Nasty Infectious Diseases You Want To Avoid - Borna Disease Virus
Borna disease virus (BDV), is a type of virus known to cause behavior disruptions and neurological disease in several animal species, and recently found in humans as well. Infection with this virus may trigger depressive episodes in humans who are already vulnerable to major depression or manic-depression.
Borna disease virus is a single-stranded RNA virus that establishes a persistent infection without directly damaging host cells. BDV infection may contribute to depressive illness by altering neuronal cells in the limbic system. The leading hypothesis is that BDV, as it inserts itself into neurons, may disrupt the function of those cells by binding to neurotransmitter receptors.
BDV causes neurological symptoms in domestic animals, which is where it gets its nickname, "crazy virus." The neurological symptoms resemble those seen in humans with manic-depression. This virus is entirely separate from mad cow disease, although the neurological symptoms are what led researchers to study BDV more closely.
The virus infects cells of the limbic system implicated in many psychiatric disorders, including bipolar depression and schizophrenia. BDV infects cells in the nervous system just as its distant viral relative, rabies, does, causing brain damage in animals and humans. Previous studies have shown that a large proportion of psychiatric patients with certain affective disorders, such as depression and manic-depressive disorder, have antibodies specific to proteins of BDV. Since Borna viral material tends to appear during episodes of depression, scientists suspect that the virus brings on depressive episodes in people predisposed to mood disorders by their genes or other factors (perhaps by disrupting communication between brain cells). In most people, however, the infection appears to cause no problems.
It's too soon to say how big a factor Borna virus might be in depression or manic-depression, and it's not clear whether Borna virus can jump from animals to people, nor how it might spread between people. However, scientists do know that humans can't get Borna virus from eating meat or other products of infected animals.
BDV was first reported more than a century ago as a cause of neurological disease in horses in Borna, Germany. Since then, outbreaks of the virus have been documented in cattle, sheep, and cats. Rats injected with BDV exhibit damage to brain cells in the limbic system, the part of the brain that governs mood and emotions. Interestingly, the virus affects various animal species differently. While rats' brains are destroyed, the virus causes only subtle abnormal social patterns in tree shrews. Further animal studies as well as larger studies of psychiatric patients may help scientists better understand how the virus causes disease and how to develop a way to diagnose and treat it.
The cause of most of the common psychiatric disorders, including depression, manicdepression, anxiety, and schizophrenia, remains a mystery. In some cases, symptoms appear suddenly and the disease follows a catastrophic course, while in other cases the disease may be intermittent. Despite a large amount of research, and a lot of familial association evidence, the search for causative genes has produced mixed results. This has helped fuel the search for other factors, such as viral infection.
One group of investigators at the National Institute of Mental Health is pursuing the hypothesis that schizophrenia might be caused by viruses transmitted from household pets to pregnant women or young children. Another group of researchers at the University of Southern California is looking for a link between chronic fatigue syndrome and "stealth viruses" (viruses that have been incorporated into the host DNA and are no longer recognized by the immune system). These viruses cannot be detected by standard immunological methods or standard culture techniques. However, they can be detected with PCR based techniques, matching DNA sequences with known viral DNA.
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