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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
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.
Acute bronchitis is an inflammation of the breathing tubes (bronchi), which causes increased mucus production and other changes. It is usually caused by bacteria or viruses, can be serious in people who have pulmonary or cardiac diseases, and can lead to pneumonia.
Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.