INFECTIOUS DISEASES AND PSYCHIATRY
The association between infection and psychiatric disorders was one of the milestones of early 20th century medicine. The identification of Treponema pallidum in the brains of individuals with “general paresis of the insane” by Noguchi and Moore in 1913 established the role of tertiary syphilis and showed that bacterial infections can cause long-term changes in both neurological and psychiatric functioning. The eventual development of treatments for syphilis and the subsequent curing of individuals with general paresis also showed that the discovery of an infectious cause of a neuropsychiatric disorder could be followed by effective treatment. The association between infection and some cases of psychiatric disorders was further solidified by the identification of an increased rate of encephalitis lethargica following the influenza epidemic of 1918-1919. Influenza control measures might be partially credited for the rarity of encephalitis lethargica in the modern era.
Since that time and until recently, the association between infection and psychiatric disorders has received less attention than other causes of psychiatric disorders such as emotional stress and genomics. However, there has been a resurgence of interest in the role of infections in psychiatric disorders because of a number of scientific advances in the understanding of how infectious agents and the immune response can alter brain functioning and affect human behavior.
One advance that has rekindled interest in a role for infectious agents is an increased understanding of the mechanisms by which a range of microorganisms can enter the central nervous system and establish long-terms persistence within the human brain. It had been previously thought that infection of the brain would lead to characteristic signs of inflammation such as white cell infiltration, granulomas, and tissue destruction.
Postmortem examination revealed that these features are uncommon in the brains of individuals with serious psychiatric disorders, thus suggesting that infection is uncommon in persons with these disorders.1 However recent discoveries have shown that many neuropathic infectious agents have complex mechanisms that allow them to lie dormant within the brain for extensive periods with little evidence of classical inflammatory reactions.2 This concept is consistent with recent studies indicating that there is substantial immune activity in the brains and systemic circulation of individual with psychiatric disorders.3
Microorganisms capable of his latency include a diverse range of taxa including viruses such as the herpesviruses herpes simplex virus types 1 and 2, cytomegalovirus, and Epstein Barr virus as well as retroviruses such as human immunodeficiency virus, measles virus, bacteria such as Chlamydiae and Borreliae, and protozoa such as Toxoplasma gondii .
Dr Yolken is Theodore and Vada Stanley Distinguished Professor of Neurovirology in Pediatrics, Johns Hopkins University, Baltimore, MD; Ms Shwartz is a Psychiatric-Mental Health Nurse Practitioner, Telecare Corporation, Alameda County, CA; and Dr Quanbeck is Associate Medical Director, Cordilleras Mental Health Rehabilitation Center, San Mateo County Health, Redwood City, CA.
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