Toxoplasma Gondii

Meet toxoplasma gondii. Well actually, you probably don’t want to meet it. Toxoplasma is a parasite that can infect almost all warm blooded animals, humans included. It’s interesting because scientists have found an association between it and neurological disorders, namely schizophrenia. In one study, women with high levels of toxoplasma were more likely to give birth to schizophrenic babies. This is because toxoplasma is thought to affect behavior and neurotransmitter function. In fact, mice infected with this parasite became fearless and were attracted to cats (thus leading to their death) because toxoplasma affects brain regions responsible for fear. Pretty interesting isn’t it?. Check out this Scientific American article for more details.


Neurotoxoplasmosis, also know as cerebral toxoplasmosis, is an opportunistic infection, caused by the parasite Toxoplasma gondii, which typically affects patients with HIV/AIDS, and is the most common cause of cerebral abscess in these patients

Clinical presentation

In immunocompetent patients, acute encephalitis is extremely rare. Even in the immunocompromised symptoms are typically vague and indolent. Development of new neurological symptoms in these patients should raise high suspicion of cerebral toxoplasmosis.


Toxoplasma gondii is an intracellular parasite that infects birds and mammals. It’s definitive host is the cat and other Felidae species. Excretion of oocytes in its faecal content followed by human contaminated uncooked consumption can lead to human infection. In immunocompetent individuals, it primarily causes a subclinical or asymptomatic infection. In immunocompromised individuals (e.g. AIDS patients), toxoplasmosis is the most common cause of a brain abscess.

‘Hijacking’ and hibernating parasite could alter behaviour

Melbourne researchers have discovered how a common parasite hijacks host cells and stockpiles food so it can lie dormant for decades, possibly changing its host’s behaviour or personality in the process.

The findings could lead to a vaccine to protect pregnant women from Toxoplasma infection, which carries a serious risk of miscarriage or birth defects, as well as drugs to clear chronic infections in people with compromised immune systems, such as cancer patients.

Toxoplasma is a common parasite transmitted by cats and found in raw meat. Around 30 per cent of the population is infected. The research projects were led by Dr Chris Tonkin, Dr Justin Boddey, Dr Alex Uboldi, Mr James McCoy and Mr Michael Coffey from the Walter and Eliza Hall Institute.

Dr Tonkin said Toxoplasma required a human host cell – such as a brain cell (neuron) – to live in. The research team discovered how the parasite hijacks the host cell to enable its own growth and survival, hibernating for decades by creating its own food reserve.

“Toxoplasma infection leads to massive changes in the host cell to prevent immune attack and enable it to acquire a steady nutrient supply,” Dr Tonkin said. “The parasite achieves this by sending proteins into the host cell that manipulate the host’s own cellular pathways, enabling it to grow and reproduce.”

Dr Boddey said some of these proteins might even influence the behaviour of the host. “There is a fascinating association between Toxoplasma infection and psychiatric diseases including schizophrenia and bipolar disorder. It is now possible to test whether proteins sent from the hibernating parasite into a host neuron disrupt normal brain function and contribute to development of these diseases,” he said.

Once Toxoplasma parasites establish infection, they can lie dormant in our bodies for the rest of our lives. In people with suppressed immune systems, such as cancer patients, the parasite can reactivate and cause neurological damage and even death.

Dr Tonkin said the teams had identified pathways that allow the parasite to establish chronic infections, unveiling potential avenues for treatment that clear the dormant parasite.

“We discovered that, similar to animals preparing for hibernation, Toxoplasma parasites stockpile large amounts of starch when they become dormant,” he said. “By identifying and disabling the switch that drives starch storage, we found that we could kill the dormant parasites, preventing them from establishing a chronic infection.”

Dr Tonkin said the finding could lead to a drug to clear chronic Toxoplasma infections, or even a vaccine to prevent infection in at-risk people, such as pregnant women.

“Cats are one of the primary transmitters of Toxoplasma parasites,” Dr Tonkin said. “If the parasites are transmitted to pregnant women, for example through contact with kitty litter, there is a substantial risk of miscarriage or birth defects.

“We hope to use our discoveries to develop a vaccine that stops cats transmitting the parasite, to prevent these potentially catastrophic consequences.”

Dr Boddey said it had long been a mystery how the Toxoplasma parasite transported proteins into the host. “Our study showed that the parasite includes a signature on the exported proteins that ‘earmark’ them for transport into the host cell,” he said. “Blocking transport makes the parasite much less dangerous in infection models, suggesting this may also be a new way of treating Toxoplasma infections.”

The research findings were published in the journal Cell Host & Microbe and in the journal eLife.

A great example of the interconnectedness of life forms on this planet and what happens when natural barriers are breached.

Cat Parasite Spreads to Arctic Beluga Whales - Potential Public Health Issue

Prof Michael Grigg at the University of British Columbia in Vancouver said tests on hundreds of beluga whales in the Beaufort Sea, on the edge of the Arctic, revealed that 14% of the creatures harboured the Toxoplasma gondii infection. The tests are the first to show the infection has reached the region.

The most likely cause of the outbreak was infected cat faeces washing into waterways and on to the sea, where fish and other marine organisms became contaminated and ultimately eaten by the whales.

The rise in pet cats among the Inuit and a warming climate which helps the pathogen survive until it finds a host could be to blame for the emergence of the infection, Grigg told the American Association for the Advancement of Science meeting in Chicago.

“Ice is a major eco-barrier for pathogens. What we are seeing with the big thaw is the liberation of pathogens gaining access to vulnerable new hosts and wreaking havoc,” he added.

A Beluga whale swimming under ice at the Arctic Circle dive center in the White Sea, northern Russia. Photograph: Franco Banfi/Barcroft Media
How Your Cat Is Making You Crazy - The Atlantic

A tiny parasite called Toxoplasma gondii might be driving people crazy. That’s what Jaroslav Flegr believes, anyway. For years he has pursued the odd, yet increasingly realistic theory that this brain-dwelling parasite could be infecting humans via household cats and affecting the way they behave. Toxo literally changes the way you produce dopamine, a key neurotransmitter.

It’s not “crazy cat lady” syndrome, per se, but if Toxo can drive rats so nuts that they walk right into the jaws of a cat, could it influence things like extroversion and schizophrenia in humans?

There is strong psychological resistance to the possibility that human behavior can be influenced by some stupid parasite. Nobody likes to feel like a puppet.

Read more about his work and how Toxo affects the brain at The Atlantic.

Bonus feature: A Radiolab segment about Toxo from 2009.

Toxoplasma infection permanently shifts balance in cat-and-mouse game

The toxoplasma parasite can be deadly, causing spontaneous abortion in pregnant women or killing immune-compromised patients, but it has even stranger effects in mice.

Infected mice lose their fear of cats, which is good for both cats and the parasite, because the cat gets an easy meal and the parasite gets into the cat’s intestinal tract, the only place it can sexually reproduce and continue its cycle of infection.

New research by graduate student Wendy Ingram at the University of California, Berkeley, reveals a scary twist to this scenario: the parasite’s effect seem to be permanent. The fearless behavior in mice persists long after the mouse recovers from the flu-like symptoms of toxoplasmosis, and for months after the parasitic infection is cleared from the body, according to research published today (Sept. 18) in the journal PLoS ONE.

“Even when the parasite is cleared and it’s no longer in the brains of the animals, some kind of permanent long-term behavior change has occurred, even though we don’t know what the actual mechanism is,” Ingram said. She speculated that the parasite could damage the smell center of the brain so that the odor of cat urine can’t be detected. The parasite could also directly alter neurons involved in memory and learning, or it could trigger a damaging host response, as in many human autoimmune diseases.

Ingram became interested in the protozoan parasite, Toxoplasma gondii, after reading about its behavior-altering effects in mice and rats and possible implications for its common host, the domesticated cat, and even humans. One-third of people around the world have been infected with toxoplasma and probably have dormant cysts in their brains. Kept in check by the body’s immune system, these cysts sometimes revive in immune-compromised people, leading to death, and some preliminary studies suggest that chronic infection may be linked to schizophrenia or suicidal behavior.

Pregnant women are already warned to steer clear of kitty litter, since the parasite is passed through cat feces and can cause blindness or death in the fetus. One main source of spread is undercooked pork, Ingram said.

With the help of Michael Eisen and Ellen Robey, UC Berkeley professors of molecular and cell biology, Ingram set out three years ago to discover how toxoplasma affects mice’s hard-wired fear of cats. She tested mice by seeing whether they avoided bobcat urine, which is normal behavior, versus rabbit urine, to which mice don’t react. While earlier studies showed that mice lose their fear of bobcat urine for a few weeks after infection, Ingram showed that the three most common strains of Toxoplasma gondii make mice less fearful of cats for at least four months.

Using a genetically altered strain of toxoplasma that is not able to form cysts and thus is unable to cause chronic infections in the brain, she demonstrated that the effect persisted for four months even after the mice completely cleared the microbe from their bodies. She is now looking at how the mouse immune system attacks the parasite to see whether the host’s response to the infection is the culprit.

“This would seem to refute – or at least make less likely – models in which the behavior effects are the result of direct physical action of parasites on specific parts of the brain,” Eisen wrote in a blog post about the research.

“The idea that this parasite knows more about our brains than we do, and has the ability to exert desired change in complicated rodent behavior, is absolutely fascinating,” Ingram said. “Toxoplasma has done a phenomenal job of figuring out mammalian brains in order to enhance its transmission through a complicated life cycle.”

Toxoplasma gondii parasite may alter signaling in the brain

It’s creepy, it’s crawly, and it infects 20 percent of people in the United States. Fortunately, most people who carry the Toxoplasma gondii parasite don’t develop the symptoms of the disease it can cause. Only a small fraction of people, typically with compromised immune systems, develop toxoplasmosis.                                

Toxoplasmosis can lead to abnormal brain function, including seizures, by changing signaling in the diseased central nervous system.  

In a study using a rodent model, scientists from the Virginia Tech Carilion Research Institute and the University at Buffalo found that the parasite-induced infection alters neural pathways specifically related to the neurotransmitter gamma-Aminobutyric acid, better known as GABA.

The researchers recently published their results in the American Society for Microbiology’s open-access journal, mBio.

Justin M. Brooks et al.   Infections Alter GABAergic Synapses and Signaling in the Central Nervous System , mBio (2015). DOI: 10.1128/mBio.01428-15

Inhibitory nerve terminals, such as GABA, are shown in red. The right image demonstrates how a Toxoplasma infection alters the inhibitory nerve terminals, compared to the healthy tissue sample in the left image.    

Toxoplasma gondii's life cycle is one of the most interesting fixtures of parasitology and biology as a whole.  The definitive or reproductive host for the parasite is the common housecat, but the life cycle necessitates transmission through the barn mouse.  Research shows that gondii’s eggs are present in a large proportion of cat’s litter boxes, which the barn mouse then interacts with via foraging behavior.  The oocysts themselves are highly resistant to weather, temperature, rupture, etc, so they spread to anything that can be contaminated, namely soil, water, food, trash, etc.  When the mouse ingests the egg, the parasite grows, and studies dictate an attraction to cat urine is promoted in the infected rodent.  The definitive host, the cat, then ingests the mouse, infecting its intestinal track with the parasite, where Toxoplasma can reproduce.  Some evolutionary theorists believe this demonstrates an “extended phenotype” which creates a linkage among these species as an adaptation by the Toxoplasma parasite which does not typically transfer directly from cat to cat.

Some human studies indicate a correlative relationship between Toxoplasma infection and mental illness or behavioral changes, but these are both controversial and purely correlative.  No causal mechanism has been discovered for the behavioral changes in humans or mice.

Pregnant women are directed by the CDC to avoid cleaning cat litter boxes because Toxoplasma gondii infection is easily transmissible through the prenatal membrane, and prenatal infection is highly correlated with blindness and mental illness in the baby later in life.

What a sweet story, right?

Sweet Valentine

By Peter Bradley, University of California, Los Angeles

Four intracellular Toxoplasma gondii parasites are shown undergoing cellular division by an internal budding process known as endodyogeny. Staining with a T. gondii surface antigen provided heart-shaped images (shot on Valentine’s Day). The definitive host of these parasites is the cat, but they infect many warm-blooded animals, including humans. While toxoplasmosis is typically a minor disease, T. gondii can cause severe central nervous system disorders of immunocompromised individuals—such as those with AIDS, organ transplants, and lymphoma—as well as birth defects in congenitally infected neonates. Eating undercooked meat and ingesting food or water contaminated with cat feces are the most common routes of infection for humans.

Sources: 1 2 3 4

Toxoplasma gondii

Toxoplasma gondii. 7 syllables sure to strike fear in to any pregnant woman’s heart. I thought I’d do a little post today to summarise what toxoplasma actually is and how it affects us and the animals around us.

Toxoplasma gondii is a single celled parasite known as a protozoa. It has a complex lifecycle involving felines as its only final host. It does, however, have a vast array of ‘intermediate hosts’ thought to include virtually all warm blooded animals. It’s a very successful parasite infecting animals and humans worldwide. In France, 84% of people are thought to be infected.

Its lifecycle is as follows:

  • A cat becomes infected through consuming the raw meat of infected prey
  • The parasite infects the epithelial cells of the cat’s gut, sexually reproducing in these cells
  • Sexual reproduction produces oocysts which are shed in the cat’s faeces. The time period from consumption to shedding is around 3-10 days. Shedding only occurs for a few weeks before the cat’s immune system fights off the parasite, resulting in a persistent but non-shedding infection that can remain for life. After one infection it is highly unlikely the cat will get infected and shed again due to its raised immune response, however immunosuppression can result in subsequent shedding
  • These oocysts develop in the environment and after 1-5 days are developed enough to infect an intermediate host
  • Intermediate host ingests the oocysts through consumption of an item or fluid infected with cat faeces. Intestinal enzymes break down the oocyst wall releasing the parasite in to the gut
  • Acute asexual multiplication occurs in the intermediate host cells and the parasite is spread around the body in the blood
  • After around 2 weeks the host develops immunity but the infection enters a chronic phase as slow-growing forms of the parasite are ‘walled off’ into what is known as a cyst, protected from the immune system. These can remain infectious for months to years and can revert to the acute form if the host’s immune system becomes depressed (FIV, AIDs, canine distemper). They are often found in the brain and muscle.
  • This cyst-infected meat is consumed by the cat and the whole cycle begins again

Cats can also get infected by consuming oocysts from other cats, however they are a lot less susceptible to this than other intermediate hosts so a large number of oocysts would need to be consumed. To make it even more confusing, intermediate hosts can get infected via carnivorism/ scavenging when they consume meat infected with cysts (e.g. a human eating undercooked, infected pork). As well as this, transplacental transmission can occur in some host species during the acute phase of the infection (however this is not seen in dogs or cats). This creates a complex web of infection. The cysts are killed when meat is cooked.

Toxoplasmosis is most often asymptomatic, with flu-like symptoms possible during the acute phase. It can be fatal in immunosuppressed individuals, however this is rare. You may have heard the parasite’s name mentioned in relation to sheep. If a non-immune ewe is infected during pregnancy it can cause foetal death, reabsorption, abortion, mummified foetuses, still births and weak lambs, depending on when in pregnancy the ewe was infected. In cases of abortion, you can see tiny white spots on the placenta and foetal tissue. Diagnosis can be confirmed through stained impression smears or serological examination of the foetal fluid or blood from the ewe. Prevention in sheep includes a vaccine which primes the immune system to the parasite. Sheep are often infected from eating infected hay or concentrates, so keeping cats away from these can help reduce infection rates.

Toxoplasma is also a favourite in the press, who claim that it ‘controls our brains’ and causes abortions and deformities. Like in sheep, infection of a non-immune, pregnant mother can indeed cause deformities in her child. Does this mean we should all kill off our cats when expecting? Definitely not, and I’ll explain why.

As I stated earlier, infected cats will only shed for 2-3 weeks in their entire lifetime, unless immunologically supressed. To become infected by your cat, you would need to have never been infected before yourself (because if you have, your immune system is primed and ready to fight it off), your cat would have to be in the shedding phase and you’d have to ingest oocytes (that take 1-5 days to become infective, so changing the litter box daily can hugely reduce this risk).  If worried, a blood test to see if you’ve been previously exposed and a blood test in your cat to see if they’ve been previously exposed may put your mind at rest. Indoor cats are less likely to become infected if their only food is tinned or dried. Humans are much more likely to be exposed to the infection through handling and eating undercooked infected meat, soil infected with cat faeces and unwashed vegetables. If you’re a vet in the making and have been on a lambing placement, you may well have been asked if you’re pregnant. This is because being in contact with aborted material from sheep with toxoplasmosis is another way to contract the infection.

As for the ‘mind control’, it has been found that mice infected with toxoplasma are attracted to the smell of cat urine and a lot less frightened of cats than those without infection. This is an incredibly clever mechanism and probably one of the reasons the parasite is so wide-spread. In humans, when analysing the number of people who are involved in car accidents, it was found that a significantly high proportion were infected with toxoplasma gondii. It has been suggested that the parasite is responsible for making people more reckless and argumentative. Toxoplasma cysts in the brain could definitely be responsible for parts of your personality, however conclusions at the moment suggest that although the infection may have some effect, the brain and concept of ‘personality’ are so complex and involve so many factors that its overall influence seems negligible.  

I hope this made sense, it’s quite confusing to explain! I’ve drawn a quick diagram to try and demonstrate the different scenarios in which we could become infected. Enjoy!

Ummmmmm …

Cats in the United States release about 2.6 billion pounds (1.2 million metric tons) of feces into the environment every year. Cat dung carries the parasite Toxoplasma gondii, a single-celled organism that creates infectious agents called oocysts. These oocysts can infect pregnant women, causing congenital problems in the baby such as deafness, seizures, eye damage and mental retardation. The parasite also infects people with compromised immune systems, such as those with HIV/AIDS.

After reviewing past studies on the parasite, a team of researchers believes the Toxoplasma parasite may be a significant public health problem, infecting people who are otherwise healthy. Other studies have even linked the parasite to schizophrenia, depression, suicidal behavior and lower school achievement in children.

… mmmmmmmmmmm


Is ‘crazy cat lady syndrome’ real?

Can cats really turn women into crazy cat ladies? Some scientists think it’s possible.


Ever feel like your kitty takes charge of your brain?

TOXOPLASMA, a new painting by Martin Hsu

Inspired by Radiolab’s episode on Toxoplasma Gondii, a potentially mind controlling parasite gifted from your cat to you. Listen here

Toxoplasma original painting created for the ZOMBIE show at Last Rites Gallery in New York.

Enjoy the kitties,
Your Cat Won't Make You Crazy: Toxoplasma Gondii
I've followed the stories about how toxoplasma gondii, a little microbe that lives inside cats, has been shown to maybe make you lose your mind a little.

We mentioned these microbes in our episode about the crazy cat lady stereotype. Always glad to get an update, especially when that update makes it clear our weirdness isn’t the fault of our cats’ bacteria buddies.


For some reason, toxoplasmosis has been coming up in both Psych classes I’m taking. So I’m going to unravel the secrets behind it a little bit, because it is quite interesting. 

First of all, we start with a little paraside called Toxoplasma gondii. 

This lil dude loves the host body of kitty cats. Toxoplasma gondii will live in the cat and continue living on in the cat poop. Thus if a pregnant woman is carelessly cleaning out her cat’s litter box, she runs the risk of contracting the parasite. It will cause an infection and devastate her unborn child’s immune system (enlarged liver/spleen, eye damage, hearing loss, jaundice, low birth weight, central nervous system deficiencies).

Here’s the crazier part about Toxoplasma gondii.

If a rat contracts the parasite, it Toxoplasma gondii will commandeer the rat’s nervous system. The rat will suddenly be enamored by cats - it will CHASE cats and walk right into the jaws of the predator. The rat is DEAD MEAT. This is an evolutionary FAIL. But for the parasite, this is an amazing evolutionary advantage! Once the cat eats the infected rat, Toxoplasma gondii increases its chances of reproducing with other members of its species potentially living in the cat.

These drastic behavioral changes prompt questions of consciousness related to control of things that are seemingly habitual or instinctual. 

nepeta asked:

I figured all my emotional bullshit would make you unfollow me, But you're still there..

having emotions is a normal human thing and i think tumblr is a great way to vent and express yourself in a safe environment :). don’t give up it gets better :D

Parasite Toxoplasma Gondii Alters Brain Signaling

In a study using a rodent model, scientists from the Virginia Tech Carilion Research Institute and the University at Buffalo found that the parasite-induced infection alters neural pathways specifically related to the neurotransmitter gamma-Aminobutyric acid, better known as GABA.

The research is in mBio. (full access paywall)

Tehehehe. I have my parasites exam today and I’m going over extra reading for Toxoplasmosis. Some findings suggest that Toxoplasma gondii infection increases jealousy and antisocial behaviour in men but increases morality, promiscuity and a ‘higher level of intelligence’ in women. In contrast, there is a higher prevalence of T. gondii infection among schizophrenics and people with depression and bipolar disorders. Scientists don’t know anything. It is also known to increase male births but the reasons for this are unknown.

So ja. I’ve fully covered 2 topics out of 7 and briefly covered 2 others. Malaria and Toxoplasma have appeared every year the past 4 years. If they don’t appear this year, I’m screwwwed :D And now I’ve started to get a cold, a sore throat and my wisdom tooth infection is coming back. Great timing since I need to pull a full alnighter tonight.