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The familiar sounds of your heart are made by the heart's valves as they open and close.
Most fungi that pathogenically affect humans live in soil. If a person is not healthy, has an open wound, or is immunocompromised, a fungal infection can be very aggressive.
Malaria was not eliminated in the United States until 1951. The term eliminated means that no new cases arise in a country for 3 years.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.