A parasite is an organism that lives at the expense of the host. The host is required to survive and to reproduce. A parasite can live either on the outside of a host (such as lice, tics and fleas) as well as on the inside of a host (such as intestinal parasites, eyeworms and tapeworms).


Parasites range from microscopic, single-celled organisms (protozoa) to larger multicellular organisms. Due to the immune responses of the body, contamination usually doesn’t lead to an infection. A person is not sick. Most parasites are already rendered harmless at the first contact with the body. In some cases, however, the parasite penetrates further into the body and then there is an infection. The immune system is activated in order to prevent further spread of the disease. Then a person becomes ill or has symptoms. Examples of dangerous infections caused by a parasite are malaria, yellow fever and sleeping sickness.


The parasite causes damage to the human body by injury and/or toxic substances. A parasitic infection leads to very different responses, which are characteristic of the specific parasite. So, for example, itch, swelling, abdominal pain, fatigue, rash, diarrhea or other intestinal problems can occur. Sometimes, symptoms begin long after infection.


The symptoms caused by parasites are often general in nature, which makes the diagnosis difficult to make. In many cases, therefore, a specialist must be consulted. Certainty can often only be obtained by demonstrating the parasite in blood, feces, urine or bone marrow. This parasitological diagnosis requires a certain degree of expertise and should usually be carried out in a laboratory.


An infection caused by a parasite is treated with antiparasitics. Such drugs prevent the production of proteins by the parasite. Without proteins, the parasite cannot grow and dies. There are currently no effective vaccines for parasitic infections.


Several chronic infectious diseases that cause complications in the long run, will occur more frequently in the future, especially among the elderly. This is because people who are infected with (HIV), hepatitis B or C at a younger age, will grow much older due to better treatment methods.


It is important to prevent infection by paying attention to hygiene: