1982 gave us the acronym AIDS formed from acquired immune deficiency syndrome. This is pronounced /eɪdz/. The fact that the final S is pronounced /z/ is notable, since a final s is typically pronounced /s/ (e.g., bus) unless it is an inflectional morpheme (e.g., dogs). There are cases such as news and lens, in which a final s is pronounced /z/, but the -s in news was originally a plural morpheme. That leaves lens, which comes from the Latin word for lentil. Apparently, it was pronounced /leːns/ in Latin, so why it has a final /z/ in English is something of a mystery to me. I cannot find another example of an English noun with a final s pronounced /z/.
This brings us back to AIDS. Presumably, this final /z/ was influenced by the homographs aids, the noun, and aids, the verb. But then in 2003 we got SARS. There is no English word sar, so there is no preexisting homograph from which to analogously get /sɑɹz/, but that is the only pronunciation I've ever heard. I've never heard anyone say /sɑɹs/. So this seems to be an extension of the AIDS analogy to aids.
And now today we have MERS. On CBC's Metro Morning this morning, Matt Galloway started out pronouncing it /mɜɹs/, which initially threw me. I'd been mentally pronouncing it with a final /z/, and indeed Galloway finished up with /mɜɹz/ (I couldn't tell what the person he was interviewing was saying, but I suspect she was using the /z/ form, given his shift.)
So perhaps we have a new rule developing: acronym-final s for syndrome is pronounced /z/.
As I was looking around writing this post, it appears that at least one other person has taken note of the pronunciation of MERS.
[John Wells points out "Latin fifth-declension nouns in -es have final
noninflectional /z/ in English, too: species, series... Why that should
apply to MERS is a further question, which I cannot answer: but compare