Parasitology is a science about parasites, and in a narrow sense includes organisms that parasitize the inside and outside of the host, as well as sometimes fungi. Parasitology deals with the biology of parasites, their occurrence and their percolation, understanding the pathology and course of parasitic diseases and developing methods for their eradication and prevention.The name of the parasite comes from the Greek word parasitos – co-traveler, freeloader. The concept of parasitism is difficult to define. This phenomenon can be defined differently from the point of view of ecology, biochemistry, pathology, hygiene or genetics. Parasitism is an antagonistic compound in which individuals of one species (the parasite) use individuals of another species (the host) as a source of food and often as a living environment, causing damage to this population. These interactions usually lead to a decrease in the growth rate of the host population. It should be emphasized that pathogenicity is a fundamental – from the point of view of medicine – characteristic of parasitism.
More than 300 species of parasites can dwell inside the human body. Contrary to common beliefs that parasites live mainly in our intestines, they can actually be found in every part of our body. Parasites live in the skin, hair, lungs, muscles, joints, liver, esophagus, blood, eyes, and in the brain. They get into the human body in various ways: by eating unwashed fruits and vegetables, poorly prepared food (raw or undercooked), drinking unboiled water, lack of personal hygiene, eating food of unknown origin or even contact with a beloved pet, which is not dewormed. In addition, foreign travel and stress become an additional factor favoring infection by parasites. The most common parasitic infection is associated with the consumption of infected water and food. Parasites get into our body by insect bites, and even through air, in which dust is a great way of transport for parasite eggs. Often, infection occurs when bathing in water reservoirs. New-born infections in the womb of the mother are also becoming more frequent.
Among the tens of thousands of animal species described in Europe, about 25% are parasites. About 50% of this group is platyolae or roundworms, then 25% belongs to arthropods and 17% to protozoa. In Poland, a human being can be the host for dozens of animal species, including more than 40 species parasitizing within his system. Most species of human parasites are widespread in the world, and their occurrence is associated with a lack of development of health education and hygiene. Due to the place of existence, external parasites occurring on the hosts body surface and internal parasites that parasitize the host system are distinguished. The host, in which the parasite reaches sexual maturity or reproduces sexually, is the ultimate host. The other hosts are called intermediaries. Physical activity of the parasite on the human body is primarily the mechanical damage to the tissue or organ e.g. skin (mites and insects), intestinal walls, muscle tissue or nervous system (tapeworms, nematodes and protozoa), but also to bring about temporary, reversible or permanent changes to organs such as the liver, lungs, brain and kidneys.Parasites are also often an indirect life-threatening cause. They produce substances that cause strong allergic reactions and inflammatory reactions (e.g. nematodes and mites). Substances derived from endogenous and exogenous parasites can also cause general disorders such as anemia and hemorrhagic diathesis. In an allergic system, even the presence of a few parasites can trigger violent reactions of the body.
Both internal and external parasites play an important role as hosts-carriers of other human pathogens, e.g. viruses, bacteria, rickettsia, protozoa and tapeworms (ticks, lice, fleas). They can open the gates of other infections by damaging tissues and even carry germs with them. Parasite infections persistently in a given host may not always cause disease symptoms. These organisms are a parasite reservoir that can be dangerous to other organisms. Man can also be infected with parasites, the harmful effects of which will be revealed only in certain specific conditions, e.g. in the case of a decrease in immunity (e.g. tumors, transplants, immunosuppressive therapy, AIDS).
According to statistical data, about 2 billion people are currently infected with at least one parasite and the total number of parasitic cases; diseases caused by parasites, exceeds 3 billion. These data are very careful calculations. According to the WHO data, over 4.5 billion people have been infected with various parasites in the past 10 years, in Europe – every third person, in the US 85-95% of the population. Parasites cause 14 million deaths worldwide a year. This gives 25% of the overall mortality rate.
In the human body, many different species of parasites can settle down, from microscopic size to those visible to the naked eye. Recent studies show that 95% of adults are inhabited by one to five species of parasites. According to statistics in Poland, the invasion of pinworms reaches 95% of the population, whistling – 80%, human worms – 50%, and infection of Giardia – lamblia for infants reaches 80%. Parasitic organisms using humans as hosts, belong to systematic groups classified as: Helminths (worms), primers, Arthropods and sometimes Fungi. Human helminthsconstitute of two large systematic groups: roundworms (Nemathelminthes) and flatworms (Platyhelminthes).