Disease the time between infection and the appearance of symptoms. The latency period is the time between infection and the ability of the disease to spread to another person, which may precede, follow, or be simultaneous with the appearance of symptoms. Some viruses also exhibit a dormant phase, called viral latency, in which the virus hides in the body in an inactive state. For example, varicella zoster virus causes chickenpox in the acute phase; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause herpes zoster (shingles). Diseases may be classified by cause,
Motor neuron disease Motor neuron disease Motor neuron diseases (MNDs) are a group of neurodegenerative disorders that selectively affect motor neurons, the cells which control voluntary muscles of the body. Commonly, the following disorders are counted among motor neuron diseases: The term “motor neuron disease” sometimes refers to ALS, but in this article, the term refers to a group of diseases listed above, which includes ALS. Motor neuron diseases affect both children and adults. While each motor neuron disease affects patients differently, they all cause movement-related symptoms, mainly muscle weakness. Most diseases seem to occur randomly without known causes, but some forms are