Trigger of infectious diseases
Infectious diseases can be caused by various pathogens, including viruses, bacteria or fungi.
Viruses such as the corona virus SARS-CoV-2 are not visible to the naked eye and are only about 20 to 300 nanometres in size. They invade animal, plant or human cells and use these living cells as so-called host cells. Even when exposed to air, they can sometimes survive for a very long time and remain contagious. However, a new host cell is necessary for long-term survival - if they do not find it, viruses die sooner or later.
Not all viruses cause disease. Our immune system often reacts quickly and fights off intruders immediately. Viruses begin to multiply in the body as soon as infection has occurred. Drugs are of limited help against viruses and antibiotics have been proven to be ineffective against viral diseases. There are antiviral drugs that only help against certain types of viruses. Since viruses (for example the influenza virus) can change, they are able to get past the body's own defences more easily. A person only becomes immune when his body has dealt with the pathogen. However, even after a disease has been overcome, immunity is not always guaranteed. Viruses do not have their own metabolism.
Compared to viruses, bacteria are many times larger. They are about 0.1 to 700 micrometers in size, single-celled organisms that are self-sufficient. They also have their own genetic material and metabolism. Bacteria are everywhere - in the air, in water, in food, etc. Similar to viruses, bacteria can survive for very long periods of time, often weeks, sometimes even months, in the environment or in the body itself. They are very adaptable and can multiply under various conditions. Only one percent of all bacteria cause disease in humans. Often bacteria are even important for health. For example, they live in the human intestine, on the skin or in the oral cavity. Those who want to eliminate bacteria can use high temperatures (for example in the form of water vapour when cleaning) or chemical substances such as alcohol, aldehydes or chlorine. In the human body, antibiotics are often used as part of a treatment. The bacteria are prevented from multiplying or even destroyed directly.
Fungi occur quite naturally on the human skin or in the body. There are only a few types of fungi that cause disease in humans, including skin fungi, yeasts or some moulds. These fungi feel good wherever it is damp: in bathrooms, niches, on damp walls or in flower pots. Foodstuffs such as bread, potatoes or flour can also be a breeding ground for fungi. Mushrooms can even be found in upholstered furniture and bed linen. The yeast fungus belongs to our natural skin flora. It lives in the skin scales and feeds on dead tissue particles. Fungi only penetrate the human body if the natural skin barrier is damaged or the immune system is weakened. Diseases caused by fungi are called mycoses. Mostly skin, nails or mucous membranes are affected. Only rarely are internal organs like the lungs affected by fungi. But if this happens, they can cause great damage.