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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.
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.
The eye muscles are the most active muscles in the whole body. The external muscles that move the eyes are the strongest muscles in the human body for the job they have to do. They are 100 times more powerful than they need to be.
Amoebae are the simplest type of protozoans, and are characterized by a feeding and dividing trophozoite stage that moves by temporary extensions called pseudopodia or false feet.
Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.

