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Popular Science: Male fertility endangered by parasites?

As much as one-third of the world’s population is infected by Toxoplasma gondii nowadays. It is known that toxoplasmosis could be harmful especially for immunocompromised patients and for an unborn fetus if the mother becomes infected during pregnancy. But does the Toxoplasma gondii parasite affect human fertility? A group of experts focused on this question. The research was carried out under the guidance of our student Jana Hlaváčová together with scientists Jaroslav Flegr and Šárka Kaňková from the Department of Philosophy and History of Science, Faculty of Science, Charles University and other specialists in this field.

Toxoplasmosis infection is connected mainly with the consumption of insufficiently washed vegetables, which are contaminated with oocysts from the excrements of infected felines. Consumption of raw or uncooked meat from infected intermediate hosts or contaminated water can also be a source of infection. Another risk of infection is blood transfusions, organ transplants, and unprotected sexual intercourse between an infected man and an uninfected woman. The final host of this parasite is felines, while other warm-blooded animals, including humans, can become intermediate hosts. In intermediate hosts, cysts usually form in the central nervous system, eyes, and skeletal and cardiac muscles, as well as in lungs, liver or kidneys, and they remain infectious. The cysts can persist for the lifetime of the host, as there is no effective treatment for this parasite. Research in laboratory mice has shown that the presence of Toxoplasma gondii has a major effect on changes in their behavior. Infected mice became fearless of the feline odor, and even began to find the smell of cat urine attractive. This mechanism supported further transmission of Toxoplasma gondii, because the mice behavior made it easier for the cat to catch and eat the mouse. And what about people?

In addition to raw meat, contaminated vegetables can also be a source of toxoplasmosis.
Source: Pixabay.com.

Previous research of the Toxoplasma gondii parasite led by Professor Flegr’s team has shown changes in human behavior. For example, they found that toxoplasmosis infection prolongs reaction times, which increases the probability of traffic accidents, for example. They also found out that chronic toxoplasmosis affects testosterone levels, which causes higher sexual activity of males and thus an increased likelihood of transmission of this parasite. Research in 2007 also showed that women who became infected shortly before conception gave birth to sons more often.

In the current research, scientist have focused on the effect of the parasite Toxoplasma gondii on male fertility. A total of 669 men who were treated at the Centre for Assisted Reproduction were examined between 2016 and 2018. Almost 25% of all men were infected. Sperm concentration, motility and morphology were primarily determined, as all these parameters significantly affect male fertility.

Men infected with Toxoplasma gondii have a higher incidence of fertility problems. These men also showed significantly lower sperm concentration and motility. At the same time, however, no effect on sperm morphology and volume was demonstrated. Another examined parameter entering the analyzes was whether the men were smokers or not. The quality of infected men’s sperm was significantly lower in smokers, but not so in non-smokers. Thus, tobacco smoking appears to exacerbate the negative impact of toxoplasmosis on semen quality parameters.

Although uncontrolled population growth associated with overpopulation is currently one of the world’s top problems, there are also increasingly more couples in the world who have a problem with infertility. Many causes for these problems are already known, although some of them are sometimes inexplicable. Even though it was thought that latent toxoplasmosis did not cause significant problems, current research has shown that the presence of Toxoplasma gondii in sperm has a negative impact on male fertility. Research into the effects of this parasite on living organisms yields fascinating findings and shows that it has a greater effect on the humans than was previously believed.

Kateřina Fraindová

Hlaváčová, J., Flegr, J., Řežábek, K., Calda, P., Kaňková, Š. (2021): Association between latent toxoplasmosis and fertility parameters of men. Andrology. 00:1–9. DOI: 10.1111/andr.12969


Published: May 24, 2021 08:55 PM

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