Infection is the process and the result of the introduction into the body of foreign agents. Usually distinguish defeats by viruses, fungi, protozoa, bacteria. Recently, mysterious prions have been added to these categories of pathogens, but we will leave them for dessert in a story about pathogenic agents.
Let us examine in more detail various pathogens that cause infectious diseases.
Not really a life
Viruses are unique creatures, because not all biologists agree to call them living entities. Painfully they are strange. They represent DNA (RNA) in a protein coat, very small and ubiquitous. A genome can only be a pair of genes, and may contain a couple of hundred of these elements of heredity. Sometimes the protein coat is covered by another, in which the proteins of the host organism are involved. For example, infectious diseases such as influenza are caused by viruses - "conspirators".
Everyone who has ever experienced mycosis of the foot or thrush, can consider that they have become acquainted with "bad fungi". Most fungi live peacefully in the body and do not interfere with the life of the host. Though there are also pathogenic. But the thrush - out of control normal fungi. Usually they are slightly suppressed by the lactobacilli of the vagina, so infectious disease thrush occurs when the population of natural lactobacilli decreases or immunity worsens. So do not use soap while washing, and drink antibiotics unnecessarily.
Sometimes the disease is caused by organisms called protozoa. They cause such serious infectious diseases as malaria, dysentery and African sleeping sickness. To biologists the name "protozoa" is not pleasant, but physicians - people in their classifications are conservative.
Bacteria are prokaryotic. They do not have a pronounced nucleus, and this distinguishes them from the simplest. Propagation by division. Evolutionarily unpromising, but very reliable. Infectious diseases caused by bacteria, a person has learned to heal best. At least, these pathogens, unlike viruses, could be seen in not the most powerful microscope.
Punishment of cannibals
Prions are strange proteins, which in themselves cause diseases, live in the brain. Similar to viruses, only without nucleic acids. Particularly common in New Guinea, where people have a sweet habit of eating the brain of the deceased. So, most Europeans do not face the disease, unless they like it. For the same reason, it is better not to eat the brain of cattle, even if they try to convince you that at least once in a lifetime a "delicacy" should be tested.
What should I do?
Now you know what causes the disease. The treatment of infectious diseases, of course, depends on the type of pathogen. Old good antibiotics will help only against bacteria. Fungi are treated with special preparations like fluconazole, and also try to restore the normal bacterial background of the organism so that useful bacteria keep pathogens "in check." Viruses are treated with special antiviral drugs that target a specific virus, as well as stimulants of immunity. Better than immunity, viruses can not be destroyed by anything. The only exception is HIV. But many viral infectious diseases we have learned to win. Protozoa are destroyed by various chemical substances, which were sometimes found by chance. An infectious disease provoked by a prion is almost always a verdict. Too little is known about these pathogens, even their nature is not completely clear.
Reminders of the need for hygiene have already filled everyone's nostrils, but we must admit that it was the increased hygiene measures that saved humanity from the recurrence of epidemics of terrible diseases that "mowed" people in the Middle Ages. So once again to wash your hands - it's not superfluous. Well, brains are better not to try ...