

J Extracell Vesicles. 2019 Dec 18;9(1):1697124. doi: 10.1080/20013078.2019.1697124. eCollection 2020.

Authors

Samuel Antwi-Baffour¹, Memory Malibha-Pinchbeck², Dan Stratton³, Samireh Jorfi⁴, Sigrun Lange⁵, Jameel Inal^{4

6}

Affiliations

¹ Department of Medical Laboratory Sciences, School of Biomedical and Allied Health Sciences, College of Health Sciences, University of Ghana, Accra, Ghana.
² Faculty of Wellbeing, The Open University, Milton Keynes, UK.
³ Faculty of Health Sciences, University of Hull, Hull, UK.
⁴ School of Human Sciences, London Metropolitan University, London, UK.
⁵ Department of Biomedical Science, Tissue Architecture and Regeneration Research Group, University of Westminster, London, UK.
⁶ School of Life and Medical Sciences, University of Hertfordshire, Hatfield, UK.

Abstract

This study sought to measure medium-sized extracellular vesicles (mEVs) in plasma, when patients have low Plasmodium falciparum early in infection. We aimed to define the relationship between plasma mEVs and: (i) parasitaemia, (ii) period from onset of malaria symptoms until seeking medical care (patient delay, PD), (iii) age and (iv) gender. In this cross-sectional study, n = 434 patients were analysed and Nanosight Tracking Analysis (NTA) used to quantify mEVs (vesicles of 150-500 nm diameter, isolated at 15,000 × g, β-tubulin-positive and staining for annexin V, but weak or negative for CD81). Overall plasma mEV levels (1.69 × 10¹⁰ mEVs mL^-1) were 2.3-fold higher than for uninfected controls (0.51 × 10¹⁰ mEVs mL^-1). Divided into four age groups, we found a bimodal distribution with 2.5- and 2.1-fold higher mEVs in infected children (<11 years old [yo]) (median:2.11 × 10¹⁰ mEVs mL^-1) and the elderly (>45 yo) (median:1.92 × 10¹⁰ mEVs mL^-1), respectively, compared to uninfected controls; parasite density varied similarly with age groups. There was a positive association between mEVs and parasite density (r = 0.587, p < 0.0001) and mEVs were strongly associated with PD (r = 0.919, p < 0.0001), but gender had no effect on plasma mEV levels (p = 0.667). Parasite density was also exponentially related to patient delay. Gender (p = 0.667) had no effect on plasma mEV levels. During periods of low parasitaemia (PD = 72h), mEVs were 0.93-fold greater than in uninfected controls. As 75% (49/65) of patients had low parasitaemia levels (20-500 parasites µL^-1), close to the detection limits of microscopy of Giemsa-stained thick blood films (5-150 parasites µL^-1), mEV quantification by NTA could potentially have early diagnostic value, and raises the potential of Pf markers in mEVs as early diagnostic targets.

Keywords: Malaria; extracellular vesicles; parasitaemia.