In times of stress, especially pregnancy, the immune system weakens and encysted worms begin to migrate again and develop into adult worms. In your mom's cat's case, the most likely scenario is that the stress of boarding allowed development of a previously arrested case of roundworms, although there are some cats that just never develop the immune response necessary to control the worms and have to be dewormed frequently throughout their lifetime. The only way to check on this, that I know of, is to do repeat fecal examinations. If they keep coming up positive for roundworms then it is necessary to develop a routine deworming program for the affected cat or dog. More often, deworming once or twice will stop the new infection and things will be OK until the next big stressful event occurs.
Tapeworms are among the best adapted of parasites, meaning that they harm their host the least.
A few patients develop diarrhea, weight loss, vomiting or just an unthrifty appearance when infested with enough tapeworms. Most cats do not have clinical signs associated with tapeworm infestation, though. I think it is worth treating for these worms when it obvious that a cat has them due to the presence of tapeworm segments around the rectum or in the stool since I don't know which patients will have problems. I would have a hard time arguing that it was absolutely necessary, though. Dear Mike, I am confused about the tapeworm and roundworm eggs being discussed on your website.