Footnotes

• Handling editor Tahir S Pillay.

• MVL and MG contributed equally.

• Contributors All authors participated in the drafting of the paper, made critical revision of the manuscript for important intellectual content and provided approval of the final submitted version.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; externally peer reviewed.