Fleas are the most common transmitter of the rare and ancient bubonic plague. They can also transmit the bacterial disease murine typhus to humans through infected rats. Flea saliva can cause serious flea allergy dermatitis in pets, and their debris can trigger similar allergic reactions in humans. Fleas are also known to transfer tapeworms and cause anemia in pets. Flea bites commonly cause painful, itchy red bumps.