These symptoms appear to be a harmless random mutation, but you can keep an eye on the plant as any infected with the virus-like Aster Yellows disease will only worsen or time and its symptoms will become more blatant. Minor and sporadic mutations like this can be fairly commonplace in daisy-family plants so the oddball flower seen now an then on an otherwise normal-looking plant is probably not an indicator of virus, or at least not one serious enough to worry about. The only significant insect vector that moves that virus-like pathogen around from plant to plant is a particular leafhopper, so excluding them from a planting is impractical, and no pesticide would be recommended in that situation anyway (even if it worked to prevent their ability to infect sap) since the host plants are often highly valuable to pollinators.

Miri