Student guest post by Zainab Khan
Schizophrenia has puzzled and often times scared not only the scientific community, but also the general public since its emergence. Cases of schizophrenia-like behavior have been well documented in history. As this disease has been studied, factors such as genetics, environment, and even personal habits have all been associated to some degree with schizophrenia. However, evidence in past years has mounted showing an association between infectious agents and schizophrenia. The three main infections associated/studied with schizophrenia have been toxoplasmosis gondii, herpes family viruses (namely herpes simplex virus and cytomegalovirus), and retroviruses. [1]
When discussing schizophrenia it is important to have a grasp on some of the basics about this disorder. Schizophrenia is a mental disorder in which an individual faces many mental and functionality problems including hallucinations, paranoia, and poor speech and organizational skills. Schizophrenia usually appears when people are in their twenties, but it can occur at any age (men tend to get it earlier and women a bit later). [2] People diagnosed with this disorder typically have elevated dopamine activity in their brains. There is no actual test for schizophrenia; all diagnosis is based on what the patient tells the doctor, leaving a lot of room for misclassification. Schizophrenia shares its symptoms with diseases like bipolar disorder, multiple personality disorder, just to name a few. Treatment for schizophrenia usually involves antipsychotic medications in combination with counseling. These patients are much more prone to develop drug dependency, have shorter lifespan, and are much more likely to be unemployed, depressed, and homeless. [3]
Toxoplasmosis gondii is a parasite that is most commonly found in rats and cats. Cats are the reservoir for this parasite to reproduce and infect humans. It is well known that the majority of people in the world have been infected with this parasite and never have any signs or symptoms. This parasite becomes dangerous typically for immune compromised patients and pregnant woman (as it can cause birth defects). However, studies have also linked this parasite with an increased chance of schizophrenia. In one study individuals who have a schizophrenic episode and have never been treated with antipsychotic medications have higher antibodies against both toxoplasmosis gondii and CMV. [4] Further evidence in this study shows that when these people are treated with antipsychotic medicines these medicines also inhibit toxoplasmosis and CMV in patients. Toxoplasmosis is also known to increase dopamine distribution in the brain which strengths the idea that it does contribute to an individual becoming schizophrenic. [4]
Another infectious cause associated with schizophrenia is a retrovirus, specifically human endogenous retroviruses. HERV are viruses that during replication the reverse transcriptase copies its retroviral RNA into the DNA of the host (it forms a haploid DNA provirus). This provirus can be integrated in the germ line of the host, and is therefore transmitted to the following generation [5] Many of these HERV have had mutations or deletions which cause the majority of them not be active, but a small amount do remain active. It has been shown that people who have recently been diagnosed with schizophrenia have about a 29% increased chance of having the retroviral pol RNA in their cerebral spinal fluid. Conversely, none of the control patients had this nucleotide sequence in their CSF. [6]
Schizophrenia is a devastating disease that can not only ruin an individual's life, but also his or her families. There is no precise answer for what is the cause of schizophrenia, so there is no way of knowing how to prevent it. More than likely this is a disease that occurs when the perfect mixture of environmental-genetic-infectious agents all come into play together. It does seem possible that if one of these factors were taken away the disease may not occur; there is no way to 'fix' the genetics of an individual, and similarly environmental stressors are a part of routine life. Therefore the easiest (easiest being a relative term) factor to try to take away is the infectious agent. More time and money should be placed in finding the connection between schizophrenia and its infectious causes and how to prevent these agents.
References
1.Harrison Catherine (January 2008) "What Causes Schizophrenia?" About.com
2."Mental Health and Schizophrenia" WebMD
3."Schizophrenia" Wikipedia
4.F.Markus Leweke, Christoph W. Gerth, Dagmar Keothe, Joachim Klosterkotter, Inna Ruslanova, Bogdana Krivogorsky, E. Fuller Torrey, Robert H. Yolken (2004) "Antibodies to infectious agents in individuals with recent onset schizophrenia" Eur Arch Psychiatry clin Neurosci 254: 4-8
5.Lewis David (2000) "Retroviruses and the Pathogenesis of Schizophrenia" Neuron 28:325-334
6.Hakan Karlsson, Silke Bachmann, Johannes Schro dert, Justin McArthus, E. Fuller Torrey, Robert Yolken (January 2001) "Retroviral RNA Identified in the Cerebrospinal Fluids and Brains of Individuals with Schizophrenia" Stanley Division of Developmental Neurovirology
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While the causes are indeed quite a mystery, there is another way to "prevent" schizophrenia, and that is to catch it in the early stages, called the prodrome, and take preventative measures. A number of studies across the country are looking at how to do so, through low doses of drugs, stress management interventions, etc. They seem to be having some success.
There is a wee bit of a mistake near the end of this otherwise very good post.
It is almost certain that not all of these multiple factors are required to cause schizophrenia. Eliminating one causal infectious factor probably won't eliminate schizophrenia, since that particular factor probably only plays a role in a certain percentage of cases. Also, there are probably several distinct diseases with different sets of causal factors lumped together into what we call schizophrenia.
Complex diseases almost always work this way, which makes sense when you think about it from a complex evolving systems sort of POV. A well studied cancer such as breast cancer provides a good model to look at.
Thanks for the interesting post. I'm particularly interested in this as the mom of a young daughter who has 22q11 Deletion Syndrome. She and so many of the kids with 22qDS are immune compromised and especially susceptible to infections. Many will go on to develop schizophrenia or other forms of serious mental illness. I don't know if anyone is looking at these two things in this population to see if there is any connection.
I agree with travc on this. Pursuing this one line of infectious disease causal factors is not sufficient in finding out more about the disease. This is an oversimplification. All the same, thank you for sharing. I've learnt something new here.
While the causes are indeed quite a mystery, there is another way to "prevent" schizophrenia, and that is to catch it in the early stages, called the prodrome, and take preventative measures. A number of studies across the country are looking at how to do so, through low doses of drugs, stress management interventions, etc. They seem to be having some success.