Protozoa are single-celled organisms. Protozoan infections can be very dangerous to humans.
What are protozoa?
Protozoa are a group of eukaryotic organisms. Eukaryotes, unlike prokaryotes, are living organisms that have a nucleus. Together with the fungi and the algae, the protozoa form the protist group. The protozoa are assigned to the animal kingdom, whereas algae are counted among the plants and fungi in turn form an independent genus. There are many different types of protozoa. They differ in size or in their external appearance. Protozoa belong to the heterotrophic organisms. In order for their metabolism to function, they depend on substances that have been built up by other organisms. A distinction can be made between commensal, parasitic or mutualistic interacting protozoa. Commensal interactions are profitable for the one species involved. For the other species, the interaction is neutral. Parasites harm their host. Mutualistically interacting protozoa live in a reciprocal relationship with the other species from which both partners can derive a benefit. However, no mutualistic protozoa are known in humans. Most protozoa have a pathogenic effect, i.e. they cause disease. According to morphological aspects, protozoa can be divided into four groups. Sporozoa (Apicomplexa) are protozoa that reproduce by sporulation. Sporozoa include, for example, Plasmodium, the causative agent of malaria. Cilia are ciliates. Their cell surface is covered with cilia, which help them to move around. The flagellates, also called flagellates, have flagella for locomotion. Leishmania, trypanosomes and trichomonads, which are harmful to humans, belong to the flagellates. The root-feet (rhizopods) form so-called pseudopodia. Rhizopods include, for example, amoebae and Heliozoa.
Occurrence, distribution, and characteristics
The protozoa of the genus Plasmodium, more specifically the species Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, and Plasmodium vivax, occur mainly in tropical and subtropical areas. The causative agents of malaria are particularly widespread in Africa, in areas south of the Sahara. Other areas of distribution are Southeast Asia, South Asia and Papua New Guinea. Until the mid-20th century, malaria-causing plasmodia were also native to the Mediterranean region in Europe. Plasmodia are usually transmitted to humans by mosquitoes. Suitable vectors are, for example, mosquitoes of the genus Anopheles. Through a bite of the infected mosquito, the pathogen enters the human bloodstream. The protozoan Toxoplasma gondii from the genus Toxoplasma is distributed worldwide. A large part of the population is infected with the parasite. Transmission to humans occurs through eggs of the protozoa. These oocysts are usually excreted with cat feces. Close contact with cats or cleaning the litter box are therefore possible sources of infection for toxoplasmosis. The eggs enter the soil via the feces. Infection is therefore also possible when gardening or eating insufficiently washed vegetables. The protozoa also enter the bodies of farm animals via the soil. The main sources of infection in humans are therefore also insufficiently cooked or raw lamb and pork. Trichomonas vaginalis, a protozoan belonging to the Trichomonadida family, is transmitted exclusively by direct contact. An infection with Trichomonas vaginalis therefore belongs to the sexually transmitted diseases. The pathogen has a worldwide distribution.
Diseases and symptoms
Various pathogens from the plamodia family can cause malaria infection in humans. Through the mosquito’s bite site, a preform of the plasmodia enters the blood and from there into the liver. In the liver, the pathogens mature and divide. The resulting forms of the plasmodia enter the bloodstream and attach themselves to the red blood cells (erythrocytes). They penetrate the erythrocytes and mature there into so-called trophozoites. After multiple divisions, many merozoites are formed, which cause the infected blood cell to burst. The pathogens then spread in the blood and infect further blood cells, so that the cycle starts all over again. The typical malaria fever develops as a result of the disintegration of the red blood cells. It occurs every three to four days.During the rise in fever, the affected person suffers from chills. The fever is accompanied by sweating. In addition to the fever, impaired consciousness, seizures and anemia may develop. In contrast, infection with Toxoplasma gondii, toxoplasmosis, is silent and without symptoms in many cases. However, in patients with a weakened immune system, foci of inflammation may develop in all organs. In addition, there are changes in the nature, seizures or paralysis. In these cases, toxoplasmosis can also manifest as pneumonia or meningitis. Infection with the protozoan Toxoplasma gondii can also be dangerous during pregnancy. Toxoplasmosis during early pregnancy often results in miscarriage. Infections in the second or third trimester sometimes lead to epileptic seizures, cognitive abnormalities, mental retardation, hydrocephalus, chorioretinitis or calcification of the brain vessels in infected children. An infection with the parasite Trichomonas vaginalis is also called trichomoniasis. A typical symptom of such a trichomonad infection is a foul-smelling, frothy discharge. Affected women suffer from a strong burning sensation in the vaginal area. The vagina may be reddened or swollen. If the trichomonads have also affected the urethra, the patients can only urinate with pain. In men, trichomonad infection can also lead to inflammation of the urethra.
