The immune system is the primary defense system in keeping out pathogens. A pathogen or infectious agent is a biological agent that causes disease or illness to its host. Chronic diseases often cannot be cured. “Any man who is intelligent, on considering that health is of the utmost value to human beings have the personal understanding necessary to help himself in diseases, and be able to understand and to judge what physicians say and what they administer to his body, being versed in each of these matters to a degree reasonable for a layman” (Hippocrates) Pathogens can infect unicellular organisms from out of the biological kingdoms. There are several substrates and pathways whereby pathogens can invade a host. There are many ways diseases are caused by blood-borne pathogens. A needle stick injury, in jury from a sharp instrument contaminated with blood or body fluids and intimate contract are some ways that people are exposed to these pathogens (environmental pathogens are defined as microorganisms that normally spend a substantial part of their lifecycle outside human hosts but when introduced to humans cause disease with measureable frequency. They are carried in the water, soil, air, food and other parts of the environment and can affect almost every individual on the planet.) The key difference between environmental pathogens and other human pathogens is their ability to survive and thrive outside the host. Their widespread occurrence in the environment makes them difficult to monitor and control. It has been proposed that brain-derived neurotropic factor (BDNF), a member of neurotropic factor family, maybe implicated in the pathogenesis of ADHD. BDNF is the neurotrophin responsible for helping aid the creation of new dopaminergic neurons and protecting the existing ones from cell death (apopotasis) BDNF is a nervous system growth factor that