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As many as 20% of Americans have been infected by the fungus known as Histoplasmosis. While most people are asymptomatic or only have slight symptoms, infection can progress to a rapid and potentially fatal superinfection.
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.
There are 60,000 miles of blood vessels in every adult human.
People with alcoholism are at a much greater risk of malnutrition than are other people and usually exhibit low levels of most vitamins (especially folic acid). This is because alcohol often takes the place of 50% of their daily intake of calories, with little nutritional value contained in it.
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
![During their annual migration, the entire population of Arctic terns move from the Arctic Ocean in t](https://biology-forums.com/gallery/47/medium_33_22_09_11_9_37_27_1802877.jpeg)
![A strike by 800 women shoemakers in Lynn, Massachusetts, in 1860. In 1851 a Lynn shoemaker had adapt](https://biology-forums.com/gallery/47/medium_375552_19_08_15_9_09_53_223271453.jpeg)