WHO Style Guide
The WHO style guide provides a series of alphabetical lists setting out general English language rules, information on easily confused and troublesome words, and preferred spelling, punctuation, medical abbreviations and WHO-specific terms. Guidance on the use of non-discriminatory language is also included.

UNAIDS' Terminology Guidelines
(Published on UNAIDS website)
These notes will help UNAIDS authors and staff members preparing manuscripts. Following these recommendations will reduce the editing necessary after IRC receives a manuscript and decrease the time needed for production.