Medical research hamster that is being used to test a vaccine. Mice and hamsters are used for medical research because their physiology is like that of humans, and they have been studied in great detail. They are also relatively easy to keep in captivity and breed relatively quickly. This hamster is being used to test a DNA vaccine for Leishmania parasites, which are spread by sandflies, and which cause the tropical disease leishmaniasis. Photographed at the Pasteur Institute, Tehran, Iran.