Infectious Diseases and Mental Illness
To the Editor: The report by Hatalski et al. (1) on Borna virus as a probable human pathogen provides yet another example of an infectious agent being tentatively associated with neuropsychiatric disorders. Earlier this year, researchers at Rockefeller University and the National Institute of Mental Health suggested that after streptococcal infection, some children may be at increased risk for obsessive-compulsive disorders and Tourette syndrome (2). The human B-cell antigen D8/17, believed to be a marker for increased susceptibility to poststreptococcal rheumatic heart disease, has been tentatively linked to this increased risk for psychiatric illness in children. Other reports of patients with complicated Lyme borreliosis, including some whose infections have progressed to encephalopathies, describe persistent verbal and memory deficits among these patients (3). In a few Lyme disease patients, the only overt symptoms of disease at the time of initial diagnosis and treatment were classified as mental confusion (4). Two newly emergent infectious diseases in the United States, leptospirosis and neurocysticercosis, have been found among inner city residents and poor immigrants, respectively. Occasionally leptospirosis has been associated with a variety of postinfectious psychiatric symptoms, including depression, dementia, and psychosis (5). Neurocysticercosis, a tropical parasitic infection, is increasingly associated with emergency room admissions for seizures and epilepsy (6). Still other infectious diseases are being examined for links with cognitive symptoms and emotional disorders.
The primary cause of many common psychiatric disorders, including depression, manic depression, anxiety, and schizophrenia, remains a mystery. The World Health Organization estimates that 1.5 billion people worldwide suffer from a neuropsychiatric disorder. Of the 10 leading causes of disability in 1990, four were psychiatric disorders: unipolar depression, manic depression, schizophrenia, and obsessive-compulsive disorders (7). The National Institute of Mental Health recently estimated that as many as 20% of young Americans ages 7 to 14 approximately 10 million children have mental health problems severe enough to compromise their ability to function (8). Infectious agents may play a role in some of these diseases to some unknown degree. A better understanding of the role of infection may speed treatment and prevention efforts and reduce the degree of disability and stigma associated with mental illness.
Vaccines and antimicrobial agents might enhance current therapeutic options for mental illnesses. Even if infectious diseases were a primary factor in only 1% of neuropsychiatric illnesses, some 10 million persons might benefit from antimicrobial therapies. Identifying those susceptible to neuropsychiatric illnesses (because of environmental factors or genetic predisposition) may also permit vaccination or antimicrobial prophylaxis and a subsequent lowering of disease incidence.
Physicians and federal agencies addressing the problems of emerging infectious diseases should examine the possibility of infection as a cause of mental illness. Better communication among infectious disease and mental health experts, as well as additional training, will be needed to shed light on the growing phenomenon of infectious diseases manifesting themselves as neuropsychiatric disorders.
Edward McSweegan
National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA