It can be. A body’s natural reaction is to increase temperature when a parasite is detected. However it can't do this for long and some parasites do send out message that actually lower the body temperature which they find much more comfortable.

It is also possible that by doing the treatment your 4 year olds immune system has kicked back into high gear and does what it considers normal response to a parasite invasion.

But needless to say, better keep and eye on that.