If you haven't tested, you don't know.
@KsKingBee 's chick looked fine until the day before it died. By then, it was too late to save it with all the wormer in the world. The worms had terminally (fatally) damaged the insides of the chick. And he had been using Safeguard in the water... but not an effective dose.
By all means, supplement... but don't base "they are fine" on the birds not acting sick.
If you don't test, you don't know.
And a vet can do a tests and look for symptoms of something weird but the tests show negative and then the animal is dead in the morning. We had that with a calf so you can't always trust tests. By the looks of the photo that parasite looks like roundworm. I've had vets tell me that the disease I lost my peahen to is rare in game birds over a year old but my peahen was 10 months old. My peahen died from 2 unidentifiable internal parasites.
