TAMPA, Fla. (March 20, 2026) – It infects nearly one-third of the global population, yet its microscopic size makes the Toxoplasma gondii parasite difficult for scientists to study.
A recent University of South Florida-led study published in Bio-Protocol promises to help scientists better understand how Toxoplasma gondii functions, paving the way for future treatments.
Infectious disease researchers at the USF Health Morsani College of Medicine adapted a fluorescent imaging system typically used to study human cells, enabling real-time observation the parasite’s growth, a promising breakthrough against an organism that that infects both humans and animals.
An unusual cell cycle
Toxoplasma typically spreads through uncooked meat and contaminated produce. When the parasite enters the human body, it causes toxoplasmosis, an infection that is often mild, but can be serious for pregnant women and people with weakened immune systems. It can be treated if caught within the first two weeks of exposure.
“Though the parasite can be repressed in the acute stage, it requires drugs that can be toxic if taken long term,” said study co-author Elena Suvorova, an associate professor who studies infectious disease and international medicine in USF’s Center for Global Health and Inter-Disciplinary Research.
“If you can’t catch toxoplasmosis during this time, the parasite turns chronic,” Suvorova said. “In this stage, it hides from the immune system and forms cysts in the brain, for which there are currently no cures.”
Developing improved treatments has been challenging in part because of the parasite’s unusual cell cycle. A typical cell cycle begins with the cell growing larger before making a complete copy of its DNA. Once everything is prepared for division, the cell splits into two identical parts.
“Toxoplasma doesn’t follow this standard pattern,” said co-author Mrinalini Batra, a research scientist in Suvorova’s lab. “Scientists knew it had to go through similar stages because it reproduces, but they didn’t know how those stages were arranged or whether they even existed in the same way as they do in human cells. That made it hard to understand how this parasite grows and spreads.”
The goal of the researchers wasn’t just basic curiosity, but part of a larger effort to eventually stop the parasite from multiplying. To do that, the team needed to map out how its cell cycle works and in what order.
Targeting Toxoplasma through fluorescence
To tailor their fluorescent imaging model for Toxoplasma, the researchers first identified proteins that appear in specific growth stages of the parasite. These proteins also needed to be in structures large enough to visualize, such as the cell’s nucleus, and they required fluorescent colors bright enough to stand out in such a tiny organism under a microscope.
Because Toxoplasma lacks many common proteins found in human cells, the process required extensive trial and error. The team tested different parts of the parasite using fluorescent red and green tags, but many markers either failed to glow brightly enough or didn’t appear in sufficient amounts to be useful.
As the team tested multiple combinations, they ultimately identified a protein called PCNA1, located in the parasite’s nucleus, that naturally shifts as the organism progresses through its growth cycle.
“When we attached two copies of a bright neon green tag to this protein, the signal became strong and clear,” Batra said. “This allowed us to determine the parasite’s stage simply by watching how the glowing protein behaved in the cell cycle. For the first time , researchers were able to clearly map Toxoplasma’s cell cycle.”
The discovery shows how the parastate moves normally through the first part of its cell cycle, but the rest of its growth stages overlap instead of occurring sequentially.
“These latter stages are similar to a fork’s structure,” Suvorova said. “Toxoplasma’s cell cycle begins with one straight handle and then several prongs that branch off, allowing as many as three cell cycle phases to occur simultaneously. This unusual pattern helps the parasite multiply rapidly and evade the host’s immune system before forming cysts in the brain.”
Now that Toxoplasma’s cell cycle has been mapped through fluorescence, the researchers are working to identify weak points in the parasite that could prevent it from multiplying. They are also testing how different drugs affect specific stages of the cycle in hopes of developing safer and more effective treatments .
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About the University of South Florida
The University of South Florida is a top-ranked research university serving approximately 50,000 students from across the globe at campuses in Tampa, St. Petersburg, Sarasota-Manatee and USF Health. In 2025, U.S. News & World Report recognized USF with its highest overall ranking in university history, as a top 50 public university for the seventh consecutive year and as one of the top 15 best values among all public universities in the nation. U.S. News also ranks the USF Health Morsani College of Medicine as the No. 1 medical school in Florida and in the highest tier nationwide. USF is a member of the Association of American Universities (AAU), a group that includes only the top 3% of universities in the U.S. With an all-time high of $750 million in research funding in 2025 and as a top 20 public university for producing U.S. patents, USF uses innovation to transform lives and shape a better future. The university generates an annual economic impact of nearly $10 billion for the state of Florida. USF’s Division I athletics teams compete in the American Conference. Learn more at www.usf.edu .
BIO-PROTOCOL
Imaging analysis
Cells
Assessing the Toxoplasma Tachyzoite Cell Cycle Phases Using Fluorescent Ubiquitination-Based Cell Cycle Indicator
20-Jan-2026