FLEAS are external parasites that live off the blood of mammals. They lay 500+ eggs over their life, allowing for phenomenal growth rates. Flea bites cause an itching sensation and some people and animals suffer allergic reactions to flea saliva, resulting in rashes. Bites generally result in the formation of a slightly-raised swollen itching spot with a single puncture point at the center and often appear in clusters that can remain itchy and inflamed for up to several weeks afterwards. They can also lead to hair loss as a result of frequent scratching and can cause anemia in extreme cases. Fleas can also act as a vector for disease, transmitting between rodents and humans by carrying Yersinia pestis bacteria (bubonic plague), endemic typhus fever, and in some cases tapeworm.