Toxoplasmas are parasitic protozoa whose final host is cats. The only known representative of toxoplasmas is Toxoplasma gondii.
What are toxoplasmas?
Toxoplasmas also carry the name Toxoplasma gondii. Thus, this species forms the only species of the genus. The arch-shaped protozoan leads a parasitic lifestyle and uses cats as definitive hosts. Other mammals, birds, or humans may also serve as intermediate hosts. Toxoplasmas are related to Plasmodium, from which malaria is transmitted. Toxoplasma gondii is able to multiply in human cells. Thus, antibodies against Toxoplasma are found in about one third of all humans. However, disease caused by the protozoa, such as toxoplasmosis, rarely occurs. This infectious disease is generally considered harmless. However, there are risks for pregnant women, their unborn children and people with a weakened immune system. Toxoplasma gondii was discovered as a parasite in Tunisia in 1907. The discoverers of the protozoan, Manceaux and Nicolle, gave it the name Toxoplasma because of its peculiar shape, which resembled a crescent moon. However, Toxoplasma was not identified as a human pathogen until many years later. In 1948, Albert Sabin (1906-1993) succeeded in developing a serological test, which was named the Dye test and worked with antibodies. This revealed the worldwide distribution of toxoplasmas in the human body. In Germany alone, toxoplasmas are present in 50 percent of all German citizens. The likelihood of infection increases with age and is about 70 percent in people over 50.
Occurrence, distribution, and characteristics
Toxoplasmas enter the human body, which, however, forms only an intermediate host, primarily through infected meat. Likewise, contact with infested cat feces can lead to infection. In this case, Toxoplasma gondii enters the organism orally and passes through the gastric passage. Finally, the parasite enters the intestinal wall via the digestive tract. From this point, it has the opportunity to colonize other tissues or organs via the bloodstream or lymphatic system and to enter the body’s cells. This usually takes place in the central nervous system, the muscles and parts of the immune system. Following successful colonization, the toxoplasmas can multiply by asexual bipartition. This leads to the formation of trachyzoites. As the defense system fights back against the parasites, cysts often form, providing protection for the protozoa. The cysts appear primarily in the muscles of the heart and skeleton, in the retina of the eye, the brain and the wall of the uterus. In turn, thousands of individual parasites occur in the cysts and can survive there without harm. They do not cause health problems. Sexual reproduction of toxoplasmas is possible only in the intestines of cats or similar animals, which are the final hosts of the parasites. During this process, the formation of oocysts (parasite eggs) takes place, which are further spread through cat feces. The oocysts can develop further within two to four days and thus become infectious for other animals and humans. This condition lasts for several months. If the environment is moist, the risk of infection is even up to five years. The average size of the oocysts is about 11 micrometers. The oocysts contain two sporocysts and four sporozoites each. The parasites survive frost well, but heat does not agree with them as much. The hatching of the sporocysts then takes place in an intermediate host. Transmission to humans can occur through the consumption of raw or insufficiently heated minced meat containing oocysts. Meat from game, pigs, goats, and sheep, as well as raw sausage, are also considered risky. In addition, toxoplasmas are sometimes found in raw fruits and vegetables that have not been washed. Furthermore, humans can become infected with the pathogen through cat feces found in cat litter, in the garden or in a sandbox.
Diseases and complaints
If Toxoplasma gondii penetrates into the organism of humans, toxoplasmosis is possible. Such an infection occurs in most people. Almost always, however, there are no symptoms. Some people, however, suffer from symptoms similar to flu.These include joint and muscle pain, swollen lymph nodes, and fever. In rodents, the toxoplasmas even cause behavioral changes. For example, the infected animals no longer naturally shy away from cat odors, which prolongs the parasites’ life cycle. Even after Toxoplasma infection is cured, mice no longer experience shyness from cat odor. Possible behavioral changes caused by Toxoplasma are also under discussion in humans. For pregnant women, infection with Toxoplasma gondii is considered risky. This is especially true if it is a first-time infection that leads to a disturbance in the development of the unborn child. In Germany, the congenital form of toxoplasmosis must even be reported. To avoid infection with toxoplasma, it is recommended for pregnant women not to consume insufficiently cooked meat. In addition, gardening and contact with litter boxes should be avoided, and hands should be washed regularly before meals. Toxoplasma in pregnancy can be effectively combated with antibiotics. A combination of sulfonamides or spiramycin with pyrimethamine is considered helpful, which kills the parasites. To date, there is no approved vaccine against toxoplasma.
