Is it possible that you are over-watering them? This causes them to 'wilt' too, as they cannot get enough air to their roots. Are they in pots or the ground?

Are you growing them in either a piece of ground, or compost which has grown pansies previously?

I planted them last November in pots using new potting mix. I will try not to water them too much. I am not sure but I suspect some sort of fungus maybe?

There is a condition called Pansy Wilt, but that occurs when you grow them in soil which has grown them before, so unless the pots weren't cleaned, that's unlikely. If you can't see any tiny insects on them, check the compost in the pots - we get something called vine weevil over here - lives in the compost and decimates the plants, so make sure you've no invaders in there. Usually with fungal infections, you'd see black spotting, fuzzy mould, etc.

Pythium blight is also a possibility, especially if you have been having warm, rainy weather. Other problems can occur if you raise the soil level, use too fine a compost as mulch, or if soil washes in around the stems. Soil piled up around the stems will kill the plants.

Thank You, Guys, for your answers!