Mainly myth.
There have been rumours about ethnic specific bioweapons for years - google on it and you'll see the usuall conspiracy blather.
In 1998 the Times carried a report about Israel working on an anti-Arab weapon
en.wikipedia.org... - which appears to jhave been a hoax.
The South Africans were also said to be working on a similar weapon, a "Black Bomb" to target certain ethnicities -
www.commondreams.org...
In WWII , the US worked on race-specific weapons to target the Japanese -
www.counterpunch.org...
Nothing has come of any of these as far as I know. There is a deep-seated problem because "race", as we now know, is not really a scientific concept
and it's hard to see how any kind of race-specific wepaon would actually work.
However, it's a terrific one for getting publicity.