Связь наличия антител к T. gondii и нейропсихиатрических расстройств не подтвердилась

Our results suggest that a positive test for T. gondii antibodies does not result in increased susceptibility to neuropsychiatric disorders, poor impulse control or impaired neurocognitive ability…  this is, to our knowledge, the most comprehensive assessment of the possible link between T. gondii infection and a variety of impairments in a single cohort.

 The Myth of “Mind-Altering Parasite” Toxoplasma Gondii?

Перинатальные инфекции и риск шизофрении

These studies have yielded a series of intriguing associations (reviewed in Brown and Derkits)[2] and are briefly summarized here. Our group demonstrated that prenatal exposure to rubella was related to a greater than 5-fold increased risk of nonaffective psychosis during young adulthood[12] and in midadulthood over 20% of subjects who were exposed in utero to rubella were diagnosed with schizophrenia or a schizophrenia spectrum disorder.[13] Influenza exposure documented by quantification of maternal antibody titers during pregnancy was associated with a 3-fold increased risk of schizophrenia for exposure in mid to late gestation and a 7-fold elevation in risk of the disorder following first trimester exposure.[14] Elevated maternal IgG antibodies to Toxoplasma gondii, an intracellular parasite and a well-known infectious cause of central nervous system (CNS) congenital anomalies,[1,15] was related to greater than 2-fold increased risk of schizophrenia,[16] a finding which was essentially replicated in a Danish sample that capitalized on filter paper blood spots taken from the infant within the first week of birth.[17] In 3 studies, elevated maternal IgG antibody to (HSV-2) was related to an increased risk of psychotic disorders, including schizophrenia,[18,19,20] while the finding was not replicated in a different birth cohort.[21] Maternal genital/reproductive infections, broadly defined, were, however, associated with a 5-fold increased risk of schizophrenia when the exposure occurred during the periconceptional period.[22] Exposure to maternal respiratory infection was related to a 2-fold elevated schizophrenia risk,[23] as well as bacterial infections broadly defined.[24]

In summary, birth cohort studies have provided several key methodological advantages that have allowed for more rigorous testing of relationships between maternal infection and schizophrenia. Birth cohort studies conducted to date have provided further support for the hypothesis that maternal viral, protozoal, and bacterial infections increase the risk for schizophrenia in adult offspring.

Although cytokines represent a leading candidate agent for the effect of infection on schizophrenia risk, other possible mediators include hyperthermia, which is teratogenic to animals;[32] fetal hypoxia, which has been associated with schizophrenia;[33,34] and over the counter remedies taken for influenza such as aspirin, which has been associated with anomalies of the CNS.

Maternal Infection and Schizophrenia

Инфекционная теория шизофрении: вирус HERV-W

By the 1980s he began working with Robert Yolken, an infectious-diseases specialist at Johns Hopkins University in Baltimore, to search for a pathogen that could account for these symptoms. The two researchers found that schizophrenics often carried antibodies for toxoplasma, a parasite spread by house cats; Epstein-Barr virus, which causes mononucleosis; and cytomegalovirus. These people had clearly been exposed to those infectious agents at some point, but Torrey and Yolken never found the pathogens themselves in the patients’ bodies. The infection always seemed to have happened years before.

Torrey wondered if the moment of infection might in fact have occurred during early childhood. If schizophrenia was sparked by a disease that was more common during winter and early spring, that could explain the birth-month effect. “The psychiatrists thought I was psychotic myself,” Torrey says. “Some of them still do.”

While Torrey and Yolken were chasing their theory, another scientist unwittingly entered the fray. Hervé Perron, then a graduate student at Grenoble University in France, dropped his Ph.D. project in 1987 to pursue something more challenging and controversial: He wanted to learn if new ideas about retroviruses—a type of virus that converts RNA into DNA—could be relevant to multiple sclerosis.

Robert Gallo, the director of the Institute of Human Virology at the University of Maryland School of Medicine and co­discoverer of HIV, had speculated that a virus might trigger the paralytic brain lesions in MS. People had already looked at the herpes virus (HHV-6), cytomegalovirus, Epstein-Barr virus, and the retroviruses HTLV-1 and HTLV-2 as possible causes of the disease. But they always came up empty-handed.

Perron learned from their failures. “I decided that I should not have an a priori idea of what I would find,” he says. Rather than looking for one virus, as others had done, he tried to detect any retrovirus, whether or not it was known to science. He extracted fluids from the spinal columns of MS patients and tested for an enzyme, called reverse transcriptase, that is carried by all retroviruses. Sure enough, Perron saw faint traces of retroviral activity. Soon he obtained fuzzy electron microscope images of the retrovirus itself.

By the time Perron made his discovery, Torrey and Yolken had spent about 15 years looking for a pathogen that causes schizophrenia. They found lots of antibodies but never the bug itself. Then Håkan Karlsson, who was a postdoctoral fellow in Yolken’s lab, became interested in studies showing that retroviruses sometimes triggered psychosis in AIDS patients. The team wondered if other retroviruses might cause these symptoms in separate diseases such as schizophrenia. So they used an experiment, similar to Perron’s, that would detect any retrovirus (by finding sequences encoding reverse transcriptase enzyme)—even if it was one that had never been catalogued before. In 2001 they nabbed a possible culprit. It turned out to be HERV-W.

Several other studies have since found similar active elements of HERV-W in the blood or brain fluids of people with schizophrenia. One, published by Perron in 2008, found HERV-W in the blood of 49 percent of people with schizophrenia, compared with just 4 percent of healthy people. “The more HERV-W they had,” Perron says, “the more inflammation they had.” He now sees HERV-W as key to understanding many cases of both MS and schizophrenia. “I’ve been doubting for so many years,” he says. “I’m convinced now.”

Through this research, a rough account is emerging of how HERV-W could trigger diseases like schizophrenia, bipolar disorder, and MS. Although the body works hard to keep its ERVs under tight control, infections around the time of birth destabilize this tense standoff. Scribbled onto the marker board in Yolken’s office is a list of infections that are now known to awaken HERV-W—including herpes, toxoplasma, cytomegalovirus, and a dozen others. The HERV-W viruses that pour into the newborn’s blood and brain fluid during these infections contain proteins that may enrage the infant immune system. White blood cells vomit forth inflammatory molecules called cytokines, attracting more immune cells like riot police to a prison break.

In one experiment, Perron isolated HERV-W virus from people with MS and injected it into mice. The mice became clumsy, then paralyzed, then died of brain hemorrhages. But if Perron depleted the mice of immune cells known as T cells, the animals survived their encounter with HERV-W. It was an extreme experiment, but to Perron it made an important point. Whether people develop MS or schizophrenia may depend on how their immune system responds to HERV-W, he says. In MS the immune system directly attacks and kills brain cells, causing paralysis. In schizophrenia it may be that inflammation damages neurons indirectly by overstimulating them. “The neuron is discharging neurotransmitters, being excited by these inflammatory signals,” Perron says. “This is when you develop hallucinations, delusions, paranoia, and hyper-suicidal tendencies.”

Gene studies have failed to provide simple explanations for ailments like schizophrenia and MS. Torrey’s theory may explain why. Genes may come into play only in conjunction with certain environmental kicks. Our genome’s thousands of parasites might provide part of that kick.

“The ‘genes’ that can respond to environmental triggers or toxic pathogens are the dark side of the genome,” Perron says. Retroviruses, including HIV, are known to be awakened by inflammation—possibly the result of infection, cigarette smoke, or pollutants in drinking water. (This stress response may be written into these parasites’ basic evolutionary strategy, since stressed hosts may be more likely to spread or contract infections.) The era of writing off endogenous retroviruses and other seemingly inert parts of the genome as genetic fossils is drawing to an end, Perron says. “It’s not completely junk DNA, it’s not dead DNA,” he asserts. “It’s an incredible source of interaction with the environment.” Those interactions may trigger disease in ways that we are only just beginning to imagine.

Torrey and Yolken hope to add a new, more hopeful chapter to this story. Yolken’s wife, Faith Dickerson, is a clinical psychologist at Sheppard Pratt Health System in Baltimore. She is running a clinical trial to examine whether adding an anti-infective agent called artemisinin to the drugs that patients are already taking can lessen the symptoms of schizophrenia. The drug would hit HERV-W indirectly by tamping down the infections that awaken it. “If we can treat the toxoplasmosis,” Torrey says, “presumably we can get a better outcome than by treating [neurotransmitter] abnormalities that have occurred 14 steps down the line, which is what we’re doing now.”

The Insanity Virus

Посмертные исследования больных шизофренией на токсоплазмоз и герпесвирусы

Herpes simplex virus (HSV), Epstein–Barr virus (EBV), cytomegalovirus (CMV), and human herpesvirus-6 (HHV-6) are viruses capable of establishing latency. All of these infect the CNS and have been detected in human postmortem brains. Toxoplasma gondii is a protozoan organism which can reactivate in the brains of previously infected immunocompromised individuals. To screen for the presence of herpesviruses and T. gondii in postmortem orbital frontal brain samples from patients with schizophrenia, affective disorders, and controls, we used nested-polymerase chain reaction (n-PCR)/sequencing. We identified HHV-6B sequences in 2/51 postmortem brain samples but no sequences from other herpesviruses. We did not detect sequences of T. gondii in the postmortem brains. Additional studies including ones directed at the sensitive detection of viral nucleic acids in multiple brain regions should be directed at confirming or excluding a role for viruses and protozoa in the etiology of these disorders.

Herpesviruses and Toxoplasma gondii in orbital frontal cortex of psychiatric patients

+ Antibodies to Toxoplasma gondii in Patients With Schizophrenia: A Meta-Analysis
+ Toxoplasmosis–Schizophrenia Research

Токсоплазмоз, шизофрения, суицидальное поведение

Studies of mice and rats infected by T. gondii have shown risky behavior changes, including an attraction to the smell of cat urine that makes them vulnerable to attacks. These findings may have parallels in behavioral changes in people, from schizophrenia to depression and reflex impairment.

Glenn McConkey, a researcher at the University of Leeds in England, reported last year that two genes in T. gondii's DNA contain instructions for the production of an enzyme that makes a brain chemical called dopamine.

"That's somewhat unusual, because other parasites don't have that [dopamine]," said Sarven Sabunciyan, Yolken's colleague at Hopkins. After all, microbes have no brains.

But in higher animals with nervous systems, dopamine is a neurotransmitter with important roles in regulating behavior. Some anti-psychotic drugs used to treat schizophrenia work by blocking dopamine action in the brain.

In May, Hopkins researcher David J. Schretien published a study suggesting that some brain changes and cognitive symptoms in schizophrenics may be caused or worsened by exposure to a herpes simplex virus. A 2005 Czech study found evidence of personality changes in humans infected by another herpes virus called cytomegalovirus. And numerous studies have suggested that flu infections during pregnancy may increase a child's risk of schizophrenia and autism.

Evidence that T. gondii infections may be a cause of schizophrenia, while not yet conclusive, is growing, Yolken said. A review of past studies, published last year by Yolken and Torrey, collected a variety of intriguing correlations. For example: People with schizophrenia have a higher prevalence of T. gondii antibodies in their blood. There are unusually low rates of schizophrenia and toxoplasmosis in countries where cats are rare, and unusually high rates in places where eating uncooked meat is customary. And some adults with toxoplasmosis show psychotic symptoms similar to schizophrenia.

Studies have linked a history of toxoplasmosis with increased rates of other mental changes, too, including bipolar disorders and depression. A 2002 study in the Czech Republic noted slowed reflexes in Toxoplasma-positive people and found links between the infection and increased rates of auto accidents.

Still, the links between schizophrenia and toxoplasmosis are not simple. For example, most people infected with T. gondii never become schizophrenic. And not all schizophrenics have been exposed to toxoplasma.

Yolken believes additional factors, such as an unlucky combination of genes, are probably needed to produce schizophrenia among Toxoplasma-infected people. The parasite's DNA may also be important, since some strains are known to cause more disease.

Studies have also suggested that the timing of the infection — early in life when the brain is developing — and the place in the brain where the cysts settle, may be important, he said.

Yolken said that while T. gondii cysts are invisible to the immune system, they are not totally passive. Inside the cysts, the microbes are alive, sensing their environment, periodically trying to break out, multiply and form more dopamine-making cysts. The flare-ups probably occur when the host's immune system is weakened by illness or stress.

Sabunciyan has reported promising results with a class of anti-malarial drugs, called artemisinins, which appear to be effective at killing T. gondii in tissue cultures. "The next step is to do that in animals," Yolken said.

Yolken, a cat owner who says he has tested positive for Toxoplasma antibodies, said the potential link between Toxoplasma infections and mental illness is no reason for cat owners to panic — they just need to keep some basic hygienic precautions in mind.

Researchers explore link between schizophrenia, cat parasite

Новые исследования в пользу инфекционной теории шизофрении

A review of studies of maternal exposure to infectious agents and schizophrenia in their offspring suggests that eliminating certain infections could prevent as many as 30 percent of schizophrenia cases...
“Humans infected with T. gondii will form the same cysts on the brain as are found in infected rodents when high levels of the gene involved in dopamine synthesis are expressed,” McConkey said. “While production of dopamine in the rodents could be an evolutionary mechanism devised by the parasite, in humans it would be merely accidental. But now suddenly, this provides a possible link to the observed correlation of T. gondii with some forms of schizophrenia.”


New Findings Boost Theory That Infection Causes Schizophrenia

Can Infection-Related Schizophrenia be Prevented?

нейропсихиатрические расстройства и токсоплазмоз

Toxoplasma gondii infects approximately 30% of the world's population, but causes overt clinical symptoms in only a small proportion of people. In recent years, the ability of the parasite to manipulate the behaviour of infected mice and rats and alter personality attributes of humans has been reported. Furthermore, a number of studies have now suggested T. gondii infection as a risk factor for the development of schizophrenia and depression in humans. As T. gondii forms cysts that are located in various anatomical sites including the brain during a chronic infection, it is well placed anatomically to mediate these effects directly. The T. gondii genome is known to contain 2 aromatic amino acid hydroxylases that potentially could directly affect dopamine and/or serotonin biosynthesis. However, stimulation of the immune response has also recently been associated with mood and behavioural alterations in humans, and compounds designed to alter mood, such as fluoxetine, have been demonstrated to alter aspects of immune function. Herein, the evidence for T.-gondii-induced behavioural changes relevant to schizophrenia and depression is reviewed. Potential mechanisms responsible for these changes in behaviour including the role of tryptophan metabolism and the hypothalamic-pituitary-adrenal axis are discussed. Copyright (c) 2009 S. Karger AG, Basel.

pubmed