Nav: Home

Researchers question lifelong immunity to toxoplasmosis

December 08, 2016

Medical students are taught that once infected with Toxoplasma gondii--the "cat parasite"--then you're protected from reinfection for the rest of your life. This dogma should be questioned, argue researchers in an Opinion published December 8 in Trends in Parasitology. Their concerns stem from a handful of case studies in which expectant mothers in their late 20s and early 30s were known to have been infected by T. gondii at birth but were actually found to lack immunological protection during screening.

Then there's the mystery of the global decrease in the number of people who test positive for toxoplasmosis immunity. For example, in the 1960s, surveys of expectant mothers in France found that 80% or more had antibodies to the parasite. This number dropped to 30% in 2010 and is expected to continue falling. This change, also observed in the United States, could be due to improved food hygiene (particularly better preparation and quality of meat--beef, lamb, and venison are especially likely to carry the parasite) as well as fewer domestic cats consuming raw rodent meat and thus transmitting T. gondii to humans.

"We put forward the hypothesis that, in the past, people kept their antibodies to T. gondii because they were very likely to become re-infected," says lead author François Peyron, a parasitologist at the Hospital Croix-Rousse in Lyon, France. "Now that the parasitic pressure has gone down, I think people are less stimulated and they lose their immunity--it's exactly what we see for malaria."

The uncertainty around the rate of toxoplasma infection is partly due to how infrequently it is reported. Aside from the immunocompromised, only a minority of people will experience side effects, typically flu-like symptoms, after coming into contact with the parasite. Once inside the body, the single-celled parasite travels through the blood into the brain and muscles, where it forms cysts. Researchers believe these cysts remain in an infected person for life and that their presence retriggers the immune system, but Peyron and his co-authors, Solène Rougier of Hospital Croix-Rousse and Jose Montoya of the Stanford University School of Medicine, are also challenging this idea.

Toxoplasmosis is specifically a problem when a mother is infected while pregnant. If undetected and untreated, the parasite will spread to the developing child and can terminate the pregnancy or cause the baby to develop brain or eye abnormalities. Some countries, such as France, regularly screen expectant mothers who have had no previous exposure to T. gondii to ensure that any infection is caught early. This standard of care might need to be revised if enough evidence shows that previous infection with T. gondii isn't enough to prevent reinfection of pregnant women.

"We have to be concerned by T. gondii, but it has been clearly demonstrated that clinical treatment is very effective at preventing fetal infection and reducing associated conditions" Peyron says. "It is our opinion that this aspect of public health has not been well investigated in many countries, especially in the United States, and that provided we keep the price of testing low, then the cost of regularly screening pregnant women for toxoplasmosis is less expensive than the cost of caring for a child that develops disabilities as a result of the infection."

The research group plans to follow up with hundreds of patients to identify when and for whom T. gondii immunity might be waning. In advance of evidence to support their hypothesis, they recommend that pregnant women continue to follow guidelines for avoiding infection by the parasite, such as practicing safe food habits and hand washing. The researchers also caution those who are pregnant not to consider themselves protected and to speak with their doctor about whether and how often to screen for the parasite.
-end-
Trends in Parasitology, Rougier et al.: "Lifelong persistence of Toxoplasma cysts: a questionable dogma?" http://www.cell.com/trends/parasitology/fulltext/S1471-4922(16)30190-8

Trends in Parasitology (@TrendsParasitol), published by Cell Press, is a monthly review journal that reflects the global significance of medical and veterinary parasites. It aims to provide a point of access for communication between researchers in all disciplines of parasitology, bringing content that is authoritative and cutting edge, yet accessible to a wide audience of readers. Visit: http://www.cell.com/trends/parasitology. To receive Cell Press media alerts, please contact press@cell.com.

Cell Press

Related Public Health Articles:

Public health guidelines aim to lower health risks of cannabis use
Canada's Lower-Risk Cannabis Use Guidelines, released today with the endorsement of key medical and public health organizations, provide 10 science-based recommendations to enable cannabis users to reduce their health risks.
Study clusters health behavior groups to broaden public health interventions
A new study led by a University of Kansas researcher has used national health statistics and identified how to cluster seven health behavior groups based on smoking status, alcohol use, physical activity, physician visits and flu vaccination are associated with mortality.
Public health experts celebrate 30 years of CDC's prevention research solutions for communities with health disparities
It has been 30 years since CDC created the Prevention Research Centers (PRC) Program, currently a network of 26 academic institutions across the US dedicated to moving new discoveries into the communities that need them.
Public health experts support federally mandated smoke-free public housing
In response to a new federal rule mandating smoke-free policies in federally funded public housing authorities, three public health experts applaud the efforts of the US Department of Housing and Urban Development to protect nonsmoking residents from the harmful effects of tobacco exposure.
The Lancet Public Health: UK soft drinks industry levy estimated to have significant health benefits, especially among children
The UK soft drinks industry levy, due to be introduced in April 2018, is estimated to have significant health benefits, especially among children, according to the first study to estimate its health impact, published in The Lancet Public Health.
Social sciences & health innovations: Making health public
The international conference 'Social Sciences & Health Innovations: Making Health Public' is the third event organized as a collaborative endeavor between Maastricht University, the Netherlands, and Tomsk State University, the Russian Federation, with participation from Siberian State Medical University (the Russian Federation).
Columbia Mailman School Awards Public Health Prize to NYC Health Commissioner Dr. Mary T.
Dr. Mary T. Bassett, Commissioner of the New York City Department of Health and Mental Hygiene, was awarded the Frank A.
Poor health literacy a public health issue
America's poor record on health literacy is a public health issue, but one that can be fixed -- not by logging onto the internet but by increased interaction with your fellow human beings, a Michigan State University researcher argues.
Despite health law's bow to prevention, US public health funding is dropping: AJPH study
Although the language of the Affordable Care Act emphasizes disease prevention -- for example, mandating insurance coverage of clinical preventive services such as mammograms -- funding for public health programs to prevent disease have actually been declining in recent years.
'Chemsex' needs to become a public health priority
Chemsex -- sex under the influence of illegal drugs -- needs to become a public health priority, argue experts in The BMJ this week.

Related Public Health Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".