Toxoplasma gondii

Microscopic cysts containing Toxoplasma gondii develop in the tissues of many vertebrates. Here, in mouse brain tissue, thousands of resting parasites (stained red) are enveloped by a thin parasite cyst wall. Photo by Jitender P. Dubey. (Credit:

TURKU, Finland — A sexually-transmitted parasite that up to 50 percent of the population carries may actually make people look more attractive to the opposite sex. Researchers in Finland say Toxoplasma gondii may be responsible for a number of different neurological disorders, including schizophrenia and psychotic episodes. However, its strangest effect may be altering the way others view people carrying the infection.

Study authors found that both men and women infected with T. gondii were rated as being more attractive and healthier-looking than uninfected individuals. The team says this strange connection could have its roots in evolution, theorizing that changes which benefit the host (an animal or human) also benefit the parasite. This symbiotic relationship would help the parasite spread through carriers having more sex.

“In one study, Toxoplasma-infected male rats were perceived as more sexually attractive and were preferred as sexual partners by non-infected females,” study first author Javier Borráz-León from the University of Turku and his team write in the journal PeerJ.

The parasite may actually change how your face looks

While previous studies on T. gondii suggest that the parasite leads to higher testosterone levels in men, others suspect that the parasite manipulates chemicals in a host’s body — including neurotransmitters and hormones.

Manipulating a host’s “phenotype,” Borráz-León says, can lead to far-reaching changing — including how a person actually looks physically.

“Some sexually transmitted parasites, such as T. gondii, may produce changes in the appearance and behavior of the human host, either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts,” the researchers write in their study.

In an experiment including 35 college students (22 men, 13 women) infected with T. gondii and 178 students not carrying the parasite, researchers looked at how symmetrical their facial features were. The team explains that fluctuating asymmetry is a measure of how different the features in your face are. Studies have linked having more symmetry in your face (lowers levels of asymmetry) to better health, stronger genes, and being more attractive to others.

Results show that Toxoplasma-infected participants had lower levels of fluctuating asymmetry than healthy college students. Additionally, young women carrying the parasite had a lower body mass index than their peers. These women also rated themselves as more attractive and reported that they had more sexual partners.

T. gondii
(A) Composite images of ten Toxoplasma-infected women and ten Toxoplasma-infected men, (B) composite images of ten non-infected women and ten non-infected men. (Credit: PeerJ)

“It is possible that the apparently non-pathological and potentially beneficial interactions between T. gondii and some of its intermediate hosts, such as rats and humans are the result of co-evolutionary strategies that benefit, or at least do not harm, the fitness of both the parasite and the host,” study authors conclude.

About Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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  1. Bill says:

    Toxoplasma is NOT sexually transmitted. It is very dangerous in pregnant women and immunocompromised patients.

    1. Captain Fun says:

      It is transmitted by cats. Mice infected with it will actually seek out cats. The Goa’uld parasite in the Stargate shows was modeled after this.

      1. Harry says:

        Mice actually seek out cats who transmit it. The mice hope to have intercourse with the cats but of course, the cats draw them in and eat them. It’s also called the “free lunch syndrome”.

  2. Edgar says:

    Legendary symptoms of the Cat Scratch fever

    1. JA says:

      Cat Scratch is NOT caused by Toxoplasma, it is caused by by Bartonella henselae.

  3. Captain Fun says:

    I should also have mentioned that people infected with it are generally those “crazy cat ladies” you read about. If you like cats, You probably are infected or are just a liberal.

  4. Gary says:

    Or…. maybe the more attractive people have sex more often with more partners leading to contraction of the virus, rather than the virus leading to more attractive people? This is an idiotic study and further proof that “science” isn’t exactly Science any more.

    1. Bryan says:


    2. Mad Mac says:


  5. Prickly Pitt says:

    This research probably was written by an infected person

  6. Bob says:

    Certainly seems like a stupid conclusion. How would a virus in one person affect the perception of another? If it is sexually transmitted, it would seem more obvious that those who can transmit it have more sex. Thus probably are more attractive already.

    1. toxobuttmosis says:

      You have it backwards it affects phenotype expression that contributes to features that are already what we find attractive as a species such as androgenic features in men and symmetry. It sounds like if it’s contracted earlier in life it may actually make you slightly better looking. XD

  7. djsmps says:

    Where might I inquire to get one of these parasites?

    1. Bjorleif says:

      A good start would be to get a cat. They are the only animals where the parasite can undergo sexual reproduction.

    2. Nada says:

      Go forage in your cat’s litterbox. The parasite is commonly spread to humans via exposure to infected cat feces.

    3. duncan Hindz says:

      cleaning the cat box, be sure to not wear gloves and then eat with your hands.

  8. Blue Thunder says:

    Clostridium botulinum does the same thing.

  9. Wolfiedude says:

    Beer goggles do the same thing.

  10. NurseJoan says:

    Not sure about these results. Smallish study sample & subjective. However, T. Gondii IS an STD & also spread by touching excreta of infected animals (or humans). Not sure why some of the reader comments are indicating this contagious parasite is not sexually transmissable. It’s very dangerous to pregnant women & their unborn babies (hydrocephalus, microcephaly, etc.); that’s why many OBs advise expectant moms to have someone else clean litter box. Check out CDC website.

  11. Trevor says:

    Toxoplasmosis Gondii is also transmitted in raw or under-cooked meat. It is more common in cultures which consume raw meat, such as France and Thailand — both of which have relatively-high road-death rates … another ‘risk-taking’, behaviour-modification characteristic of the parasite. A premature death, in animals at least, meant that evolutionarily their meat — and the parasite — would continue its life cycle.