Discus thrower Traves Smikle has become the latest Jamaican athlete to test positive for a banned substance.Smikle, who competed at London 2012, returned a positive result after the Jamaican trials in June.Compatriots Asafa Powell, Sherone Simpson, Veronica Campbell-Brown and fellow discus thrower Allison Randall have also recently failed dope tests. "I must take responsibility for whatever is found in my body," Smikle, 21, said in a statement."However, I didn't knowingly or wilfully ingest any banned substance. I have requested analysis of the B sample."Smikle failed to reach the final of the discus competition at London 2012 after recording a best throw of 61.85m.Former 100m world record holder Powell tested positive for banned stimulant oxilofrine, as did Simpson, a 4x100m relay silver medallist at last year's London Olympics.World 200m champion Campbell-Brown and Randall have both tested positive for a banned diuretic.Jamaica's team for the World Championships in Moscow next month has also been affected by the withdrawal of world 100m champion Yohan Blake because of a hamstring injury.