|
|
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.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
There are more nerve cells in one human brain than there are stars in the Milky Way.
This year, an estimated 1.4 million Americans will have a new or recurrent heart attack.