A fluorescent image of a human body louse with Yersinia pestis infection — that's the cause of the plague — depicted in orange/red in the glands.
plague/National Institute of Allergy and Infectious Diseases
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Fleas carry the bacteria that cause cat-scratch fever, so if your kitty is flea-free, you should be in the clear. Sara Lynn Paige/Getty Images hide caption
A mosquito lurks, eager to score some Halloween candy. Ben de la Cruz/NPR hide caption
Meet some of the nightmarish parasites that live in London's Natural History Museum. Fortunately, they reside in jars. Rich Preston for NPR hide caption