There are several ways of spreading infectious diseases. A common way of spreading respiratory infections is through a cough or sneeze of the infected person. A healthy person can get infected when he or she inhales infectious agents that are found in the contaminated air. Bowel infections are transmitted through the feco-oral pathway, usually via contaminated water. Other infectious diseases are spread by body fluids, such as blood.

Our body has non-specific and specific defenses. There are three types of non-specific protection – the skin and mucous membranes with its glands, inflammatory response and the fever. The skin and mucous membranes provide mechanical protection and only if their continuity is interrupted, bacteria and viruses can pass. Mucous, tears, and saliva contain an enzyme that is called lysozyme, which dissolves the wall of bacteria. After infection or injury, our body attempts to localize the tissue damage and cause an inflammatory response, which is defined with local pain, swelling, redness, higher temperature and loss of function. Cells of the immune system discharge high amount of TNF which affect the hypothalamus to raise the body temperature. That can speed up the immune reactions and reduce the growth of some infectious agents.

Our immune system recognizes antigens as “self” if they belong to our organism and “other” if they are foreign particles. It is very important for white blood cells to be exposed to the antigens of its own body during the maturation process because they won’t attack our cells after they enter the circulation. Leukocytes are able to distinguish foreign molecules, induce chain reaction that leads to the destruction or inactivation of the unknown particles in order to protect the tissue from damage.

The HIV is a human immunodeficiency virus that can lead to the acquired immune deficiency syndrome or shortly AIDS. The HIV is transmitted through the blood and bodily fluids. The initial symptoms are flu-like, after which starts the latent period. This disorder leads to the reduction of the T helper cells which affects the immune response and causes the vulnerability of the body towards the infections. When their number goes below 200 cells per µL, or when the patient has some illnesses that can be related to the HIV infection, the AIDS can be diagnosed.

Since the cause of AIDS is an HIV virus, therefore it can be classified as an infectious disease. Pathophysiologically, AIDS is a disorder that leads to the reduction of the T helper cells which affects the immune response and causes the vulnerability of the body towards the infections. When their number goes below 200 cells per µL, or when the patient has some illnesses that can be related to the HIV infection, the AIDS can be diagnosed. We can conclude that this is also an immune disorder.

Our body has non-specific and specific defenses. There are three types of non-specific protection – the skin and mucous membranes with its glands, inflammatory response and the fever. In non-specific defenses, our body responds in the same way when it comes in touch with the different infectious agents. However, in the specific defenses, the immune response is very exact because our leukocytes act like little soldiers. They recognize foreign molecules, induce chain reaction that leads to the destruction or inactivation of the unknown particles in order to protect the tissue from damage. White blood cells also memorize every foreign molecule that they got in touch with, so, if this antigen strikes again, their response is much faster and more effective than the first time.

Toxic chemicals can cause illness by inhaling or ingesting them, or even by skin contact because they are present in our environment. One of the toxic chemicals is lead. It has been widely used in households as an ingredient of home paint and as a material for water pipes. Lead accumulates in the body and causes the impairment of cell structure. Symptoms in children include weight loss, abdominal pain, vomiting, seizures, delay of development. Symptoms in adults are high blood tension, pain in the abdomen, muscles, and joints, headache or loss of concentration. Treatment includes an elimination of the source of poisoning and chelation therapy.