Its nematodes for sure, that symptom is classic. You live in a cooler climate? The real problem is stopping them because they spread very slowly (a few inches per year). So you can treat the soil naturally or with chemical
ANYWAY The plants of this year are going to die . But you can tret for next year. Plant African Marigolds really densely. Heavy seed. This will make the nematodes sterile.
Youve probably brought it in with the soil or mulch.. Pumpkins usually recover if you companion plant lots of radish seeds. (Theyll also protect against vine borers.