LIFE IN THE 21ST CENTURY: Vets Face Rising Worry Over Resistant Fleas. “Last summer, Mark Conrad a freelance photographer in Fairfield, Conn., noticed his golden retriever Tia scratching more than usual. Mr. Conrad said he suspected an allergy rather than fleas because the dog had been treated diligently every month for three years with a leading flea treatment that contains the chemical fipronil, which has been shown to be highly effective against fleas. Soon, however, he discovered that his dog and home were infested with fleas.”