A field trial of a PCR-based Mansonella ozzardi diagnosis assay detects high-levels of submicroscopic M. ozzardi infections in both venous blood samples and FTA® card dried blood spots

Jansen Fernandes Medeiros,Tatiana Amaral Pires Almeida,Lucyane Bastos Tavares Silva,Sergio Luiz Bessa Luz,James Lee Crainey,Felipe Arley Costa Pessoa,Jose Miguel Rubio

doi:10.1186/s13071-015-0889-z

Jansen Fernandes Medeiros, Tatiana Amaral Pires Almeida + Show 5 more

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https://doi.org/10.1186/s13071-015-0889-z

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Abstract

BackgroundMansonella ozzardi is a poorly understood human filarial parasite with a broad distribution throughout Latin America. Most of what is known about its parasitism has come from epidemiological studies that have estimated parasite incidence using light microscopy. Light microscopy can, however, miss lighter, submicroscopic, infections. In this study we have compared M. ozzardi incidence estimates made using light microscopy, with estimates made using PCR.Methods214 DNA extracts made from Large Volume Venous Blood Samples (LVVBS) were taken from volunteers from two study sites in the Rio Solimões region: Codajás [n = 109] and Tefé [n = 105] and were subsequently assayed for M. ozzardi parasitism using a diagnostic PCR (Mo-dPCR). Peripheral finger-prick blood samples were taken from the same individuals and used for microscopic examination. Finger-prick blood, taken from individuals from Tefé, was also used for the creation of FTA®card dried blood spots (DBS) that were subsequently subjected to Mo-dPCR.ResultsOverall M. ozzardi incidence estimates made with LVVBS PCRs were 1.8 times higher than those made using microscopy (44.9 % [96/214] compared with 24.3 % [52/214]) and 1.5 times higher than the PCR estimates made from FTA®card DBS (48/105 versus 31/105). PCR-based detection of FTA®card DBS proved 1.3 times more sensitive at diagnosing infections from peripheral blood samples than light microscopy did: detecting 24/105 compared with 31/105. PCR of LVVBS reported the fewest number of false negatives, detecting: 44 of 52 (84.6 %) individuals diagnosed by microscopy; 27 of 31 (87.1 %) of those diagnosed positive from DBSs and 17 out of 18 (94.4 %) of those diagnosed as positive by both alternative methodologies.ConclusionsIn this study, Mo-dPCR of LVVBS was by far the most sensitive method of detecting M. ozzardi infections and detected submicroscopic infections. Mo-dPCR FTA®card DBS also provided a more sensitive test for M. ozzardi diagnosis than light microscopy based diagnosis did and thus in settings where only finger-prick assays can be carried-out, it may be a more reliable method of detection. Most existing M. ozzardi incidence estimates, which are often based on light microscope diagnosis, are likely to dramatically underestimate true M. ozzardi parasitism incidence levels.

Highlights

Mansonella ozzardi is a poorly understood human filarial parasite with a broad distribution throughout Latin America
In this study we have shown that M. ozzardi parasitism incidence estimates in the Rio Solimões region, made using light microscopy-based diagnosis in isolation, are about half those made using the method in combination with ModPCR assays
Our results will ensure that if such M. ozzardi global estimates are made in future they will take into account submicroscopic infections and by doing so could potentially double estimates made solely from light microscopy incidence surveys alone

Summary

Introduction

Mansonella ozzardi is a poorly understood human filarial parasite with a broad distribution throughout Latin America. Most of what is known about its parasitism has come from epidemiological studies that have estimated parasite incidence using light microscopy. In this study we have compared M. ozzardi incidence estimates made using light microscopy, with estimates made using PCR. Mansonella ozzardi is a New World human filarial parasite that is broadly distributed throughout Central and South America. Acquired M. ozzardi infections have been reported in a diverse range of communities throughout Latin America, spanning from Mexico (in the north) to Argentina (in the south) [1]. While many symptoms have been attributed to the mansonelliasis condition, there is presently no universally agreed symptom-set used for its clinical diagnosis [1, 9, 10]. The condition is not presently the subject of any major international or even national control programmes and is not presently regarded by the World Health Organisation (WHO) as one of the world’s 17 most Neglected Tropical Diseases [11]

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