One of the world’s most effective parasites doesn’t spread through mosquito bites or undercooked snails — but through the common house cat.

Called toxoplasma gondii, the parasite is a single-cell organism that primarily spreads to humans via cat turds, but also through raw or undercooked meat, contaminated water, and from a mother to her fetus. Its symptoms range from mild aches and pains to debilitating neural impairment, which makes it all the more horrifying to learn that it currently has no cure.

According to a paper published in the journal PLOS Neglected Tropical Diseases, as spotted by Gizmodo, the infection of this protozoan parasite known as “toxoplasmosis” is “one of the most common parasitic infectious diseases affecting humans,” and the number one “intraocular infection” — meaning inside the eyeball — on the planet.

In the research paper, a team of international scientists makes the case that toxoplasmosis meets the criteria for recognition as a “neglected tropical disease.” That designation would free up significant resources for further studies and the development of public health policy “to address the substantial burden” the parasite has on human health.

And it is substantial. Some researchers estimate that roughly one-third of humanity —roughly two billion people — is infected with the parasite, including about 60 million people in the United States alone. Though a healthy immune system can keep the worst impacts of the eye-ball dwellers in check, worst-case scenarios can include significant damage to the eyes, brain, and nervous system.

As Gizmodo notes, some research has suggested that long-term toxoplasmosis leads to personality changes in infected rodents, wolves, and humans; in the latter case, it could even raise the risk of schizophrenia. One 2020 survey of the parasite’s impact on cognition notes that the presence of the parasite in the host can upend the brain’s ability to process dopamine, “which may alter cognitive, behavioral, and motor activities.”

Justine Smith, ophthalmologist at Flinders University and one of the study’s co-authors told Gizmodo that “there is no commercially available vaccine against toxoplasmosis. And the drugs we give patients can limit a flare-up of the disease, but there is no drug that cures it at this point.”

Firmly establishing toxoplasmosis as a neglected tropical disease is key to combatting the disease, the study’s authors say, especially across the global south.

Given that poor populations are already more susceptible to parasitic infection, toxoplasmosis represents “a disproportionate burden” to those living in poverty. Because it can be passed from a pregnant mother to her child, the researchers describe a horrifying scenario where the poorest families in the world become trapped in a parasitic loop.

“Infants who survive congenital infection face lifelong health consequences, such as visual and neurologic impairments, which undermine school performance, employment opportunities, and economic participation,” the paper reads. “These negative outcomes contribute to the poverty trap that exists for other [neglected tropical diseases]: families already facing socioeconomic vulnerability absorb the long-term costs of disability, repeated medical visits, and lost income.”

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