Scientists discover ‘Trojan Horse’ virus hidden in common human parasite

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An international team of researchers led by the University of Toronto has discovered a new RNA virus hiding within a common human parasite.

This virus, named Apocryptovirus odysseus, was found along with 18 related viruses through a detailed analysis of human neuron data.

The goal was to understand the link between RNA viruses and neuroinflammatory diseases.

The study suggests that this virus worsens the effects of toxoplasmosis, a disease caused by the parasite Toxoplasma gondii.

“We found A. odysseus in human neurons using the open-science Serratus platform, which searches through over 150,000 RNA viruses,” said Purav Gupta, the study’s first author and an undergraduate student at the University of Toronto’s Donnelly Centre for Cellular and Biomolecular Research.

Serratus identifies RNA viruses by detecting an enzyme called RNA-dependent RNA polymerase, which helps the virus replicate and spread the infection. This study was recently published in the journal Virus Evolution. T.gondii is a widespread parasite, infecting about one-third of the global population. It can live in various cell types, including neurons, forming cysts inside them.

The parasite spreads when infected cells burst. Most T. gondii infections go unnoticed, but the disease can be severe for pregnant women and people with weakened immune systems.

“We believe the virus and parasite work together to cause disease in humans.

The virus hides inside the parasite, like a soldier in a Trojan Horse, to enter the human brain,” Gupta explained. “Our research is the first to connect toxoplasmosis to a virus.”

The newly discovered A. odysseus virus is found in two highly virulent strains of T. gondii, named RUB and COUGAR. RUB has been found in French Guinea, causing severe fever and organ failure, while COUGAR has been linked to ocular toxoplasmosis, a leading cause of infectious blindness, in British Columbia.

These strains have been found in different locations at different times, showing their potentially wide-reaching effects.

Symptoms of toxoplasmosis can become worse due to a hyperactive immune response. The virus-carrying parasite triggers this response when the immune system detects the virus’s foreign RNA.

“The group of 19 RNA viruses we found are strong indicators of parasitic infection,” said Artem Babaian, the study’s principal investigator and an assistant professor of molecular genetics at the Donnelly Centre and the Temerty Faculty of Medicine.

“It’s clear that the A. odysseus virus could be a valuable marker for identifying severe toxoplasmosis and other parasitic infections. The next step is to test whether treating a parasite’s viruses could help manage symptoms caused by parasitic infections.”

Babaian also noted that zoonotic viruses, which infect other living things before reaching humans, are expected to cause most new infectious diseases in humans. “This study highlights the importance of looking beyond viruses that infect humans directly and considering the broader virome,” he said.

This discovery could lead to better understanding and treatment of diseases caused by parasitic infections, improving health outcomes for affected individuals worldwide.