Toxoplasmas are understood to be parasitic unicellular organisms whose end hosts are cats. The only known representative of toxoplasma is Toxoplasma gondii.

What are Toxoplasma?

Toxoplasma also carry the name Toxoplasma gondii. So this species is the only species of the genus. The arched protozoa leads a parasitic lifestyle and uses cats as end hosts. Intermediate hosts may also be other mammals, birds or humans. The toxoplasmas are related to the plasmodium from which the malaria is transmitted.

Toxoplasma gondii is able to multiply in human cells. Thus, in about one third of all people antibodies to toxoplasma. However, a disease caused by the unicellular organisms such as toxoplasmosis occurs only rarely. This infectious disease is basically considered harmless. However, there are risks for pregnant women, their unborn children and people who have a weakened immune system.

The discovery of Toxoplasma gondii as a parasite occurred in 1907 in Tunisia. The discoverers of the single-celled, Manceaux and Nicolle, named it Toxoplasma because of its particular shape, which resembled a crescent moon.

As pathogens in humans, however, the toxoplasmas were identified many years later. In 1948, Albert Sabin (1906-1993) succeeded in developing a serological test called the Dye Test, which functioned with antibodies. This highlighted the worldwide spread of toxoplasma in the human body. In Germany alone, 50% of all Germans have toxoplasma. The likelihood of infection increases with increasing age and is around 70 percent in people over 50.

Occurrence, distribution & characteristics

In the human body, which, however, forms only an intermediate host, the Toxoplasmen get mainly by infected meat. Similarly, contact with an infested cat feces may lead to infection. In the process, Toxoplasma gondii enters the organism and crosses the stomach. Finally, the parasite enters the intestinal wall via the digestive tract. From this point he has the opportunity to colonize via bloodstream or lymphatic system other tissues or organs and to penetrate into the body cells. This usually happens in the central nervous system, the muscles and parts of the immune system.

Following the successful colonization, the toxoplasma can multiply by asexual division. This leads to the formation of trachyzoites. As the defense system defends itself against the parasites, it often causes the formation of cysts that provide protection for the unicellular. The cysts show up primarily in the musculature of the heart and skeleton, in the retina, the brain and the wall of the uterus. In the cysts again occur thousands of individual parasites, which can survive there without damage. Health problems do not cause them.

Sexual propagation of the toxoplasma is possible only in the gut of cats or similar animals that are the final host of the parasites. The formation of oocysts (parasitic eggs) takes place, which spread through cat feces. The oocysts can evolve within two to four days and become infectious for other animals and humans. This condition lasts for several months. If the environment is wet, the risk of infection is even up to five years.

The average size of the oocysts is about 11 microns. The oocysts contain two sporocysts and four sporozoites each. Frosts survive the parasites well, but heat gets less. The hatching of the sporocysts then takes place in an intermediate host.

Transmission to humans can be achieved by eating raw or under-heated minced meat in which oocysts are present. Meat from game, pigs, goats and sheep as well as from raw sausage are considered risky. In addition, the toxoplasmas sometimes occur in raw fruits and vegetables that have not been washed. Furthermore, humans can become infected with the pathogen through the cat droppings, which are found in cat litter, in the garden or in a sandbox.

Diseases & complaints

If Toxoplasma gondii gets into a human body, toxoplasmosis is possible. Such an infection occurs in most people. Almost always there are no symptoms. However, some people suffer from symptoms that are similar to flu. These include joint and muscle pain, swollen lymph nodes and fever.

In rodents toxoplasmas even cause behavioral changes. The affected animals, for example, no longer have a natural aversion to the smell of cats, which prolongs the life cycle of the parasites. Even after a cure for Toxoplasma infection, mice no longer feel shy of the smell of cats. Also in humans, any behavioral changes caused by toxoplasma are under discussion.

For pregnant women, infection with Toxoplasma gondii is considered risky. This is especially true if it is a primary infection that leads to a disruption of the development of the unborn child. In Germany, the congenital form of toxoplasmosis must even be reported. In order to avoid infection with toxoplasma it is recommended for pregnant women not to consume insufficiently roasted meat. In addition, gardening and contact with litter boxes should be avoided and the hands should be washed regularly before meals.

The toxoplasma in pregnancy can be effectively combated with antibiotics. Helpful is a combination of sulfonamides or spiramycin with pyrimethamine, which kills the parasites. A licensed vaccine against Toxoplasmen does not exist so far.

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