FAO of experts in worm infestations in dogs

Can anybody answer this simple question. I've googled it in Yahoo and can't find a satisfactory answer.

If a b***h has puppies and the the b***h is fully wormed by a decent wormer. Where does the worms come from that puppies seem to get straight away within a week or two?

Thank you muchly.

Posted By: harry boulders, Jan 30, 15:15:20