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Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
There are more nerve cells in one human brain than there are stars in the Milky Way.
The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.
More than nineteen million Americans carry the factor V gene that causes blood clots, pulmonary embolism, and heart disease.
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.