MAR 18, 2015 04:17 PM PDT

Mechanism May Help Parasites Manipulate Their Hosts

WRITTEN BY: Judy O'Rourke
Rodents infected with a common parasite lose their fear of cats, resulting in easy meals for the felines. Now, Indiana University School of Medicine researchers have identified a new way the parasite may modify brain cells, possibly helping explain changes in the behavior of mice -- and humans.

The parasite is Toxoplasma gondii, which has infected an estimated one in four Americans and even larger numbers worldwide. Not long after infecting a human, Toxoplasma parasites encounter the body's immune response and retreat to a latent state, enveloped in hardy cysts that the body cannot remove.
Brain astrocyte cells
Before entering that inactive state, however, the parasites appear to make significant changes in some of the brain's most common, and critical cells, the researchers say. The team, led by William Sullivan, PhD, professor of microbiology and immunology, reported two sets of related findings about those cells, called astrocytes, March 18 in the journal PLOS ONE.

Astrocytes are found throughout the brain and are involved in a variety of important brain structures and activities. Sullivan and his team evaluated the proteins in astrocyte cells and found 529 sites on 324 proteins where compounds called acetyl groups are added to proteins, creating a map called an "acetylome," much like a map of all the genes in a particular species is known as its "genome." In addition, 277 sites on 186 of the proteins had not been reported in previous studies of other types of cells. This process of acetylation can alter the function, location or other aspects of those proteins in the cells, providing new insight into how these cells operate in the brain.

Having created the first acetylome for astrocytes, the researchers then found a significant number of proteins that were acetylated differently in brain tissue infected with Toxoplasma parasites.

"We don't know the impacts of these changes yet, but these discoveries could be particularly significant in understanding how the parasites persist in the brain and how this 'rewiring' could affect behavior in both rodents and humans," Sullivan says.

In a separate article, newly published in the March 2015 issue of the popular science magazine Scientific American MIND, Sullivan and IU School of Medicine colleague Gustavo Arrizabalaga, PhD, professor of microbiology and immunology, describe research by others dating back to the 1980s showing that rodents infected with Toxoplasma behave differently, including not only being unafraid of cat odors, but actually attracted to them. In effect, research suggests, Toxoplasma modifies the host rodents' brains so that the animals will be eaten and the parasites can make their way to the cat intestinal system -- the only place where Toxoplasma can sexually reproduce.

Intriguingly -- and much more speculatively, Arrizabalaga and Sullivan warn -- some research has suggested that Toxoplasma infection could alter human behavior, and that changes could vary by gender. One study found that infected men tend to be introverted, suspicious, and rebellious, while infected women tended to be extraverted, trusting, and obedient. Others have suggested an association with schizophrenia.

"The studies in humans have been relatively small and are correlative. In contrast, the behavioral changes seen in mice infected with Toxoplasma are much better characterized, although we still don't know the mechanisms the parasite employs to alter host behavior," Sullivan says. "But our analysis of the astrocyte acetylome changes could move us toward better understanding of Toxoplasma's actions and the implications for behavioral impacts."

Initial Toxoplasma infection generally causes symptoms similar to the flu, while the latent form of infection has little physical impact on healthy people. However, the parasites can become active again and cause tissue damage in people with compromised immune systems, such as patients receiving chemotherapy or infected with HIV.

In addition, if a woman's initial infection with Toxoplasma occurs while she is pregnant, miscarriage or birth defects can result.

Humans can become infected if they don't wash carefully after collecting cat litter containing Toxoplasma. Gardens and other areas frequented by wild and feral cats can become reservoirs for Toxoplasma, so experts recommend using gloves and masks when working in such areas. Unwashed vegetables and undercooked meats can also lead to Toxoplasma infection.

[Source: Indiana University]
About the Author
  • Judy O'Rourke worked as a newspaper reporter before becoming chief editor of Clinical Lab Products magazine. As a freelance writer today, she is interested in finding the story behind the latest developments in medicine and science, and in learning what lies ahead.
You May Also Like
JUL 17, 2018
Immunology
JUL 17, 2018
Powering up the Elderly's Immune System
Use of drugs that inhibit the TORC1 pathway has bolstered the immune systems of the elderly, leading to a decrease in potentially deadly infections such as pneumonia and influenza....
AUG 02, 2018
Immunology
AUG 02, 2018
Chronic Infections Outsmart the Immune System
Chronic parasitic infection shown to take advantage of a mechanism to sustain infection and induce death of white blood cells essential to immune response....
AUG 04, 2018
Microbiology
AUG 04, 2018
The Viral Link to Irritable Bowel Disease
We now know of the importance of the microbiome, but most of the research focus has been on bacteria....
AUG 06, 2018
Immunology
AUG 06, 2018
Maternal Dengue Immunity Protects Against Infant Zika Infection
Maternal Dengue immunity produces CD8+ T cells that protect against fetal Zika infection preventing zika-related malformations....
NOV 13, 2018
Immunology
NOV 13, 2018
What Do Heart Disease and Autoimmune Diseases Have in Common?
Researchers at Washington University identify the link between autoimmune diseases and heart disease in mouse model...
NOV 14, 2018
Immunology
NOV 14, 2018
Stress in Youth Can Mean Depression as an Adult
A research team investigates early life stress and its relation to adult depression and anxiety...
Loading Comments...