FEB 21, 2016 8:25 AM PST

How the "Toxo" Parasite Sneaks into the Brain

WRITTEN BY: Xuan Pham

A staggering 30-50% of the world’s population is estimated to be infected with the parasite Toxoplasma gondii. This parasite is known to invade the brain and affect behaviors, but until recently, researchers had no idea how the organism crossed the blood-brain barrier. Using a powerful multi-photon imaging technique, researchers record for the first time how “Toxo” hijacks into the brain by way of endothelial cells.
 
Toxoplasma gondii, also known colloquially as “Toxo,” can infect virtually any warm-blooded animal. However, the parasite can only undergo sexual reproduction in domesticated cats, and so most people know Toxo as the disease that humans can get from changing and accidentally ingesting contaminated cat litter.
 
Toxoplasmosis, the disease caused by Toxo, can be life threatening for people with compromised immune systems, such as infants, cancer patients, or HIV/AIDS patients. In addition, pregnant women can transmit the parasite to their unborn baby. Toxo invasion of the brain has been linked to adverse behavioral changes, though no one really knew how the parasite sneaked across the protective barrier in the brain.
 
"Crossing the blood-brain barrier is a rare event in part because this structure is designed to protect the brain from pathogens," said Christopher Hunter, senior study author and the Mindy Halikman Heyer President's Distinguished Professor at Penn Vet. "And yet it happens and we have now been able to visualize these events. It's something that no one had seen before."
 
Using innovative imaging techniques with the multi-photo microscope, the team at Penn filmed exactly how Toxo invades the brain. The team used mice engineered to have green fluorescent endothelial cells, which make up the lining of blood vessels. They then infected these mice with a modified form of Toxo that glows red.
 
The video shows how Toxo squeezes its way in through the endothelial cells. And after two weeks, the researchers saw Toxo bursting out of infected endothelial cells and invade into the brain tissues next to the green cells.
 
The team also performed subsequent experiments, which showed that Toxo invasion of the blood-brain barrier happens independent of other carrier cells, dispelling the so-called Trojan horse hypothesis.
 
Another interesting finding was the surprising number of Toxo parasites that existed as free floaters in the blood. They found that free parasites in the mouse blood made up about a third of the total parasite load. But the good news is that this parasite load in the blood was gone in about 10 days time, suggesting a transient nature.
 
"From a treatment perspective," Hunter said, "that means if a pregnant woman gets infected for the first time, there is a fairly short period of time when the parasite can cross the placenta and affect the fetus. That tells us that targeting these stages in the blood during this narrow window could be effective at preventing congenital transmission."
 
Now that scientists know how Toxo invades the brain, they have better targets for treating and preventing the parasite infection. This mode of action could also give scientists fresh insight as to how Toxo influences human behaviors, and even cause psychiatric diseases like schizophrenia as some research have suggested. The mechanisms behind Toxo’s invasion may also illuminate how other pathogens breach our defense to the brain.
 
Additional sources: Nature MicrobiologyEurekAlert!
About the Author
  • I am a human geneticist, passionate about telling stories to make science more engaging and approachable. Find more of my writing at the Hopkins BioMedical Odyssey blog and at TheGeneTwist.com.
You May Also Like
NOV 12, 2020
Clinical & Molecular DX
Study Shows 1 in 5 COVID Tests Are False Positives
NOV 12, 2020
Study Shows 1 in 5 COVID Tests Are False Positives
  A study published in The BMJ has brought to light that the rapid finger-prick COVID-19 test may not be quite as r ...
NOV 18, 2020
Clinical & Molecular DX
Nerve Damage as a Prognostic Marker for Rare Autoimmune Disease
NOV 18, 2020
Nerve Damage as a Prognostic Marker for Rare Autoimmune Disease
Researchers have identified a new prognostic biomarker for Guillain-Barré syndrome (GBS), a rare autoimmune disor ...
NOV 25, 2020
Cancer
Using RNA to Diagnose HPV Associated Cancer
NOV 25, 2020
Using RNA to Diagnose HPV Associated Cancer
Diagnostic tools are critical to modern medicine. They might be less exciting than a good therapy or drug, but doctors a ...
DEC 01, 2020
Cardiology
The Benefits of Exercise on Adipokine Levels for Post-Menopausal Women
DEC 01, 2020
The Benefits of Exercise on Adipokine Levels for Post-Menopausal Women
The benefits of a healthy lifestyle don’t just stop when you get older. Being active has been shown to improve pos ...
DEC 14, 2020
Clinical & Molecular DX
STR Genotyping for Human Sample Identification
DEC 14, 2020
STR Genotyping for Human Sample Identification
Human sample identification is an essential element of many research projects employing human cells, tissues, or mixture ...
DEC 16, 2020
Clinical & Molecular DX
Gene Marker PACS a Punch for Cervical Cancer Treatments
DEC 16, 2020
Gene Marker PACS a Punch for Cervical Cancer Treatments
In cervical cancer, mutations in healthy cells cause cells to grow and multiply uncontrollably, invading surrounding tis ...
Loading Comments...