Mosquitoes like this one (Anopheles quadrimaculata) are not generally dangerous to people on their own—apart from irritating itches. However, mosquitoes are vectors for several deadly diseases, including malaria, yellow fever, and dengue fever. A vector is an organism that carries and transmits a germ or disease to another organism. Mosquitoes transmit these diseases by picking up a virus in one "blood meal" (like this one is enjoying) and passing it along in the next.

Photograph by Darlyne A. Murawski, National Geographic

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  • On August 20, 1897, British doctor Ronald Ross proved that malaria could be spread by mosquitoes. Ross was practicing medicine in Secunderabad, Andra Pradesh, India, and began studying the disease after he himself fell ill with it.

    Ross’ groundbreaking experiment had four major phases. First, Ross let uninfected mosquitoes feed on a patient already sick with the disease. Second, he tested the mosquitoes, showing they were now infected. In the third phase, he let an uninfected mosquito feed on an infected bird, then on an uninfected one. Finally, in the fourth phase, he tested the second bird, showing it had become infected after the mosquito bite. Ross won the 1902 Nobel Prize in Medicine for this important discovery.

    Malaria is a tropical disease, mostly affecting people who live in hot and humid areas. Every year, about 216 million people suffer from the disease, and about 655,000 die.

  • Term Part of Speech Definition Encyclopedic Entry
    discovery Noun

    something seen, documented, or noticed for the first time.

    disease Noun

    a harmful condition of a body part or organ.

    experiment Verb

    to try or test an idea.

    groundbreaking Adjective

    innovative or pioneering.

    humid Adjective

    air containing a large amount of water vapor.

    infect Verb

    to contaminate with a disease or disease-causing organism.

    malaria Noun

    infectious disease caused by a parasite carried by mosquitoes.

    mosquito Noun

    insect capable of piercing the skin and sucking the blood of animals.

    Nobel Prize Noun

    one of five awards established by the Swedish businessman Alfred Nobel in 1901. Nobel Prizes are awarded in physics, chemistry, medicine, literature, and peace.

    phase Noun

    stage in a process or transformation.

    tropical Adjective

    existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.