Flagellates are single-celled organisms that travel by flagella. Some flagellates can cause disease in humans.
What are flagellates?
Flagellates are eukaryotic living organisms. Eukaryotes are all those living things that have cells with a nucleus. Flagellates have exactly one cell with a nucleus, since they belong to the unicellular organisms. Flagellates owe their name to their flagella. In technical language, these whips, which serve for locomotion, are also called flagella. But the protozoa do not only use their flagella for locomotion. With the help of the small projections, they can also anchor themselves to structures or fetch food particles. The group of flagellates was first described in 1866 by botanist Karl Moritz Diesing. However, final recognition did not occur until the end of the 20th century as a genus of protozoa. The flagellates that are pathological to humans can be divided into three groups: Trypanosomes, Leishmania, and Trichomonads.
Occurrence, distribution, and characteristics
Trypanosomes are protozoa found mainly in fluid tissues. They are found in the blood, lymph, or cerebrospinal fluid. Trypanosomes can also live in pericardial fluid. Trypanosomes can be transmitted by insects such as bugs. Pathogen reservoirs are domestic and wild mammals. The bugs ingest the pathogens while sucking blood and excrete infectious forms of the flagellates in their feces. The trypanosomes then enter the human body through micro-injuries. Transmission is also possible through contaminated blood transfusions, through breast milk and placenta, and through infectious human feces. Leishmania is also transmitted by insects. The main vectors are sandflies of the genus Phlebotomus. The main areas of distribution of the pathogens are India, Africa, China, Iraq, and the southwestern Arabian Peninsula. Trichomonads, on the other hand, are not transmitted by insects or animals. Infection occurs during unprotected sexual intercourse via vaginal fluid or semen.
Diseases and symptoms
Trichomonads, especially the species Trichomonas vaginalis, can cause infectious diseases of the reproductive organs and urinary tract. The moisture and pH in the vagina and urethra provide optimal living conditions for the flagellates, allowing them to survive there for extended periods of time. In women, colonization by trichomonads leads to severe inflammation with purulent discharge. A burning sensation develops in the entrance area of the vagina. Sexual intercourse is possible only with severe pain. The purulent discharge smells unpleasantly fishy. This is due to the fact that the infection is often associated with colonization of the vagina by Gardnerella vaginalis and various stool bacteria. Inflammation of the vagina and urethra may be accompanied by lower abdominal pain. Men infected with trichomonads usually show no symptoms. Occasionally, the urethritis causes burning during urination and ejaculation. Purulent discharge from the urethra may also occur. It should be noted that women with trichomonad infection have a higher risk of contracting HIV due to the mucosal defects. For HIV-infected individuals, trichomonad infection increases the risk of passing the virus to other sexual partners. However, trichomonads can colonize not only the genital area but also the intestinal area (bowel). Thus, the pathogen Trichomonas intestinalis can cause enterocolitis. The flagellate Leishmania, on the other hand, causes leishmaniasis. Possible causative agents of leishmaniasis are Leishmania brasiliensis, Leishmania infantum and Leishmania tropica. In total, there are 15 different human pathogenic leishmania. Leishmaniasis can be divided into cutaneous, mucocutaneous and visceral leishmaniasis. In cutaneous leishmaniasis, the infection is confined to the skin. Thus, spots form at the bites of the sandflies, which can subsequently turn into small blisters. These enlarge quite quickly and become bumps, which then ulcerate. In the mucocutaneous form, there is severe inflammation of the face. The nasal mucosa is also affected, so that a chronic rhinitis can develop, which is accompanied by destruction of the nasal mucosa.The visceral form is characterized by the involvement of internal organs. There is fever, swelling of the spleen and liver, anemia, diarrhea, and hyperpigmentation of the skin. The third major human pathogenic group of flagellates are trypanosomes. The most important representatives are Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense, and Trypanosoma cruzi. Trypanosoma cruzi is the causative agent of Chagas disease. Chagas disease is divided into an acute and a chronic phase. In the acute phase, fever, skin lesions, and generalized inflammation of the lymph nodes occur. It is not uncommon for the acute phase of Chagas disease to be misinterpreted as a normal flu-like infection. During the chronic phase, various organs enlarge. The gastrointestinal tract shows progressive paralysis, causing patients to suffer from weight loss, dysphagia, and chronic constipation. Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense are both causative agents of sleeping sickness. During the first week after infection with the pathogen, a swelling with a vesicle in the center develops at the injection site. This skin condition is called trypanosome chancre. One to three weeks later, patients develop fever, chills, swelling and rashes. The second stage, the meningoencephalitic phase, is characterized by seizures, sleep disturbances, impaired coordination and weight loss. In the final stage of the disease, patients fall into a sleep-like stupor. After several months to years, sleeping sickness is usually fatal.
