Strongyles or bloodworms are going to be a little more difficult to get rid of then the normal dog worms and they can cause damage to blood vessels (large type) or the lining of the colon or cause severe stomach ulcers (small type). They can remain encysted in the intestinal wall (dormant) and not show up or be affected by wormers. So your breeder is probably telling the truth that the pup was wormed, but the stress of changing environments probably caused them to become active.
Of course, the dog came to you with them unless you have a horse around - I think she should pay for the treatment, but would take into consideration, like Doortego mentioned, the price paid. |