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Competing Interests

The authors declare they have no competing interests.

Author Contributions

Sphiwe Madiba conceived and designed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables.

Mathildah Mokgatle conceived and designed the experiments, analyzed the data, prepared figures and/or tables, reviewed drafts of the paper.

Human Ethics

The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):

Ethical clearance was obtained from the Medunsa Research Ethics Committee (MREC/H/168/2012: IR) of the University of Limpopo


The study was funded by the University of Limpopo research grants. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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