Ok, I've done some reading but I still want to do a bit more. It seems like Fenbedazole is the preferred treatment in lab animals, although I'm not sure why. The cleaning regimen you described is more feasible (realistic, practical) in a sterile environment where rats are often kept alone or in small groups in aquarium style enclosures.
http://www.google.ca/url?sa=t&rct=j&q=& ... TyA6XAmY8A
The abstract for this article says that Ivermectin is effective on one species of pinworm (Syphacia muris) and that the eggs can survive on surfaces for 17 days without a host. If you're able to keep them in a different cage and let them out in an easy to clean area for 3 weeks (like a washroom) and clean after they're out that should help. After 3 weeks any eggs on a couch, a bed, carpeting, etc. should have died on their own.
http://www.ncbi.nlm.nih.gov/pubmed/8459683
There are several species of worms, including 3 species of pinworms that can infect a rat. It may be that some are more sensitive to one treatment than others. Did they do a tape test at the vet to confirm that it's a pinworm and not some other type of worm?
Here's another article where 100% of rats that received four or five treatments of Ivermectin one week apart were found to be parasite free even 6 months after treatment was ended.
http://www.ncbi.nlm.nih.gov/pubmed/8799934
There are also a few articles that talk about the eggs being airborne, so rats and mice do not have to be in direct contact to catch them from one another. Is there any possibility that there are wild mice in your building? (Rats and mice can both be infected with all three species of worm.)
The efficacy of Revolution to treat for worms is unclear. This study found Revolution 100% ineffective in treating two of the species of pinworms that can affect rats and mice.
http://www.ncbi.nlm.nih.gov/pubmed/16642966/ This one found it effective on almost half of rats but much more effective on females:
http://www.ncbi.nlm.nih.gov/pubmed/18540211
Like most parasites, many rats are infected but few show symptoms - usually only the ones with severe infestations or when the rats immune system is otherwise compromised. If you have an air purifier or a central air conditioning/furnace with a filter you can change, I would do so as well.
It looks like Fenbendazole and Ivermectin are both effective at treating pinworm so if one hasn't worked, I would try the other. Ivermectin is a lot cheaper and as long as you do at least four consecutive treatments (for other parasites it's usually only three), a conventional cleaning regiment (10% bleach solution) should be fine. If you're still a student you may have access to these articles in full if you want to read them.
