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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.
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.
Today, nearly 8 out of 10 pregnant women living with HIV (about 1.1 million), receive antiretrovirals.
In 1835 it was discovered that a disease of silkworms known as muscardine could be transferred from one silkworm to another, and was caused by a fungus.
Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
![The respiratory system. (a) Sagittal section of the head and neck, revealing the organs of the upper](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_23_09_100491445.jpeg)
![Schematic representation of MHC class I molecule, consisting of 3 α domains and 1 β2-microglobulin ...](https://biology-forums.com/gallery/31/medium_398119_11_07_17_4_50_36_315051108.jpeg)
![Schematic representation of MHC class II molecule, consisting of 2 α-domains and 2 β-domains, the ...](https://biology-forums.com/gallery/31/medium_398119_11_07_17_5_39_03_315251076.jpeg)