Pippin has pinworms

[Freebird]

My mom had to take one of the chihuahuas to the vet today for a pre-surgery checkup and also brought in a sample of Pippin's poo for the vet to look at. He has pinworms. He has an oral medicine that he is supposed to be given once a week. I'm a little worried that the dossage might not be enough because Pippin has grown some since the vet actually saw him. We'll call him later to ask if the dossage should be changed. Pippin is only reptile in this house. He has no physical contact with the dogs or cat. I bought him on the 13th of December could he have had them this whole time?