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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.
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.
Thyroid conditions cause a higher risk of fibromyalgia and chronic fatigue syndrome.
The familiar sounds of your heart are made by the heart's valves as they open and close.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.