The most successful parasite in the world

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Focus on Acta Physiologica

Review: Xiao, J., and R. H. Yolken. “Strain hypothesis of Toxoplasma gondii infection on the outcome of human diseases.” Acta Physiologica 213.4 (2015): 828-845.

Toxoplasma gondii is a very common protozoan parasite affecting approximately one billion people world wide. Therefore a solid understanding of its virulence, diversity and life cycle is paramount.

When is toxoplasmosis dangerous?

A Toxoplasma infection can be everything from asymptomatic to very severe and may lead to death if the patient is immunodeficient (when the immune system is not functioning properly). Immunodeficiency develops in individuals with AIDS, cancer (due to immunosuppressive medications) or after organ transplants. The parasite is thus very problematic in sub Saharan Africa where both AIDS and the toxoplasmosis are widely spread. Furthermore, Toxoplasma infections in pregnant women may pose a risk to the child.

If a patient is immunodeficient medical intervention is necessary. Otherwise, the infection often subsides after a few months during which the patient often experience swollen lymph nodes and flu-like symptoms. Unfortunately, infection by this parasite can result in reoccurring bouts. The nasty habit of Toxoplasma to form cysts in neural tissues has been linked with a variety of human psychiatric disorders such as schizophrenia, dementia and depression.

As for most parasites, the life cycle of Toxoplasma involves secondary hosts; in this case mainly cats and members of the cat family. This is why it is advised that pregnant women should refrain from cuddling cats.

The life cycle of Toxoplasma gondii (image credit: LadyofHats)

The life cycle of Toxoplasma gondii (image credit: LadyofHats)

How do I prevent Toxoplasma infections?

The main routes of Toxoplasma infection is drinking contaminated water, ingestion of undercooked meat and contact with contaminated soil. Infection apparently also frequently occurs when people are cleaning their cat litter boxes. Mother-child transmission during pregnancy and through blood transfusions may also occur though the latter is extremely rare.

Toxoplasma gondii, the most successful parasite in the world

Toxoplasma gondii is not the only human parasite protozoan in the phylum Apicomplexa. Other famous members are Plasmodium spp. (malaria) and Cryptosporidium spp. (causes diarrhea and other gastrointestinal symptoms). However, despite the success of the malaria parasite, T. gondii beats malaria in number of people infected. Therefore, one could call Toxoplasma gondii the most successful eukaryotic (multi-cellular) parasite in the world.

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It has been discovered that there is great variation in Toxomplasma gondii genotypes (different genetic versions of the same species) and that these have different degrees of virulence. Investigations into this may aid in the understanding of this  wide spread parasite and enable more targeted medical interventions, particularly in patients that have immunodeficiency.

Suggested reading

In a recent review in Acta Physiologica, Xiao and Yolken discuss methods of Toxoplasma gondii strain determination as well as how virulence (how easy the illness is spread) and the severity of the illness is determined by said strains/genotypes.

If you would like to read more, click HERE to access the review article by Xiao and Yolken. It is not yet open access, so if you are at an institution you will need to use your credentials to get access.

This is the first in a series of article-highlights from the high ranking peer reviewed scientific journal Acta Physiologica (impact factor 4.38).

Xiao, J., and R. H. Yolken. “Strain hypothesis of Toxoplasma gondii infection on the outcome of human diseases.” Acta Physiologica 213.4 (2015): 828-845.

Governmental fact sheet on toxoplasmosis (HERE)

Posted in Acta Physiologica, Biology, Medicine, The Biology of Disgusting and tagged , , .

Dr. Anna

Dr. Anna Zakrisson is a multifaceted biologist with degrees from world-renowned institutions such as Cambridge University, U.K. and the Max-Planck Institute in Germany. She has published a range of high-ranking scientific papers and crossed oceans on research vessels. She runs The Imaginarium science blog and YouTube channel and speaks English, German and Swedish fluently.

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