Yes. They are. At least they can be. And not only are they dangerous, they are actually deadly in many parts of the world. In fact, the mosquito is widely accepted as the most deadly animal on earth, accounting for more than a million deaths each year. Fortunately in the United States, mosquitoes are primarily a nuisance, with a very small risk of exposure to a potentially lethal virus. Nevertheless, the risk of exposure remains, and should be taken seriously.