<p>Parasites are living things that use other living things - like your body - for food and a place to live. You can get them from contaminated food or water, a bug bite, or sexual contact. Some parasitic diseases are easily treated and some are not.</p> <p>Parasites range in size from tiny, one-celled organisms called protozoa to worms that can be seen with the naked eye. Some parasitic diseases occur in the United States. Contaminated water supplies can lead to <a href="https://medlineplus.gov/giardiainfections.html">Giardia infections</a>. Cats can transmit <a href="https://medlineplus.gov/toxoplasmosis.html">toxoplasmosis</a>, which is dangerous for pregnant women. Others, like <a href="https://medlineplus.gov/malaria.html">malaria</a>, are common in other parts of the world. </p> <p>If you are <a href="https://medlineplus.gov/travelershealth.html">traveling</a>, it's important to drink only water you know is safe. Prevention is especially important. There are no vaccines for parasitic diseases. Some medicines are available to treat parasitic infections.</p>